| Author | Message | ||
| Keith Mahan (Gyrokeith)
New member Username: Gyrokeith Post Number: 3 Registered: 4-2003 |
Ben.. I see many theorists and book learners in this posting. I thought I would give you some of my hands-on knowledge, having built a half dozen or so high rpm extreme stroke aircooled VW engines. I try and shoot for .5 grams or so. Same with the pistons (dry w/ rings included). Unless you had your crank cut, it should be ok. Get that flywheel close, too! I have regularly driven a 2.2 litre V-dub to 7200 rpm, more like 7500 during a good burnout. All my engines have shown no extra wear on the bearings when compared to the same milage stock ("unbalanced") 4600 rpm engine at dissassembly. I will admit the horizontal 4 is has better dynamic balance than a v-8. Since connecting rods change shape and size according to forces applied to them (different rpm, decel., uneven combustion forces from imperfect ports, compression height, ect.)the actual balance will be different at high rpm then static tests. They tend to grow longer at high rpm. Half a gram balance seems to work fine. Hope this helps you. It always seemed to me that auto manufacturers just make a crap load of rods and sort them to some reasonable weight grouping. Ferrari just had a higher standard to reflect the higher rpm useage of their engines. | ||
| Mark Eberhardt (Me_k)
Member Username: Me_k Post Number: 471 Registered: 5-2002 |
Agreed, do the best you can, it's only a little of your time. It may help and it certainly won't hurt. | ||
| Mitch Alsup (Mitch_alsup)
Member Username: Mitch_alsup Post Number: 474 Registered: 4-2002 |
Just to be clear: my point is that you should balance your rotating and reciprocating parts as good as you can, and then give up and don't fret about the residual imbalance. When half a part in in the rotating domain and the other half of that part in in the reciprocating domain, you don't balance these parts by getting the total weight the same. You balance these parts by getting the rotating weights all the same and then getting all the recprocating wieghts the same. And if you've done a good job, the toatl weights will also be the same. My other points are that people don't understand the architectures of various engines--to this end I will nag them into understanding. Things like flat (180d) V12 is one of these issues, and these engines are fundamentally different than the horizontally opposed porsche engines. | ||
| Ben Millermon (Brainsboy)
Junior Member Username: Brainsboy Post Number: 225 Registered: 5-2001 |
Thanks for all the posts, I did the static balance and got everything with in .6 grams. My viewpoint is that even though some of you dont feel .6g will make a difference, I see it as that all the small changes together add up. | ||
| JRV (Jrvall)
Intermediate Member Username: Jrvall Post Number: 1241 Registered: 11-2002 |
>>Boy, you guys are all over the field.<< All over the field and taking comments out of context in order to nit pick this thread apart. How boring. All "examples" were sited as "examples" of increases or gains from various types of procedures and mods that are documented improvements of their respective situations. No engine builder of note or worth would adhere to the "don't waste your time balancing" line of reasoning being pushed here. One of the First rules of success in building cars is "Laziness Will Get You Nowhere". There are plenty of books on the subject of Engine Mods...there are No Books on the Subject of "Don't Bother"...perhaps you x-spurts could fill the void and write a book on the Benifits of Doing Nothing. I'll keep an eye out for it on Amazon . | ||
| Mitch Alsup (Mitch_alsup)
Member Username: Mitch_alsup Post Number: 471 Registered: 4-2002 |
In the case of Ferrari flat (V12) engines, two pistons are connected to a single throw on the crank, so as one piston heads left the other piston heads right so the volume in the crankcase remains the same. In the case of Prosche flat (HO6) engines, two pistons are connected to two different throws 180 degrees apart on the crankshaft. So as one piston heads left the other heads right. Porsche engines have better balance at the cost of air pressure variance in the crank case; Ferrari engines have enough cylinders (12) that the balance issue is moot (two inline sixes) and the equal volume crank case is benefitial (stronger). Ferrari:flat V12 // Porsche: Horizontaly opposed 6 | ||
| Bruce R. Morehead (Brm)
New member Username: Brm Post Number: 21 Registered: 4-2002 |
Boy, you guys are all over the field. You are confusing many types of engine prep. Factory specs are fine for street uses. The engines have to live through the warrantee. Blue printing makes sure the engine meets the factory specs to comply with 'stock' rules, but gives little performance. Static balancing looks good on paper, but my engines are not often static. Dynamic balancing is the way to go for a reliable rotating engine mass. you match static balance the rods, pistons, pins, rings and etc. then you make bob weights on the proper weight and attach to the crank. The crank and bob weights are spun at an appropriate speed and the unbalance is corrected then all the other rotating pieces are added one at a time and once all the unbalance is corrected the engine is 'balanced'. You could still have an expensive piece of metal that does not produce much more power. To make a race engine you have to use all the proper parts, stress relieve the block and crank, correct all the cylinder and bearing bores, flow the heads and manifolds, cc the combustion chambers, balance the rotating parts and assemble everything with the proper torque. You now should have an engine that if you did everything correctly will blow apart on the cool down lap. So Ben just put it back together and enjoy driving it. You will have saved enough to do the next rebuild and have had a lot of fun driving. Just put the leftover parts in a box for next time. | ||
| Ben Lobenstein 90 TR (Benjet)
Intermediate Member Username: Benjet Post Number: 1084 Registered: 1-2001 |
JRV - Hate to jump into the mix here, especially since it's not on point with the topic, but.... >> If memory serves me correctly Ferrari has a wide variety of FLAT -- Horizontily opposed engines. Which Ferrari Flat (road car) engines are Horizontally Opposed (car name/model is fine, I'm not asking you to tell me the name of the engines)? -Ben | ||
| JRV (Jrvall)
Intermediate Member Username: Jrvall Post Number: 1238 Registered: 11-2002 |
>>>Since there are vanishinly few engines that get knifed edged cranks that are not also blueprinted, you have not shown that this particular mod is 'all that valuable' in the large scheme of things.<<< LOL...prove it's not!!! If memory serves me correctly Ferrari has a wide variety of FLAT -- Horizontily opposed engines. But all the above aside....Blueprinting & Balancing is unlikely to go away or be deminished in value by a few guffhaws on a chat board....that actually can't read very well and found the time to take the inportant aspects out of context. So I'll continue to balance, tweek and massage in the future just as I have in the past. There are "production" specs and there are higher levels of perfection & quality specs, always have been, always will be. | ||
| Mitch Alsup (Mitch_alsup)
Member Username: Mitch_alsup Post Number: 469 Registered: 4-2002 |
point 1): Posche engines have pistons that move opposite each other to achieve balance. That is while one piston moves east, the other piston moves west with the same acceleration and at the same time and in the same phase. This means that the space between the pistons changes markedly. When one pistons are at BDC both pistons are at BDC. When a typical V8 engine has one piston at BDC the paired piston is about 1/2 stroke. So Porsche engines have bigger problems in air managemnt in the crankcase than V8s. point 2): take a random brand new (japaneese) motorcycle engine. Disassemble completely. Blueprint the engine to the hilt but do not port/polish, lighten any components. Reassemble the engine perfectly using all blueprinted 'stock' components. Presto; 10% power gain. So, yes, a Porsche engine might benefit from knife edging of the crank, and adding air ports between crank case sections. But, the gains you are talking about are well within the realm of just expert blueprinting with bone stock components. Since there are vanishinly few engines that get knifed edged cranks that are not also blueprinted, you have not shown that this particular mod is 'all that valuable' in the large scheme of things. | ||
| Matt Morgan (Kermit)
Junior Member Username: Kermit Post Number: 123 Registered: 8-2001 |
A couple of thoughts on this topic. First off , haveing balanced a "couple" over the years, the topic of how close is in some respects a bit of a moot point when you find out that about 3 drops of oil on the scale how to be at least .5 grams! Never the less, I still strive for perfection, as it does help. I too have been wondering why the cranks were never knife edged from the factory. No doubt cost is an issue. If I could somehow find out the cranks alloy, a bit of weld buildup could easily be more effective than expensive heavy metals. And while Your at it perhaps a stroke increase, to go with a nice overbore, heh heh heh. | ||
| JRV (Jrvall)
Intermediate Member Username: Jrvall Post Number: 1229 Registered: 11-2002 |
Mark, the facts are plain...there's been more than enough Dumbing Down of America and the whole world for that matter. A Ferrari Forum...and especially a thread about Balanceing Engines just isn't a place for more of it. | ||
| Mark Eberhardt (Me_k)
Member Username: Me_k Post Number: 467 Registered: 5-2002 |
>>Well sport, �<< Name calling? You seem just a little sensitive, and more than a little confused. The confusion appears to be primarily related to poor reading comprehension skills. It turns out all the words in a sentence matter if you want to understand what has been said. Lets review the facts. You said �Porsche engines get an approx. 10% HP gain from Boat-Tailing the Mains/Cutting P-Skirts...from the decrease in Crankcase Pressure & Turbulance--Documented in Any Porsche HP Engine Book---25-30HP gains for a little machine work is a good thing!� My post simply pointed out that the primary problem in a porsche is the poor venting between cylinders, and that is what boat-tailing and piston skirt cutting addresses and is why they gain HP at high rpm. Neither a chevy non a ferrari show similar gains form that type or work because they don�t have the problem to start with. That�s why you only find the HP numbers discussed in porsche books. I also said �Ferrari's come with parts that are matched within a reasonable amount unlike most production vehicles�. Which doesn�t contain the word �balanced�, it uses the word �matched�. Ferrari matches connecting rods in sets as Ben and Henry discussed at the beginning of the thread, US auto makers don�t to the best of my knowledge. As far as what is a reasonable limit for matching components, Ferrari says 4 grams is reasonable and I think Mitch covered why that is quite well. I hate to be the one point this out to you, but Smokey Yannucks made his career at cheating in nascar, which it turns out never set the standard for anything. It�s a long way down from f1 to nascar. Sorry. | ||
| JRV (Jrvall)
Intermediate Member Username: Jrvall Post Number: 1228 Registered: 11-2002 |
>>which are in fact quite different from chevys. << Well sport, if Smokey worked on Chevy's which have BIG OPEN SUMPS like V-8's...then CC Pressure is a Problem on V8's with Big Open Sumps Exactly like Ferrari Engines....JUST LIKE I SAID ! >>Ferrari's come with parts that are matched within a reasonable amount unlike most production vehicles<< Huhhh???? Who decides what a reasonable amount is? you??? LOL Name a few engines that aren't balanced for the folks. >>but real doesn't help that much either, it a diminishing return game.<< Once again.."YOU" don't make the Rules. The Rules are made at The Top of The Game and work their way down...in the case of Engines it's AeroSpace & Racing that Sets The Standards of Excelence that the game is played by! If you don't choose to follow the Guidelines of Excellence that's your Biz, but it's not really friendly to others to try and convince them 1) you know more than the experts and 2) to follow a path of lazy sloppy work ethics and procedures is a good idea. | ||
| Mitch Alsup (Mitch_alsup)
Member Username: Mitch_alsup Post Number: 463 Registered: 4-2002 |
"I found a chart showing grams vs rpms. 7g weight @ 8000rpms = 125 lbs of external force" This is (as lawrence of Aribia once said) a triffling. Consider the conbustion chamber of a 10:1 compression engine at 100% volumetric efficiency with perfect combustion, at TDC on the power stroke, the cylinder pressure is about 1400 PSI. An F355 piston has a bore of 3.35" has a piston crown area of 8.8sq" for a total force of 12,000 lbs. Another 125 lbs (of imbalanced weight) is 1% of the operating stresses of the engine at full throttle. | ||
| Mark Eberhardt (Me_k)
Member Username: Me_k Post Number: 466 Registered: 5-2002 |
>>I suggest you pick up a copy of Smokey Yannucks Book also.<< Hmmm, I have it, but I can't find any reference to Smokey ever working on porsche engines, which are in fact quite different from chevys. >>Then of course one could make the argument that Blowers are ridiculas when all you have to do is Squirt in Nitrous and have the option to pick & choose when you want it or need it. At a Fraction of what any blower type set-up costs.<< Absolutely, unless you plan to want the power for more than 10 seconds at a pop...... >>Anyone that thinks balancing isn't a good idea is off their rocker.<< Basic balancing is a fine idea, that's why Ferrari's come with parts that are matched within a reasonable amount unlike most production vehicles. Better can't hurt anything, but real doesn't help that much either, it a diminishing return game. | ||
| JRV (Jrvall)
Intermediate Member Username: Jrvall Post Number: 1227 Registered: 11-2002 |
>>As for spending money to loghten and knife edge the crank, that is one of the last places I would look for HP. << Who said anything about doing it on a street car or even suggested doing it at all? I said it's done by those who seek the ultimate as compared to plain Production Tolerance Motors! >>Making the passages as big as possably helps make it act like a more open block, like say a ferraris for example.<< I suggest you pick up a copy of Smokey Yannucks Book also. >> or turbo/blower will have a much much bigger HP/dollar return. << Then of course one could make the argument that Blowers are ridiculas when all you have to do is Squirt in Nitrous and have the option to pick & choose when you want it or need it. At a Fraction of what any blower type set-up costs. Anyone that thinks balancing isn't a good idea is off their rocker. | ||
| Ben Millermon (Brainsboy)
Junior Member Username: Brainsboy Post Number: 216 Registered: 5-2001 |
It may not be meaningless. I found a chart showing grams vs rpms. 7g weight @ 8000rpms = 125 lbs of external force. If half the engine is 5g more then the other side, it would seem to me a big deal in the realm of harmonics at least. Lets assume you can't balance a motor because of too many variables, like oil spash certain rpms, ect.. Wouldnt it be better to have an equal amount of unbalacing then to have 1/2 the motor too heavy and half too light causing strange harmonics? Logic would tell us the higher the rpm the more important it would be to be with in 1g. Maybe you cant have a perfect balance because of variables but at least it would be an even force on every cylinder | ||
| Mark Eberhardt (Me_k)
Member Username: Me_k Post Number: 465 Registered: 5-2002 |
From what I understand, the prosche guys boat-tail the mains and cut piston skirts because their engines are a 180 degree configuration with 7 main bearings which tends to trap air. Making the passages as big as possably helps make it act like a more open block, like say a ferraris for example. As for spending money to loghten and knife edge the crank, that is one of the last places I would look for HP. On a race car where ever little bit helps, sure. On a street car, a new exhaust, a set of cams, or turbo/blower will have a much much bigger HP/dollar return. | ||
| Lyman White (Lyman)
New member Username: Lyman Post Number: 3 Registered: 4-2003 |
JRV.Yes I have a copy of Smokey Yunicks book Power Secrets,for about 20 years now.This is verbatim from page 33.Frankly , I think engine balancing is anything but an exact science, and you don't need to get upset if things are a little off.Theres no such thing as an engine thats perfectly balanced at all engine speeds.You can determine a recommended balance weight according to the formula that the crank manufacturers use, and pick a crank speed , say 500 rpm to put in the formula; then when you refigure the formula with a different crank speed- say 7500 rpm, the recommended weight will be different.So at best you can only gain a"true" balance within a very narrow crank speed range. And from what i've seen, this true balance is at best an approximation. When you look inside the oil pan as the engine is running at high rpm, there is a tremendous amount of oil cought up in the windage from the spinning crank and wrapped around the crank throws.This oil has a lot of weight, and as the engine runs, this oil will migrate all over the assembly.Sometimes it hangs around the front throws, sometimes it moves to the back and sometimes it is in the middle. The pattern is totally random, and the size of the oil cloud can get larger or smaller. All of this happens in a test engine sitting on a dyno, so who knows what it's like when the engine is in a moving car and you have all sorts of front, rear and side loads in the picture.This oil cloud must affect the balance of the operating assembly, and ther is no way to account for it, so i see little reason to worry much about engine balance. Smokey's words not mine.So chase that .5g. it's meaningless. | ||
| Paul Hill (348paul)
Junior Member Username: 348paul Post Number: 206 Registered: 12-2002 |
Great thread! Ben - Love the "Z" !! - Where can I find more info on it??? Paul | ||
| '75 308 GT4 (Peter)
Advanced Member Username: Peter Post Number: 2626 Registered: 12-2000 |
Rob, at least it gave me an idea of what it is in the first place...  Thanks! | ||
| Rob Lay (Rob328gts)
Board Administrator Username: Rob328gts Post Number: 4262 Registered: 12-2000 |
My head is spinning, but great thread everyone! Peter, well, I was partly right on your AW question. | ||
| Ben Millermon (Brainsboy)
Junior Member Username: Brainsboy Post Number: 213 Registered: 5-2001 |
Who ever said be careful and take you time wasnt kidding. Its easy to say you want .5 gram but the scale is so accurate that just blowing soft air on it changes the weight. It doesnt take much sanding to change .1 gram on these rods, you could easily over sand by accident. | ||
| Richard Ham (Hampappy)
New member Username: Hampappy Post Number: 4 Registered: 2-2003 |
>>If your going to do a static balance why not be as accurate as you can?<< absolutely, if you're going to do it then it should surely be done as well as reasonably possible. I sure don't want to knock anybody's work. Reducing the windage and trying to keep the oil off the crank is definitely current practice. It should reduce the drag losses and also reduce the air-foam content in the oil. Too much air in the oil is not good for the bearings. | ||
| JRV (Jrvall)
Intermediate Member Username: Jrvall Post Number: 1224 Registered: 11-2002 |
>>>It would make sence going from 5 grams difference to only .5 difference would make the engine last longer and smoother especialy at high rpm. If your going to do a static balance why not be as accurate as you can?<< Yes if you have the time, patience, and an attitude of doing the finest workmanship you can, it makes sense. I think the counter points here are to justify not bothering trying to maximize the quality of a custom rebuild. The benifits of Balancing & Blueprinting are well documented and practiced across the Entire Spectrum of Engine Building, some simply 'practice better' than others. I doubt arguments to the contrary will ever grow wings. | ||
| JRV (Jrvall)
Intermediate Member Username: Jrvall Post Number: 1223 Registered: 11-2002 |
>>Reality check.I have not seen any measurable gain on the track or dyno,<< Porsche engines get an approx. 10% HP gain from Boat-Tailing the Mains/Cutting P-Skirts...from the decrease in Crankcase Pressure & Turbulance--Documented in Any Porsche HP Engine Book---25-30HP gains for a little machine work is a good thing! Additionally you might want to pick up a copy of Smokey Yannuks, Secrets to HP, and read about the lenghts the Bg Boys have gone thru to study, understand and eliminate Crankcase Pressure & Turbulance! >>but have had a problem with them axial "lifting",pulling the crank foward,severely wearing the thrust bearing.<< What Motor was this Axial Lifting in? My guess would be the thrust surfaces got hammered because they were loose to start with. | ||
| Ben Millermon (Brainsboy)
Junior Member Username: Brainsboy Post Number: 211 Registered: 5-2001 |
Richard not to disagree with you but I found a balance table showing, 7 grams weight @ 8000 rpm's turn out to be 112lbs of external force on the crank. It would make sence going from 5 grams difference to only .5 difference would make the engine last longer and smoother especialy at high rpm. If your going to do a static balance why not be as accurate as you can? | ||
| Richard Ham (Hampappy)
New member Username: Hampappy Post Number: 3 Registered: 2-2003 |
My 2 p�s worth. I think matching the weights of the rods and pistons more accurately than the manufacturers specs is not really going to come up with the goods. It�s done originally because it has a small effect on the running smoothness, but it doesn�t reduce the main loading on the components. This is many many times greater than the forces from a few grams mis-match. In any case, the smoothness of the flat plane V8 crankshaft arrangement isn�t ideal because it produces a whacking great 2nd order oscillating vertical force which is not affected by the weight matching. Before you all say this guy obviously doesn't know zip, my job is doing this sort of stuff for a major diesel manufacturer, and again before y�all fall off your chairs laughing about noisy smelly engines, these are tested for hundreds of hours at 40% overspeed where the inertia forces are double the rated speed values. How many Ferraris, discounting Schumi�s , would survive at 10000 rpm? Anyway, there doesn�t seem to me to be much justification for doing this matching work. You�d be better off improving the gas flow or whatever. Also on the question of the rods, although polishing normally increases the fatigue strength by improving the surface finish, this won�t be the case for a shot peened component. Shot peening plastically deforms the surface, which produces a layer of high compressive stresses, up to the yield stress value, and this really does improve the fatigue strength. Polishing it off wouldn�t be a good idea. Just like to say I bought a 308 some months back, and for me, this site is ideal. I log-in every day. Over here in Switzerland there seems to be a Ferrari myth. Nobody dares lift the bonnet (trunk to you?) let alone fiddle about with the engine underneath. So it�s great to see that it�s possible. Thanks for a great site. | ||
| Lyman White (Lyman)
New member Username: Lyman Post Number: 2 Registered: 4-2003 |
The leading edge of the counterweight is bullnosed and the trailing edge is knife edged, sort of like an airplane wing. A lot of material is removed, thus weight.This is an expensive operation.Now,during the rebalancing,weight has to be added that was taken away by the knife edging operation.A heavy metal such as tungston or depleted uranium has to be added to your front and rear counterweight cheeks.The heavy metal comes in rounds of different diameters which have to be cut to length then inserted into the crank cheeks.This is done by drilling and reaming your crank cheeks for however many peices are required.A press fit is required.The slugs are then pressed in and welded.Another expensive operation.Edging crank $300,balance crank $200,add to install heavy metal $100,six pieces heavey metal $300. Total $900. Reality check.I have not seen any measurable gain on the track or dyno,but have had a problem with them axial "lifting",pulling the crank foward,severely wearing the thrust bearing.Save your money, put it to some other performance mod. | ||
| Mitch Alsup (Mitch_alsup)
Member Username: Mitch_alsup Post Number: 461 Registered: 4-2002 |
After knife edging, and con rod balancing, you set up a set of bob weights* bolt them onto the crankshaft and then balance the crank dynamically. *Based on the con rod, piston, piston pin, and bearing weights | ||
| '75 308 GT4 (Peter)
Advanced Member Username: Peter Post Number: 2624 Registered: 12-2000 |
I've been thinking about this knife-edging process and I have another question: If you're shaving material off of the counter-balance for "aerodynamics", isn't that going to upset the balance between the weight of that counter-balance and the con-rod pin? If so, how does one achieve a new balance (seeing as there's not much "useless" material to take off on the pin-side)? | ||
| Lyman White (Lyman)
New member Username: Lyman Post Number: 1 Registered: 4-2003 |
New to the board and am interested in the Testarossas.As far as weighing your components 2-3g. is just fine. Typicaly you add all of your components weight together(rings,pins, pistons, small and big rod ends,rod bearings and here is the kicker,OIL.An educated guess would be 7g. for a 308 and 15g. for the flat 12.Now you add all these together and come up with a bobweight.The weight is now reproduced and clamped to your crank throws.The crank is now spun in the machine between 480 to 530 rpm. depending on crank size and bobweight.By the addition or removal of material on the crank throws it comes into balance.(simple account)We now have a balanced crank at lets say 530 rpm.Is it balanced at 2000 rpm, how about 6000 rpm when your crankshaft is turning at 100 revs per second and the big ends of your rods begin to pick up a little weight. What about oil spray comming from the rods and mains hitting the bottoms of the pistons with x amount of force and all this oil mist buzzing around inside the crancase, pure chaos.Well, how can you dynamically balance a rotating assembly for all engine speeds? you cant.Time could be better spent in other areas than trying to get your stuff to one tenth of a g.It sure is amazing how this stuff holds together isn't it.It's also a long winded first post.Thanks for a great forum. | ||
| Matt Morgan (Kermit)
Junior Member Username: Kermit Post Number: 122 Registered: 8-2001 |
-------------------------------------------------------------------------------- JRV, Henry, et al hit a lot of it right on. Blueprinting is a very involved procedeure in that starting from the crank centerline, assumeing it is true. The decks, or head gasket surfaces are then machined true to the crank bores. This ensures an even piston rise. A minimum is cut,and the sleeves will have to be adjusted by machineing for the proper projection. watch for too much piston rise though. And on, and on. It get quite involved, but is worth it on some engines. Balanceing is as picky as one wishes to be. I have been known to go down to a tenth of a gram(in the right application, as it takes time). Material removal can be done a follows for the DYI:You can do a great job with a 60 or 80 grit flapper wheel, being damn sure that the scratches are going along the length of the rod, not across, as that will cause stress risers. Concentrate on the forgeing flash removal first to lighten. Rods are commonly steel shot peened, so as that is a surface hardening treatment, going past the effected area is not considered by some to be adviseable. I have polished them to remove friction with none blown up yet though. An abrasive "Tootsie roll" or cartridge roll is great for giving all sharp corners a slight rounding to eliminate stress risers in the bolt area. Mitch brought up a very important point. The rod end weights being important, as the small end is factored into the equasion (SP) as reciprocating, and the bearing end as rotating.Take care that theyare not bound up from not hanging true. I use a small cradle with class 5 bearings on the ends to insure that they are in the center of the bore. It can be tricky to center with knife edge settups. My experience, although not dyno proven, is that a motor will run smoother, and pull harder with this amount of effort put into it. Longevity is no doubt improved as well. | ||
| JRV (Jrvall)
Intermediate Member Username: Jrvall Post Number: 1221 Registered: 11-2002 |
>>Knife edgeing a crank refers to the counterweights,<< Correct. >>On a dry sump it doesn't help as much as with a wet sump engine.<< Well, not neccesarily the case. Wind resistance and crankcase pressure along with turbulance are considered factors (problems) in wet or dry sump engines.. It has been common practice on 911 engines (and derivatives) to Boat Tail the Mains and Cut the Piston Skirts to reduce tubulance and the parasitic drag it causes and they are Dry Sump. | ||
| Ben Millermon (Brainsboy)
Junior Member Username: Brainsboy Post Number: 201 Registered: 5-2001 |
guess i mis-understood what he was saying. I read something about the procedure I mentioned, it was the first time I had heard of it | ||
| Bob Campen (Bob308gts)
Member Username: Bob308gts Post Number: 479 Registered: 9-2001 |
Knife edgeing a crank refers to the counterweights, instead of a flat at the outer edge they are tapered to slice though the oil instead of pushing at it. On a dry sump it doesn't help as much as with a wet sump engine. | ||
| Ben Millermon (Brainsboy)
Junior Member Username: Brainsboy Post Number: 199 Registered: 5-2001 |
I think he is refering to setting the crank on two knife like edges, then you add the weight of the piston,rod,bearings,rings, and machine a peice of metal to the same weight to fit around the rod journal. if the crank weight is heaver then the crankshaft should roll to that side. I read something about this a few weeks ago, seemed like alot of work to it. | ||
| '75 308 GT4 (Peter)
Advanced Member Username: Peter Post Number: 2622 Registered: 12-2000 |
JRV: "...as well as Knife Edgeing the crank..." I had asked a question about this on Rob's other forum (autowrench.com). Would you mind explaining the purpose and reason for this procedure, please... | ||
| JRV (Jrvall)
Intermediate Member Username: Jrvall Post Number: 1218 Registered: 11-2002 |
Balancing the rods (and pistons/pins) has nothing to do with balancing the crank..totally different deal...one is static balancing (rods) the crank is dynamic balancing. Also, serious Rod Balancing is done end to end as well as rod to rod. Additionaly shot peening the rods and even polishing is considered an acceptable/normal step when really taking a bottom end to the next level, as well as Knife Edgeing the crank..and even lightening the crank for full out race engines. It would really surprise me if you could get .01 grams...as .05 (1/2 gram) is considered extremely close...you'll probably see what what I mean when you get after them. | ||
| Ben Millermon (Brainsboy)
Junior Member Username: Brainsboy Post Number: 197 Registered: 5-2001 |
I had talked to several machine shops some say 5gram difference is ok, some say 4 grams, some said 1 gram. Thats why I bought my own scale. Right now all the rods are with in about 2.8 grams to be exact, If I make lets say all the rods weight 549.12 for talk sake with in +/- .01, do i really have to balance the crank again? If half the machine shops only use a 4 to 5 gram weight system what good is it to balance the crank. Although I want perfect, they will consider it within tolerance. | ||
| Mitch Alsup (Mitch_alsup)
Member Username: Mitch_alsup Post Number: 449 Registered: 4-2002 |
There is a big end and a little end on each conrod. To properly balance conrods, you need to get all the big ends to the same weight, and all the little ends to the same weight. You do this by setting up a fulcrum (dull knife edge will work) and put the fulcrum inside the little end (don't knick anything) adjust the conrod so that it is perfectly horizontal, and the weight the big end. Get all the big ends to the same weight. Then set up the fulcrum so that you are weighing the little ends with the conrod perfectly horizontal and the fulcrum in the dead center of the big end hole. Get all the little ends to the same weight. A careful balance target is 0.1 grams each end and 0.1 grams for the total conrod weight. Although since its only your time, you can go for the limits of your measurement equiptment. Good luck and enjoy | ||
| JRV (Jrvall)
Intermediate Member Username: Jrvall Post Number: 1213 Registered: 11-2002 |
>>A "balanced" engine, to me, is one that is within the factory specs.<< Sorry ...but it's not balanced, and factory specs aren't considered close enough to be called balanced...it's as close as they cared to get from different piles of like rods or like pistons, if it was really balanced they would sort thousands of rods or pistons into groups "exactly" the same. Balancing is finishing the job a factory starts...F1 or Indy Motors "are balanced". Street Motors are not balanced. Blueprinting is not balancing. Blueprinting is the art and science of machining every angle and spec and distance exactly as the engine was drawn on "the blueprint". Street Motors are not blueprinted, they are simply built to production specs (hopefully).. | ||
| Ken (Allyn)
Member Username: Allyn Post Number: 805 Registered: 10-2001 |
Blueprinting is expensive but if you're doing a total rebuild it might as well be done. If you've never done it, take it to someone who has and has learned the tricks. I would imagine for a Ferrari engine it's NOT a DIY thing. A bluprinted engine has more power, a higher safe RPM range and should last longer. | ||
| Henryk (Henryk)
Member Username: Henryk Post Number: 620 Registered: 8-2001 |
A "balanced" engine, to me, is one that is within the factory specs. My TR WSM also states a range of 4 grams.......people call this engine bullet-proof......it HAS to be well balanced. If many cars only require 12 grams, then 4 grams shows how Ferrari is more critical of it's motors, than most. One can call this "custom-balancing". There is nothing wrong with trying to get to closer tolerances, but then this would be called blue-printing.....right? | ||
| JRV (Jrvall)
Intermediate Member Username: Jrvall Post Number: 1210 Registered: 11-2002 |
Weeeell....nooooo...not exactly...many companies allow 12-14 grams....but it's not 100% really balanced because it's a 'street motor' "built to production specs". Which is not the same thing as a "Balanced" engine. Nor are they "Blueprinted"...they are built to production specs, which allows for a certian percentage of error...or variance. | ||
| Henryk (Henryk)
Member Username: Henryk Post Number: 619 Registered: 8-2001 |
JRV: Are you saying that Ferrari engines come from the factory, unbalanced? | ||
| JRV (Jrvall)
Intermediate Member Username: Jrvall Post Number: 1209 Registered: 11-2002 |
>>The weights, in all letter levels seem to have a range of 4 grams.<< That's correct, factory spec is 4 grams. A Balanced Engine should be within .05..half a gram...for a comparison, a 1 Dollar bill wieghs 1 gram. Be carefull if this is your first set...go real slow & easy. | ||
| Henryk (Henryk)
Member Username: Henryk Post Number: 617 Registered: 8-2001 |
If you are going to balance the rods to that close tolerance, then you should also have the crank balanced, and have the pistons within .01 grams also. Doing just the rods, without doing the others probably won't be a benefit. If you super-balance one of the moving parts, then you HAVE to do the others. | ||
| Henryk (Henryk)
Member Username: Henryk Post Number: 616 Registered: 8-2001 |
Ben: The letter H corresponds to a weight of 548-552 grams. It can't hurt. Simple balancing is called "balancing"; whereas, precision balancing is called "blue-printing". In blue-printing, all tolerances are brought closer together; as in getting the rods within .01 grams. I would think that you have to be very careful where you remove the metal, on the rod. | ||
| Ben Millermon (Brainsboy)
Junior Member Username: Brainsboy Post Number: 187 Registered: 5-2001 |
They are listed as an H , but Im curious if making them all with in .01 of a gram will help with the balancing, any thoughts | ||
| Henryk (Henryk)
Member Username: Henryk Post Number: 614 Registered: 8-2001 |
Ben: A 308 service manual lists the connecting rods by letter.....A-V. Each one corresponds to a different weight. If you give me the letter, I can give you the correct weight. The weights, in all letter levels seem to have a range of 4 grams. | ||
| Ben Millermon (Brainsboy)
Junior Member Username: Brainsboy Post Number: 186 Registered: 5-2001 |
I have measured the rods from my 308 and they are all with in 3 grams, does anyone know if this is an exceptable tolerance? I bought a scale that can read up to .01 grams, I want to bring all the rods with in .01 grams, I am assuming I wont have to re-balance the crank because I am not changing that much weight. |