Titanium rods ?

I would like to know more .There is talk of coating ?what is it and what does it do ? There is also the issue of rod journals gauling ( is that the sides of the rods next to each other )?The galvanic corrosion ,what causes it ?Can you use the rod bolts more than once ? How easy is it to replace the smallend bushes ? There was talk of a bigger bigend bearing clearance because of different expansion rate ? The weight saving is substancial .I am asking these question re the 355/360 rods are there records of rod failiers in these motors .

 

All excellent questions…..

The gauling issue is the sides rubbing, many materials have this type of problem. Porsche uses thrust bearings on the sides to solve it and ferrari uses a coating, but I don’t know what it is.

Galvanic corrosion happens any time you have dissimilar metals in electrical contact with each other. It is accelerated by water (in your engine from condensation or a combustion by-product) or acid (combustion by-product). I know it’s seen in used rods but I don’t know how serious it is.

I don’t know the answers to any of the other questions. I suspect the bearing clearance issue has more to do with the low stiffness of Ti more than the expansion rate, but that’s just a guess.

 

Titanium rods have no more corrosion problems than any other rods. I've never seen any problems with corrosion on connecting rods to begin with. Metal parts in constant contact with motor oil = no corrosion, unless they are left to sit for really long periods. Most rod manufacturers use a moly coating on the side to prevent galling, the same with titanium valve stems. Pin end bushings are no harder to change than with steel rods, and the big end clearance (from the rods I've used) is no different. Aluminum rods on the other hand do expand at a different rate and as such, have less "bearing crush" and require a dowel in the cap to positively locate the bearing. Rod bolts are all reusable, not difference upon what kind of rod material they're used in. As long as they are not stretched and fatigued. Titanium rods are an excellent choice, cost is the only factor that prevents more racers from using them.

 

Titanium, particularly the high strength alloys are sensitive to crevice corrosion at temperatures above about 70C and in an acid environment. These conditions are present between the rod and the shell of the bearing and in the rod bolt threads when the oil is not changed frequently enough allowing acids and moisture to be present. This is an issue on a race car where the oil is changed at least every run weekend but would be an issue on a street car where the oil is changed once every year or every couple years.

Crevice corrosion is very real on Ferrari Ti rods the only question is how serious a problem is it. I haven’t heard of any rod that ever failed because of it. I’m thinking if I buy a set I will just plan on re-sizing the big end to get a clean new surface and start the clock over.

The galling is a common problem on titanium parts. It’s solved on connecting rods by coating them, but coatings are not forever. The main problem is during startup when the rods are dry. Race engines tend to be started, warmed-up and then run hard for an extend period so start-up issues tend to be minor with most wear (90%+) coming from run time due to hard use. Street cars on the other hand dry start often, tend not to be warmed up properly and most wear (90% ish) is due to start-up, not run time. Street use is the type of use that would and has failed the protective coating on the sides of the rods.

All rod bolts require replacement after a specified number of re-torques or race hours.

Threads in titanium are better than in aluminum due to (I think) the increased harness of titanium which is about RC36 for 6Al 4V. The rod bolt will be up in the RC 62 range and can very easily damage the titanium threads or cause galling if not properly lubricated.

Until very recently Ti rods have been a “factory team only” thing. I’ve be racing various things for over 20 years and have never even known anyone who ran Ti rods. The math says they are better than sliced bread, but they are sensitive and most racers and OEMs simply choose not to mess with them. For a factory team that can afford to throw rods away every tear down it’s a non-issue, but for the rest of us that need to re-use them it’s a much hard decision.

 

OK When you resize the rod big ends you are surely removing the coating (not on the side faces ) does this coating aid the corrosion ressitance ? How difficult is it to recoat ? A mate of mine make salt chlorinators for swimming pools , he uses titanium plates in the cells these are coated ? is this the same coating ? If you find a gauled rod can it be lapped and recoated ? (obviously depending on the severity )
You say Ti rods are for " factory team only " but Ferrari have been using them since the 355?
Mark you also mentioned that you new of bearing shell that had spun?

 

There should be no coating inside the bearing surface of the rod, it is only applied to the sides to prevent galling so resizing would not be an issue....but it may not be required either, you'll need to examine the rods.

The coating can reapplied on the sides as I understand it with no problem.

Titanium acts very different in an opened environment like a pipe or plate and is much more corrosion resistant. Also purer (lower strength) alloys are significantly more corrosion resistant than the high strength alloys. I’m not an expect here, I had to look it up so may info is from “Principles and Prevention of Corrosion” 2nd edition….I know only a true geek would own that book…..

I said “Until very recently Ti rods have been a “factory team only” thing”. Ti rods have gotten better for sure. The main issue here is re-use. A production engine is put together and intended to stay together vs a race engine that will come apart often. The re-use question on Ti rods is how many times is it safe to re-torque them and I do not know the answer….I’ve heard every thing from the comments posted by enginefxr that there is no issue to 3 is the limit (and the factory uses 2 of them). I honestly don’t know the answer here.

On spun rod bearing with Ti rods I am aware 3 with the 355/360 rods with unknown causes….I don’t know what that means though because I don’t have any way to compare it to anything. It might be less than the steel rods in the 348 and old engines, I just don’t know.

 

You know, they may have banned the use of beryllium for connecting rods in F1, but there certainly is nothing to stop you guys from using it, other than cost, of course

 

I saw carbon fiber rods in a 2 stroke GP bike once.

 

Thanks Mark

 

Now we need somebody who's actually used them to chime in with the important details that are missing here

I love the thought of Ti rods for my engine, but I've got more questions than answers and that would lead me to steel rods that don't come with questions.

 

...and don't forget that machining beryllium must be done in a protective enviroment since the small particles are very toxic to humans. Don't try this at home.

 

Now here's something! To get the proper fit the engine needs to be run in or dyno'd, the engine disassembled, the rod big end resized and the engine put back together, this according to an engine building buddy of mine who works for Ray Everham.
Now this never made sense to me and I am pretty sure that Ferrari does not do this with its engines, anyone with any experiance here?

 

I can remember way back in the early seventies when you ordered a Porsche 911 you could special order Titanium Rods - it was about $1600 IIRC. This was on a car that cost about 9.5 to 11.5 K by itself!

My question (both then and now) was simply - what was the primary point of this? Was it to reduce weight or to increase strength? I know - somebody is going to say "both", but I mean - are TI rods really made to the same strength as a steel rod, (thus being just a little lighter), or are they made to the same weight as a steel rod (thus being maybe a little stronger)?

I guess I am having a little problem with the cost/benefit ratio of this...

 

They are made lighter. A stock 308/328/348/TR/400 ect rod is in the 520-600 gram range, most at the top end as I understand it. After maket steel are around 504-510 grams. The 355/360 Ti rods are the same size and 380-408 grams

 

Well, that is a lot lighter (compared to steel) than I thought. So, I guess this is done for lower rotational inertia - i.e. so the engine can rev quicker?

I would not think that it would affect the overall H.P. all that much in a 12 (fully balanced), but maybe in a flat crank 8 it has a big advantage.

 

rev quicker and I think you could raise the redline of the engine to some extent. With a higher redline you can "pump more air" thus producing more horsepower. If I'm not mistaken that's why little 2.4 liter normally aspirated v-8's in current Formula 1 cars can produce 800~850 horsepower (or whatever they make now). The redline is around 19,000 rpm. They pump a lot of air!

 

The corrosion issues about titanium rods in an engine are really overstated in this thread. At the user level, just don't clean them with chlorinated solvents. The difficulty of the material is mostly at the manufacturing level. The material is notch-sensitive and galls during machining (read: gums up)

Titanium rods were standard in the Porsche 959 of the 1980s, the Acura NSX, and newer cars like the Carrera GT, GT3, and GM LS7.

 

"They are made lighter" ,but being lighter they have to carry less load .A rods motion is both reciprocating and rotating .Compared to a std rod they are almost 200g lighter . I don't no how the maths work but assume half the weight is off the reciprocating mass that's a 100g ,so it's like having 100g lighter pistons , and a 100g of the rotational mass per rod /piston .Some where it was said 1 kg of the crank /flywheel is so many hp .Now I'm not so much worried about the hp as the load on the rod and how the weight reduction affects the revability of the motor not the maximum rev's .Does running long duration cams will the lighter rotational mass help the motor come on cam sooner (lower down the rev range ) or has that got to do with airflow ?

 

Well, I usually have no trouble making a fool of myself empirically, so here goes:

a) I would think that for a well balanced engine the lighter weight would only affect the dynamic change rate in RPM - it could "rev up" and "rev down" faster. Notice I said "well balanced". I could be wrong for a flat crank V8 without balance weights.

b) I would further think that as has been posted the lighter loadings due to weight might even make it possible to increase RPM. This by itself (without valves, cams, intake design) probably would not in itself make more H.P.

c) I wonder if pretty much the same thing could be accomplished by just lightening steel rods and making lighter pistons?

But then, this does seem to be very very popular with the very high end of racing/high perf. engine design.

 

I haven't seen the rods personally yet, but I have it from 2 sources (that I trust completely) who have that of the 1/2 dozen engines (mostly 355s) disassembled every rod shows at least some corrosion under the bearings. The question isn't if it happens the questions in my mind are how serious is it and does it happen even with frequent oil changes (the engines that had to be torn down had to be torn down for a reason I guess).?

 

If you lighten the steel connecting rods to the same weight as the aluminum or titanium rods the steel would be much weaker than the titanium or the aluminum.

The steel is great if you want a small profile and need strength but the titanium and aluminum are stronger pound for pound if you can use the larger volume/cross section.

 

I dont know if anyone ever done back to back dyno runs after changing reciprocating mass, but in theory it more horsepower should be made at the same speed with lighter reciprocating parts.

In the four cylinder, two sets of rods and pistons move in arcs that are 180 degrees opposed. At half rotation, all four are half way in their stroke, with each pair moving in opposing directions. The last cyclinder that fired has to provide the motive force to keep in motion all four rods, pistons, the crankshaft, and ultimately the entire car. Any extra mass anywhere would seem to act to absorb that force. The pistons do not balance out each in the area of force, only in balance. The energy to accelerate them to high speed at half stroke MUST be supplied by the last cylinder that fired. Any reduction in mass will cause an increase in power and efficiency. And vice versa.

 

Excellent info.

I don't know anyone with any engine that would change their oil only once a year, so to me, corrosion is a non-issue with titanium. If an engine is started and run so little as to worry about corrosion under the bearings, my biggest concern would be the damage to the rings and rust in the cylinder walls from non-use!! And as stated, never clean titanium with chlorinated chemicals--ie: brake parts cleaner. I've used titanium rods in IHRA drag race engines and also in dirt late model engines-- the only reason for there not being more widespread use is the cost issue. As JCR stated, titanium rods are used in the Acura NSX, and as I remember, was the first production car to do so. I doubt seriously that any car maker would risk putting such a high tech and expensive item in a production car, if there was any doubt about the quality or longevity of the part. Rod bolts are not an issue either, a good engine builder will log the untorqued length of a bolt and during subsequent rebuilds re-log the length and a bolt that has stretched beyond a certain amount has gone beyond it's useful life. (yes, re-torquing a bolt or too many cycles will naturally stretch a bolt - upper end race teams have calculated through years of experience how many cycles a bolt should last, much the same as the aviation industry) Galling on the threads is also a non-issue, because to achieve the proper stretch or torque amount, every bolt manufacturer requires the use of a specific thread lubricant on the threads and under the bolt head, to obtain correct readings. A rod bolt actually stretches a certain amount to provide the right clamping load.
As far as galling on the sides of rods, the moly coating, if applied correctly, will last for a very long time. You have to remember- the oil fed to the rod bearing is also pushed out between the rods and a lubricates the rod sides too. Too much side clearance and the oil is flushed from the rods too quickly resulting in low oil pressure, too little side clearance and the oil at the rod becomes overheated and results in damaged bearings and flaking of the moly coating.

Lighter weight results in more horsepower, period. An engine with lighter rotating weight can be driven deeper into a turn and accelerated more quickly out of the the turn because of less rotational inertia, resulting in faster lap times. The only advantage to a heavy rotational weight would be in drag racing with a manual transmission car with a very small cubic inch engine. Some modified eliminator cars use a 50+ lb. flywheel to keep the engine rpms up during upshifts to keep the engine in it's powerband, because the small engine decelerates so quickly. Inertia.

 

It's about 10 hp on a V8 from what I've read. The gain is from reduced friction in the bearings due to the lower loads. You would see more I guess on an inertia type dyno.

The extra rod weight act the same as flywheel weight really. The energy you put in to accelerate them is exactly the same as the energy you need to take out to decelerate them so the net is zero.

 

I know a lot of them, myself included. On a car that only drive 3k miles a year, I generally only change the oil in the fall when I park it.

There should be oil under the bearing ever but it leaks in and it's the oil that causes the corrosion, not a lack of oil. Crevice corrosion is a very different animal form what you normally think about when you think corrosion. What is seen on old used Ti rods is like crazing or cranking up to a few thousandths deep, deep and wide enough to catch a finger nail in is the description I was given. This would never happen in a race engine that is torn down tha the parts cleaned on a regular basis, but leave it together for 10-15 years and there it is.

Car makers are not concerned about forever or multiple rebuilds. 10 years or 100k miles and 1 assembly is all they care about. The the rods we're talking about here are up to 13 years old now and still working just fine so the factory engineers have done there jobs.

The question I have is are the 13 year old rods still acceptable as a used part to put in a fresh engine that I don't expect to touch again for another 10 year? Do they still have full strength or is the corrosion causing stress risers and fatigue in the big end? I suspect that you're right and they're just fine but I don't want a whole in the side of the block I've spent 3 month working on either. New Ti rods (that I can't afford) wouldn't scare me a bit...it's the old ones I can afford that worry me a bit.

Strech and fatique are very different thinks. A bolt can be fatiqued and on the verge of failure and still mearsure as new in length. To me it seems best to just replace them every season or 2-3 tear downs and not worry about it.

Galling on the thread is a non issue [bold]IF[/bold] the correct lube is always used and the bolt threads properly cleaned and in good condition. Just something to look at and Ti is more sensative to prblems than steel.

yes, the question is how long and how do you know when it's time to recoat?

My only concerns are just how long is it safe to continue to use and reuse Ti rods....I don't know and I haven't been able to find anything information to guide me in any way.