Thats a lot of technical reading if one was to go through it all at one time. Hiw about I summarize and you guys correct me if I am off. So piston stop method dived by two will give tdc readings within .5 degrees of the ferrari way. The ferrari way will retard bith intake and exhaust by that same amount. Does nOt matter in reality because even 1 degree off either way will not yield any noticable power changes anyway. Only important thing is to ensure timing is close so piston to valve clearances are good. Putting new belts on will advance the timing by 0.5 degrees max based on belt stretch. John still remembers his physics decades after graduating Daves going to be building and selling piston stops at stickyrx And finally John likes using Paint much to Daves dissatisfaction. I hope I got most of it. At least the semi non technical parts. Have a great new year everyone
This is wrong. I was getting an estimate based on the spread sheet James pointed to. That appears to be incorrect. In fact, wrist pin off set makes no difference. It changes how far the piston moves up and down the bore, but the motion remains symmetric about TDC, so no error with piston stop or Brian's suggestion.
Just a couple of thing: Piston stop gives TDC to within the accuracy you can read angles with your glasses on. Ferrari method will always have some uncertainty because you can't know what will happen until after it happens. Belt stretch has nothing to do with it. My belt stretched over an inch, but I still wear size 32 pants. I remember a lot of things. Most I can't talk about, but in this case it geometry. Dave will be making Sticky Stops. Paint is cool! Dave? Yes, Happy New year to all.
I think that this deserves a serious summary. 1) The Ferrari method. Put a dial indicator on the #1 piston. Rotate the engine is the forward direction. Observe where the dial indicator stops. Call that TDC. The method depends on the accuracy of the dial gage and the ability of the person making the measurement to correctly observe the motion. It can be sensitive to clearances, for example if you rotate slightly past TDC and try to back up. Piston motion is also insensitive to crank angle around TDC. To be accurate you must approach TDC for the direction of normal engine rotation. Best done with a highly accurate analog gage. 2) Piston stop method. Insert the piston stop in cylinder #1 and measure the crank angle in the CW and CCW directions when piston hit the stop. TDC is 1/2 between the two angles. This methods will give TDC to within the accuracy with which the degree wheel can be read if the wrist pin is centered in the piston. It is insensitive to clearances. If the wrist pin is offset an error will be introduced dependent on the size of the offset. The error will increase with greater offset and with how far the piston is down from the TDC position when the angles are measured.
Piston stops are available for the 355. I purchased a Ducati piston stop some years ago. Works fine, low cost.
In a prior post, you said you thought you needed to modify it. From what I recall, it's a hex body which likely won't fit into the small diameter counter bore of the cylinder head. We will produce a quality tool, from stainless steel, knurled shaft with internal hex as shown in this thread, with protective case at a very reasonable price point. And, it will be Made in USA, not China
Never leaving well enough alone I wanted to know the error in TDC when using the piston stop due to wrist pin offset. Since the offset in a 355 is unknown I did a parametric study for different offsets and stop depths. Here are the results for the 355. A 5mm offset would be 0.2" which would seems extreme. As stated, the error increases with offset and stop depth. But even in the worst case is only on the order of a tenth of a degree. For more reasonable values the error is insignificant. Dave Rock quotes 0.5mm offset for a GM piston. Image Unavailable, Please Login
Not even mentioning that the cam is half of that error. BFD if it compounded over the four camshafts, stop overthinking this, it isn't an F1 engine.......Modern engine management systems more than compensate for any cylinder to cylinder errors. Y'all are talking about a car that just MIGHT get driven 3-5000 miles a year, and mostly to and from the ego boosting weekly Cars and Coffee meets. 75% of the rice burner millenial cars will blow you away
Well, not really as we are simply discussing the methods of finding TDC which is the baseline of the entire cam timing process. Regarding if the precision is needed, that's an entirely different discussion and John and I share similar opinions on that subject. Why does it bother you or anyone else if we wish to discuss these topics and give them due thought? Let us overthink all we want - not sure how this effects you, Brian?
Just measured the pin offset of a BMW piston (M3 S14 engine) - about 0.5 mm so 355's pistons can't be far off.
Which is exactly why I hold the position that retiming the engine at every belt change is a waste of time and effort.
Per your chart, The shorter the dead stop, the more accurate? (obviously splitting hairs of hairs here ) I'm also thinking a larger degree wheel angle is more accurate to split vs say splitting 2 degrees? So, I'm thinking this would be a compromise? I'm on the first cup of coffee
A number of articles on the net say that the piston pin offset is in the range of 0.25 to 1 mm. One article mentions that it is typically 0.5 to 1 per cent of the bore diameter.
Just to give you an idea, the stop depth values are referenced to distance below the TDC position. With a 5 mm depth you are already some 28 degrees from TDC, 10 mm almost 40. With regard to error, now that is pretty much academic. There just isn't any that's relevant.
When designing the prototype, I just selected an aribtrary distance. I did not have the cylinder head drawing and did not measure with any accuracy how much length was needed. I'll screw my prototype into the cylinder head and measure how far out it projects, consider the head gasket thickness and get a value.
Good post I think it would be nice to have a gear reduction mechanism to turn the crank bolt. Could easily turn it very slowly/smoothly. Necessary? No, but I would like it.
Now that you mention it, what street car engine is more similar to an old F1 car, the F50? I only drive about 1000 per year. If dialing this in takes me an entire weekend and results in one more HP I'm happy with that. What's the definition of rice burner millennial car? Wouldn't need to line up with a new NSX or GTR to know the outcome but would try the rest If none of this matters in the least why all those extra holes in the cam gears? Could have saved a lot of time by just making all this stuff just bolt together in one position like a Chevy.
I'm going to do some experiments like I did the fist video to check repeatability. I'm going to go back and forth in rotation and see how much the lash is (if I can measure it).
It does matter, but once you have the pin in right hole nothing changes except the belts unless something fails. I'm still waiting for someone to tell me how changing belts can change timing more than that associated with the tolerance of the belt, about +/- 1/2 degree. We have an engine and cams and pulleys made of steel and aluminum. How to the dimensions of these things change if something doesn't fail or wear out? Ok, metal expands and contracts. Do we have to specify an ambient temperature at which the cams must be timed? All I every hear is denial.
Agreed if there is no wear the timing shouldn't change. Is there ever any measured wear on the cams? Lash between crank gear and lower timing belt drive gears? Maybe checking it is just an assurance there is no abnormal wear anywhere. Once the cam pulleys are in the right position are they ever changed again over time? Not sure, would be best to hear from someone that serviced the same car over a long period of time.
Just for the people interested inthe amount off a cam can be. I have heard that about 1 degree when the cam marks were lined up. If this was true what is your guys estimation in hiw far off of the alignment marks to make it as perfect as we can with these tools? Are we talking the thickness of the marks? Maybe 2 mm? Just a question i was curious about
I think one of the points John is making, and if not, I'll make it: With all the possible errors in methods and measurements, one is likely to undo proper timing than correct something that's not broken
Just trying to figure out how much the timing could be off and for the guys with no tools that just want a visual to understand that likely its only off maybe double the thickness of the cam marks. Or something along that line, thats all. What we are all talking about is the diff between the two methids as well as the accuracy you could get. I am also intersted in the precision one could expect with tools costing less than 500 bucks. My guess at this point, after reading the thread, is that Ferraris tollerance of +- 0.5 degrees is about all that can be expected for most owners anyway. That being said if we could quantify it for those people just looking at cam marks I am sure it would be appreciated. I think you kinda all ready said that above as well.
