Piston pin

Hello every one

Tell me, is there any formula for calculating the load-bearing capacity of piston pins? I have Wiseco pistons with S625 pins and have written several letters to the manufacturer, but unfortunately have not received a response.

I assume that when a certain torque is exceeded they will begin to destroy the pistons, but I need data, I don’t have time for experiments. 100-125-150 nm per cylinder?

Do you have experience in increasing the clearance of the pin and piston and how, in your opinion, is it correct to do this (if this statement is true)?

What, exactly, are you planning to do, and why do you have concerns? I really think you're overthinking this from a limited understanding of the whole loading question, especially with the use on N.m for the supposed loadings.

I don't recall the last time I even heard, or read, of the 'pin being a problem - in every failure I've been aware of for decades it's been either down to piston failure or connecting rod failure, with just one or two instances of retainers coming loose or lubrication break down.

The piston manufacturers have the tools required for calculating the loadings on the 'pin, and will have build in massive strength reserves for bending and shear resistance, and the crush loads on the pin locations in the small end and piston.

Remember, the problem isn't the "torque", per se, as that doesn't actually mean that much and isn't the correct terminology or application. It's the PEAK compressive loads, that might be present with detonation or extreme boost level, and the tensile loads.

While you can calculate the shear, bending, and crush loads from the pin dimensions and material, and the piston and the connecting rod dimensions, it won't mean that much unless you know exactly what the loads from the piston are, in either direction.

My advice is to use what is supplied with the pistons, install them correctly, and stop worrying about the 'pins - there are many other concerns that will potentially destroy an engine well before a pin failure is even on the horizon.

If you are, however, really paranoid, you may be able to upgrade the pins when purchasing the pistons, or buy them from specialist manufacturers.

I don't think I'm being paranoid) But thanks anyway. Unfortunately, I did not receive information other than value judgments.

I actually upgraded one of my engines to Wiseco S710 piston pins rated at 1000HP+. The engine is used in drifting, where there are quite long loads on the combustion chamber. We actually drive EFR 8474 on six-cylinder engines and alcohol-containing fuel. And yes, I do worry about the piston pins. Sorry

And yes, I understand that it is more correct to measure the load by pressure in the combustion chamber, but torque is its derivative, which I consider appropriate to use

Ah, pins aren't going to be anywhere near a concern - what you're going to need to be aware of is the thermal loading on the pistons, if you can do so, use oil squirters on the underside of the crowns. Make sure you have good oil, charge and coolant coolers, good fans with plenty of airflow to draw air through them, and some means of monitoring their temp's. An alcohol percentage will help lower temps a little, but you're still putting a lot of heat into the fluids.

By their nature, "value judgements" are subjective, and while you can calculate the pin's strengths - you know the material and hence it's limits, which with the known dimensions and piston mass, acceleration profiles, etc. which will get you in the ball park for the dynamics. But unless you have also logged the cylinder pressure profile, you don't know the applied forces from combustion. What you should know is that the risk of a pin failure, by empirical testing (the lack of people reporting breakages or other failures), is negligible.

Is there any particular reason for this fixation?

Thank you. I realized that I could potentially ignore this problem. But I can not )

The specific reason is that every aftermarket piston manufacturer has a line of heavy duty piston pins for their products (CP, Wiseco and other). And I think there are engineers out there who understand the limitations of their products and their view is that for high power applications you need to use thicker piston pins. I don’t think that the presence of these products on the market has only marketing meaning. I also saw destroyed pistons in the piston pin area, and fortunately this was not my own example.

Based on the above, I would like to understand these limitations, and not just hope that everything will be fine

The 'pin upgrades will usually be of a better material ($$$) to allow a lighter 'pin to be used, or for custom piston designs that are able to take greater loadings and need a pin to work with the higher forces.

With the pistons being destoyed in the 'pin area, were you able to check on the condition of the pin(s)?

What will almost invariably be the problem is a/ the piston was subject to rpm well above its design limits and the piston tore off the pin, b/ the rings were gapped too tight and/or a "power adder" was used and the rings butted and the rings jammed which let to the pin pulling out of the bottom of the piston c/ the piston clearance was insufficient, which led to the piston seizing in the bore and the pin being torn out of the bottom of the piston.