lighter wrist pins?

[Zuffenwerker]

I pulled a set of lightened wrist pins out of an engine. What’s your guys take on using them? They are noticeably lighter than stock. I’ve never seen these before and haven’t ever heard any talk from rebuilders using these on performance engines.

Light pins up top - a cp pin and a stock pin on bottom these are all 22s

[MoreGAS]

Hey- first weigh the pins you want an opinion of, next can you ID what they are made from?
If not , lighter may be better to a point, beyond that point when one of these fails you have nothing left to rebuild as it saws the engine in 1/2...I once looked down from the top and saw the ground through the shroud on one engine ....And if this is for a streetcar you are totally wasting your time as 90 pct of your time is spent below 5K rpm...what do you think you will gain? We once had the good fortune to pull apart a whicked- up Drag Tbo engine, and the pins were very hard to remove, being a more standard tool steel they actually bent a little, and we could chuck them up in the lathe w dial indicator, or crudely roll them on the table, and they were bent. One doesn't get this opportunity to check these out often and get a warning w the bending. Plus more brittle higher end metals(there are atleast 3 common metal choices) and Ti don't bend; when their strength is exceeded, it goes Kaput.
The piston manufacturers can consider your rpm, stroke to get mean piston speed, component weight Piston, pin, ring pack ...) and help guide you on what is reasonable risk or totally safe. Ask them what their model puts in for a max as if you share 7400 is your max RPM. One backhole will perhaps be 7400 +2K depending on the gear mis-selected. Make sure the model takes this in to consideration and ask .
My general feeling is Porsche doesn't put that 1/4" thick pin in a stock 3.2,3.6,3.3 Tbo cause they like wasting material (and they don't use poor Quality materials) on a chugged around streeter. It should give you pause.... ask the experts, take an educated guess thereafter.

Kevin
GAS Motorsport

[Henry Schmidt]

The best source for wrist pin specs is the piston manufacturer.
That said, lighter has it's benefits. FSR and X Brace piston wrist pins are much lighter because they a much shorter [sometimes 30%].
One caveat: In early JE racing pistons, the wrist pin bosses were seeing a multitude of failures [cracks] on pistons with high hours.
Two things were happening:
Amateur racers were exceeding the life expectancy of high performance parts and thin wall pins were flexing. This created a stress on the forging resulting in fatigue crack and eventual failures.

[Zuffenwerker]

The pins came from a high performance 2.0 engine real similar to an R or 906. I think those 2.0 engines used standard pins? Maybe they should be replaced due to the fact I don’t know anything about them. The pistons and cylinders are exceptional with great clearance and no oval or taper issues.

Thank you Kevin and Henry

[dannobee]

Inspect them for roundness and for any wear. If you have a machinists table, v-blocks and a dial indicator, verify that they're still round and true.

I'd run lighter pins on anything but a big hp turbo engine.

[Ollies930]

Unless you can identify the material the pins are made of, the dimensions are somewhat meaningless. You could reuse them or play it safe and talk to one of the better wrist pin manufacturers (like BME) and have them spec you a set of tool steel pins based on stroke, piston weight and rpm. How much is piece of mind worth to you?

[Zuffenwerker]

Never thought of checking wrist pins for runnout I might do that just out of curiosity in these thin wall pins. The little ends and piston pin holes don’t show any signs of unusual wear.

I’ll reach out to BmE and see about a new set, it’s a customer engine so I guess I’ll err on the side of caution