wrist pin fit

[andyelan]

Hi there

Just remember though, racers often run wide clearances because a free engine will produce more BHP. The fact that it might be noisy and have limited life before it needs a rebuild won't be a problem for them as BHP means everything. For a road engine things are different. Here smooth quiet running and long life usually take priority over ultimate power. Also, in general, a road engine can usually be given a longer and gentler running-in period after a rebuild than can a race engine.

I suspect this sort of thing could be a problem if you give an engine intended for road use to even a reputable race shop unless you explain exactly what it is you want from them.

Andy

[rgh0]

The only area a race engine may need wider tolerances is piston to bore clearances and exhaust valve clearance. These may be required due to hotter exhaust valves and piston tmepratures in a race engine.

In all other areas such as bearing clearances while you may select a specific point in the normal tolerance band and that may be at the high end of the spec range you typically dont increase the clearances.

For gudgeon pins to pistons the clearances become bigger at the higher operating temperatures in a race engine than in a road engine as has been observed in othr posts and I dont see the need to increase this clearance from the manufacturers spec if your confident in the manufacturers tolerancing and check that it is OK when you recieve them. Some people like fully floating gudgeon pins that float in both the small end bearing and in the piston. The JE fit is effectively fully floating as the light finger push fit into the pistons at room temperature will dissappear at operating temperature. I dont beleive you should or need to hone the pistons to make it freely floating at room temperature. The only reason to hone it if the fit was to tight in the first place due to incorrect manufacture and maybe some engine shops have got into a hait of honing all pistons to ensure they get a fully floatig end result.

cheers
Rohan

[rdssdi]

Rohan

Again I am in agreement.

It appears to me that automatically honing a piston wrist pin bore is most likely a habit based on some engine or after market piston that may have needed that done and it carried over to doing it with every engine many shops rebuild.

I am still conflicted as to what I should do. Use my pistons with the honed pin bore or attempt to get a new set of pistons which will match my present bore diameters.

Bob

[andyelan]

Hi Bob

Just to clarify my position, I no more agree with modifying parts anymore than does Rohan. I may check items, but I've never found it necessary to alter anything. I was simply stating the things I've heard said by others who beliveve it necessary. Personally I think they're wrong.

None of this helps you of course who now has a set of pistons which, right or wrong, have been messed about with. Certainly complaine to the guy who did the work but in the end I think you'll end up using the piston as they are. I can't really see there will be a problem, especially if the 1 to 2 tenth (1 tenth = 0.0001 inch) clearance is correct. I really wouldn't have thought it nesessacy to go as far as buying new pistons. Whats happened might not be ideal but I'm sure you'll be ok.

Regards
Andy

[rdssdi]

That seems to be the consensus.

If I were to contact the shop who did the honing of the wrist pin bore they would become indignant and bore me with details of their 30 years experience. It would not just be justifying their actions but they honestly believe it the correct thing to do. If pressed on why I am certain their answer would be suspect.

I always try to get the best possible information so when a job is done it doesn't have to repeated at a later date.

Thanks to all ho responded. Once the car is running I will listen for any wrist pin knock.

Bob