what size of piston do I have?

[42JOHNNY]

I took a piston out of the block and it mic'd out at 4.458,I thought 502's were 4.466 standard. was I told wrong?
If so what size do I have??
The guy who pulled my motors said they were new pistons and they look new.
Only markings on the pistons are SRP 75f ???
I need to get a ring set, even if these look good...

johnny

 

[J.T.]

12524293 is the GM part # for the ring set ( individual, not 8)
for a std bore 502

 

[42JOHNNY]

12524293 is the GM part # for the ring set ( individual, not 8)
for a std bore 502

But what size do I have?? standard??


johnny

 

[J.T.]

But what size do I have?? standard??


johnny

Sounds like standard to me.....next increment would be .030 over
or 4.5"

I used the 12524293's when I rebuilt my stock bore 502's
earlier this year.

I had to file them to get the gap at the right mfg. spec. though.

 

[cigdaze]

The standard GM 502 bore is 4.466"

 

[42JOHNNY]

The standard GM 502 bore is 4.466"

Maybe me or my mic is off a little.

Thanks all.

 

[RMBuilder]

42JOHNNY
The standard bore size for the newer GM 502 is 4.466”, some previous Gen blocks delivered @ 4.468”. If (big if) you have the SRP OEM replacement pistons for the 502 they would be part # 281916. The .002” over on the SRP pistons would accommodate the hone, while keeping the piston to bore in spec. The P/W on the SRP line is significantly tighter than a 2618 alloy (JE) piston.
Bore Size: 4.470
Oversize: 0.002
Dome Volume: 1cc
Weight: 665
The ring set is as follows;
JE Pistons Part#: J100S8-4470-5
Description: 1/16-1/16-3/16 4.475 4.475 MOLY TOP/CAST 2ND/3PC STD OIL

Ideally you would validate both the bore & piston size prior to ordering the ring set.

Bob

 

[42JOHNNY]

Will do and thanks again.
I was told when I bought the boat, the new owner wanted the motors pulled and rebuilt even though they had little hours on them, then he had it and lost a bearing where it sat for years before I bought it.
He did not know what was wrong with the motor as it had good oil pressure and ran fine, just something was not right so he parked it.
that is when I took it out to launch and found this out to, something was not right. So we pulled the motor, and found a spun bearing. But the pistons/bores looked good. so, now the bottom end is fine and now need to work on the other parts, I have not got into the other motor yet to see if all is the same with it though.

johnny

 

[jeffswav]

42JOHNNY
The standard bore size for the newer GM 502 is 4.466”, some previous Gen blocks delivered @ 4.468”. If (big if) you have the SRP OEM replacement pistons for the 502 they would be part # 281916. The .002” over on the SRP pistons would accommodate the hone, while keeping the piston to bore in spec. The P/W on the SRP line is significantly tighter than a 2618 alloy (JE) piston.
Bore Size: 4.470
Oversize: 0.002
Dome Volume: 1cc
Weight: 665
The ring set is as follows;
JE Pistons Part#: J100S8-4470-5
Description: 1/16-1/16-3/16 4.475 4.475 MOLY TOP/CAST 2ND/3PC STD OIL

Ideally you would validate both the bore & piston size prior to ordering the ring set.

Bob

Bob, glad to see you here. I was not sure if you posted on this site. For those of you that do not know Bob, he is a true expert on engine building. If you want to go fast, build power in a usable RPM range with a good idle. This is the guy to talk to!!!