Piston question

[Sonicman]

I have an 69 c10 with a 250 inline 6 and had it about 2 months. I am rebuilding the engine. Well my buddy and I were putting the rings on the pistons and he dropped one and cracked the side. Now where can I find one. We took it to a local machine shop and they said it didn't look like the original piston and that it is bored .060 over. This is my first rebuild so I'm clueless. I've looked at pics on ebay and seen pistons to a chevy 350 that look like my pistons and are bored .060 over.

Can someone please shed some light for this newbie.

[pritch]

Someone will correct me if I'm wrong-but I think they are the same as a 307 piston. But either way, they should be pretty common.

[LandonL]

Alright, first of all you know for SURE it's bored .060 over? If so the standard bore for my inline 250 was 3.875 so when you add the .060 over it brings it to a bore size of 3.935
Here are all the pistons with a bore size of 3.935 (.060 over) http://www.summitracing.com/search/P...eyword=Pistons

The ones that don't have pictures may have valve reliefs like yours have now.
Also, did your cylinder walls have a ridge you could catch your fingernail on?

[Sonicman]

I don't believe there is a ridge. The cylinder walls are completely smooth.
The one shop I did take my piston to told me that it is bored .060 over. I've only had the truck for just over a 2 months. I don't know the history of the the truck. What are the valve reliefs for? Does their placement matter?

[LandonL]

Well, you need to know the bore size before you buy your piston, if you find theres a ridge you can catch your fingernail on you might wanna have it bored again, not sure if you can go much more though.

[dwcsr]

Whats stamped in the red circle? is it 060? if it is then its a 60 over piston. 6 cylinders usually have flat tops or dished but not valve reliefs.
I have read that you can take a 250 six cyl. and put 283 rods and flat top pistons, so maybe what you have are 283 pistons and rods. There should be a casting number on the rod and piston

[Sonicman]

Yes the pistons are stamped 60. I see no markings on the rods.

[dwcsr]

I see that 307 pistons are 1.655 Compression height and the same bore as the 250 piston having a 1.640 Compression height, pin diameter is the same. You may well have 60 over 307 pistons in there. The book say the 307 has valve reliefs and the 250 is dished.

[raycow]

I agree completely with the previous posts. Those are definitely V-8 pistons, because an inline wouldn't have valve reliefs on both sides. Valve reliefs are needed on some engines to prevent piston to valve contact at the top of the exhaust stroke. Replace it with another of the same type, just in case there is a weight difference between the 6 cylinder and V-8 pistons. Install the pistons with the small notch facing the front of the engine.

Ray

[Davetopay]

Originally Posted by dwcsr

I see that 307 pistons are 1.655 Compression height and the same bore as the 250 piston having a 1.640 Compression height, pin diameter is the same. You may well have 60 over 307 pistons in there. The book say the 307 has valve reliefs and the 250 is dished.

Hmmm..if he does in fact have the taller pistons, that could be a cool hotrodding trick to bump compression.

[pritch]

Ah-I remember now. It's the 230 that is a direct exchange for 283 pistons.
Compare part numbers here for example:
http://www.flatlanderracing.com/trwpistonschevy.html

I keep forgetting that some PO had stuck a poorly rebuilt 230 in my Panel. I had to replace a piston 2 seperate times in the several years I drove it around before the tear-down.

[Sonicman]

Finally got my pistons, and who would of thunk it.....I got'em from O'Reily's. They are .060 for a 250 L6. I got all 6. There are no valve reliefs in them just a "D" shaped compression. Can't wait to drive her again.

Will get it all buttoned up in the morning. Gona take a break for a bit and then hope to get Clifford Performance exhaust headers and intake. Once again, thank yall for the help

[Sonicman]

Thank yall for sharing your knowledge. This is my first rebuild and I am really enjoying it. Keep it coming!!!!

[cdowns]

i'd get in touch with EGGE and see about sending them the bad piston so they could either matchup with an over the counter piece or if not they can reprroduce it

[dwcsr]

As cheap as these pistons are I would just replace them all with either the 6 cylinder or the 307's and be done with it, providing a bore job is not needed. If not lip is seen the clean it up with a finishing hone and measure the bores.

[PanelDeland]

I agree the one you posted looks like a 307 piston.If you can replace them with 307 ones or the 250 pistons for use with propane.The compression ratio will be higher 9:1 vs 7.5-8:1 which will give you a bit more power even in a stock rebuild.You may need to replace all of them to get a match.And they do need to match.