hello

I have an engine that is already 30 over if i
go up to 40 or 60 will I need new pistons or
just the rings? the pistons look fine.

thanks, Muff

 

If you are going to go up in bore size you must get the pistons to match. No way around that.

 

why do you need to bore out? are the bores scarred? don't bore if they are not bad, it won't increase power it is just to clean up the cylinders. and if you go up past .040 over you will have overheating problems. stay with the .030 over if boring is not needed.

 

F100guy

The bores not scarred as far as I can tell.
I was considering boring after talking to the local
machine shop on the phone. I told them that I pulled the
heads off and found a small ridge at the top of the bore
and the pistons are stmaped 30. They told me I would need to
bore the block and redue the heads. I know the ridge is normal wear and I'm notrealy looking for more power (more power is good) but this is my brothers daily driver and I want it to be reliable. If it is possible to just remove the ridge and hone the cylinders a little that would be great it would save time and money. I think I would still have the heads done. any more
information you can give me on this will be appreciated.

Thanks, Muff

 

Oversize rings must be fitted with oversized pistons and not used to correct a worn bore by themselves. Generally, clearances normally run somewhere between .0008" to .002" piston to wall.

If the clearances are to great, you will hear the pistons slapping the bore! The pistons don't have equal pressure applied to them as they move up and down, it is actually on one side of the piston during compression and flips to the other side on the firing stroke.

Also, because oversized rings are designed to be fitted to oversized pistons, fitting them to standard pistons would result in the ring not protruding far enough into the groove on the piston and would not be an effective seal for compression.

521_Ford

 

Lisle Tools used to make a fairly inexpensive ridge reamer, check at a local, quaity auto parts store.

 

You also need to check to see if the cylinders are out of round not just for scoring. It would also help alot to know which engine were talking about. If you stay .040 overbore you should be alright.

 

sorry about that

It's a 79 351m

So from the replys I guess I do need to bore this block.

 

You or your machine shop should be able to check the bore to see if it's in specs. If he doesn't want to check them first it might be time for another shop. After all it's cheaper to check and not need bored than it is just to bore it. With that motor I think you can go 60 over if needed.

 

Daily Driver? If it were me, and I could barely catch a fingernail on the ridge (or a little bit more on most cylinders), I'd ream the ridge, glaze break the cylinder walls, and plop in a set of new rings. If it is running decent now, and not using a LOT of oil, doing that will pump up the compression, and probably cut the oil use. (I'd also do the heads)

If the cylinders were out of round before, it'd be using a bunch of oil... and be gutless... Just how well did it run? Take stock also of the value of the vehicle before pouring money into an engine.
Just my opinion, of course..
tom