Thread: What are boring oversize limits?

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Update on my 46 flathead, The only cracks(other than the guaranteed stud to water jacket) were in two valve seats which have been repaired. The machinist here found my .040 cylinders were tapered about .022-.025 from top to bottom, so an .060 oversize bore will not quite cover the wear. He recommends .080 or .100 oversize, but I cannot find any pistons in these sizes. Speedway sells some 4-ring .125 pistons, but is this going too far?
This guy has worked on a lot of flatheads and says they have plenty of meat on them, but I don't want to go out any more than is necessary.
Any ideas? Or sources for .080 pistons?
Thanks,

I'm by no means a flathead expert,But that sounds way too much for my taste. I kinda understand that flatheads always ran hot and 80 over is gonna compound that problem I would think...

I was thinking the same thing, but he seems to know his stuff and also why would they make them in .125 over?

Lots of 59a flatties were bored 3/16 over. True, some were water heaters, but 1/8" was considered mild. A good sound block is too hard to find to chuck it because of bore wear. Flathead Jack sells pistons for it.

if your not comfterble having it bored .100 over, have .066 over pistions made by EGGE this will cover what you need. he only deals with Cast pistions but will make anything you want, and he's resonable

Sonic check the block. You need minimum 0.130" wall after boring and honing.

Originally Posted by techinspector1

Sonic check the block. You need minimum 0.130" wall after boring and honing.

there ya go, I'd take what Techie says as gospel....

Just a bit over an 1/8th huh! I would have thought there was more than that. So how thick are sleeves? I guess if you were going back to STD that would give alot more room for a sleeve. Now the problem, I live in North Pole, Alaska. Sonic testing hasn't even been invented up here yet! Is there another way to measure it, say at the base of the cylinder?

Sleeves are 0.125"
I suspect that you'd have to move up the cylinder to get to the water jacket to find the wall thickness, but then....whoops....too late....now what??

I wonder if it's possible to get in touch with the folks who manufacture these sonic tools and find out if you could rent one for a short period. I assume they have mail service up there????????

Of course we have mail! It arrives by dogsled once every six months. Now that you mention it, are the tools your talking about the same as say a paint thickness gage? I think eastwood sells them to tell how many layers of paint (or Bondo) you have.

The general consensus is you can bore and 8-BA block to 3-5/16" without any problems. I have mine at 3-3/8" but the block was sonic tested beforehand. The bad news is that the machinist who did it is no longer in business. Try the motorcityspeedequipment.com web site.

Yea, I know what you mean, the guy that's doing mine is losing his shop soon due to a construction right of way. He said after they buy him out he will probably retire and he is the only guy in town I would trust with a fathead. What would the Cubic inches be at 3-5/16" bore with a 3-3/4" stroke. Thanks for all the info.

How soon is he losing it? CID would be approx 258 for an 8 cyl. 6 cyl will aprox be 194.

I'm not sure exactly when, but it's been in the paper as a proposed street change. One thing about Alaska there are only two seasons, winter and construction. I checked with EGGE as Matt167 suggested and they carry the .080 pistons I need which will keep me .040 under maxing the cylinders out. And after reading the motor city web site it sounds like I won't have any trouble going the .080 over.

I think Don Shillady still has a 4" Mercury crank for sale. Email him and ask.