max overbore?

john mullen

john mullen

Senior Member
I have found a 52 8 RT block that is .040 overbore. I'm not sure what it will take to clean up the bore as it has quite a bit of ridge in it . and I want to know how far can I safely bore it. the block looks fairly clean on the inside of the water jacket from what I can see. I will have it cleaned and checked out before I do to much. Any advice from the experts? thanks John
 
.125 over is quite common, any more you should have block sonic tested for wall thickness. The late great Rumbleseat had his bored to 3-3/8 +.030 but that is getting pretty scary.
 
john mullen said:
I have found a 52 8 RT block that is .040 overbore. I'm not sure what it will take to clean up the bore as it has quite a bit of ridge in it . and I want to know how far can I safely bore it. the block looks fairly clean on the inside of the water jacket from what I can see. I will have it cleaned and checked out before I do to much. Any advice from the experts? thanks John
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Hi John, we sell a bunch of kits with the 3.312" finished bores, it's really the most popular o'size we are involved with.

Sometimes I personally prefer to keep the bores at a mimimum to extend the block's life?? If your's is at .040" I would try .060" first, then go up from there. Most customers here don't get many choices/options, especially on the Flatheads, but the o'size we do leave up to them!

I have never had a (late) block that wouldn't take the .125" over.

(Add) If you're looking for power gains the ring choice/size becomes VERY important!

Thanks, Gary in N.Y.

P.S. Couple items strongly recommended, first, pressure test the block, do NOT rely solely on "magging", second, have it finished-honed with a block plate (if possible), and third, install 16 bronze-lined guides. There are others but we feel these are fairly important.
 
John,

My 8CM is .125 over and no problems there. I am sure .060 pistons and rings are available and I feel sure .080 are too.

If I had mine to do over I probably would not have gone more than .080 just in case I needed to bore it again somewhere down the road.
 
Ted!
I'm like you I don't want to go any bigger than I have to. I hope .060 will clean it up and if not... well whatever it takes . I thought .125 was something I read somewhere but just wanted more info. Thanks everyone. I'm going to use my newly purchased 75 year old kwik-way boring bar.. I'm gone do some on an old cracked block until I get the hang of it. thanks everyone and Wish me luck.
 
You do realize you should have your new pistons in hand to measure before boring so that you can "sneak-up" on the finished size with hone, FWIW. DD
 
The machinist that bores my blocks insists on having the pistons on hand so he can sneak up to size like DD says. Maybe you can talk to your piston supplier and work out a return guarantee to the next available size if the bore doesn't clean up. Just a thought worth trying.
John
 
I have a set of EGGY .060 and .080 pistons on the shelf I plan to work the .060 pistons first and hope it cleans up before they max out
 
The trick here is to bring the bore up to .003/4" from finish size and the block honed to finish size.
 
Thanks OL'Ron I'm gona practice on a bad block before I do a good one. I'm sure I can do it just want to practice first.John
 
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