Advice needed: 35-36 21 stud block

C

ckh

Member
After a sonic test showing uniform wall thickness, what is the maximum safe
overbore on a 35-36 block?
Thanks,
CKH
 
I try to always have .100”. No matter what year block. Sonic checking is just a good guideline. It too can fail you.
 
If it looks like the first picture in the water jacket it can have a hole at .060 like the block in the picture.—- the LB blocks have thin cylinder walls.
The second picture is a block bored to 3-3/8 and the thinnest spot is .220 ( a 59AB block with a long story and one of the cleanest water jacket I have seen)
 

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Kurt in NJ said:
If it looks like the first picture in the water jacket it can have a hole at .060 like the block in the picture.—- the LB blocks have thin cylinder walls.
The second picture is a block bored to 3-3/8 and the thinnest spot is .220 ( a 59AB block with a long story and one of the cleanest water jacket I have seen)
Click to expand...
577083


577084
 
Thanks for the replies. I bought this block (not an LB) some time ago. It had ben freshly

bored .060 over stock. I haven't had it sonic tested yet. Assuming there is no core shift, is

.060 over stock pushing the limit?
 
Last edited:
You should be fine with a .060 overbore. With that said, always have the block magged and then pressure tested. I've seen a lot of "good blocks" end up with issues after thorough testing.
 
.060 should be fine. I had a friend that bored one .100, that was pushing the limit. I'm not sure I would want one bored that mush unless you were just going to race it.
 
Thanks to all for your replies. You have now given me the info I need. I bought this block several years ago and had it magged, head surfaces, pan rails etc. No cracks
anywhere. The next step will be a sonic test which I should be able to have done
locally in Las Vegas where I live. If the sonic test shows no core shift, I should be able
to pressure test it myself as finding anyone in Las Vegas to pressure test any flathead
is a loseing proposition.
Thanks again for all your help.
The Ford Barn come thru again.
CKH
 
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