How far 409 overbore possible?

[wally409]

At Christmas my family and I visited my brother and I swapped him a small block for a 409 truck engine he'd had in his garage for a couple of decades.
It was apart and I saw that there was a ring ridge at the top of all cylinders and an especially deep ridge on the number 7 hole. I looked at the top of the pistons and initially didn't see any indication that they were overbore.
Last Wednesday I took the block to the machine shop I always go to and was told the fellow I usually go to (my age - over 50 and has built 409's) was gone for the holidays so a young fellow measured the bores and told me they were all
.050-over with the #7 hole, .080-over.
I thought that he had made a mistake and it didn't make any sense to me until yesterday when I cleaned up the tops of a couple of the pistons with a wire brush and discovered that they are .030 over.
Seems like his measurements were correct so I'm assuming I'll have to go to at least .090 over to clean everything up.
I'm going to take the block back to my friend at the machine shop when he's back in a week and a half - and the numbers probably won't change.
Can I safely bore it to 90-over or more? Or should the #7 cylinder be sleeved?
The block looks good in every respect - no visable cracks or breaks anywhere.
Appreciate any input.
Thanks, wally

 

[CDNpontiac409guy]

Wally, .030" pistons in bores measuring .050", is pretty "surprising"
in an .080" bore ?... pretty "fishy".

I recommend waiting until the head guy ( no pun intended ) gets back. I think you'll find the measurements to be VERY different.


As for max bore ?
I know of a number of 409 blocks running at .125" over. No issues.
However, none of us that I know of, want to see more than .060".

 

[Phil Reed]

Over-size pistons

Wally:

You can get just about any size pistons you want but NOT the rings. You just have to make sure that you can match the rings to the bore size you need. .070" over pistons take a standard bore 455 Buick ring. Other than that, Aubrey is right on....for street use I wouldn't go over .60" either.

JMHO

 

[wally409]

Thanks for the input guys - I'll have to wait until Don gets back to the shop in a few days and then we'll see what the next step will be - hope the block is salvagable.
I had not thought about the rings - that's a big issue of course.
Where did the guys with the .125-over pistons get theirs from?
And do they run them on a regular basis or do they have to be careful about how hard they mash the accelerator? Or do the 409's just look pretty between the fenders?
Thanks. wally

 

[Skip FIx]

On a related question what is the least clean up bore size that there are decent ring sizes for?

 

[CDNpontiac409guy]

On a related question what is the least clean up bore size that there are decent ring sizes for?

.008"
Then maybe .028"

 

[Tom Kochtanek]

.100 over

I'm running a 1964 "422" truck block in my '62 Impala SS that was .060" when I got it. Had one bad hole (corrosion) that cleaned up at .100" (after sonic checking the wall thickness) so I had 'em all bored to .100" over. CPG supplied the pistons (Ross forged) and the ring package.

I have about 3000 miles on her this first year, no overheating and she seems to be OK. Mostly street and highway driving .

Initial inspection of the cam area in the front of the block can tell you a little about whether the block suffered "core shift" when initially poured, but a competent machine shop will help a lot .

Good luck!

TomK

 

[Skip FIx]

Both my blocks were cast piston blocks and have pretty decent bores so thought about as little as possible.

Still kick myself for that one with a dinged cylinder from a dropped valve we threw in the dumpster in the 70s, along with the exhaust manifolds from the header swap! A sleeve probably would have saved it.

 

[oldskydog]

A slightly different and probably dumb question on the same subject.
There is common knowledge about sonic testing but I have never seen anything about what the results mean. I had my 61 block sonic tested at .060 over and the maximum thickness in some areas of the non-sleeved cylinders was .240 and the minimum on the sleeves was .100". What is the generally acceptable minmum wall thickness?

 

[Fathead Racing]

A slightly different and probably dumb question on the same subject.
There is common knowledge about sonic testing but I have never seen anything about what the results mean. I had my 61 block sonic tested at .060 over and the maximum thickness in some areas of the non-sleeved cylinders was .240 and the minimum on the sleeves was .100". What is the generally acceptable minmum wall thickness?

.100" is what I belive is the minimum thickness.

 

[dq409]

A slightly different and probably dumb question on the same subject.

My roommate says,,,,

"There are no dumb questions,,, just stupid people !!!"

 

[wally409]

Aubrey - you were right.
I found out that Don was back at the machine shop today so I brought the block over to him and he measured it.
It was his son who had previously measured it and he's just starting his apprenticeship so I'll have to cut him some slack.

Anyway, seven of the cylinders will clean up nicely at .040 over - but the # 7 hole has to be sleeved. It really got deeply worn. You could lift up the block with your fingernails on the ring ridge.
He thinks it never got enough oil just after it was rebuilt to .030 over and asked me to bring the crank over to see if it failed somewhere at that point.

S0 - this is good news for me. I'll be able to save the block and begin the rebuild sometimes in the next few months.

Don says he has a couple of sets of resized big block rods in his shop so I think I'll look for an excellent set of used 11.5:1 pistons that I can mill down to use in the rebuild.

Again, this site is way better than any university or technical school in the country.
Wally: bang