The absolute 'MINIMUM' cylinder wall thickness....

[BRENT in 10-uh-C]

"Granted, no one wants to spend $500.00 to sleeve a block back to 3.875, ...but they also complain when their block was bored too thin causing heating issues."

Spend the 500 bucks.

Brent, I’m not an expert by any means but would like to see if I can condense the comments. You seem to want an opinion and short of talking to the engineer that did the original blueprints anybody’s opinion is going to be biased based upon their own experience. If, theoretically, based upon sound engineering princeaples, a number (over bore/wall thickness) was put forward, there would be some that got a less than perfect original casting that would have failed. On the other hand, you could get get an exceptionally thick casting that would tolerate a much bigger overbore. If you are looking for a hypothetical number based upon original blueprints, that’s a commendable question for sure but there are very few (if any of us) qualified to answer the question in an unbiased opinion. Real life experience is all we have to go by. I’m not saying that your question is unreasonable or unanswerable but few if any of us are qualified to answer it.

Your points are valid. In society today, it seems most people need 'scapegoat' to pin the blame on when things go catastrophically sideways. If the newly rebuilt engine is overheating, the blame can easily be pinned onto the Rebuilder because they should have advised me before I spent this pile of money with them on a rebuild. This is why I am asking for a general consensus on where the line needs to be drawn on minimum cylinder wall thickness' so this never becomes something I need to deal with.

 

[BRENT in 10-uh-C]

All blocks are not the same! I have 2 diamond Model B blocks that differ quite a bit in the port area. One has very large intake valves and ports and they are just fine, the other has stock size valves and smoothed ports, not really enlarged. I ran the second one for quite a few years with no problems. I rebuilt it a few years ago and cleaned up the ports using only a sanding drum. When done I noticed a spot in the port, so I picked at it with an awl, and it went thru into water.

Yes, ...this is one of the main reasons why I purchased a sonic tester just to be able to find thin spots on these engines. Imagine if you had finished all of the machine work on that engine only to then discover that thin area!!

 

[Pete]

If you had to stake all your worldly possessions on getting this answer correct, I am asking this question regarding overheating due to cylinder bores that are too thin. What would you say the absolute minimum wall thickness an A-6015 Model-A Cylinder Block should be bored/worn/eroded/whatever to that you would GUARANTEE that a rebuilt engine would not overheat as a direct result of too thin of cylinder walls?

This is not a trick question, but a sincere question regarding giving someone sincere advice about. I honestly am not looking for 'He Said/She Said' answers about someone who got away with...., -but instead I want to discuss Ford's engineer's design tolerances, and what we would feel comfortable in giving sincere advice about. Thoughts??

As I see it, the answer to your question has 2 parts.

1 - If I was doing engine rebuilds like you do, I would first, sonic check the
cylinder walls to be sure it was a valid candidate for rebuild. To me, this
would mean an absolute minimum overbore from stock, not to exceed
.060.
2 - If you were doing builds like I do, there would be no warranty so all you
have to do is protect your reputation with quality work and consistently
build winners.
For those that may not know, all out race engines come with no warranty.

 

[BRENT in 10-uh-C]

As I see it, the answer to your question has 2 parts.

1 - If I was doing engine rebuilds like you do, I would first, sonic check the
cylinder walls to be sure it was a valid candidate for rebuild. To me, this
would mean an absolute minimum overbore from stock, not to exceed .060.

2 - If you were doing builds like I do, there would be no warranty so all you
have to do is protect your reputation with quality work and consistently
build winners. For those that may not know, all out race engines come with no warranty.

#1 - Yes, based on the thoughts of mine and several others, the prudent method is a maximum overbore of 0.060 and then sleeve back to 3.875" on a used cylinder block. The only other caveat is the cylinder walls still need to be more than 5MM or 0.200" when finished resizing at 0.060. That basically allows room for 0.020" of rust or pitting damage to the inside of the block.


#2 - Yep.

 

[johnneilson]

As I see it, the answer to your question has 2 parts.

1 - If I was doing engine rebuilds like you do, I would first, sonic check the
cylinder walls to be sure it was a valid candidate for rebuild. To me, this
would mean an absolute minimum overbore from stock, not to exceed
.060.
2 - If you were doing builds like I do, there would be no warranty so all you
have to do is protect your reputation with quality work and consistently
build winners.
For those that may not know, all out race engines come with no warranty.

It has been proven that 4.000 bores or larger do not necessarily cause overheating as the primary source
I just do not subscribe to this over overbore theory


However I have stopped doing any rebuilding and machine work unless it is done to my specifications ie oiling system, bearing setups, and part preparation including the final assembly.

J

 

[Flathead]

I'm always fascinated by the "just sleeve it back to standard" kinda like it never was overbored. If you are worried about thin cylinders why bore it more and then press in a sleeve with an interference fit that will be pushing on that thin cylinder wall 24/7.
I'm running a .100 over block with no issues and runs cool 5.5 head. Engine put together about five years ago.

 

[nkaminar]

Brent, You are not going to get an exact answer to your question. I agree with Updraught that liners should be installed. For one thing, they are harder than the original cast iron and will last longer. After spending thousands on rebuilding an engine, the cost of the liners is in the noise level.

The Alfa Romeo wet cylinder liners are 0.111 thick so you can use this as a rough gauge. The bore is a little over 4 inches.