Acceptable cylinder wall thickness

[Fision]

So I got the results of my sonic check today and the thinnest spot is .239”. Since the test is a spot-check of many points there may be spots that are thinner. The cylinders are consistently thinner at the tops, and are well over .300” as you travel toward the bottom.

I would need to bore ~.030” to clean up the cylinders, which will remove a further .015” from the wall thickness. The engine is true a factory turbo with 201k miles and an unknown history (I’m assuming “neglected” based on the condition of the truck I pulled it from and the engine internals).

What is the acceptable minimum wall thickness?

Anyone come across actual recommended specs?
It’s very easy to spend other people’s money and say “just sleeve all 8”, which I may do, but at $800+... I’m already going to have more in this engine than the truck is worth. Additionally a 1/8”(.125”) sleeve doesn’t “add” thickness other than what is recovered getting back to a stock bore (about .015 in this case).

The machinist also mentioned the possibility of a ceramic coating of the coolant passage, something he’s done on the race engines he’s built. Anyone heard of this?

 

[Thewespaul]

There’s no spec for cylinder thickness as far as I am aware but most guys won’t bore past 20 thou, 30 thou is really pushing it. As far as ceramic coating the cooling passages I’d stay away from it, you don’t want an insulator between the cooling passages and the block in a daily driving application. In a racing situation it is common place to do that

 

[Fision]

Thanks for the input Wes.
I don’t like the idea of boring the block at all, much less .030. But my feelings aren’t based on either real-world experience or on any hard engineering/metallurgical facts/understanding. This is why I keep pestering y’all with questions.
As to the ceramic coating, I assumed it was a conductive formulation rather than insulating (as it is on piston coatings, which I’m also looking into...). Why would anyone want to insulate the cooling jacket?

 

[Oledirtypearl86]

.239 is over 1/4 inch in my book that's good are you worried about cavation

 

[Fision]

.239 is over 1/4 inch in my book that's good are you worried about cavation

Possible cavitation, cylinder wall flex, long term durability, etc. From this point on I can control its maintenance, so hopefully further cavitation won’t be an issue, but if the wall is already too thin...

 

[Oledirtypearl86]

I'm no expert but 1/4inch is quite a bit and will hold a lot of stress I feel any motor has great benefits from being maintained properly and if any further cavitation can be prevented from proper filtration and sca supplements that's my two cents worth and I wouldn't **** .020 in my bore

 

[Macrobb]

I had mine bored out .030. It had no issues for a year until a connecting rod decided to snap in half.
It still held coolant for another year till I took it apart. Long term, I don't know, but it would probably be fine as long as you put good coolant in it.

 

[Fision]

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This is the sonic report.

 

[Fision]

Anybody else get a sonic check or have numbers/experience to report? Like oledirtypearl86 has said, 1/4” seems pretty good, and most of the cylinders will be at least close to that even after boring...

 

[Oledirtypearl86]

How do the walls look and have you checked them for absolute round

 

[Fision]

How do the walls look and have you checked them for absolute round

Excellent question. I don’t know that is has been checked for round yet. 2 of the cylinders had definite wear at the top that you could feel, but overall they looked ok (as I recall. It’s been 4-6 weeks since I dropped it at the machinists). I suspect at least 2 holes will need sleeves because .030 probably wouldn’t clean them up. But that’s just a guess on my part.

 

[Thewespaul]

Sonic measurements are good to get an idea of how much cylinder wall material you have, but it’s not going to pick up what’s the real killer with the 7.3s which is pinhole cavitation. I’ve sleeved a ****** bore 7.3s that had a pinhole from cavitation without ever being bored out, the amount of material you have is plenty to hold combustion in, but there’s no way to predict cavitation. The way I look at it is 30 over in any 7.3 becomes a risk, and if you are restricted with time or money and need this engine to work you have to decide if that’s a risk you can take, otherwise you would be best off finding a block that’s bores look better.

 

[Oledirtypearl86]

I second what theWespaul said if you have 2 you can feel I'd either sleeve them or wait till the could get a block if it comes down to a block let me know I have one and am itching to take a trip to Alaska

 

[Garbage_Mechan]

I second what Wes said about the pinholes. You can't see the coolant side of the cylinder wall on these engines. But I have seen the cavitation holes in Big Cam 400 Cummins and IH DT466 liners which are removable, you can hold in your hand and look over the coolant side. It is not a general thin spot but an actual pit that almost looks like there was air in the casting when made. Usually a cluster of them each no bigger than a pencil lead. I once had a DT466 in my fleet we did an inframe on, was running great for 2500 hours (about 40,000 miles) the started getting coolant in the oil. When we pulled the cylinder liners they still looked brand new on the coolant side except one had a cluster of pits and one all the way through. Turned out my boys forgot to put Nalcool in the coolant.

I had a 90 7.3 that I acquired at 99,000 miles. Was really happy to get it at a great price. One week later, it was hydrolocked with coolant on top of the piston due to a pin hole. No body knew much in 1994 but I took it to a trusted shop and they sleeved it.

Moral of the story: I would not trust any 7.3 IDI block to NOT have cavitation unless I personally was in charge of maintenance for it's prior lifetime.

I'm sure there is a pattern of what cylinders and what location in those cylinders normally get the cavitation. If it were generally in the same spot, the it could be narrowed down by testing the exact location with sonic. But I would still sweat it.

John, the Garbage Fleet Mechanic

 

[Garbage_Mechan]

Anybody know the cylinder wall thickness on the 6.9? guessing about 1/8 in thicker?