cylinder wall pit

riotwarrior

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To the OP

IMHO and it's just mine, now that we have some clear concise info and background we can offer up suggestions and advice.

Clearly anyone reading this thread understands how the nature of INTERNETADVICE works...someone asks a ? and if there isn't enough data we start WAG right off the hop!

So when we get info, those WAG usually are well....slightly off for the most part.


Lets look at this realistically, shall we.

It is said to be rain damage with a bore and hone to 0.030" on a 6.9" block.

How deep is the pit clearly you can "pick" it with a pick but realistically how deep is it. In you best WAG what is depth of that pit?

From what I can see, I'd say upwards of 0.010-0.020 deep but small in size.

Is this a RACE engine making max power for 500 miles? Nope it's a slow methodical engine that makes good power and is reliable.

Our engine speeds are not very high, and the piston speed as it travels in the bore at run speed isn't all that fast but quick enough to pass over that mark quickly enough to not warrant a large concern. Once the first ring passes there is a micro second before the 2nd and third rings pass.

Bottom line unless you intend to make BIG boost, or run this engine WOT it's likely NOT going to be a significant issue.

Best case, Sleeve that hole....

Or

Run it!

Choice is yours.

JM2CW

Al
 

Mikey89014

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i guess i will try it and see what happens.. hopefully its just an insignificant flaw. this is an 83 block, but there are no cracks in it. I have another 87 6.9 block that is .030 over, however i tapped a headbolt hole with a 7/16 /24 tap , accidentally, instead of the right tap, now i dont trust that hole.. thanks all
 

bike-maker

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You could always heli-coil that head bolt hole. I've had to heli-coil lots of big block chevy's; they're notorious for pulling the threads out of the deck.
 

gatorman21218

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for those of you who think boring a 7.3 .030 is risky consider this... when you bore .030 over, you are taking .015 off each side of the cylinder wall. .015 is about the thickness of a playing card. If that uncovers cavitation, then the block was about a sneeze away from cavitating anyway.
 

racer30

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Now that we know its a 6.9... Run It..... The root cause of cavitation is vibration of the cylinder wall. Cutting a 7.3 cylinder wall thinner will make it more flexable and then more likely to cavitate. Using sca's is the only way to reduce cavitation at a chemical level. Boring a 7.3 block with a known coolant history would be the best case. boring a 7.3 block with a unknown coolant history is not a good choise. Boring a 6.9 .030 is nothing to worry about. Having a pit in the cylinder won't cause any problems.
 

idiabuse

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Education

for those of you who think boring a 7.3 .030 is risky consider this... when you bore .030 over, you are taking .015 off each side of the cylinder wall. .015 is about the thickness of a playing card. If that uncovers cavitation, then the block was about a sneeze away from cavitating anyway.

POW! you hit the nail one time on the head, you dont need anymore pounding. WELL DONE! Oh The Sky is falling spend another $300 machining a block cause lack of information takes too long to absorb cookoo

Sleeve= Decking=$$$


LOCK THIS THREAD!



JAVIER
 

yARIC008

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I think the true answer to this is more about what type of person you are. Are you a measure once, cut twice kinda guy, or are you a measure twice, cut once kinda guy?

If you want it right you fix it, if you don't, don't fix it.
 

idiabuse

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I think the true answer to this is more about what type of person you are. Are you a measure once, cut twice kinda guy, or are you a measure twice, cut once kinda guy?

If you want it right you fix it, if you don't, don't fix it.

OMG fearmongering
 

jaluhn83

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If you're going to use that line of logic you'd better sleeve all 8 cylinders..... and x-ray the entire engine just in case there's cracks.... and replace every piece that *might* possibly have wear on it just in case...

This isn't rocket science or nuke gear - good enough is ok.
 

PwrSmoke

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If you're going to use that line of logic you'd better sleeve all 8 cylinders..... and x-ray the entire engine just in case there's cracks.... and replace every piece that *might* possibly have wear on it just in case...

This isn't rocket science or nuke gear - good enough is ok.

The key to the "good enough" philosophy is when you can look at a part with your own eyeballs, measure it up and have the knowledge to evaluate its condition against the projected future use of the engine. All we have here is a not-so-close-or-sharp digital photo to go by yet here we are making proclamations like Carnac-the-magnificent-mechanic. Overall, it's foolish to both accept the advice you get under those circumstances and silly to make it. If you advise someone under those imperfect circumstances, it's best to err on the side of caution. If a guy spends the extra money to do something that may be overkill, well at least he can go about his life with no trouble. If he ignores a problem based on advice here and then has an oil burner, or worse, coolant in a cylinder, he's got the added expense and effort of a second teardown to fix a problem that was staring everyone in the face all along. I really don't think that's the case here. The most important consideration I found here was that the machinist wasn't too worried. He's the guy who had his eyeballs on the problem and his opinion should be at the top of the list. The only point I'm making here is to reinforce what was said above... we're just a bunch of internet jockies that have not seen the problem up close and our advice is worth just as much as the OP paid for it. The machinist made his estimate knowing he would be at least somewhat responsible if he made the wrong call.

PS: I recently overhauled my 6.9. Take note of the difference between a "rebuild" and an "overhaul." In the latter, you evaluate what's there and replace only what's needed right now and in the foreseeable future.
 

jaluhn83

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That is true.

However, I can state with 99% certainty that the defect that is seen is *not* cavitation, as can anyone who really understands the science behind cavitation and doesn't just say "OMG, cavitation-Ah!!!!!!"

The OP is obviously going to know there's something a bit off in that bore, but his question wasn't "if I want to fix it right what do I do," it was "do I **need** to do anything to this to have a functional reliable motor" 2 different questions.
 

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