Big Bore Kit - Big Problem

[toanjo]

JB Weld is excellent for low pressure areas...I have used it to seal 3" cracks in the water jackets of a jet boat engine, and it survived vatting the block 2 years later during rebuild time.

When you worked with JBWeld, did you have to apply then sand/shape? If so, what tools did you use? Would a dremmel work?

My only use of JB Weld was when I stripped the threads on a weaver sight rail for a ruger 10/22. I sanded the top of the receiver and JB Welded the sight rail to the top of the receiver. If seems to be holding up just fine, but there is no temperature issue on the gun like there might be on the bike.

 

[KRmilo]

The repair was on the outside of a 428 ford engine. I ground a trench the length of the crack and slopped the jb weld in the groove...There wasn't any need to shape it as it wasn't a mating surface of any kind.

 

[King Herald]

I'd suggest leaving it. It sounds like it was not causing the leak you saw, as like you say, that was on the other side of the motor. The gasket still has a narrow area to seal on, so I'd say a thin smear of gasket goo in that area would ensure no oil leaks out.

 

[toanjo]

I wanted to give everyone an update.

After speaking to about three different mechanics, we decided to just swap out the gasket and see what happened. Our plan was that if this failed, we would then try a liquid gasket, and if that failed, jbweld, and if that failed, actually welding the case.

So, after just swapping the gasket our for a new one, no leaks! So that is good, and everyone who suggested that the damage didnt go all the way through were correct.

We only have about 30 miles on the bike so far, and we are keeping our fingers crossed, but everything is running tip top as of tonight.

Now, moving on... one thing that didnt sit right with me during this whole fiasco was how the problem occurred in the first place. Now I am not a real mechanic (i.e. get a paycheck for being a mechanic), so I can understand if I make a mistake and I can live with that (God knows I make enough mistakes). But with this particular problem there were two pieces of metal on each cylinder head. Each piece of metal was exactly the same size and shape. Each divot left in the crank case and cylinder head were exactly the same size. Each divot was spaced exactly 5/8" from the corner bolt hole on each cylinder head.

So there were two spots that were damaged in exactly the same way. The probability that I could have screwed that up is crazy. I dont think I could do that if I tried to.

I would suggest that if anyone does this mod, that they inspect their parts before putting them on the bike. I cant help but think that these pieces of metal that caused the damage originated from the big bore kit (either the gasket or the cylinder head). I know that from now on, I will inspect very carefully any gaskets or parts that seat/seal for fit and abnormalies.

Again, I would like to thank everyone for their help and Ill try to give another update in a few hundred miles. Without your help, we wouldnt have had the confidence to fix this problem ourselves (and would have spent life changing money getting it fixed).

 

[King Herald]

It's hard to tell from the pics, but the chunk of metal that caused the damage looks worryingly like a piece of broken valve collet, the little semi-circular clip you use to hold the valve in place in the valve spring.

And if you hadn't found that chunk of metal I'd have said the damage was caused by someone using a screwdriver and hammer to separate the cylinder from the crankcase.

Anyway, glad to hear it is leak free. As I advised earlier, a small dink like that shouldn't make any difference to the seal, as there is no great pressure at that point.

I'm a machinist by trade, but currently earn a crust wrenching on 2000 psi air compressors in the offshore oil industry.