TOPIC:

I got my exhaust hole welded so I decided to try getting my bike running today. Ran into two problems at the cam chain tensioner.

One, the threads for the top bolt are stripped (this explains the leak I had on my 3k mile ride). The bolt spins in the hole and even wiggles some.

Then I found this:



A crack in my block across the tensioner's mounting surface.

I could use a recommendation on what to do. I love this bike and have spent a good deal of time and money on it, including having the cylinders honed, so if the answer is to cut my losses junk it, please break the news softly.

I was thinking maybe I could take the engine to a shop and have them grind out the crack and weld it back, then re-tap the threads while they're at it, but that sounds expensive.

thats a bummer but i think its in an ok spot to be welded. The only oil that spot would keep from leaking out is oil spashed by the cam chain.

Id bet a good weld job would work, and the only other option is new juggs.

good luck on getting it fixed man

bummer indeed...

wouldnt be hard to weld but add to the cost fly cutting the block top surface too. to do a good job youll want to weld the top of the crack too and you'll have to take a light cut to make it straight,

look at the bright side, you'll have higher compression now

are you on stock pistons? if you mange to find an ebay stock sized block in good condition and do a simple swap i think it'll be cheaper than welding and fly cutting.

what's a bit worrying is why this happened in the first place, would check that after taking it appart, quite odd.

TG

Tap the top bolt hole to 1/4" if it's not too sloppy and don't worry about the crack. It doesn't look that bad from what I can see of it.

Or you could stress relieve it and JB Weld it.

Looks like someone missed a bolt when trying to get cylinder head off?

That's a fresh crack. Before any type of repair is done you need to find out what caused it in the first place. Personally, I'd swap out the block.

Is the long white line an extension of the crack?

Patton wrote:

Is the long white line an extension of the crack?

That's what I was thinking. And it appears to be fresh. Theoretically that whole chunk of aluminum could break off.

That white line is part of the crack. It sounds like I need to replace the block. I have no idea what caused the crack, but there's a chance it's been there for a while. In fact, I think the top of the chain tensioner is flattened out in line with it.

Replacing the block is.. probably possible. I just got the sleeves honed and matched to my rings and did a great job wearing them in. It'd be a shame to waste that money and work. How easy would it be to swap those into a new block?

As for the cause: the only thing I can think of that's odd in there is I used two new bolts in tightening the head on and these bolts come straight through to that point. I bought stainless steel ones and ground them down to size. I tightened them per the torque schedule in the Clymer manual and in the specified order. There is a slight chance that I popped the nuts loose and not the bolts with the valve cover on. I doubt I was that stupid but it's possible.

It's pretty clear now that I can't have this welded and fixed in-frame which was my lingering hope.

Damn, not good man.

I've got a block here, if you need it let me know....

It should be very easy to swap the sleeves. Once you get youe new block (should be like $20 on ebay, any kz/gpz750 4 cylinder block will work). Put the new block in the over at 450* when the wife is not around (it will stink) put it on a junk cookie tray head side UP, and wait till you hear the thud of the blick sliding down the sleeves.

Do the same with your block but make sure to number the sleeves so you can have them installed in the right hole! As far as I know the sleeves do need to be pressed back into place with a hydraulic press... but having a shop or buddy do that will be alot cheaper than the welding and resurfacing of the old block.

i have a block also if you decide to go that route.
looks to mee like there was a little oil in the hole when you tightened it.
compressing the oil will crack it as well.