Bad News

fr8shkr · Jun 22, 2009

Pulled the cylinders off yesterday. Everything looked good - pistons, cylinders, rods, cam, and head all in really good shape....and then I discovered....

Hopefully it can be welded up, but it looks like the bolt hole has already been heli-coiled once which will probably complicate things....

ILLF8ED · Jun 22, 2009

Ouch, you really have my sympathy! And it's the part with the engine number. Let us know how you resolve it. I think I'd at least check into welding. The helicoil can be pry'd out. Once you get the end loose, grab it with pliers and pull slowly.

BillT · Jun 22, 2009

It looks like the thread was stripped, and the helicoil put too much pressure on the case corner , causing the break-out.

The helicoil can be removed, that corner repaired, and a new thread tapped.

Cookie · Jun 22, 2009

Yup,

That's very repairable but it is going to cost a few bucks because of the several surfaces that will have to be machined.

splatt · Jun 22, 2009

I had been told that they may crack at the corner of the case stud were it is machined for the washer and nut, but that looks like the through bolt has hydrauliced on gasket goo or just plain bottomed out and pushed the top off the case, still it's totaly repairable at a cost.

Keith1069 · Jun 23, 2009

Really sorry to see that but it is repairable. When I replaced my damaged Maney barrels with 850 style 750 parts the new Norvil supplied bolts were too long by 040". They would not clamp even with an 030" base spacer. I check everything these days so was not surprised.

bigstu · Jun 23, 2009

My sympathy.
I think the hole had oil in it and on assy hydraulic pressure was locked in. If it was due to thin walls resulting from the helicoil repair it would have cracked through the side but not pulled the whole corner of the case off, surely?
There is a set of cases on ebay.co.uk.....both 750 and 850.....look at this number....220415471338
Stu

maylar · Jun 23, 2009

Threaded inserts were installed in those 4 holes at the factory. Someone must've tightened that one way beyond 30 ft lbs.
Find a good machine shop, it's fixable.

Seeley920 · Jun 23, 2009

That can be welded successfully. As for the ones on EBay, I've thrown better ones in the skip and wouldn't even use them as a doorstop :shock:

Coco · Jun 23, 2009

BillT said:
It looks like the thread was stripped, and the helicoil put too much pressure on the case corner , causing the break-out.

My guess is it's then heli coil that caused that also. Bolts tightened too much maybe?

swooshdave · Jun 23, 2009

fr8shkr said:

I think I'd be more worried about the RTV between the cases and falling in the crankcase. :shock:

fr8shkr · Jun 23, 2009

swooshdave said:
I think I'd be more worried about the RTV between the cases and falling in the crankcase. :shock:

That was all part of my Dad's handywork :mrgreen: He also broke and re-welded the front center cylinder mounting stud location. I've been giving him a hard time about some of the hack-job stuff that he did to the bike some 25 years ago (when he was my age :shock: ). He was definitely a fan of the RTV..

Jeandr · Jun 23, 2009

fr8shkr said:
swooshdave said:

I think I'd be more worried about the RTV between the cases and falling in the crankcase. :shock:

Click to expand...

That was all part of my Dad's handywork :mrgreen: He also broke and re-welded the front center cylinder mounting stud location. I've been giving him a hard time about some of the hack-job stuff that he did to the bike some 25 years ago (when he was my age :shock: ). He was definitely a fan of the RTV..

Be kind to your dad or one day your kid will give you a hard time :mrgreen: After all 25 years ago, RTV (the red one especially) was the best thing to keep oil inside a British bike.

Jean

swooshdave · Jun 23, 2009

Jeandr said:
fr8shkr said:

swooshdave said:

I think I'd be more worried about the RTV between the cases and falling in the crankcase. :shock:

Click to expand...

That was all part of my Dad's handywork :mrgreen: He also broke and re-welded the front center cylinder mounting stud location. I've been giving him a hard time about some of the hack-job stuff that he did to the bike some 25 years ago (when he was my age :shock: ). He was definitely a fan of the RTV..

Click to expand...

Be kind to your dad or one day your kid will give you a hard time :mrgreen: After all 25 years ago, RTV (the red one especially) was the best thing to keep oil inside a British bike.

Jean

Outside of not putting oil in it in the first place. Actually 25 years ago wasn't Yamabond available?

Cookie · Jun 23, 2009

It may have been but it takes a while to become accepted. A very thin layer of silicone seal used to work fine so 25 years ago that's probably what I would have used too. It seems lots of folks were a bit too liberal with it though.

chris plant · Jun 23, 2009

hi all,you need to use rtv very sparingly,dont cover the whole sealing area just the outer half of the mating surface,that way you will get more squeezing out than in.