Danno

" but what is Yamabond and where can it be purchased?"

Yamabond-4 is available at all Yamaha motorcyle dealers and comes in a black tube (part# ACC-YAMAB-ON-D4).

It's not really a gasket sealant, closer to a gasket maker; it's thick, has high viscosity and never really dries. Really good for those two-part crankcases on motorcycles that have metal-to-metal mating surfaces that doesn't have a gasket. The Yamabond will fill the gaps and seal even when the surfaces fret against each other. They say it will seal metal-to-metal gaps of 0.1mm, but I've found that it can seal gaps of up to 0.5mm (depends on pressure behind it I guess). Good for headgaskets too (some 2-stroke gaskets come pre-coated with Yamabond).

It's much, much better than any silicone-type sealants (which are weak and slippery).

Tips on re-installing the cam-tower:
<ol type="1">[*]clean all mating surfaces with acetone to remove all traces of oil, put locating dowels on head[*]make sure gasket lines up! It can be rotated 180-degrees and LOOK like its OK, but some oil-holes will be covered[*]apply thin layer of Yamabond to bottom of gasket and install on head[*]line up gasket and put thin layer of Yamabond to top of gasket[*]install cam-tower and tighten to spec.[/list=a]

Here's where I found out about the virtues of Yamabond:

<a href="http://www.landsharkoz.com/articles/jatmm02.htm" target="_blank">928 Australia</a>
<a href="http://www.928oc.org/tip/tip341.htm" target="_blank">Cam Tower Leak Repair</a>
<a href="http://www.italian-cars.com/html/tech/biturbo.html" target="_blank">Maserati Tech Page</a>
<a href="http://www.turborick.com/turbobike/archive/0584.html" target="_blank">SOHC Honda headgasket problem</a>

lejams

After visiting the shop today and examining the cam gasket with a good magnifying glass, here is what my tech and I have decided to do. It is very clear that the crack that has developed is certifiably the source of the leak. It originates from the oil channel which is fed by thru the oil relief valve. We have concluded that the origin of the crack is the source of pressure which is causing the crack. We have ruled out blow-by because for that to be the source of pressure, it would have to originate from the very inside edge of the gasket on the other side of the oil channel where the drain ports would be feeding the blow-by pressure. The car has excellent compression, but we considered the blow-by as a possible culprit due to running the car at a high boost level, (17 – 18lbs.), theorizing that under a full boost/heavy load, with the modifications to the car, there would probably be some deterioration of compression and possible some blow-by that wouldn’t have shown up on the leak test.

So that leaves only one other possibility that we can see, and that is the oil regulator valve. According to the oil pressure gauge on the car, for all practical purposes, the oil pressure has been normal. But to follow deductive reasoning, we are going to replace the oil regulator, (hope it won’t be too expensive). We also lightly block sanded the surfaces of the head and cam housing and re-checked with an engineered straight edge again, and concluded that they are in a pristine state. However, when we re-install the cam housing, we are going to apply an Aviation sealant by Napa called form-a-gasket, #765-1210. This stuff acts more like a bonding agent than a gasket material which should strengthen the gasket in that area. It will be applied within 5” of where the cracks have been occurring and the oil pressure relief valve area. We think/hope this will fix the problem.

Thanks for your feedback and if you have anymore ideas or comments, I’m certainly interested. I’ll update this topic as the time goes on with a progress report .

Jim

1989 951 46K, Autothority Stage-ll MAF, Powerhaus hybrid K27, Head O-ringed/Port & Polished, Lindsey Stage-ll Intercooler & scoop, Lindsey Wastegate and manual boost control @ 17lbs., Custom chips at Autothority on Location. Cat by-pass w/ B&B muffler, short-shift, Strut-brace.

lejams

[QUOTE]Originally posted by Danno:
[QB]" but what is Yamabond and where can it be purchased?"

Yamabond-4 is available at all Yamaha motorcyle dealers and comes in a black tube (part# ACC-YAMAB-ON-D4).

Thanx for that and the tips. Good advise to use a solvent like acetone to prep the surfaces. Well here goes nuthin, Back together she goes!

David Salama

Well, I took my camhousing cover off today. I too have a torn gasket in the bottom right corner (standing on the passenger side) which is right under the narrow convoluted channel on the cam housing. On close inspection, I notice how the cam housing gasket overlaps the oil passage significantly (1/4 inch). I'm wondering if this overlap causes a flapping of the gasket under full load which weakens it and eventually tears. I think in addition to using Yamabond, that I will trim the excess gasket over the oil passage. What do you think ?

lejams

[quote]Originally posted by David Salama:
<strong>Well, I took my camhousing cover off today. I too have a torn gasket in the bottom right corner (standing on the passenger side) which is right under the narrow convoluted channel on the cam housing. On close inspection, I notice how the cam housing gasket overlaps the oil passage significantly (1/4 inch). I'm wondering if this overlap causes a flapping of the gasket under full load which weakens it and eventually tears. I think in addition to using Yamabond, that I will trim the excess gasket over the oil passage. What do you think ?</strong><hr></blockquote>

That's interesting. I'm going to look and compare with mine again tomorrow and I'll let you know.

David Salama

Lay the gasket on the head and look at the oil passage at the far right side. Put your finger into the passage and feel under the gasket. There is significant overlap. See what you think.

lejams

[quote]Originally posted by David Salama:
<strong>Lay the gasket on the head and look at the oil passage at the far right side. Put your finger into the passage and feel under the gasket. There is significant overlap. See what you think.</strong><hr></blockquote>

Are you descibing at the front of the engine, (cyl. #1)? If so, I'll look there to see what you are pointing out, however the problems I'm describing are at cyl. #4 near the firewall. That's where the oil pressure relief valve is dispersing the oil from the head into the cam channel.

Bill_396

When I replaced mine last fall besides the split you all describe I also had one by #1 on the top side. I originally thought it was excessive crankcase pressure but someone the the pelian board convinced me that this was just typical 951. So far so good but mine is stock.