Airhead main seal again.

[pommie john]

Here's the crack.





It extends between the two red arrows. Up under the rim near the breather housing, and down, right across the rim at the bottom.





Here it is in close up.






I've already had a chat with the local indy BMW shop and they've got plenty of cases. They will sell me one at a very good price.

[Infracaninophile]

Any idea of the root cause of the crack? Flaw during manufacture? Bike crash with impact to motor case? You can't seal it from the outside?

Tom

[pommie john]

Originally Posted by Infracaninophile

Any idea of the root cause of the crack? Flaw during manufacture? Bike crash with impact to motor case? You can't seal it from the outside?

Tom

No. No idea. I have heard of another race bike that cracked too. Being a race bike it has crashed on numerous occasions, but nothing too hard. The hardest crash was a front end lose in the wet which cracked the rocker cover, but didn't smash it. I can't imagine that that would cause a crack in the crankcases.

It has been producing something like twice the designed power for about 15 years, so I can't complain too much.

I'm not inclined to try to repair it. Too much risk of distortion, and my local friendly welder curses me every time I bring him a piece of alloy that has been immersed in oil for 20 years.

I have been offered a replacement for $150. It'd cost that for the welding.

[jackd]

That's quite the crack there. Does it start at the top right hand transmission mount hole? I've questioned Snowbum about whether the plugs which seal the oil delivery galleries for the top end ever leak and his response was that it was also quite rare. I'm going to give my case a major going over when I go back in. Thanks for posting these shots and good luck.

[jackd]

I just had a look at your previous shots from this thread, before you changed the rear seal. You can actually see the crack - it just hadn't opened up yet. I will definitely give mine a very close look.

[Wirespokes]

The one I'd seen before had several cracks extending radially from the rear main.

[bereahorn]

Subscribed

[Max Headroom]

A friend of mine had an R100RS which developed a persistent leak some years ago. We initially suspected the rear main seal to be the culprit. After we'd replaced it twice along with the oil pump o-ring, we started looking elsewhere. We ran the engine with the flywheel fitted and the gearbox removed one Saturday morning and waited for a leak to appear. It revealed itself as a similar crack to Pommie John's engine, although on the other side of the rear main bearing straight through the oil gallery feeding the crank. I attempted to patch it up by removing the gallery plug and fitting a thin sleeve I'd machined to line the oil gallery, and although it reduced the leak substantially it wasn't a satisfactory solution.

I've often thought about the possible reasons for the crack appearing, and I now wonder if it hadn't been caused by getting too enthusiastic with a big hammer while removing and installing new crank bearings. The crankcase was never designed or intended to cope with too much pounding axially without proper support to localise the forces involved.

Just a thought . . .

[jackd]

Having replaced my seal more than a few times, I can say that I have given the area a pretty good going over. Unfortunately the area is squeaky clean and there is no tell tale stain in dried up clutch dust. I'm going to run it with the tranny off, as well - a real pain in the ass actually to set it back up with the exhaust going back on, battery back in, tank back on, etc. We'll see what I find when I try this. I'm really hoping not to find a crack. Some Porche owners have commented that the crank can settle (if it's worn) and leak for that reason. My bike only has 46K miles on it - it's still quite young in real terms. I'm somewhat pleased that I'm not the only one going through this little private hell.

[wirewrkr]

What is that horrible sound?
Say it ain't so, but me thinks that the
SKY IS FALLING!!!!

[pommie john]

Originally Posted by Max Headroom

... and I now wonder if it hadn't been caused by getting too enthusiastic with a big hammer while removing and installing new crank bearings. The crankcase was never designed or intended to cope with too much pounding axially without proper support to localise the forces involved.

Just a thought . . .

Good point. How much bashing does it take to fit a rear main bearing? When I rebuild my motor into a new ( old) crankcase it will need new main bearings, so I don't want to go through the same game again.

[Cogswell]

Well it certainly sucks that the case is cracked but,

You know your installation of the rear crank seal was not the cause and you now know the source of the leak.

Best of luck on a quick and hopefully no too expensive repair.


Mike

[BOOTLACE]

G'day John. That's bloody amazing, never seen the likes of it. Oh well, at least you now KNOW!
If you'd like to PM me your email, I can send you some pix from the Island. My work 'putr won't allow me to upload pix to photobucket or the like, so can't post any till I'm out of here.(Minesite..).
Back to the Island this weekend for flag waving at WSBK tests, then same the next weekend, for first round. WOOHOO!

[bmwrench]

Originally Posted by pommie john

Good point. How much bashing does it take to fit a rear main bearing? When I rebuild my motor into a new ( old) crankcase it will need new main bearings, so I don't want to go through the same game again.

You shouldn't need to use a hammer at all. If the case is hot enough, the bearing will drop in.

[pommie john]

Originally Posted by bmwrench

You shouldn't need to use a hammer at all. If the case is hot enough, the bearing will drop in.

Excellent. Thanks for the info. Maybe I'll try it myself.
Am I right in thinking that I can just fit the same size bearing as the old cases have?
I have a good set of digital callipers but my micrometer is too small to measure the journals.