Oil leak

[greenmonster]

at horizontal exhaust port, where the Oring is, between head-cylinder, not much but disturbing.

Anyone know the reason & cure for this? Just a bigger Oring maybe?
Have it on both my bikes, -97 M900 & -91 907.

[Howie]

A photo might help.  I can't visualize your leak.  In the meanwhile, you may want to look at your cylinder head studs.  There were stud breaking issues back then, but I don't remember what years.  Put a wrench on the nuts and turn, but less force tan you would use to torque them.  Also note the color.  If the studs are shiny they are suspect.

[Norm]

Check for broken stud, leaky freeze plug, replace the O rings while you're in there. I'd replace all the studs with 9*6 type while you have it open.

[greenmonster]

I can't visualize your leak.

Looking fr front on horizontal, just above exhaust.

leaky freeze plug

Is that another name f the location pin that helps cyl-head to fit?


Studs are all of right kind, think a series bikes 94-95 had issues.

[clubhousemotorsports]

Most likely the head to cylinder fit on the 907 is warped . These water cooled 2 valvers (906,907,st2) always warp between the cylinder studs above the exhaust port. you can go in and freshen up the gaskets and lap the cylinder to the head and it will buy you more time before you leak again. FYI: having a built motor seems to make things happen quicker so keep that in mind. Although 907/944's do run great!

The 97 900 should have the good studs already, I would freshen up the o-rings and lap the heads on that one too. 900 air/oil cooled motors do not seem to have as much of a problem with warping the heads.

WARNING!!!! when the cylinders are off you have to decide if you want to know if your crank plug is in or out. Do not look If you do not want to know. the 900 motors in that era have a 50% chance of having them out. You have to split the cases to properly fix this, you don't want to have to ride around knowing the plug is out and machining itself to bits inside your motor do you?

good luck

[Ddan]

WARNING!!!! when the cylinders are off you have to decide if you want to know if your crank plug is in or out. Do not look If you do not want to know. the 900 motors in that era have a 50% chance of having them out. You have to split the cases to properly fix this, you don't want to have to ride around knowing the plug is out and machining itself to bits inside your motor do you?

good luck

+1

Don't look, trust me on this.

[Norm]

The studs in question are silver in color and went into most or all the air cooled bikes at least between '93 and '97. The better ones are bronzish in color. The freeze plugs I refer to aren't really freeze plugs, but it's the best way to describe them, they are a brass cup lightly pressed into an oil passageway. on the jugs - you can't miss 'em.

[greenmonster]

Thx f the help. 
Both my oil galley plugs are luckily OK.

lap the cylinder to the head

Could that be done by hand or is machining a must?

[clubhousemotorsports]

Yes you can lap them by hand.
I use clover 320 and lap until all is well.

[greenmonster]

Thx! 

320 wet sanding on a thick glass plate f e?
Any trick to check it`s OK before mounting?

[clubhousemotorsports]

sorry to get back to you so late.
No you cannot lap on a surface plate you have to put the lapping compounds between the cylinder and head and lap the two together just like a valve and seat.
lap the two together until you have a uniform lapping mark all the way around.

[greenmonster]

sorry to get back to you so late.

No problemo, winter is long here in Sweden...

Will follow your advice, thx. 

[greenmonster]

Small follow up on this:

leaky freeze plug

You were right on thiis, Norm, one plug was too high.  Combined w a broken valve seal,
quite a nasty leak.
More info will follow.