Oil leak near exhaustpipe

[ErikB]

Hi, both cylinderheads have a oil leak near the exhaustpipe. I have bin told to replace the o-rings.
Doe anybody have any pictures off the head\cylinder so i have a impression what i have to do?
Mayby some tips?

[paso750]

I guess what they mean are the O-rings on Tav.7 of the parts catalogue.

G.

[Finnpaso]

First before do anything more: retighten sylinder heads with right torque. If its leaking still after that, then its propably just those old o-rings in in water cooling lines and oil lines between head and sylinder... I have suffered same problems and it was in my case too old o-rings...

[duckboy]

This is what the (green) o-rings look like

Horizontal cylinder


vertical cylinder


as you can see, these were leaking as well.

[jcslocum]

Hi, both cylinderheads have a oil leak near the exhaustpipe. I have bin told to replace the o-rings.
Doe anybody have any pictures off the head\cylinder so i have a impression what i have to do?
Mayby some tips?

Can you send a picture??

Maybe the valve covers are leaking??

[ducapaso]

I think you'd better have a look to the guide-valves and their sealing... A too leak gap in this part is the main cause of oil in the exaust

[paso750]

cleaning the oil spill and keeping an eye on it would be the first thing to do to have a chance to see where the oil comes out. If its the valves covers it`s easy, if you have to remove the cylinder heads you can check and/or replace all gaskets while you`re at it.

[ErikB]

Hi Guys,

I am 100 % sure the leak(s) are similar like the pictures off Duckboy. I tried to retighten the cylinders but that did not helped. The pictures are very helpfull, THNX!!

Soon i will take off both heads & replace the o-rings. First I am going to enjoy my leaking Bike during this lovely weather!

Greetings,
Erik

[duckboy]

Hi Erik
while you have the heads off, don't forget to replace the o-rings at the base of the cylinders (eg. between the cylinder and the crankcases, and the base cylinder gaskets as well.)

[Finnpaso]

Some advice still: those o-rings MUST be VITON (FPM) material, NOT normal o-rings !!! Sometimes no need to change gasgets between sylinder and case, IF You managed take heads out very carefully without moving sylinders, but You have to be very carefull. I do such last time and no any leak between sylinders and cases...

[jomo]

When I first bought my 906 with 17,000Km on the odometer, the Dealer told me he was surprised the heads weren't leaking and it was a common fault. He said it must have allready had the heads machined and new o rings fitted. Within 2,000km it started leaking. I thought he must have loosened the head nuts! I have replaced the o rings and it did not help so maybe he was right about machining.

[Tamburinifan]

Also have leaks as in pic above w new Orings.

He said it must have allready had the heads machined

Exactly where are heads machined?
There are a 0,35mm gap between heads & cyls all around when cold.
Oring should seal that gap.

Could the leak occur because gap cyl-head is too small?

[higgy]

I would not machine any head or cylinder without checking it myself with a good straight edge and a reliable feeler gauge. also re-torque on a 20 year old viton o-ring is a waste of time
JM2C

[persempre907]

I would not machine any head or cylinder without checking it myself with a good straight edge and a reliable feeler gauge. also re-torque on a 20 year old viton o-ring is a waste of time
JM2C

Since I also have a little oil leak, do you suggest only replace the orings and then retorque the heads?
Ciao

[higgy]

Any time you take off a head it is a good idea to check the head and the cylinder to be sure it is true. A good straight edge only cost between 20 and 30 dollars(USD) in the size required.Feeler gauges are also relatively cheap as well. Also like stated earlier in this thread don't forget the o-rings under the cylinder.
If you do find you head is warped it is a much better idea to straighten it first and only as a last resort should you have it resurfaced. If the surface is out of true,then the cam bores are also out of alignment and this is much more critical than the gasket surface. Broken timing belts are much worse than any annoying oil or coolant leak. Straightening a head is a little more involved
(meaning more money) than machining but not difficult. You do need a steel plate that is true(flat= big dinero ) and large enough to take the strain of torquing the head to it and heating the whole assembly in an oven to 425F(218C) then letting it cool slowly and rechecking it for trueness and repeating the process till it is true By the way you don't want to do this in any oven that is used for cooking
Hope this helps and just let me know if you need more detailed info

PS: Gert,the heads are resurfaced across the entire gasket surface if the surface is pitted or has low spots and even then the proper way to do it is to add metal to the low spots by welding AFTER the heads have been straightened by heating and torquing to a flat plate and then machining the welds to match the rest of the surface. IT IS NEVER A GOOD IDEA TO REMOVE METAL FROM ANY HEAD