rear head gasket
 

I have a 916 and noted a couple of weeks back it dropped of onto one cylinder. after removing the tank and rear plug cap i noted that the clug cap had moisture on it and the plug was a darker colour that the front plug.
After swapping the plug cleaning the plug recess its running find. this was a couple of hundred miles ago and i have checked the plug cap since and all is well.

Im thinking however that the rear head gasket will need replacing at some point. the question is can this be dont in frame? and is this a common fault?

The bike had been sitting for a number of years and just rebuilt (didnt clean the plug recess) and it had just had its first wash so..
And im thinking that if i have done a couple of hundred miles since in may have cured itself (all that heating and cooling down).
But i dont think i am that lucky!

Your comments please.

Yes you can change the head gasket in the frame. However, I do not think that is your problem. Incorrect fuelling seems to be the issue.

Yep understan where you are coming from but the rear plug was only a dark brown not black.
And i did note a rusty coloured deposit in the rear plug recess and the plug cap connector had rusted!

I'd agree its a fuelling setup issue to. Corrosion in the plug recess is caused by water getting behind the plug cap, not a head gasket problem.

You know what? it may have just been some water not from the head gasket, possibly from the time standing or the rebuild.
I was thinking head gasket as i had seen some coolant on the rear cylinder just under the exhaust port. But the weekend with the pannels off after a spirited ride i noted the coolant needed topping up and with the left panel off the water pump was covered in coolant.
So ran it up to temp and could see a leak just behind the pipe.
So coolant was running back over the pipes and onto the rear cylinder!!

So stripped cleaned and sealent later we shall see.

It may be that the coolant expansion tank has split along the plastic seam - a very common problem on the 916 line!

Checked that this weekend and all good.

I went on a 20 mile slow ride and noted thumb nail full of coolant pool at the bottom of the cylinder :mad:.

So cleanded and let her tick over for a while, fan came on three times nothing :confused: .

Went out for a 40 mile blast on Sunday, nothing :confused:

Will keep an eye, dont know if its slowly sorting itself or not!

Rund aroung for about 150 miles from 90 > 100mph motorway to in town riding and no leak :)
But dit a 10 mile flat out (most of the way) and found coolant on the rear cylinder :confused:

Im almost tempted to put some expensive rad weld in it!
But the engineer in me says NO its not the right thing and a bodge :eek:

But going to check the rad cap first just to make sure that is doing what it should...the only reason i say this is that i cant see any coolant in the overflow tank. and if it was over pressurising?

That's normally when the seam goes - the coolant gets hot and the pressure expands the coolant tank and it splits along the seam. It may be about to pop big time! Worth checking to see if you can figure it out.