1979 GS1000 Oil control problem

[Tpalmer1359]

Hi. 1979GS1000 is using oil. Getting more noticeable and 2 plugs are black and oily. However, the bike runs very well, and the last compression test with warm engine reads 145, 145, 146, 145.

thoughts? Am I looking at an issue with the head, likely old valve seals? Hoping refreshing the head cures this and no need to pull the cylinders.

Thanks in advance.

[Brendan W]

Valve seals usually leak down to the combustion chamber and burn off in the first minute or so after cold start up.
Have you any smoke at that time?
Exhausts are usually the first to suffer and you could pull an exhaust header to have a look at the valve. A leaking seal will be fairly obvious.
How much oil is it using?

[Nessism]

Any time the head comes off the cylinder should also because removing the clamp load on the base gasket could make it leak.

There are threads here on how to change the valve stem seals with the head still on the bike. It takes some inventiveness but it can be done.

[Tpalmer1359]

Valve seals usually leak down to the combustion chamber and burn off in the first minute or so after cold start up.
Have you any smoke at that time?
Exhausts are usually the first to suffer and you could pull an exhaust header to have a look at the valve. A leaking seal will be fairly obvious.
How much oil is it using?

Using enough that I need to top off every few rides depending obviously on length and how hard I ride. The greater the time at higher RPMs the greater the consumption. A little bit of blue smoke even when fully warm, but not always.

With my compression readings my hope is that the head is the only source of excessive oil consumption.

only 1 way to find out I guess.

[GregT]

Probably stem seals, yes, but the extra oil from those will possibly have added to any bore glazing.
I'd budget on deglazing the bores while the head's off.

[bitzz]

If it's valve seals, you'll get a puff of smoke after a downshift, when the vacuum is high
If it's rings it'll smoke on heavy acceleration. If it's rings a wet compression test will give you higher numbers.

If I was doing anything, it'd get rings, seals and a valve job... at least. The thing is 43 yrs old.
... and YEAH, you're going to disturb the base gasket taking the head off... so yeah you have to replace that too.
What do the guides look like on your 43 yr old bike?
If it's rings, is the bore still square?

[Big Block]

I did the valve seals on my 79 1000 about 10 years ago on the bike. It is a finicky job but I'd try that first. If you have a helper with small fingers and a magnet it will make it easier.

[Tpalmer1359]

Probably stem seals, yes, but the extra oil from those will possibly have added to any bore glazing.
I'd budget on deglazing the bores while the head's off.

Pulled the head. The valves look terrible with a bunch of crud, and I question how well they had been seating.

the tops of the pistons are carboned-up too, however the cross hatches look great to my untrained eye.

[Tpalmer1359]

[Tpalmer1359]

Will post photos tomorrow

[Tpalmer1359]

Probably stem seals, yes, but the extra oil from those will possibly have added to any bore glazing.
I'd budget on deglazing the bores while the head's off.

Here is a photo of one cylinder. Looks like the oil is migrating from the head above rather than through the rings.
Cross Hatch1.jpg

[Tpalmer1359]

Cross Hatch2.jpgAnother cylinder.

[Tpalmer1359]

The valves.
Valve 1.jpg

[Tpalmer1359]

Last picture.
Valve2.jpg

[Nessism]

How long have you had this bike? The cylinders look to have been honed fairly recently.

The carbon buildup looks perfectly normal to me. The oily look of the cylinder/head suggests oil usage as you have been experiencing. My guess is valve stem seals.