Oil Burning

[suzuki fan]

I got a complete 83 GS750T parts bike from a local dealer for a price I couldn?t refuse. Since my original engine was done I decided to put the 83 engine into the 82 as everything on it was in much better shape. So after about the second or third time starting it up we noticed that it was smoking a lot. So we knew it was burning oil. I rode it the season with the intention to tear it down and fixing it, thinking it was probably rings. I also noticed that it was leaking oil. The front of the engine became covered in oil and when you slowed down to stop you could smell the oil. So I tried to isolate where the oil was leaking from. It turned out the oil was coming from the valve cover. When I was replacing the gasket I noticed it was leaking because there was no gasket there! A poor job of silicone was someones cheap fix. After I replaced the gasket and cleaned the oil off, my oil consumption was cut substantially. The engine always smoked quite a bit on start up. A pretty good cloud for the first 5 - 10 minutes. The left pipe always had a slight visible smoke that the right pipe didn't have. But I still didn?t like the rate of consumption or the small head gasket leak. So I?ve disassembled and didn?t find what I was expecting.
I found oil sitting on top of the #1 piston. So I then began looking at the valves. The seals all look good, are soft and have no cracks. The valve seals all seem to have about the same amount of drag on the stems and would seem to not be the source of our problem. The guides all have about the same amount of play but they haven't been precisely measured.
We are stumped why oil is sitting on top of #1 piston.
None of the cylinders are scored, the engine ran reasonably well with good power. We were starting to have plug fouling issues with #1 cyl towards the end of the season.
So my question is what should I look at next?

 

[rustybronco]

So my question is what should I look at next?

On the stem side of the valves is there a oil deposit build up also?

 

[Guest]

Three possiblies
Cracked head
Leaky valve guide
Bad valve stem seal

What was the compression?

 

[suzuki fan]

I did a compression test and I got about 148 psi on the burning cylinder and mid 150's on all the others.

 

[49er]

Can you give us a pic of the #1 chamber, showing the valves.

The carbon buildup on the piston crown, indicates that the oil is coming into the chamber from the inboard inlet valve and the bulk of it is exiting via the exhaust valve on the same side of that cylinder. You may have a cracked head around the inlet valve guides, probably closest to the inboard valve.

The head pic should be more conclusive.

 

[suzuki fan]

Here is a pic of the head for cylinders 1 & 2. Not the best lighting in the pic.

 

[49er]

Here is a pic of the head for cylinders 1 & 2. Not the best lighting in the pic.

Not sure that my initial diagnosis is correct. It appears that both #1 & 2 are burning significant quantities of oil, in fact #2 looks worse than #1.

As mentioned above, check for carbon build up on both sets of inlet valve stems. If they are coated with carbon, between the valve seal and the underside of the valve, your seals/guides are the culprit. You need to dis-assemble the valves and do some measuring for wear/tolerances. Check Basecliff's site for a manual for your bike, ft you don't already have one.

It's possible that you have worn/damaged oil rings on the pistons too. Your good compression figures steered me away from this conclusion initially, although the carbon pattern around the top of #1 bore suggests that oil could be bypassing the rings. If #3 & 4 chambers are similar to 1 & 2, I would suspect your rings.

 

[suzuki fan]

Here is the head. On the first cylinder the oil ring had the gaps lining up. They weren't turned properly. But this wouldn't put oil on top of the piston.

 

[suzuki fan]

Here is one of the cylinders. I'll have to check if there is carbon, between the valve seal and the underside of the valve

 

[Nessism]

Since the engine is torn apart I'd replace the rings, hone the cylinder, lap the valves and replace the valve stem seals. Measuring piston to cylinder clearance is recommended or course since if they are worn, oil burning will result regardless of the new rings. It also would be a good idea to check valve to guide clearance. Measure everything up and go from there.

 

[49er]

Here is one of the cylinders. I'll have to check if there is carbon, between the valve seal and the underside of the valve

There is a score line on this bore at around 2 o'clock. If others have similar marks, the problem will be rings. There is still a hatch pattern on that bore. I wonder if a PO has had it apart and got the rings mixed up between the bores!!

 

[focus frenzy]

you can have good compression yet be sucking oil past the rings if the oil control rings are stuck. the piston goes down on the intake stroke and it sucks oil past the compression rings.

my money is on bad valve seals, looking and feeling good is not the same as being good. I had a distributor base oil o-ring fail and it leaked oil like a stuck pig, pulled it apart and the o-ring looked good and could not tell differance between new and old o-ring but it was bad.

you already have it apart go ahead and do the seals and rings make sure the bores are round and in spec.

best to do both now and not have to mess with anything for a long time.

 

[Dave8338]

I'll also suggest to replace the rings (after a good hone) valve lap and seals and new gaskets. How many miles were on the 83 engine?

You may get away with just pulling the rings and giving everything a good clean and spec and reinstall, but I myself am not a big fan of reusing old rings. I've broken one too many in the past, after everything was back together and running perfect.

 

[suzuki fan]

The odometer says around 29 000 km. The PO had
definitely been in the engine before. I plan on buying new rings and deglazing the cylinders. I also plan on measuring everything you have suggested.