1981 GS650GL Bad compression results

[Tijmen]

Hey all,

Been some time since I posted on this forum. Good thing, because everything was going fine. The GS650 however started to, noticeably, burn more oil. Driving behind it on my GS450E wasn't pleasant.

So I went ahead and got myself a compression meter. The results are labelled 1 to 4, with number 1 representing the left most cylinder and 4 the right most, from the driver's perspective.

See post on page 2.

Am I correct in assuming that my valves are not leaky? This looks to me like a piston issue. Next the spark plugs:
1 -
2 -
3 -
4 -

Yes, there was actual gunk on sparkplug 1... The oil is being burned in the left exhaust (clearly visible while driving). So 1 and/or 2 are burning oil noticeably.

Gee, what should I do with this one? Looks to me it is in pretty rough shape...

The motorcycle itself is rarely used, once a month maybe. My mother drives around on it, myself maybe once a year after pulling it from storage. It is a 1981 GS650GL and has been in our possession since 2 years I believe. Before that an older man owned it who barely drove it as well (back problems, said he'd go around the block once a month with it). First known owner was his son who imported it from the USA, he worked there for a few years and bought it there from someone... not much is known from the son or the unknown previous owner.

[eil]

Compression is supposed to be measured with the engine hot in order to get any meaningful numbers. However, for a cold engine, those readings are not out of the ordinary.

The burning oil and fouled plugs are probably symptoms of the bike's history of being ridden for a few minutes and then put away. These engines were designed to be run at reasonably high RPMs for extended periods of time. Put on a helmet, find some back roads, and cruise for an hour or two. Let it run. Don't be afraid to whack open the throttle from time to time.

[tkent02]

What he said, plus look at the petcock. #2 looks rich, not oil fouled. #2 is the one with the vacuum port going to the petcock. Coincidence? Probably not. I would suspect a leaky diaphragm in the petcock.
I'd also do as eli suggests, except I'd do it on a big motorway, run the heck out of it for an hour or two. Or ten. Might help, might not.
The last two spark plug pics look fine, except they look a lot richer than plugs usually do from a stock 650G, which are usually almost white. Not that some color on the plugs is bad, but I'm thinking maybe something is going on inside the carbs, or maybe someone rejetted it richer for some reason.

[Steve]

Yep, what you need to do first is to put some new plugs in and do an "Italian Tune-up".

Check the plugs after the "Italian Tune-up". Run the bike a few hundred miles, THEN re-check the compression.

.

[Tijmen]

Thanks, both of you! I have just gone for a test run and it rides fine (20 km of highway). What kind of RPM would "running the heck out of it" be on the highway? 7k?

Is the oil burning temporary then or has the history of short rides done permanent damage? Is it something I should fix, or just carry some additional oil with me when taking it?

And maybe the better question: should I sell this bike to someone who can ride it more often? Because I already got two motorcycles of my own... Can't really ensure that the third will be used plenty as well. Because maybe what we need is a motorcycle a bit more resilient against this abuse (I know, it will always be abuse). As much as I like the motorcycle (GS650GL) for its power and comfortable riding position, I really need a smaller one for my daily travels (lots of traffic jams, GS450E fits nicely through it!).

Edit: Reason it was measured cold is that I didn't really have time to ride it warm. Unless 20km is enough, but I've been told before to do at least 50. I didn't know that measuring compression with a cold engine was useless. Is that just for air cooled engines, or any engine?

[Tijmen]

8..... or 9. Open and close the throttle. Make the engine work.

Redlining it, roger I'll see to it.

On the Dutch forum people have suggested replacing the valve stem seals, but I assume I need to do the Italian run first before possibly wasting money. I shall return once I've had some highway time with it. Thanks again!

[Steve]

Hopefully the situation is temporary. You mentioned that it is ridden only rarely. And by your mother. If she rides it like many women drive a car, she might not get over 3000 RPM or so before shifting. These little engines are meant to SPIN. Take it out for a blast in the country (after putting in new spark plugs). Engine speed itself is not all that important at this time, what you want is to give it the gas, run it up through the gears. Close the throttle, let it coast down a bit, then repeat. Of course, you will need to make sure there is no traffic behind that would get upset over this driving style, but you want to load both sides of the rings by accelerating and decelerating.

You should be turning about 6k RPM at 70 MPH (about 110 kph) in top gear. Don't be afraid to use third gear to get to 70, which will keep the RPM up very nicely. But, as mentioned, it's not all about speed, it's more about the CHANGE of speed, to see if you can get the piston rings de-gunked so they seal better. If you do this for several hundred miles (does not have to be done all at one time) with no improvement, it will need some work, but I'll bet it should clear up rather nicely.

Compression checks should be done at full operating temperature on ANY engine. That will ensure that everything has settled into position and specified clearance. You also need to do it with the throttle WIDE OPEN to let the engine breathe as much air as it can. With a closed throttle, it simply might not be able to ingest enough air to compress into a meaningful number.

.

[tkent02]

8..... or 9. Open and close the throttle. Make the engine work. Accelerate hard, decelerate and do it again. The idea is to get the rings loosened up in there, make sure they aren't stuck in their grooves. Blow chunks of carbon out of the exhaust ports, burns water out of the oil, loosens up rust on anything rusty inside, don't know what all it does but it makes engines run better.

I have had a few engines that wouldn't run worth a hoot, just nothing. Wring them out on the highway, after a while they start to run better, several hours of this they are purring and making as much power as they did when new.

No guaranties, but sometimes it works wonders.

My buddy Gene had an old Norton 750 Commando, it wouldn't go but about 55 or 60mph. Gene rode it like a little old lady, because that's how it always ran. Going home from work at about 2AM, I had him just hold the throttle wide open and keep it there, after a while it started going faster. 70, 80, pretty soon I had my GS550 wide open, laying down on the tank, and Gene was getting small in the distance. I started seeing little glowing red balls laying in the road, looked up at Gene a half mile ahead, you could see these bright glowing balls coming out the tailpipe. By the time I went by they were not so bright, just dull red balls laying on the pavement. And he held the throttle open. So far ahead I couldn't see him anymore. So far ahead the little red balls were out by the time I went by.

He was halfway through his second beer by the time I got to the house, big grin on his face. Said he didn't let off the throttle until he had to slow to make his exit, 50 miles or so up the road. Then he blasted down all of the little back roads all the way home. He had no idea that old Norton would do anything like that. I didn't either.

It was a very fast bike after that.

[tkent02]

The redline is mostly just a suggestion.

[eil]

Edit: Reason it was measured cold is that I didn't really have time to ride it warm. Unless 20km is enough, but I've been told before to do at least 50. I didn't know that measuring compression with a cold engine was useless. Is that just for air cooled engines, or any engine?

Well, not totally useless. If you're getting more than 50-75 psi, the engine should at least start. Less than that and you may have starting issues. A compression test is normally used to verify the condition of the valves and rings. These things tend to be loose (or stuck) when the engine is cold. Service manuals often give a range of acceptable compression numbers, these are only valid when the engine is fully up to temperature (with the ignition disabled and the throttle wide open).

[Tijmen]

Thanks Eil. Will do a warm engine test soon then. The Italian run will have to wait a little longer. I shall update the thread with those results ASAP.

Edit: As a "small engine lover" I can totally understand the cruising at 3k rpm. The GS650 has so much more torque down below compared to my GS450, heck you can even pull away nicely anywhere above 1.5k rpm. Only on the highway I find myself running it to 5k rpm. I shall try to drive it like my GS450 and push it a little harder. Should have a track day with it or something.

And well, eh, with the Jawa (2 stroke) it is pretty much full throttle or no throttle. Those bikes love the higher rpms

[Tijmen]

New results! Hot engine, approximately 70-80 kilometers with 40 of those lots of throttle use (return trip, bit of provincial roads which include roundabouts on a 60 mph road, so a good moment to do some sprints, ended with highway where we did 80 mph for fun). Throughout the ride the rpm has been AT LEAST 3K rpm as a target, to try and get rid of that "car attitude" of keeping the rpms low. Judging from the sound it made I think it was doing a lot more "motorcycle" rpm's than before. Once it rides it sounds real nice and consistent.

Warm engine, no oil
1 - 100 psi
2 - 105 psi
3 - 110 psi
4 - 115 psi

Warm engine, squirt of oil
1 - 110 psi
2 - 125 psi
3 - 125 psi
4 - 130 psi

It has a somewhat rough idle when driven for a while, and a rather high idle rpm (1500-2000). Should probably sync the carbs at some point. It drove fine though, not a single second of doubt when applying throttle, blasted along fine on the highway.

I know this isn't the proposed Italian run, this was a spontaneous action as we decided to go and have dinner some place 40 km south. Figured I might as well do a compression test once we returned.

Anything new in these values? Can I conclude that the piston rings are fine? Should I start by replacing the valve stem seals?

Pictures of the sparkplugs:
1 -
2 -
3 -
4 -

Yup, they need replacing badly I'll get some fresh plugs asap, due to their strange dimensions I can't get them at the local shop though.

[Tijmen]

Pulled the valve cover off today, checked the clearances. Only one, intake, valve requires a smaller shim (cilinder 2 if you're wondering). Nothing crazy happening in there. Something that was crazy was the air filter being completely broken apart. Like rotten wood it has fallen apart. Judging from how crumbled it is the engine might have eaten a few pieces of the foam.

Well now I have a reason to add this vehicle to my maintenance rounds, looks like our agreement to take it to the shop once a year didn't work I suppose this must have had a detrimental effect to the engine. Running it with essentially no filter without adjusting the carburation can't have been good. Anything I should check? Already poked around in the intakes and there wasn't junk left in there. Maybe I'll pull it off the carbs to make sure there really isn't any left overs sticking around in it.

Something else I noted was that most valve buckets were sitting in oil except cylinder number 2, the intake was rather pristine. Could this be a sign of worn out valve stem seals?

Mods / Admins: Is there a way to rename this thread? The subject should be about oil burning, not so much compression loss I realize now. Sorry for the inconvenience!

Update 15-06-2016
Replaced the tight shim and replaced the spark plugs. Installed the new air filter. First thing: it starts noticeably easier now with a proper air filter, so that is good. It is now ready for the Italian run over the highway! I shall post again when done.

[eil]

Maybe I missed where you said it, but how do you know you're burning oil as opposed to just running very rich? Oil level dropping considerably? Blue smoke when it runs?

Those compression numbers are not great but decent. Your rings and valves are probably okay. Things might improve when the bike is taken out for a good run. When you do that, consider 4k RPM to be more of a minimum. All of these GSes are good for a wide range of RPMs in any gear.

It's good that you found the issue with the filter. I would definitely rebuild the carbs, it's entirely possible that you have bits of filter material inside them.

You still might need to replace the valve stem seals if is is indeed burning oil but troubleshooting issues like these is all about checking the low-hanging fruit first.

[Tijmen]

Blue smoke indeed. It is especially present after sitting on the side stand for a while. Oil consumption is noticeable. The smell when you drive behind it reminds me a bit of my old Jawa 350cc twin two stroke, but worse.

I am a bit skeptical about rebuilding the carbs, it all looks a little crusty and I fear I might strip the heads. I think it is not uncommon to replace the boots as well? The rubbers between the carbs and the cylinders that is.

Agreed, the low hanging fruit should indeed be the first things I look at. The problem however is tearing the thing apart. Coming weekend I will check out a GS850G from 1984 (on the license papers, might be a different year of assembly), if that's all good I can afford tearing into the GS650GL. The Suzuki GS450E has since been sold too, lovely little bike but just not comfortable doing high speed riding for extended periods of time. I am hoping the seating is better and engine noise is a little less with the GS850G. If not I might look into the BMW K series (K75, K100). The GS850G does come with a nice collection of spare parts (top end, fuel tank, fairings, side covers, starter motor, etc.)... so I hope it will do. First owner, so that should be a big plus.