GL-1000 Compression question

[Offcenter]

My '76 GL with "supposedly" 68,000 miles is showing about 92 pounds
of compression on cyls 1,2, and 4. But cyl 3 is reading 122.
What should the compression read on this bike?
I'm beginning to think that the odometer has turned over once
and the engine has more like 168,000 miles.

 

[zman]

Should read about 10 percent of each other. If the bike has sat and hasn't been run you might get low readings like that. That is really low, be sure you have the throttle wide open when you crank it over and crank it for at least 5 revolution, you`ll here it hit the compression stroke when you do.
Even if it had gone around 1-2 times should be better then that, are you sure your guage is reading right? May be a good idea to barrow another if you can..

 

[slabghost]

If it's been sitting a while the rings may be stuck in the piston grooves. A few hours of run time usually get's them free and reseated.

 

[Offcenter]

Yes, this bike has been sitting for quite a few years.
What should the compression read on a "good" engine?
Compression gauge is brand new. Just purchased recently.

 

[Steve83]

Squirt a little oil into the plug holes and spin the engine a bit, then re-check the compression. Wide-open throttle and choke as stated above. These engines, when healthy, should have 150-170 PSI compression if I remember correctly.

 

[Offcenter]

150 to 170? Thanks. That's what I wanted to know.
The test compression test was done by my mechanic with
my brand new gauge. I have to guess that he knew what
he was doing.
I'll have to try running it a while and see if it gets better.

 

[joedrum]

wide open and choke steve ? ....i be spraying cleaner penetrate oil in the cylinders and turning over first by hand then starter ...of coruse with plugs out ....dont skimp on spray

 

[zman]

joedrum » Mon Nov 10, 2014 4:36 pm[/url]":36ar4g0j]
wide open and choke steve ? ....i be spraying cleaner penetrate oil in the cylinders and turning over first by hand then starter ...of coruse with plugs out ....dont skimp on spray

Thinking he meant choke open, in other words like it was already warmed up. Book says 150-170 but dont be worried if it is 140-150 either, If it has sat a long time it will be low till it has a thousand or so miles.

 

[joedrum]

yea ..looks like something id do in a post :hihihi:

 

[Steve83]

Guess I should've said throttle and choke wide open. Sorry for the confusion...

 

[bronko37]

Personally I don't read too much into the compression readings. My bike has had low readings but it doesn't run like it has low readings. Also it doesn't burn a drop of oil. As long as the compression readings are within the 10% as stated above of one another you should be good. Now, if the bike is burning all kinds of oil and smoking all the time you should be a little concerned. If not, ride it like you stole it.

As far as the mileage is concerned, 168k would be impressive. Remember, its real easy as well for people to swap the gages around on these bikes too. I had a '75 that the guy said had 40k miles on it. Turns out the gages were off of a 78-79 model so I really had no idea how many miles were on it. It did smoke like crazy though, unlike my 76 with "low" compression readings. I was not as educated then as I am now on these machines.

Personally I think that the pistons only really seat proper in the cylinder when the bike is running. When doing a compression test the piston may "lay" in the cylinder a little bit more giving lower readings. This is one of the reasons you hear so many people coming up with various readings on the compression tests. Personally I look to the oil burn, consumption, and engine power to gage the the compression. Bike should be a rocket.

 

[Offcenter]

Thanks guys. I had planned to take it out and run it a bit
to see if it got better. But as of this morning the plan changed.
I picked it up at my mechanic and a half mile from his garage I
had total electrical failure. No volts, no amps, no watts.
Gotta be something stupid for EVERYTHING to quit, especially
with a good, NEW, battery in it. Weird.
So....I'll have to sort that out first before I can take it out and
run it.
Damn. (sigh)

 

[joedrum]

hmmmm bringing the dead back is no easy process ...hang in there

 

[slabghost]

Sounds like the main fuse on the solenoid gave up.

 

[bronko37]

I agree, sounds like a main fuse. To avoid issues like this in the future consider adding a dedicated ground as described in the article below. This was clipped from Randakks blog. There is a wealth of useful information there about common electrical issues and how to solve and test them.

https://www.randakksblog.com/gl1000-cond ... /#more-610

 

[ekvh]

Timing off or valves out of adjustment can affect compression numbers. It wouldn't take much to check valves and timing marks.

 

[joedrum]

yes on unknown bikes it is not good to not go over everything while trying to bring one back from dead

 

[NCScooter]

The timing belts should be changed immediately. Or sooner.

 

[ekvh]

Belts being off a tooth might also give theses numbers. Advancing my cam gear 3.5 degrees raised the compression 15 lbs. Retarding would drop it. Being one tooth off is close to piston/valve interference.

 

[Offcenter]

Thanks guys, but....
C5 ignition, freshly installed.
I changed the belts when I first got it and
I triple checked it to make SURE I had it
on the proper tooth. (new Gates belts!)
As of now, it's snowing here and the bike is still
sitting in his shop. Won't be able to check
anything 'til I get it home.