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Compression Question - 80' GS850GL

  • Thread starter Thread starter Nightmare
  • Start date Start date
N

Nightmare

Guest
I recently purchased a 1980 GS850GL near the end of the summer and after parking it for the winter I started doing some tuning and cleaning. I decided to complete a compression test to get a base line for all of my future tests/maintence and the results were rather concerning...

Dry Test
Cyl 1 - 112psi
Cyl 2 - 112psi
Cyl 3 - 90psi
Cyl 4 - 112psi

Wet Test
Cyl 3 - 145psi
Cyl 4 - 145psi

From everything I have read, there appears to be a problem with the rings/cylinders on my #3 as the reading is way below the service limit and the difference between cylinders is too great...

I found this fairly hard to believe as the bike has only 32,000km (even though i'm the 3rd owner) and a friend who has a 1982 GS1100 suggested that the piston rings have not worn enough to seat properly. He said that when he purchased the bike the sales rep told him to "ride the bike like you stole it" for the first 25-30,000km in order to seat the rings.

Any suggestions would be greatly appreciated.
 
Go ride it like you stole it for a while...

Go ride it like you stole it for a while...

Seriously, go put some miles on it. Anything with less than 1,000 miles per year for over twenty years needs to be run. Use clean oil, keep it correctly tuned and go ride. Might try soaking the rings with some M.M.O. for a week or so, can't hurt.
But what it really needs is riding.
 
Did you do both copmpression tests when the engine was hot and with the throttle wide open? Was the oil metered correctly between cylinders so that the test conditions were identical for the wet test?
Have you checked your valve clearances since buying the bike?
Did the bike start easily before you parked it up for winter?
If the answer is yes to all these questions, put some miles on the bike and re-evaluate it.
A PO may have stored the bike incorrectly for a long period. This will shorten the life of parts like the rings,bores,valves, cam lobes and clutch discs especially if the bike was left on the side stand.
Another thing to check is the airbox crankcase breather. The internal vents can become comletely blocked with rust and cause the crankcase to pressurize and forcing oil up past the worn rings.
Good luck.
 
Nightmare said:
I recently purchased a 1980 GS850GL near the end of the summer and after parking it for the winter I started doing some tuning and cleaning. I decided to complete a compression test to get a base line for all of my future tests/maintence and the results were rather concerning...

Dry Test
Cyl 1 - 112psi
Cyl 2 - 112psi
Cyl 3 - 90psi
Cyl 4 - 112psi

Wet Test
Cyl 3 - 145psi
Cyl 4 - 145psi

From everything I have read, there appears to be a problem with the rings/cylinders on my #3 as the reading is way below the service limit and the difference between cylinders is too great...

I found this fairly hard to believe as the bike has only 32,000km (even though i'm the 3rd owner) and a friend who has a 1982 GS1100 suggested that the piston rings have not worn enough to seat properly. He said that when he purchased the bike the sales rep told him to "ride the bike like you stole it" for the first 25-30,000km in order to seat the rings.

Any suggestions would be greatly appreciated.
Click to expand...

The psi on my 1100 was about 145 dry. The fact you experience a 30 psi rise in pressure after adding a lubricant into the cylinders is a tell tale sign you need rings and/or a valve job.
 
Those numbers would not get me to tear my motor apart unless it was running poorly or had terrible fuel economy.
 
Thanks for the replies guys!

I did check the valve clearences and they appeared to be in check, (while doing this I checed the cam breather and its as clean as a whistle)

Compression test was completed with full choke and wide open throttle, however, I didn't measure the amount of oil (gee, that seems like a REALLY obvious thing to do NOW) but it should be roughly the same between the 2 cylinders I did the wet tests on.

The bike was sitting for quite a while, whether or not on the side stand i'm not sure, but knowing the previous owner nothing would suprise me (he said it needed an oil change... what he forgot to mention is it was missing 30% of the oil and the 70% left was jet black)

As for gas milage, the very short time (isn't it always too short?) I was able to ride before parking I had fairly poor gas milage, but i think that might be partly to blame on my carbs, which were gummed up a bit (think he would have emptied the tank/carbs when he changed that oil before storing it... sigh) and needed to be tuned bad as they were running very rich (sooty plugs, carb spitting, etc).

Basically, I was quite concerned with the numbers and since this is my first bike I don't know what poor or good performance is yet. With the carb problems I've been having (and hopefully fixing, next up, pods and rejetting) I'm hoping to follow the advice that was given on this forum. "Before tuning the carbs, make sure everything else is working (good compression, valve clearence and ignition)"
 
Road_Clam said:
The psi on my 1100 was about 145 dry. The fact you experience a 30 psi rise in pressure after adding a lubricant into the cylinders is a tell tale sign you need rings and/or a valve job.
Click to expand...

Or that the bike has been sitting and the cylinders are dry. The light film on the walls helps to seal thing up and on a motor that has been sitting a couple of drops can make huge differences when nothing is really wrong at all.
 
Put maybe 2 tablespoons of marvel Mys oil in each cyl. let it soak for 24 hours. crank the motor to clear the oil, then reinstall the plugs. Ride it at least 2 hours & then recheck the compression
My 850 has 125 across all 4
 
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