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Compression 60PSI

  • Thread starter Thread starter sugi
  • Start date Start date
S

sugi

Guest
Hi
I am new here and I have a 1978 GS750 that I got about a week ago. I checked the compression with one of the Autozone loaner compression gauges. 60PSI on all 4 Cylinders. ALl plugs removed full throttle. Very dirty plugs. Bike had 1 owner all original and has 45k miles. Stood parked for the last 5 years. Are the rings worn out or the valves not closing properly? I am in the LA area.
Thanks
Sugi
 
Drop some oil in the cylinders and try again. If the compression goes up it's the rings. If not it's the valves.
If it's the rings that's good news since you probably need to run the p!ss out of it to reseat the rings from it sitting so long.
You really should check the valve clearance also before riding it.
 
Adjust the valves, if they are too tight there can't be much compression.
 
Ok
Thanks. I am going to learn how to check the valves and if they are in check I will clean the carb and ride it for a while before I recheck the compression.
Sounds good?
 
Where's indan wells?
I looked
212 miles
 
Last edited:
chef1366 said:
Where's indan wells?
I looked
212 miles
Click to expand...
He said he's in the LA area, but the only Indian Wells that my map finds is between Palm Desert and Indio. :-k

Well, OK, there is another one, but it's up near Ridgecrest, in Kern County.

Neither one is what I would call "in the LA area".
icon_shrug.gif


.
 
Adjust the valves and ride the crap out of the bike. 45k is nothing for a GS750. :)
 
Steve said:
He said he's in the LA area, but the only Indian Wells that my map finds is between Palm Desert and Indio. :-k

Well, OK, there is another one, but it's up near Ridgecrest, in Kern County.

Neither one is what I would call "in the LA area".
icon_shrug.gif


.
Click to expand...

What you never heard of Lower Alabama or LA area :) it includes the western Florida panhandle also
 
Last edited:
I am in Indian Wells, CA. Close to Palm Springs. But for a more general direction I say Los Angeles.
 
LA is a pretty fair descriptor for most people not familiar with SoCal, but a little too nonspecific for the technically-minded folk around here. In the next province over we have an LA (Lethbridge, Alberta), too.

Do you ride dirt? Looks like some great off-roading in the area.

Yeah, get in there and check the valves. I'd be surprised if all of the valves are slammed so far shut that you are consistently reading 60psi on all four cylinders, but better to start from a known point before jumping to conclusions. I had compression on my 650 jump from 100 PSI to 140 after a valve adjustment.
 
BigD
I am not a dirt rider. I ride the racetracks only. Usually with my ducati 1199 or gsxr750. Been o. Putnam Park close to Indy, Barber, my favorite Road Atlanta, Streets of willow. Soon Chuckwalla. This bike is going to be my street bike.
 
Did you run the engine for any time at all? Was it hot when you did the test or cold? An engine that hasn't moved in a while will give you numbers like that. If the engine has stood for a long time I would always oil the bores, cams and valves before trying to turn it over.
 
I checked the valve timing and that is spot on according to the manual. Then I checked the valve clearances with the gauge I currently have that only goes as small as .051mm. All valve clearances are smaller than that except for exhaust valve #4 which is between .006 and .007, which seems fine. As soon as I get the proper gauge in the mail I will check how tight everything is. I try to get everything to .05-.06mm. Looks like the cams look amazingly clean for a 35 year old bike with 45k miles. I will keep this updated as I go along.
 
It's likely you found your compression problem. Did you do my shim spinning trick?
If you can spin the shim in the bucket there is at least some clearance, probably one size thinner will put you around .05mm at least. If you can't spin the shim, there is no clearance, go two sizes thinner and it may be in the ball park. Hopefully there are no burnt valves if this is the case.
 
Ok here it is. I can spin the shims. But every single valve clearance is out of spec. 0.002mm or less. That is tight. Time to get 8 shims.
 
Time to remove each shim and record what thickness is in each position. You might be able to move a few of them around and not need to order eight new ones.
 
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