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Help needed with compression numbers!

  • Thread starter Thread starter zuty13
  • Start date Start date
Z

zuty13

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Hi I have GS550L 82'.(8 valve). with around 45k miles.Bike is generally running fine, except not too much power after 65mph (top is around 80mph). 5 years ago I've changed piston rings and valve seals ,cam chain (mehanic told me cylinders where within specs in that time and I think no valve job is done...I didn't know too much about mechanics in that time)

compression numbers from this morning are(full throtle and warm engine):
1st- 9kg/cm2(130psi)dry and 14kg/cm2(200psi)wet
2nd-9.5kg/cm2(135psi)dry and 14kg/cm2(200psi)wet
3rd- 9.5kg/cm2(135psi)dry and 11.5kg/cm2(165psi)wet
4th- 10kg/cm2(145psi)dry and 12,5kg/cm2(170psi)wet


2 years ago numbers where the same except for the first cylinder was 9.5kg/cm2(135psi)dry... I didn't do wet cylinder test in that time..
that increase in wet cylinder test looks strange to me can someone explain me is there top end repair in near future or am I too paranoid..????

Also I have small oil leaks at cylinder gasket at end bolts where bellow 1stt spark plug and 4-th spark plug... do I need to change the gasket or no??
 
Your numbers are fine and nothing to worry about.
How small is the leak in your head gasket? If it's something you can live with I'd do just that. If not it's a head off job.
Your top speed looks a bit on the low side but, forgive me if this is way off mark, if you're heavily built and wear gear with a high drag coeff. that might be all that's limiting you to 80 (plus the bike being an L as well with high drag coeff. of its own). Could be loads of other reasons why she's a bit low at the top as well - carbs, air filter, timing and so on.
 
I agree that the compression is fine. Are you keeping up with valve adjustments per the normal service interval?

Regarding the top speed problem, is the bike stock or modified? A stock 550 should top 100 mph with a long enough road while hunkered down on the tank. If the exhaust has been changed, or the intake system changed, without adjusting carb jetting the bike could be running lean and limiting the power...it also will damage the engine by running too hot. Hopefully this is not the case.

Hope this helps.
 
Nessism said:
Are you keeping up with valve adjustments per the normal service interval?

Regarding the top speed problem, is the bike stock or modified? A stock 550 should top 100 mph with a long enough road while hunkered down on the tank. If the exhaust has been changed, or the intake system changed, without adjusting carb jetting the bike could be running lean and limiting the power
Click to expand...

Valves are regullary checked and clearances are fine...
Bike is stock, only exhausts are a little bit shorter 4-5 inches and new iner pipes are in the mufflers ..stock was rotten and cut off ... rear sprocket is 50..maybe thats preventing higher speed..
Spark plugs are nice colour- dark tan...
Why is that compression raising so much when oil is added ..and only in 1st and 2nd cylinder change in numbers is dramatic?
 
Most likely the oil flowed out better in the cylinders with higher compression, or you put more oil in those cylinders unknowingly.
 
? is what RPM are you at when doing 80mph does it have the stock sprockets. 50 doesn't sound stock???
 
SqDancerLynn1 said:
? is what RPM are you at when doing 80mph does it have the stock sprockets. 50 doesn't sound stock???
Click to expand...

80mph is at 7000rpm ..and thats maximum RPM I menaged.. 50 rear sprocket is standard on GS550LZ 82'... I cant find smaller sprocket since I have cast wheels with drum brake at rear(different OD then on disk brake rear)..funny but at 82' they return to drum brake instead like disk rear in previous 2 years...
 
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