low compression


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Swarley
Posts: 6
Joined: Wed Dec 19, 2012 12:57 am
Location: Cut Bank, MT
Motorcycle: 77 Gl1000

low compression

Postby Swarley » Fri Jan 17, 2014 3:59 pm



I have a 77 GL1000 that I bought last year. I noticed the heads where leaking coolant onto the exhaust so I did a compression test and got 2 cylinders at 90, one at 100, and a 110 psi. I pulled the heads and got new head gaskets. The cylinders looked perfect, even had faint signs of crosshatches and no rings on top of cylinder. New gaskets on and no leaks but compression is still about the same tested with plugs out and WOT. Bike runs great when warmed up but runs rough on startup and idles barely running until warm. Do I need to have cylinders bored and new pistons or maybe just a ring job?



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Fatwing Chris
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Motorcycle: 2004 ABS Model Goldwing

Re: low compression

Postby Fatwing Chris » Fri Jan 17, 2014 4:59 pm

These things don't run all that great until they're warmed up anyways,but I would maybe check it with another guage unless this is a known good compression guage that you are using.I'd be leaning more towards carbs that need a good cleaning.
If I'da known it would last this long,I'da taken better care of it.
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Swarley
Posts: 6
Joined: Wed Dec 19, 2012 12:57 am
Location: Cut Bank, MT
Motorcycle: 77 Gl1000

Re: low compression

Postby Swarley » Fri Jan 17, 2014 9:26 pm

I should check it with another gauge, however, it was checked with a professional mechanics gauge but maybe it is worn out. The carbs where completely rebuilt after i got it. The manual says a max of 190 and no less than 175 psi which is a long ways from 90 to 110. I'm assuming it has never been bored or honed but the original owner is dead and the family I got it from doesn't know anything bout it and he had the carbs all off for unknown reasons whic is why I just went ahead and rebuilt them, but maybe he had it honed or bored and it glazed the cylinder before breaking in the rings which is why the cylinders where glass smooth but had crosshatches still? I could prolly live with the rough start since it seems to ride nice but being a mechanics son I can't get over the very low numbers and want to make sure it's not on the edge of destruction. Thanks for the help!

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Sagebrush
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Re: low compression

Postby Sagebrush » Sat Jan 18, 2014 8:05 am

If your engine has sat, not running, for an extended period of time then I wouldn't worry too much about compression just yet. The rings take a set to them when left idle and it takes a few hundred miles for them to regain a good seal. These bikes will run with very low compression its more important that they are relatively even from one cylinder to the next.

You could try and put a little oil in each cylinder before doing the compression check, if the numbers come up then it indicates rings. But I wouldn't personally do anything to it until you run it for at least 500 miles and see where you are at after that. These bikes are notoriously bad runners until thoroughly warmed up.

Swarley
Posts: 6
Joined: Wed Dec 19, 2012 12:57 am
Location: Cut Bank, MT
Motorcycle: 77 Gl1000

Re: low compression

Postby Swarley » Sat Jan 18, 2014 10:10 am

That's good to know about the notoriety of startup. I guess I'll put another season on her and reevaluate after that. Thanks for the advice!

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Fatwing Chris
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Re: low compression

Postby Fatwing Chris » Sat Jan 18, 2014 10:22 am

I would bet that the crosshatch is the original.Like was said earlier,just ride it for a while and then recheck as the rings could be sticking a bit.Maybe dump your favorite oil additive(everyone seems to have one.I used to like Resilone back when I was buying wrecker motors) to it for a few tanks and then check.These motors are pretty stout and will take a lot of abuse.
If I'da known it would last this long,I'da taken better care of it.
Chris
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Swarley
Posts: 6
Joined: Wed Dec 19, 2012 12:57 am
Location: Cut Bank, MT
Motorcycle: 77 Gl1000

Re: low compression

Postby Swarley » Sat Jan 18, 2014 2:32 pm

Good idea on the additive. If it is the original crosshatch then there shouldn't be hardly any wear in the cylinders/ pistons correct? The odometer reads in the 30,000s so it must be reading correct and not rolled over. Thanks again.

bustedwing
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Re: low compression

Postby bustedwing » Sat Jan 18, 2014 11:05 pm

Just a thought did you have the throttle wide open? That would make a dramatic difference in your test. And yes these engines are notorious for rough running when cold, I had a 1200 that was the same way. It would buck and snort, you had to leave the choke on half for about 5 minutes. After that it ran great. Tried several things, never helped. Just when it's cold don't get in a hurry. Ride safe.
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Swarley
Posts: 6
Joined: Wed Dec 19, 2012 12:57 am
Location: Cut Bank, MT
Motorcycle: 77 Gl1000

Re: low compression

Postby Swarley » Sun Jan 19, 2014 3:10 am

Well that sounds exactly like mine, and yes test was with wide open throttle, plugs out, and not after it had sat for a long time.




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