Very low compression on one cylinder


Information and questions on GL1200 Goldwings (1984-1987)
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surveywaters
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Motorcycle: 1984 GL1200a, 1978 CB750k, 2005 XV1700, 1974 CB125, 1972 XL125, 1987 XR250r(L Frame), 2002 DL1000, 2002 DRZ400, 1989 TW200, 1974 & 78 XS650

Very low compression on one cylinder

Post by surveywaters »



'84 GL1200 - cylinders 2,3 & 4 have 155psi but cylinder #1 has 60psi.

These were all done at WOT with a good battery and plugs out. I shot some oil in #1 and the reading went up to 130psi.

The bike sat for years, only 28k on it. Any chance it's stuck rings? What should I do or try next before pulling the right head off?



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Aussie81Interstate
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Re: Very low compression on one cylinder

Post by Aussie81Interstate »

Have you adjusted the valve settings ? If not I would give it a good run and see if the compression comes up.

Maybe time for a small bore scope usb camera to see if you can find any damage to the top of the piston?

surveywaters
Posts: 17
Joined: Fri Jan 27, 2017 6:57 am
Location: Cayce, SC
Motorcycle: 1984 GL1200a, 1978 CB750k, 2005 XV1700, 1974 CB125, 1972 XL125, 1987 XR250r(L Frame), 2002 DL1000, 2002 DRZ400, 1989 TW200, 1974 & 78 XS650

Re: Very low compression on one cylinder

Post by surveywaters »

I have not done a valve lash adjustment because it was my understanding that the bike has hydraulic lifters. Am I overlooking something here?

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Aussie81Interstate
Posts: 1178
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Location: Penrith Australia
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1982 CX500 Turbo (Historic registration - finally)
1981 GL1100 Interstate (sold)
1988 GL1500 (sold)

Re: Very low compression on one cylinder

Post by Aussie81Interstate »

You could have a bad valve seat causing low compression - but with oil down the cylinder and compression going up I would consider stuck rings a good possibility..

surveywaters
Posts: 17
Joined: Fri Jan 27, 2017 6:57 am
Location: Cayce, SC
Motorcycle: 1984 GL1200a, 1978 CB750k, 2005 XV1700, 1974 CB125, 1972 XL125, 1987 XR250r(L Frame), 2002 DL1000, 2002 DRZ400, 1989 TW200, 1974 & 78 XS650

Re: Very low compression on one cylinder

Post by surveywaters »

I'll run a bore scope down it today as well as a leak down test.

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WingAdmin
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Re: Very low compression on one cylinder

Post by WingAdmin »

Generally speaking, when you have low compression, and then shoot oil into the cylinder, if it is a valve problem, the low compression will persist. If it is a ring issue, the compression will go up, which is exactly what has happened in your case. So I doubt it is a valve issue.

This is actually a fairly common problem with bikes that have sat for years. And it is not entirely uncommon for it to fix itself after the bike has been ridden for a few weeks: the rings "wear in" against the cylinder bore, and things seal up once more.

So my suggestion for now would to be to do nothing except go riding, then check the compression again later on.

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virgilmobile
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Re: Very low compression on one cylinder

Post by virgilmobile »

I have done this once.
Taking all fuel spill precautions...remove that one spark plug..dump a shot glass full of 50/50 mix of ATF and acetone in the plug hole...Lay the bike on its side with that cylinder up for a day or two.
Crank the engine without starting it a few revolutions to blow any residue out.
Put the plug back in and run it.
Expect smoke out the tail pipe and fouling the plug.Replace it and run it again check the compression after several miles.
The ATF mix often can loosen a stuck ring.
Be sure to do a oil change soon.

surveywaters
Posts: 17
Joined: Fri Jan 27, 2017 6:57 am
Location: Cayce, SC
Motorcycle: 1984 GL1200a, 1978 CB750k, 2005 XV1700, 1974 CB125, 1972 XL125, 1987 XR250r(L Frame), 2002 DL1000, 2002 DRZ400, 1989 TW200, 1974 & 78 XS650

Re: Very low compression on one cylinder

Post by surveywaters »

Very reassuring fellas. Thanks and I'll update ya'll in a bit.



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