GL1200 Compression stuff

[TheRepoGuy]

I’m going to have to go the ignorant route for this one - if my head gaskets are cooked which I’d gather is entirely possible that’s one place to look for bad compression but I have always thought (lack of experience tearing down motors...I’ve replaced them never fully rebuilt one) that the piston rings also were connected somehow to the compression of the motor no?

I’m thinking I might just order the top end rebuild kit for mine, retorque everything down to spec and see if I can get it back up to par though I don’t know if that’s my actual problem or not I figured it was a good place to start! Getting my pressure gauge tomorrow so hopefully that will answer some of my problems!
Nate


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[TheRepoGuy]

Brain farted big time on this one ha!

I have no clue if this motor had ever been run “hot” however my coolant reservoir was empty when I got the bike, and when I drained the radiator the fluid was pretty sick looking. My timing belts are new so that would lead me (in theory) that the head gaskets May have failed but again won’t know until I get the gauge on them. If it was run hot then I’d look at piston rings, knew my brain was on the right track there for a second!


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[joedrum]

Hmmm keep trying to start it .....if it’s timed right ..getting spark ..and gas ...it should start ..or do something

 

[TheRepoGuy]

Hmmm keep trying to start it .....if it’s timed right ..getting spark ..and gas ...it should start ..or do something

She burped last night - sounded like it came out of the number one side. I messed with the timing a dozen and a half times with this bloody thing, had a friend of mine make sure and hold the crank on the T1 mark while I put the belts on JUST to be safe. Might have to go back to that step again and triple check it.


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[OldCrow]

TheRepoGuy » Today- 0:48[/url]":2r87sthp]
I’m going to have to go the ignorant route for this one - if my head gaskets are cooked which I’d gather is entirely possible that’s one place to look for bad compression but I have always thought (lack of experience tearing down motors...I’ve replaced them never fully rebuilt one) that the piston rings also were connected somehow to the compression of the motor no?

I’m thinking I might just order the top end rebuild kit for mine, retorque everything down to spec and see if I can get it back up to par though I don’t know if that’s my actual problem or not I figured it was a good place to start! Getting my pressure gauge tomorrow so hopefully that will answer some of my problems!
Nate

Yes the rings are a critical part as well as intake and exhaust valves, head gasket and flatness of the head and cylinder deck. Also if we had dual overhead cams, phasing.

To diagnose low compression symptoms, I typically I use a leak down tester to get a good look at cylinder condition. You need an air compressor capable of at least 200psi, and a leak down tool/gauge. You apply pressure through the leak down tool/gauge check if it holds pressure. If not you then check where it's leaking e.g. intake or exhaust valves, rings(listen in the dip stick hole) or the gasket.

A much better test then a simple compression test.

 

[saganaga]

TheRepoGuy » Yesterday, 11:48 pm[/url]":djvycvxh]
I’m going to have to go the ignorant route for this one - if my head gaskets are cooked which I’d gather is entirely possible that’s one place to look for bad compression but I have always thought (lack of experience tearing down motors...I’ve replaced them never fully rebuilt one) that the piston rings also were connected somehow to the compression of the motor no?

Low compression is commonly due to worn rings, or bad head gaskets, or valves not sealing. Can be any of those. Probably if the piston rings don't look like they are the problem, then as far as I know, its not worth bothering with them.

 

[pidjones]

Check it first - don't just assume poor compression. Be sure to hold WOT with choke OFF when doing it, too. You say it burped - might be trying. Setting timing static usually can get you started, but it takes a lot of cranking to get the fuel bowls filled.

 

[TheRepoGuy]

Check it first - don't just assume poor compression. Be sure to hold WOT with choke OFF when doing it, too. You say it burped - might be trying. Setting timing static usually can get you started, but it takes a lot of cranking to get the fuel bowls filled.

Agreed - My timing is straight, gonna start with a replacement coil and see what happens from there.


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[DaveKamp]

When I'm trying to get one started that has dry bowls, I spray penetrant into the airbox. One can use starting fluid... I prefer penetrant because it's a little less aggressive, and of course, I have ready access to lots. It's particularly better on 2-strokes, but these aren't 2 strokes (wouldn't that be a rush... a 1200cc flat four 2-stroke!)

Not so easy to do with a motorcycle engine, but when I'm working on tractors, I turn the hand crank over two full turns, and feel for compression on each cylinder. Not hard to discern when there's an imbalance in compression somewhere. If it's had the belts off, I'd expect either valve timing, or a bent valve as the most compression-oriented issue, but Crow's suggestion of a static compression tester is the best shop-method, particularly with respect to his last few words re. LISTENING for air leaks. USUALLY, Air leaks through the intake mean either a valve or port... air leaks through the exhaust mean same for exhaust valve or port. Air leaks into crankcase mean rings or piston. The only thing I'd add... is to put a coolant cap pressure gauge on the radiator, and watch THAT... as it'll demonstrate a leak from combustion chamber into the cooling system. In some cases, a blown gasket will leak into the cooling system, in others, it'll leak into the crankcase. In some cases, a crack in a head will leak to an intake or exhaust port, or both.

Oh, and while that's all the case, a static (leakdown) compression test will NOT identify camshaft timing problems... that's a 'dynamic' test (cranking). Dynamic compression is determined by piston position with respect to valve seating position. If you close the valves when piston is at the very bottom of the stroke, you'll have considerably higher pressure indication than if you delay the closing of the exhaust valve for half the engine's stroke... but a static compression test will indicate everything as perfect... so keep that in mind.