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'83 GS-550ED Crazy Low Compression

  • Thread starter Thread starter GS550ED
  • Start date Start date
G

GS550ED

Guest
Hey all,

Guess my profile got purged a while back, I've been overseas for the Army so haven't had a chance to visit here.

I've been back for 6 months or so, and tuned my GS-550E back up after taking it out of storage. Ran just as good as it did a year ago, if not better! However, about a month after getting it back on the streets, I had a catastrophe. On the highway it overheated and dumped out most of it's oil from a few gaskets. I set to taking the bike down to the jugs, and replacing the gaskets and any hardware that got damaged.

For the most part, I think I dodged a bullet. No metal bits in the crankcase, no scoring of the cylinder walls, etc. I dressed the fella back up, timed it, and gave the carbs a good soak, clean and reassembly and put them back on.

When it was go time, I had crank, but no start. So I set to checking the basics, and the results:

Good spark, nice blue arc from each plug wire (also new plugs and wires)
Good fuel delivery, fuel in float bowls and fuel reaching cylinders (from the gas smell after pulling plugs)
Good timing, pulled off cam cover and double checked timing marks, not to mention making sure the engine cycled smoothly when turned by wrench before attempting a start
Head bolts torque'd to spec.

Then I performed a compression test. About 70-75 on each cylinder.

I should mention the bike sat with it's head off for 2 months, because I went on another short escapade for the Army, so I'm not sure if that had an effect on anything. Here's where you're free to call me an idiot.

I did not change the piston rings, but they seemed within spec, and I did not check valve clearances, because I felt I lacked the knowledge and quite frankly was antsy to get the bike running again. My conclusion is that it was the valves perhaps?

So, friends and wizards of GS bikes, is it a safe bet to say it was just my negligence to check the valves that is causing this conundrum? Or could something else cause such dismal compression ratings? I've heard that some bikes CAN start on 75 or so PSI, so I'm curious why I can't even get a single cycle, just turning on the starter ad infinitum.

Thanks, as always!
 
GS550ED said.....
"I did not change the piston rings, but they seemed within spec, and I did not check valve clearances, because I felt I lacked the knowledge and quite frankly was antsy to get the bike running again."

All this work (pull head, check timing,etc. ) and you ignored valve clearances ?????
If head was off for a while, rings might be dry leading to low compression, but I think even 75 psi should fire; make sure plug wires are on correct spark plugs- this is real easy to mess up in your haste.
 
How you do the test will affect the outcome. The correct method is:
Warm engine
Throttle fully open
All plugs removed (spins easier)
Hit starter button until gauge stops incrementing
Take reading.
Is this the procedure you followed?
 
tom203 said:
GS550ED said.....
"I did not change the piston rings, but they seemed within spec, and I did not check valve clearances, because I felt I lacked the knowledge and quite frankly was antsy to get the bike running again."

All this work (pull head, check timing,etc. ) and you ignored valve clearances ?????
If head was off for a while, rings might be dry leading to low compression, but I think even 75 psi should fire; make sure plug wires are on correct spark plugs- this is real easy to mess up in your haste.
Click to expand...

Yeah, stupid stupid stupid, I know. I just checked my shop manual that I got courtesy of Bikecliff's site and I am waaaaaaaay unprepared and unqualified to check the valves. What can I expect to pay to get someone more qualified to do it? Will anyone even do it for a bike this old?
 
koolaid_kid said:
How you do the test will affect the outcome. The correct method is:
Warm engine
Throttle fully open
All plugs removed (spins easier)
Hit starter button until gauge stops incrementing
Take reading.
Is this the procedure you followed?
Click to expand...

I did all of those except for the warm engine, which I can't do because it won't run. Will the heat affect it by a large margin? I got a steady 71 minimum to 77 maximum on all 4 cylinders.

Also I should mention I checked my plug wires, and we're good in that regard. I took many pics during the teardown.
 
No, the throttle opening will affect it more, and is the most often overlooked.
Checking you own valves is very simple, compared to everything else you are going to have to do to maintain this bike.
Use this
And this
 
Last edited:
GS550ED said:
Yeah, stupid stupid stupid, I know. I just checked my shop manual that I got courtesy of Bikecliff's site and I am waaaaaaaay unprepared and unqualified to check the valves. What can I expect to pay to get someone more qualified to do it? Will anyone even do it for a bike this old?
Click to expand...

1.Feeler guage - in proper increments
2. Zip ties
3. Steve's valve spread sheet
4. Possibly extra valve cover gasket
5. Cheap caliper from Harbor Freight

That's all you need for starters. If you need thinner shims, check the Shim Club

75 is a bit low for a cold compression reading.

Make sure you have the plugs wires on nthe correct cylinders
 
Put up a location, there is sure to be a few members locally who would be happy to lend a hand.
 
tkent02 said:
Put up a location, there is sure to be a few members locally who would be happy to lend a hand.
Click to expand...

I live in northern AZ, but would gladly drive practically anywhere in Arizona for some help. Money and/or beer would be imparted to guide me through the process.

Before I go to a shop or anything, though, I'll take a look at these guides and take to heart what BigT and Koolaid Kid offered. Got some reading to do. Thanks guys! And if anyone is in the area, it'd be great to meet up so I can make sure I do it all correctly.
 
Big T said:
1.Feeler guage - in proper increments
2. Zip ties
3. Steve's valve spread sheet
4. Possibly extra valve cover gasket
5. Cheap caliper from Harbor Freight

That's all you need for starters. If you need thinner shims, check the Shim Club

75 is a bit low for a cold compression reading.

Make sure you have the plugs wires on nthe correct cylinders
Click to expand...

this is a rocker arm engine.
 
Doing valve adjustments on a rocker arm engine is much easier IMO. Got a set of feeler gauges? just check them first for clearance.
Reassembling the top end without at least breaking the glaze (honing) or replacing the rings is probably a large part of your problem.
 
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