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Disassembled GS750 - want to test compression

  • Thread starter Thread starter a3tripod
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a3tripod

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Hi all! I have a 1982 non-running (never cranked) GS750 that has basically been completely disassembled and the motor is mounted to an engine stand. With the starter cover removed, i see a large black wire (assuming this is ground) and then 3 small wires. Yellow, white/blue, white/green. I thought by simply providing voltage (via car battery) to one or more of these leads would force the starter to crank. Apparently I'm doing something wrong. Can someone lend me a hand? Sorry - I'm a total newb.
 
The big black wire that connects to the starter itself is the power lead to the starter. +12v to it from the battery through the starter relay and the starter turns, hopefully the engine does too. The starter grounds to the engine case...

The other pretty colored wires are the stator wires. Usually they are cooked black on one end. Stator, not Starter! Don't use them to crank the starter!
 
Ok, so i need to dig the starter relay out of the storage totes and hope its still functional? I was hoping i could eliminate everything and go straight to the starter itself, because we had a no-crank condition when we first got the bike.


tkent02 said:
The big black wire that connects to the starter itself is the power lead to the starter. +12v to it from the battery through the starter relay and the starter turns, hopefully the engine does too. The starter grounds to the engine case...

The other pretty colored wires are the stator wires. Usually they are cooked black on one end. Stator, not Starter! Don't use them to crank the starter!
Click to expand...
 
Ok -clearly im doing something wrong - or the starter is just plain dead. This is what I'm working with.

2vtr3hf.jpg
 
I've tried energizing the black wire on the starter directly, not using the relay.
I've tried the configuration pictured above, energizing the red cable (which was never removed during dis-assembly, its connected to the original terminal)
 
That green/yellow wire on the solenoid needs its connection back into the harness; how did it get cut?
 
If the starter isn't dud, then connecting the battery positive to the thick black wire that goes to the starter and connecting the battery negative to the engine casing will make the starter operate. You don't need to putz around with the relay to do this.
 
First, check that the engine spins freely without the starter motor. Take the spark plugs out, and put a wrench on the end of the crank - if it spins freely then proceed.

Jumping the starter motor with a car battery should work, assuming you have a good ground connection on the engine. Are you connecting the positive wire from the battery to that yellow connection in the pic? If you are trying from the red wire in the pic, you'll need the green / yellow wire hooked up as mentioned above.

If all else fails, pull the starter motor out and test it separately (they spin fast as hell with no load though). The starter motor might be junk, or it may just need a rebuild kit.
 
There is no harness. the bike is completely disassembled. What you are looking at is a motor mounted to an engine stand. I'm trying to energize the starter to crank the motor to test compression.

cowboyup3371 said:
That green/yellow wire on the solenoid needs its connection back into the harness; how did it get cut?
Click to expand...
 
This is exactly what I thought! Nothing happens when i do this however. I'm connecting the positive terminal from my car battery (engine not running) to the black cable on the starter, and grounding the negative jumper cable end to the case (and car frame respectively).

Grimly said:
If the starter isn't dud, then connecting the battery positive to the thick black wire that goes to the starter and connecting the battery negative to the engine casing will make the starter operate. You don't need to putz around with the relay to do this.
Click to expand...
 
The GS750 was last started in 1987. I imagine the starter (and numerous other parts) need replacing/refurbishing. Thanks everyone for the sound advice. I was really second guessing myself!

Big Rich said:
First, check that the engine spins freely without the starter motor. Take the spark plugs out, and put a wrench on the end of the crank - if it spins freely then proceed.

Jumping the starter motor with a car battery should work, assuming you have a good ground connection on the engine. Are you connecting the positive wire from the battery to that yellow connection in the pic? If you are trying from the red wire in the pic, you'll need the green / yellow wire hooked up as mentioned above.

If all else fails, pull the starter motor out and test it separately (they spin fast as hell with no load though). The starter motor might be junk, or it may just need a rebuild kit.
Click to expand...
 
a3tripod said:
The GS750 was last started in 1987. I imagine the starter (and numerous other parts) need replacing/refurbishing. Thanks everyone for the sound advice. I was really second guessing myself!
Click to expand...

I have restored numerous GSes that have sat that long or longer. Haven't needed a starter yet, most of them fired right up once I fixed whatever problem it was that got it parked in the first place. in 97.2% of them, it was tight valve clearances, corroded wires in the charging system, or carbs clogged up from sitting a few months, and thirty years later they are still clogged. Imagine that.

Usually they only parts they need is a few new seals and a gasket or two.

Now if this bike has been stored in a rust bucket location you may not be so lucky.
 
@tkent02
I hope you're right! As for now, however, I can't get the starter to spin :(
 
Remove the two bolts at the end of the starter, slide the starter toward the middle of the crankcase, lift it out. Clamp it in a vise or hang on VERY tightly. Connect the positive jumper cable to the black wire (or its mounting stud), make sure you have a good grip on the starter, touch the ground wire to the starter housing.

That eliminates ALL other possibilities and will tell you if your starter is good.

.
 
Thanks Steve! I was looking through the service manual to see how to remove the starter. I wasn't sure if i needed to remove the cover over the starter gear to remove the starter or not. I'll do this test right away!
 
While you have the starter out and are, presumably, doing a bunch of other maintenance, feel free to change the o-ring on its 'nose'.

.
 
We will be completely refurbishing everything that needs it. Was hoping for some positive data regarding compression. I did test the starter as you suggested. I removed it and clamped in a vice. once i hooked it up to a battery i heard the faintest noise, so i tapped the starter housing with the handle of my screwdriver and it started to rotate VERY LOUDLY and with almost no rotational speed. Thing is toast :). I was able to stop the rotation with almost no pressure.

I then proceeded to remove the side cover and hooked up a drill and 17mm socket to "manually" crank the motor over. 60psi :(. Ran out of time to do any more testing to see if its valves or seals...
 
You have compression so before worrying about other things email Steve and get his handy dandy spreadsheet that does all the math for you.Then go and check the valve clearances.Like tkent said 97% of the times it's things like that gets bikes parked.The starter may not be beyond saving either,there are rebuild kits available so it's worth your while to take it apart first.
Edit:Opps you have an 82 750,you can skip the email to Steve as that's for 2 valve with shim motors.Go here http://www.mtsac.edu/~cliff/storage/gs/GS750_16valve.pdf
and follow the procedure outlined for checking the valve.I have both types and the locknut adjust is WAY easier.
 
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60 on all of them is actually very good for an engine that's sat for years. Once you adjust the valves correctly, fix everything else and run it hard a few thousand miles it will have very good compression. I guarantee it. If it had burnt valves or broken rings or anything like that they wouldn't all read anywhere near the same.

I have had quite a few of these engines "fix themselves" this way.
 
I took apart the starter - holy cow it was filled with black soot! no wonder it wouldn't spin! I cleaned it up but unfortunately my friend who was helping me, managed to break the brushes with a Q-tip!! I LOL'ed and have subsequently named him Q-tip. We will go with a rebuild kit. Got a favorite out there? As a side note, there is quite a bit of wear on the end where the brushes touch - looks concave somewhat:

ephbia.jpg
 
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