Bad vibration with used engine.

[Anonymous]

Recently purchased a used engine from a ?reputable bike salvage"
I was present for the compression check. #1 showed 145psi, #'s 2,3 &4 showed 168 psi.
I bought and installed the engine. Fired it up and I could not be more disappointed. My 78 GS1000 now vibrates worse than a Harley firing on one cylinder.
Did the normal checks only to find that when I checked the compression with MY compression gage I found #1 and 4 at 90 psi. #2 & 3 at 130 psi.
Can this difference in compression make the bike vibrate so bad.
I have spark and fuel to all cylinders. Timing has been checked repeatedly. It remains spot on as set during the first run.
Any Info you guys can supply would be a great help.

[Anonymous]

I would suspect a clutch basket that's shot.

[Mr. Jiggles]

Have the carbs been synch'ed recently??

[first timer]

compression shouldn't matter to much with vibration. my 78 1k motor i am working on has 90, 130 ,130 , 110 or sumtin like that, and before that #1 didn't have any compression.

any ways i rebuilt the carbs got the motor running carbs not synced and it doens't vibrate for me. so i would guess it is somthing eles not compresion. maybe you have a dirty carb or bad spark and it is not running on all cylinders.

to see if you can get some compresstion back on the bike, run the motor till it's nice and hot then spray some water down the throat of each carb, using a spray bottle. the water will turn to steam instantly and help break carbon off the valves to help get a better seal to have better compression. you will have to run the bike at around 5k so it doesn't stall on you.
watch all the black crap shot out the exhaust.

after you do this you might want to change your oil and filter.

-ryan

-ryan

[Anonymous]

Vibration can be caused by a number of things. The first thing I would do is check the condition of the motor as it doesn't do any good fixing a clutch problem is the motor is bad.

The compression must be checked with the engine warm and the throttle open. If there is low compression on any cylinder, squirt a little oil into the spark plug hole and check again. If the compression improves then you have bad rings, if it stays the same, then the valves are bad.

If you have motor problems, find out what is wrong and get an estimate on repairs then go back to where you bought it and ask for money back or a refund.

The vibration could be carb problems or something out of balance. My initial guess is that the carbs are so dirty and out of sync that this is the problem. It could be something else as others have suggested however.

[Anonymous]

I would suggest checking the valve clearances, too. The compression test with the oil will give you an idea if the valves are suspect, so do that first.

[SqDancerLynn1]

All of the sugestions are good Another possibility the crank could be twisted. You would need to check #1 & #4 at top dead center and check the timing marks

[redliner1973]

In all eventuality, a 'tune up' must be done on this engine to find out where you stand. This involves, as the above posters have said, Carb cleaning, carb sync, valves adjusted, plugs replaced, Ignition checked for proper operation, coils and caps checked for proper resisitance and obvious visual defects, oil/filter change, compression check AFTER all this has been done first. You cannot get to the heart of the problem unless you rule out all the above first, as each of these can lead to 'vibration' if defective. Do all of that, then post back if it fixed it, or if it is still running bad. remember, it is a used engine that you know nothing about, nevermind the fact it has probably been sitting for a great deal of time. Good luck.

[Anonymous]

Thanks to all that responded to my vibration problem.
I am working on the problem, using your input. I will post back and let you all know what fixes the problem.
Note: This bike was purchased new by my Mother for my Father
in 1978, Got to get it running right so Dad and I can ride the Dragon (US 129) in Tennessee next next summer.
THANKS AGAIN TO ALL FOR YOUR HELP.

[Don Lobacz]

They probably put oil in the motor before you got there for your compression test so it would be higher. It's odd that 1 & 4 are lower compression: usually they are higher because they get better cooling. A plugged pilot circuit or main can cause a little vibration, but usually it's loss of power. You have spark, but is it in the right place? Check to make sure that 1 and 4 are firing from the same coil. Did you recheck all motor mounts? Also, if the motor was crashed hard on the left side then the crank could have been bent (salvage yards would have no qualms about removing the stator cover and rotor and putting on used items).

[Anonymous]

They probably put oil in the motor before you got there for your compression test so it would be higher. It's odd that 1 & 4 are lower compression: usually they are higher because they get better cooling. A plugged pilot circuit or main can cause a little vibration, but usually it's loss of power. You have spark, but is it in the right place? Check to make sure that 1 and 4 are firing from the same coil. Did you recheck all motor mounts? Also, if the motor was crashed hard on the left side then the crank could have been bent (salvage yards would have no qualms about removing the stator cover and rotor and putting on used items).

The carbs came off of my original engine. I just borrowed some carb sticks to check and balance them. No luck yet guys, It's driving me nuts, but I'll get it soon.
Thanks all again for the input.
Derek

[RacingJake]

This is what I would do,

Check all engines mounts

Run a big wooden dowell with a o-ring around it in cylinders 1-4, then 2-3 at TDC and see if the o-ring moves. Then turn motor over untill pistons are halfway between TDC and BDC and check all cylinders with dowell again.

Check clutch assy and nut

Check rotor assy

Check cam timing and rocker arms for proper operation

Good Luck

[Dark Jedi]

Run a big wooden dowell with a o-ring around it in cylinders 1-4, then 2-3 at TDC and see if the o-ring moves. Then turn motor over untill pistons are halfway between TDC and BDC and check all cylinders with dowell again.

Just to add, watch that dowel does not get cocked off to the side.

That is what started my rebuild project.. broken dowel inside the cylindar, so the head had to come off.

As long as the head was off, might as well rehone the cylindars. And rings, rings are good. Look at that cam chain, may as well replace.... :roll: