Engine vibration?

[1BDJP]

I have a 93 Yamaha WR500, my wife loves it is the only reason it is still around. When I bought the ski it had two loose engine mounts. I replaced all four with new Yamaha mounts and aligned the couplers. Now I have a vibration when accelerating or decellerating. Once it is up to speed it is not as bad. There seems to be no vibration at idle. I removed the jet pump, vibe is still there. I removed the intermediate housing, vibe still there. I pulled the engine, replaced the bearing that supports the shaft, in the end cover, no luck. When I reinstalled the engine, I got the alignment with the couplers and intermediate housing perfect. No luck. When I had the jet pump out the bearings, seals, impeller, impeller housing, and impeller shaft were all replaced. The engine had good compression, 138psi front 142psi rear. What am I missing? Could the crank or rods be bent? Help!!!

[Joe St. Louis]

There are many things that can make an engine vibrate, bent rods could be one reason. You may want to check your engine mounts again, I know you replaced them when you bought the engine, but they could be bad now. They may have even been defective. Here's a few other suggestions, Loose flywheel, loose stator plate, poor compression in one cylinder, fouled spark plug, Crank out of faze (not likely), Faulty ignition coil, bent drive shaft. I sure there may be one or two more that I'm missing, but it’s a start.
:D

[1BDJP]

I did not purchase an engine. When I bought the ski, I found that it had 2 loose mounts. I then replaced them. That is when I noticed the vibe. How could I inspect them? The plugs are not fouled, first thing I checked. Cylinder compression is good. Ignition coil is new. Drive shaft is also a new part. I will check the suggested parts. Does anyone know how to inspect for defective engine mounts? Any help would be great.

[raider1100]

1BD to check for the engine mounts what you want to do is grab a hold of the exhaust pipe and try to pull the motor towards you. Have somenoe look and see if the motor mount is flexing. Do that on either side of the ski. Also did you have any shims that went on top of the motor mounts? if you did and they were put in the wrong palce or swapped and now they are sitting on the wrong motor mount then that could also be a source. the motor may look like its aligned but its cockeyed in the wrong way. persoanlly Im not sure if the shims really do a lot but they are there for a reason so I always put them back where they belong after i pull a motor
Rob

[1BDJP]

Raider 1100,
I have checked the mounts like you suggested. The engine does not move. The shims were replaced as found and the alignment was verified with the manual. I had the vibe even when the intermediate housing and jet pump were removed. I have isolated the vibe to the engine.

[wrenchin]

I had a vibration problem with my 97 Sea-Doo GS that wasn't heard but kept breaking exhaust mount bolts. It was driving me nuts! I kept blaming it on inferior bolts. Finally took it to my local dealer to have the driveshaft aligned. When the tech rotated the engine without the driveshaft installed we could hear the crank bearings rise and fall (clacking). I solved this problem with a fresh 720 from SBT last August. Haven't broken a bolt since!

[1BDJP]

Wrenchin

If you read the first post, I am leaning in that direction. It is the only possibility that has not been looked at. Thanks I will check that.