90 motor in a 92

[woodcreekpete]

Greetings:
  Anybody ever swap an early model motor into a 91 or newer? The motor in my 92 seems to have not enjoyed running with little or no oil in it. I've got a good 90 motor here and want to swap it in.
  Anybody ever source the front mounts? If not, are they a pain in the ass to pull out in re-useable condition?
  I was also looking at the rear mounts from the 90 - they take a 12mm bolt and would slide into the fronts but I'm wondering if they'd be up to the task with the revamped mounting set-up. Any ideas would be great.
Pete

[Pat Conlon]

Following...

[fj1289]

Following...

Aww - come on Pat ...

[roverfj1200]

I have gone the other way. You may have to drill the rear mount to fit the rubber mounts. That said I went the other way.

[Alf]

It is not difficult: you only have to adapt the upper crankcase to fit to the chassis
the pre 91 rear lower engine mount cant be fitted on 91 chassis

[woodcreekpete]

Here's the gospel (according to Pete anyways) about swapping the motors.
91 and newer into older bikes: Rover is correct - late motors don't have the lower rear mounts machined out. They would need to be drilled out to 28mm to accept the rubber mounts. Not a job for the 18v Bosch that I have though.The front mounts would have to be pressed out and the aluminum slug installed on the left side. Re-install the rubber bushings and it's good to go.

90 and older into the newer chassis:   Front mounts are unobtainable and I didn't think the ones in the 91+ would survive being pressed out for re-use (they're brass, I believe). Tony, the trusted machinist whipped up a pair for $40.
 The aluminum slug needs to be removed and here's where things went wrong. I removed one from a broken set of cases, using a lot of heat, a drift and a sledge hammer. Didn't really want to try that on my good motor so I made up a puller with some pipe and a 10mm bolt. Stripped it right away. So, figured I'd drill it out. Went through all my bits, up to 1" (the hole is 1.1" (28mm). Still no movement. This is when the misguided idea of helping it out with some delicate sawzall work occured to me. Apparently, delicate and sawzall are two things that don't happen together. Went right through the sleeve and into the cases a fair bit. This is going to require a trip to the welding shop when the lockdown is lifted. Not a terminal error but a little patience would have been handy here. Next time, a 3/4" piece of threaded rod in the puller should do the trick.
 To mount the 90+ rear motor mount, Mr. Yamaha enlarged the diameter of 2 of the case bolts to 10mm. I sleeved the cast steel bracket to take the 8mm case bolts of the 90 motor but I was a bit worried that they might not be up to the load. Decided to make a new mount using 3 of the 8mm case bolts to spread the load around a bit more. Again, Tony to the rescue. Used 10.9 grade bolts threaded as deep as they could go into the cases. Still not totally convinced it'll be strong enough though.
 Glued the aluminum slug from the left front early mount into the hole where the lower left used to be. There's a little rubber bushing threaded into the newer frames which pushes on the lower left casting where the mount used to be. I'm guessing it's there to counteract the thrust when the motor's under load.

All that's left now is to get the cases welded, ream out the hole and put 'er back together.