GS 450 Engine shot what options??

[jimfj]

I looked at a 1980 GS450 yesterday and the bikes in really good shape but the motor, while it starts, has horrible screaching and knocking sounds coming out of it. I figure a rebuild is prolly not the easiest solution here.

What motor choices do I have for a direct bolt up do I have besides another 80 Gs450? Anyone have a spare motor laying around?

Thanks for your help

Jim

[Matchless]

I would pull the stator cover and make sure its not something stuck to the rotor magnets - starter clutch springs or something simple.

[pete]

I would pull the stator cover and make sure its not something stuck to the rotor magnets - starter clutch springs or something simple.

+1... could be something really simple... and I rebuilt mine myself, it's actually not that hard if you're careful, take your time, and measure stuff properly...

[SqDancerLynn1]

Doesn't cost anything to take it apart and see if it is repairable !!!

[tom203]

I would pull the stator cover and make sure its not something stuck to the rotor magnets - starter clutch springs or something simple.

Yes, indeed- offer $200 and take a chance.

[jimfj]

I tested compression in both cylinders and got about 105 and 110. I had another GS friend take a look at it with me and when we tried to fire it up he just about cried, the sound was so bad.

I apologize. part of the story I forgot to mention was that a previous owner ran the bike with a screwed up oil drain plug. (no oil or very low) I don't think the motor seized but i believe something somwhere starved for oil.

thus the determination of the shot motor.

[Big Rich]

The "modern" GS500 engine may be an option. Except the exhaust ports are at a different angle.

[koolaid_kid]

Sounds like you need a new bottom end. You could move over the trans and even the top end, but if it sounds that bad I doubt a crank rebuild would be possible.

[SqDancerLynn1]

You need a GS500 bottom with your GS450 head

[Big T]

I tested compression in both cylinders and got about 105 and 110. I had another GS friend take a look at it with me and when we tried to fire it up he just about cried, the sound was so bad.

I apologize. part of the story I forgot to mention was that a previous owner ran the bike with a screwed up oil drain plug. (no oil or very low) I don't think the motor seized but i believe something somwhere starved for oil.

thus the determination of the shot motor.

You need to do more diagnosis.

Was you compression test done cold? If so, you have plenty of compression

I'd look at 3 things

Starter clutch

Clutch

Cam chain tensioner

These motors will run with no oil (ask me how I know)

If the lower end was shot, it would be knocking, not screeching

Screeching is rotating metal rubbing against something

[Billy T.]

GR650(tempter) should bolt in fairly easy as well. Kind of a rare motor, though. That said, there is one on ebay for 500 plus 280 in freight. But you will need to source some carbs, too.

My 450 moves out pretty well as is, the 650 done up right would make one of these little bikes a screamer.

[Big Rich]

Actually, a GR motor is about 1.5" taller than a GS450 motor. So you would need carbs and exhaust.

[Flyboy]

If it ran low on oil, the bottom end should be fine, these motors are bullet proof, and mostly splash lube low pressure oiling systems anyway.
I would suspect cams worn in the cam caps, as they would be the last to get oil and would account for the screeching noise.
In which case, you probably only in for a new head.

[Mekanix]

, these motors are bullet proof, and mostly splash lube low pressure oiling systems anyway.

Unfortunately these twins are plain bearing engines.

Before 1980 they had all the benefits of the larger 4 cylinders.

On 4 cylinder Roller bearing engines, they are much more forgiving.

All GS/X 4-5xx are plain bearing engines after 80.


What would fit ??

1980 + gs 400. 450, 500 BASE with any head you want to use as long as its newer than 80. Even your own if you find its still within specification.


The GS500 is a direct bolt in but you need the carbs to go with it and you need to manufacture an exhaust system.

Another gs 450 would be best.


If you want to fix it, start with the simple things.


1 take a video.
2 post it wherever
3 link it here and we can help narrow it down.
4 dont run it longer than necessary.




After that depending on the noise its making,

It could be

Main bearings: they are the first to get oil and at the highest pressure directly from the pump unrestricted. Oil from there then goes to the connecting rod big ends.

The cylinder and small end get splashed with oil coming out of the connecting rod big end.



At the same time oil is going to the balance shaft but it is restricted.

And then to the clutch shaft bearings which are also restricted.


And the most restricted and last in line to get oil is the top end.




SO with lack of lubrication my thoughts on what failed first would be:

Top end.

Main crank bearings (Makes a deep knock sound)

Connecting rod bearings ( makes a faster sharper knocking sound)

Balance shaft baring ( similar to main bearing failure)

All these are plain bearings by the way.

the clutch shaft probably survived.

[Flyboy]

OK...oooops I will shut up now and stick to what I know.