Engine Rebuild/Replacement Help

[zanza14x]

Hello again, I appreciate the past help and advice on my 1978 GS550. It seems that the engine has given out on me at just under 20,000 miles, to my dismay, but I do not want to part with the bike, too much time and worry into it . Anyways, it has lost alot of power and is sending alot of white smoke out of the right tailpipe, along with the 3rd cylinder being cool to the touch and no idle. Now, I will say right away that a few people have suggested it could be some crap in the carb, all of which were rebuild and cleaned last fall, or that I could have a bad plug. I am not ruling this out, but most people have said it sounds at least like a problem with at least one piston, etc.. I will be performing a compression check and all other checks neccessary to verify, but if worst comes to worst, I would like to rebuild or replace the engine instead of scrappin' 'er. I also realize that asking about upping CC's or engine replacements is frowned upon on this site (from what I have read), but I simply want to make sure another GS stays on the road. Therefore, does anyone know someplace I could pick up an "engine rebuild kit" at a reasonable price, if such a thing exists anymore? Also, I have seen quite a few similar motors on ebay for 100$-300$, and if I could ensure that it ran well, what are the size limits a '78 GS 550 frame/bike could take as far as an engine? The reason I ask is b/c it seems that most of the GS engines for sale are 650's or 750's, and I was wondering if either size would work, or if I would need to stick with a 550? Lastly, what would the year range be for an engine to be compatable with my bike? If possible, I would like to "upgrade" away from the points ignition system. Sorry this is a little long, but any advice is GREATLY appreciated. Thanks.

 

[SqDancerLynn1]

In the MC world their are no rebuild kits as such. You Have to purchase the individual parts. A compression test is a good place to start. I understand a 650 top end will fit. I don't know the specifics. A few more CC's never hurts.
If the compression checks Ok I would still go back and check for spark on all cylinders and maybe another carb clean. Even if they were cleaned last week it is still possible to get some crap from the tank.

 

[zanza14x]

Hello again, I was also wondering if I were to "upgrade" to a higher engine displacement, if I would have to include the stock transmition that came with the "new" motor, or if the tranny, which works fine, from my 550 would still work? Any other input onto engine sizes and years that would work would be GREATLY appreciated. Thanks.

 

[BassCliff]

Hi,

What I would do, if it were the worst case scenario, would be to rebuild the top end. Get a gasket set, new rings, valve seals, etc. Pull the jugs and head, hone the cylinders, etc, put it all back together.

I don't think you can put a larger top end (like from a 750) on your 550 crankcase. If you put a bigger engine in the frame you would need welding and fabrication skills to mount it in the frame, new motor mounts and such.


Thank you for your indulgence,

BassCliff

 

[Nessism]

A 650E engine (chain drive) may fit into the chassis but that's about it. The 700/750+ engines are way larger. If you want more displacement the 650 top end on your 550 bottom end would be the easiest solution, but not easy per say.

If I were you I'd figure out what's wrong with the engine you have. I doubt the problem is mechanical related unless some idiot previous owner of your bike never adjusted the valves or ran the bike without air filters and/or with seriously messed up carburators which were too lean. GS engines are super tough and just about the only way to mess them up involves operator error.

 

[zanza14x]

The previous owner was truly an idiot, believe it or not, so it is believable that the bike did not receive much TLC from him, but that is neither here nor there. So, worse comes to worse, a 650 should work with the 550 frame and tranny? Thanks again so much for the advice.