Replacing crankshaft on gs650, requesting tips for a proper swap

[PrinceJellyfish]

So I laid my baby down a couple years ago. The ignition cover ripped off and in the process destroyed the points plate and the advancer. Unfortunately it also damaged the pin on the crankshaft that the groove on the advancer rides. I have a new donor crank from a 650, the rest of the necessary ignition parts and finally the space to do the work.

What do I need to know about swapping a crankshaft on a GS? Any random detail appreciated.

Also just looking at the original damaged crank I assumed I needed a new one. If this is not true please correct my ignorance.

[PrinceJellyfish]

Photo of old crank

[PrinceJellyfish]

Photo of donor crank

[PrinceJellyfish]

Damaged end

[Rich82GS750TZ]

I guess it depends on experience level and/or your willingness to pull the engine out of the frame, split the cases and do a complete bottom end rebuild. Not sure if this can be done without pulling head and cylinders off too, but I’d think you might as well go whole-hog.

edit. I see you’re already there.

[Grimly]

Given that the bearing shells are a selected fit, you'll need to be prepared to hunt down some shells after carefully measuring crank journals of the old and new cranks. Who knows, you might be lucky, but new shells are rarer than hens' teeth nowadays.

[PrinceJellyfish]

So if I pulled the donor crank from another engine that I split I should use the donor shells?

[hank2]

So if I pulled the donor crank from another engine that I split I should use the donor shells?

Not an engine builder here, but Grimly is right! It would still take plastiguage checking of clearances to check. Just glancing at the 650G manual, there were 2 different crankshaft ID code markings, A & B. 3 different crankshaft OD code markings, A-B-C. Figure out which crank it is. Crankshaft and rod bearings still available from Suzuki in about 4 of the different "color codes" for each, but no longer available in all the sizes. Probably the light wear slight undersize optional ones are the missing ones. The manual shows the clearance specs and allowances for the different cranks as well as the specs on the different color code bearings. If you use the online pdf for a 650G on Basscliff's site, its in section 3-45. Best luck and hoping it can live again!

[Nessism]

Not an engine builder here, but Grimly is right! It would still take plastiguage checking of clearances to check. Just glancing at the 650G manual, there were 2 different crankshaft ID code markings, A & B. 3 different crankshaft OD code markings, A-B-C. Figure out which crank it is. Crankshaft and rod bearings still available from Suzuki in about 4 of the different "color codes" for each, but no longer available in all the sizes. Probably the light wear slight undersize optional ones are the missing ones. The manual shows the clearance specs and allowances for the different cranks as well as the specs on the different color code bearings. If you use the online pdf for a 650G on Basscliff's site, its in section 3-45. Best luck and hoping it can live again!

Nice job. When in doubt, crack the factory manual!

[GregT]

If your original crank is straight, reuse that with it's own shells.
That end damage isn't significant. It'll clean up well enough to reuse.

To go down the path of changing the crank plus clearancing the shells is something for an experienced engine builder.
Avoid it if you can. I wouldn't do it without linishing the crank and plastigaging everything.