Possible Crank Shaft Issues

[Adnan]

Hi guys,

I am new to this forum and joined because I have owned a GS750 (1982, not sure, though it is the 16 valve version with rectangle side covers), for about a year now and have been going on about it, to friends and colleagues who were not interested but put up with me anyway! I felt it was time to be a part of a group who perhaps share the same feelings about the GS, as I was tiring fast of one sided conversations.

Another reason for joining was to try and get some advice as well. My mechanic recently told me that the bike needed a new crank shaft as the old one had gotten worn out. (I am still not sure whether he is being honest or trying to make a quick buck and am trying to figure this one out so advice and suggestions are welcome).

Also I was wondering that if I did need to put in a new crankshaft, could someone suggest where I might be able to find one, considering it is extremely hard to find!!

Thanks and regards,
Adnan Husain

[posplayr]

Welcome aboard; you should be able to get plenty of GS discussion here , Bass cliff will come along soon with an official welcome.

As to your question ; Are there any indications you need a new Crankshaft? Engine knocks, low oil pressure, anything?

Posplayr

[chef1366]

Can you see the crankshaft through the crankcase?

[almarconi]

The bike must have well over a million miles on it, that why the crank is worn.

[rphillips]

I'm not a fan of the 16 valve 750 crankshaft, but just cause it has a lot of miles doesn't mean it needs a crank. Just my opinion.

[Adnan]

Re: Possible Crank Shaft Issues

Dear posplayr, chef1366, almarconi and Rphillips,
Thank you for your welcome message and respective responses.
For the record I am unfortunately, not very mechanically savvy. I kind of know the engine basics, can identify most engine parts and how they work, i.e. I am familiar with the overall theory of the internal combustion engine, however when it comes to practical maintenance, I suck at it!
The bike belonged to a friend of mine who abandoned it. It stood outdoors for a couple of years during which time it saw a lot of rain and had construction material stored on it as well. Needless to say when I got it, it was no more than a rusted shell. I had most of the necessary bodywork done including the brakes and rear shocks, wiring, coils, etc.
To my surprise, the mechanic was able to clean the carbs, change the plugs and get it to start just like that, however the left silencer (four into two), was smoking. Therefore I had the rings and pistons changed. Used the bike for about a year, during which time the engine seemed to sound and feel great. They only thing I noticed was it used to heat up quite a bit in city driving, (though in all fairness the climate here is very hot).
Over the last couple of months I noticed a very faint clicking sound which would appear at lower revs but disappear if I revved the bike up a bit, however the bike still seemed to run fine. [At the same time I noticed that one of the headers where it joins the head had a spot of rust where a pin sized hole had appeared. I could only barely see the hole but could feel some of the exhaust escaping from there, so I figured that was the source of the noise].
A few weeks back, the bike started acting a little sluggish, this increased to a point where I could tell something was definitely wrong! I took it to the mechanic who simply started it, revved it a little and apparently just by hearing the sound, informed me the crank needed replacement, he made no other inspection, however to his credit the clicking sound was a little more pronounced at this point.
Now the thing is I know this guy can be a bit of a crook, however for the lack of anyone better I have stayed with him as he has kept the bike running for the better part of the year.
Now, somehow I can’t seem to shake the feeling that it isn’t really the crank, but don’t know how to verify, because even if he pulls it out and shows it to me I won’t really know what to look for! Therefore I figured if it was really bad, rather than letting him try and re-machine it I may as well try and locate a new one which would perhaps give me better odds of success!
Regards,
Adnan

[Don-lo]

I would check the valves

[almarconi]

I'm not a fan of the 16 valve 750 crankshaft, but just cause it has a lot of miles doesn't mean it needs a crank. Just my opinion.

I was totally kidding, the statement I made was as ridiculous as the diagnosis. While it is possible a crank can go bad, how can you tell without tearing the engine apart and inspecting it?

[hampshirehog]

I was totally kidding, the statement I made was as ridiculous as the diagnosis. While it is possible a crank can go bad, how can you tell without tearing the engine apart and inspecting it?

You can really hear when these bottom ends go - it's the only thing on the bike that sounds like it and it's a 'big' noise i.e. not something you really have to hunt and listen for.

[gearhead13]

You must have paid that guy a fortune over time to get/keep it running
IF the noise is coming from the bottom end(crankshaft) the most it should need is new bearings. I rebuilt mine that had 60k on it and the crank was great, didnt even have to put in new main bearings, just rod bearings.

[chef1366]

Can you put up some audio so we can hear it run?

[Adnan]

re:Possible Crank Shaft Issues

Thanks again for all your valuable advice! From what you all have told me it seems that the crank really may not be the issue. I’ll try and get some audio going over the weekend and put it up on the site!
I also appears that I’ll have to start searching for a new mechanic cause this guy seems to have gotten greedy!
Ps: I am loving being a part of GS Resources!! Thank you for this great site!
Best regards,
Adnan