Loud Knock with my 750

[Graves Lee]

I have poured all kinds of money into this. Now after having the carbs professionally rebuilt, new carb rubbers, rebuilt petcock, oil filter, two oil changes, I replaced the stator, regulator/rectifier, new gauges, new handlebars, put in new clutch springs and scrubbed plates, new clutch cable, new battery, plugs, adjusted the valves, and probably some other time consuming things that I have left out. I have approximately $1900 into this bike and a Lot of time.

Now.. I have been about 400 miles with no problems.

Then.. The **** goes down and I notice it starting to get a little weak at midrange rpm. Then it starts knocking more and more on the way home and by the time I make it back (30 miles) its terribly weak and barely cripples home. There is a loud knock i believe in cylinder two because it gets hot the fastest.

I guess my question is what to do next? I am terribly disappointed, should I try to find a junkyard gs750 motor and hope its good and just put my fresh carbs on that motor? Or do i do some kind of leakdown compression test and how? Or do i roll it into a pond with it tied to my legs? Or do I try to rebuild the current motor and what steps should I begin to take?

Sorry to be so down,

This is tough for me since it is my first bike and I have put so much dedication and what very little extra money I have into it.

[bwringer]

Firstly, stop sniveling!

Secondly, what sort of 750 is this? Is it a Suzuki? GS? 8 valve or 16? Lots of motorcycles are 750cc, and there are several Suzuki models that fit that description.

Thirdly, remove the ignition cover, remove the spark plugs, and see if you can rotate the engine using the large 19mm hex. Clockwise only, please. What do you hear and feel? What do the spark plugs look like?

[tkent02]

Probably whoever rebuilt the carbs got them too lean?
could be something else.
what actually failed?

[TheCafeKid]

Yeah, dont going killing yourself over it. Think of the poor guy who'll have to clean up that mess!

S'ok man. It CAN be fixed. First, what year 750? Im jumping the cliff and assuming its a GS since you asked if you could put a junkyard GS motor in it. INFO!

We have the technology, we can rebuild him...

[Graves Lee]

.

sorry guys, its a 1982 GS 750L

Oh and by the way it will still turn over with the starter and it seems to turn over Ok.

[psyguy]

you may have a burnt/bent valve
a compression test would be a good start

and don't worry, you'll love your bike so much more after you rebuild the engine - yourself :-D

[rapidray]

If it is an 81/82 16 valve 750 chances are it ate the rod or main bearing. Sorry to tell you this but it was a habit with them. Normally it is the rod bearing in these. Since you say # 2 is the odd one I would look there first. You can take the motor out of the bike & remove the lower case half without even pulling the valve cover. I used to roadrace one in the early & mid 80s & no matter how good the maintenance was or oil used, I only had 1 motor out of 4 live. I didn't even try to figure out why as the Suzuki dealer there was sponsoring me & just gave me new engines. Ray.

[posplayr]

So it is the roller bearing GS1100 TSCC that is

Bullet proof and not the 16V gs750? I guess I will keep by spare 80 GS750 after all.

Posplayr

[psyguy]

oh, also, welcome to the forums :-D
you may want to put your bike model into the signature line, helps not to have to repeat it all the time in the posts

[Graves Lee]

.

If it ate a rod or main bearing are the cylinder walls/wall scored to heck?
If it is a burnt or bent valve is that replaceable/repairable?

Basically I need to do a compression test and get back to ya.

[TheCafeKid]

Listen, if it turns out your motor is toast, In my basement sits an 80 16v TSCC motor with a bad TOP end (I'll keep my bulletproof 8V GS motors thank you!) I dunno where you are at in the world, but aside from a couple peices that ive promised out to some people (just covers and what not) find out what it will cost to ship to you, pay that, and you can have it. Its just taking up space in my basement. Now swapping over all that stuff, thats all you ]


ORRRR.... Looky here.

http://cgi.ebay.com/ebaymotors/1980-Suzuki-GS750-motor-Engine-runs-well_W0QQitemZ150223974650QQcmdZViewItem?hash=item150223974650

For bout 400 bucks you can have a fresh(er) working motor. Heh.

[psyguy]

In my basement sits an 80 16v TSCC motor ... you can have it

you dont happen to have an 1100 8v to give away, do you? :-D

[TheCafeKid]

Nope, Im actually in the process of buying a WHOLE 1100G\\/

And really, he'd be seriously doing me a favour. The only reason i still have it is i figured at some point, someone here was going to need something off of it. It is the last of my 80 parts bike. Officially, aside from it, and a couple of things i have here promised out to some people, that bike is completely gone

[catbed]

when i had a bent valve, it sounded like someone snapping their tongue against the top of theri mouth at first and then a constant ticking after that. is that what yours sounded like? if ti does have a bent valve, its not that hard to fix. a new valve is like 20 bucks from flatout. the hardest part for me was to get the old gasket off, and that was only with experience on lawn mower engines and reading.

[bwringer]

Turning the engine with the starter doesn't tell you much, other than it's not seized.

Turn it by hand as described so you can listen for odd noises and clunks to help you narrow down the source of the noise. Note how often any noises appear (every revolution? every other? at random?), what they sound like, whether that piston is a TDC, etc.

Also, how's compression?