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Engine Issues

Posted: Sat Feb 27, 2010 9:29 pm
by Crashfangio
Full rebuilt 750GT engine has just been started for the first time since rebuild.

To my total horror, there is a loud, even, metalic clatter coming from what best I can tell is the gearbox area as soon as the engine starts.

It almost sounds like a spring loaded sprag gear engaging, similar to the kick start assembly.

Now here are the clues. Motor turns over evenly with the kickstart and the kickstart is engaging properly to turn the motor over. there are no like sounding noises when motor is turned by hand. The gears seen to be engaging cleanly.

Yes there is oil in the motor and I'm convinced that it isn't coming from the actual engine (eg big end or heads).

Does anyone have a similar experience and if so what was the cure? Please tell me I don't have to strip the motor... :-(


Posted: Sun Feb 28, 2010 5:22 am
by Lumpy
I`m not that round case literate but the only sprag gear I know of in there is the kicker. I guess the safe way is to pull the crankcase cover off and have a look. Maybe, and I say just maybe, you could start the engine and slowly move the kicker down a little. I know on my square case treasures they make that ratcheting noise if you move the kicker down at all with the engine running.
What i`m trying to say is if the sound changes pitch or sound or stops you`ve pin pointed the problem.
You don`t mention who did the work. If it was someone who took money for it maybe have a word to them. One other option is to take the plugs out and roll it over with the back wheel while it`s in gear. That way you eliminate the engine running sounds and maybe able to better pinpoint the area it`s coming from. Even pushing it in gear with plugs out, may need a friend on this one though.
Does it change gear and kick over like it should??

Posted: Sun Feb 28, 2010 8:28 pm
by wdietz186
It is possible that the kickstarter shaft was assembled wrong and the tang on the shaft isn't engaged in the notch in the case.In the squarecase shop manual it shows having the kickstart shaft turned counter clockwise about half way when the cases are being mated.This allows the tang[actually a ramp] to clear the notch in the case that holds the ratchet apart when the shaft is in the upright position.The good part is it probably hasn't damaged anything,the bad part is you need to split the cases to get to it.

Posted: Mon Mar 01, 2010 2:50 am
by Crashfangio
OK, begining to understand what maybe the fault.

For info, I am aware of the clicking sound you get when you engage the kickstart while the motor is running. It's definitely not that, as with my problem the 'clunks' are a lot slower in frequency and a hell of a lot louder and sharper in sound. The kickstart is engaging and disengaging correctly, so I'm sure this isn't the problem. I took extra care in ensuring that locator tang on the kickstart shaft engaged as I closed the cases together. Anyway, even if it wasn't assembled right it can't be the problem as the shaft doesnt rotate.

Lumpy, did what you suggested and removed the plugs. On the stand I steadily turned the rear wheel and selected 1st gear, no noise. Kept turning the wheel and selected 2nd, still no noise. I tried to select 3rd and found that the selector would rotate to 3rd no matter how persuasively I tapped the shifter. I havent removed the selector unit as yet but I reckon I may have found the problem.

Is there any chance that a selector arm may be stuck on the drum and semi engaging a dog gear? I would have thought that the rear wheel would be locked solid if there was such a gearbox fault.

Any more ideas?? Looks like dissasembly is innevitable...

Posted: Mon Mar 01, 2010 2:52 am
by Crashfangio
Typo, I meant that I COULDN'T select 3rd gear.


Posted: Mon Mar 01, 2010 5:23 am
by Lumpy
Once again I have to stress the only thing I`ve ever done to a round case is drool on it. Both mine are square cases but I beleive there are similarities, in particular, they both have selector boxes. I`m hoping, and I bet you are too, that it`s just the selector box giving trouble.
While what you say would possibly seem to point to case splitting I guess at this point you gotta make sure. Nothing worse than diving in with the evidence in hand and ripping her to bits, finding it was`nt the problem and having to put her back together to simulate the problem to fault find it again. A sad sad state of affairs, ask me how I know...........................
I guess I would be paying some very close attention to the selector mechanism. Another way to check gearbox operation without engine running and possibly giving a little more feel is to remove the clutch plates. From there you can spin the clutch centre or rear wheel. Do that while trying to select different gears. Provided your lay and main shaft are correctly assembled how much can go wrong with a selector drum and forks?? Yeah........well..............probably heaps but I have`nt encountered it.
I think what I`m trying to get at is make absolutly sure your selector mechanism is in fine fettle, correctly adjusted and all the springs, in particular the main hair spring is in good nick.
A good way to check gear selection and pin point the selector mechanism as the culprit is remove the selector mechanism and mannually rotate the selector drum tang to select all gears. This is easy done with the clutch plate removal method or plugs out and wheel rotation. If you can get all gears, it`s the selector.
If it makes you feel any better I re-built my GTS and first ride she`d do this wired jump into 2nd from 1st with this huge CLUNK and leap. It was just the selector mechanism.

Posted: Mon Mar 01, 2010 6:47 pm
by wdietz186
Crash, You can take the selector box off completely and engage the gears by rotating the shift drum directly and see if third is engaging.If you are very careful you can do it with the engine running and see if the noise changes with different gears engaged. As to the kickstart,the idler gear gear on the shaft does spin when the engine is running as it is engaged with 2nd? gear on the mainshaft. Is it possible the circlip has come off the end of the shaft allowing the idler gear to move over and engage the ratchet or knock against the edge of the mainshaft gear?

Posted: Tue Mar 02, 2010 8:36 pm
by Crashfangio
Yep, thanks for clarifying that. I removed the selector box and sorted that out. It's going through the gears as it should now.

The problem is that it is still making the noise despite being started and run through the gears on the stand.

I've basically conceded that it will require being stripped again. (aaahhhh..!!!!) so I've made a start.

I'll post my findings after I've taken a look.

Posted: Wed Mar 03, 2010 5:14 pm
by wdietz186
At least it is clean and you don't have to fret over the shimming again.Plus having already done it once it will fly apart and back together in no time.I think we've all been in your position,In my case more than once.