750GTL engine noise

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AndyB

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Here's one for the Breganze 750 experts. I have a 750GTL that has a rattle from the engine that I can't identify. It's a tappety sound that isn't there on tickover or when I blip the throttle when stationary, it only appears under load after about 1,500 rpm. The tappet clearances are all fine, it's not a deep enough sound to be coming from the bottom end in my opinion (but I may be wrong) and the rattle aside it pulls like a train. To start with I adopted the time honoured principle of wearing earplugs and hoping it would go away - but it hasn't and my conscience won't let me run it any longer. There doesn't appear to be anything untoward in the oil. Any ideas?
Andy
 
Andy,

Might be excessive end-float of the rockers on their shafts or worn valve guides.  In both cases, no cause for panic, they go on for years in this state!  Worn guides will eventually cause smoking and high oil consumption.  Also check condition of valve tips and adjusting screws, worn valve tips will cause the guides to wear quicker.

The rocker axles sometimes creep out slightly, depending on their fit in the head casting, giving the rocker more room to move around.  Remove the cam end covers and give the axles a tap.

Applies to all Breganze 750s, not only GTLs... :D

piet
 
Thanks Piet, I'll stop worrying then!  :)
She's not smoking yet, but I will check the valves and adjusters to be on the safe side.
Many thanks
Andy
 
also check the keyway between the two camshaft halves.
Do this by removing both camshaft end covers and the spark plugs, plus the generator cover,then sit on the bike and lay on the tank and with your left hand finger tip "feel" the camshaft centre and do the same with your right (simultaneously), then get a mate to turn the crankshaft with a spanner, as he revolves so you will feel the cam ends revolve, what you are looking for is sychronisation, as the valves open and close the cams will turn and revolve, if you fell any hesitation or snatch where one cam is not 100% joined to the other then the keyway is letting go.
CLEM
 
I agree with Clem about the camshafts as I had this problem on my 750GT making a tapping sound and I have seen it on another 750. If you have the problem, replacing the key won't fix it. The key only lines up the camshafts as is not supposed to take any load. The camshaft collars that bolt to the cam gear are supposed to be a tight press fit on the cams and take all the load. If it does not take a puller to get them off the cams, they need to be replaced.

And finally if you get the head good and hot, the rocker spindles and cams will all slide very easily out of the head without the need to bash the cams with a drift to get them out.

Bruce
 
I had the keyway problem recently on my racebike, it's generally very easy to diagnose, as Clem described, or even in my case even with all the engine covers on you could simply hear a "click" when rotating the crank by hand.  With valve covers and cam end plates off it was totally clear what was going on.  In my case it did not really make any major mechanical noises, but instead showed itself as a very strange sounding idle.  Again, as per Clem, it's the fit of the drive flanges that is the problem, not the key itself.

One other possibility that's easy to check is the plastic roller on the camchain tensioner.  A friend had his fracture which caused some very strange and horrible noises in an othersie fine-running engine.

Cheers
Steve B
 
Same happened to my SF2 way back in the late 70s, can't remember how I fixed it, probably brought a new cam. Bet the old cam is somewhere in one of my boxes. If I remember correctly the keyway in the cam had opened up slightly. I'd put my money on that being the problem.
 
I have heard, although I have never seen in the flesh, the the factory race bikes did (sometimes) have the camshaft flange edges welded together in 3 points around the periphery, which must have  been done through a leather shroud or some such, in situ.That must have made dismantling a lot harder as well,

has anyone actually seen this, or witnessed it, or is it another of those myths and ledgends, like the one about me laying a 40 metre black line away from the ILOC AGM, when in fact it was a 60 metre line.
CLEM
 
Thanks to you all for your helpful responses. I think I'll work through them starting at the simplest (and cheapest?) first and see what happens. I'll let you know what I find.
Andy
 
AndyB said:
Thanks to you all for your helpful responses. I think I'll work through them starting at the simplest (and cheapest?) first and see what happens. I'll let you know what I find.
Andy
Click to expand...

Did you fix your problem?
regards
George
http://www.laverdaforum.com/forum/index.php?topic=82672.0
 
breganzebike said:
Did you fix your problem?
regards
George
http://www.laverdaforum.com/forum/index.php?topic=82672.0
Click to expand...

Well George, not exactly. We took the head off and about the only thing we could find wrong was damage on the top of a couple of the valve stems, which meant the valve clearances were about double what they should have been, as that didn't show up when you slid a feeler gauge in. So we put that right, stuck it back together and it runs much quieter on tickover and at low revs, but as soon as you put it under load the rattle comes back. There's no play in the keyway, which was the thing that was bothering me, so I'm just going to put earplugs in and run it until after the Manx GP and see how we go...
Andy
 
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