GT 750 top end rattle 3-4000 rpm.

The Sock said:
You could accurately set the valve clearance with a dial gauge, though with pitting that deep re-facing/re-hardening might be a better option.
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hammering result of way to much valve clearance, impossible to get it right with feeler gauges. Another solution could be to use 8mm valve protection caps that Andy Wagner has.
 
dial gauge not needed, feeler guages will go in, albeit a little contorted, there is even a picture of it in the factory handbook (can someone please post that picture ,I cannot) but (of course) as you know the two surfaces either side of the feeler gauges must be good, a dished valve tip will give innacuarate results, but you knew all of that, what I have in my box of "special" tools is a feeler gauge that I deriveted, and took out all the blades except, points gap, inlet, gap and exhaust gap, it is a long fingered series gauge and this makes them far easier to use, a bit fiddly, but you at least dont have to rummage the shim box, or get the grinder/oil stone out etc, just screw and locknut.

A very long time ago when away on my nearly new SF1, maybe in 74, or 5, in a town at slow speed, I was instantly aware of a change of engine noise at tickover, like a switch, me thinking, "what a great bike" and then three seconds later it sounds like a small end is hanging out, a stop, a mile or two later in a petrol station, and I took to checking the exhaust valves, being the easiest to get at with the tank off, one of them had a MASSIVE clearance of about 300 thou (guess) , I was able to re-adjust the tappet with the threaded bolt still within range, and carry on, it wasnt until '79 when I stripped the motor as it aproached the EGLi frame, and found that one exhaust vave wouldnt come out, the head went to Toddy, then at (memory here) 235 green lanes Mitchum? was that correct Phil? and he noted that the hardened tip of the valve was missing and that the stem had flared over the 30,000 miles or so done since, one new valve and a gas flow/polish job while we are at it, later that month I stripped the bottom end and found the little blighter in the sump, amasing that it lasted without it, but it did, they are made in one piece these days instead of three (had a mushroom head come off on a triple as well!)

CLEM
 
peerfleuren said:
hammering result of way to much valve clearance, impossible to get it right with feeler gauges. Another solution could be to use 8mm valve protection caps that Andy Wagner has.
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That’s handy to know- yank V8’s use them with varying degrees of success . Anyone had any experience with them on a 750 ? VW ones are 8mm and add 1.5mm to valve height, could be a good solution.
 
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Exmoor beast said:
That’s handy to know- yank V8’s use them with varying degrees of success . Anyone had any experience with them on a 750 ?
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I fitted some (about 1.5mm thick iirc) to an SF that had some shortened car valves fitted, in case the valve tips weren't hard enough. They all broke up so I removed the bits and it is still running ok without them, so the valves were fine. I use the Rotax adjuster screws with the swivel foot on my own bike.
It is important that valve length is correct in relation to the rocker pivot, which will cause excessive guide wear. Check that there isn't anything impeding oil flow to the cam, either chips of plastic in the hole in the rocker arm, or the studs can block the oil channel across the top of the head.
 
Tippie said:
I fitted some (about 1.5mm thick iirc) to an SF that had some shortened car valves fitted, in case the valve tips weren't hard enough. They all broke up so I removed the bits and it is still running ok without them, so the valves were fine. I use the Rotax adjuster screws with the swivel foot on my own bike.
It is important that valve length is correct in relation to the rocker pivot, which will cause excessive guide wear. Check that there isn't anything impeding oil flow to the cam, either chips of plastic in the hole in the rocker arm, or the studs can block the oil channel across the top of the head.
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Oh well thought it sounded too good to be true, last thing I want is a shattered hardened lumps running around in the motor.
Ive read with interest your modded rockers/ rotax adjusters, I’m going to get in touch with a guy that does KTM motors that run those adjusters. My top end was awash with oil so I’m not worried about oil starvation.
 
Exmoor beast said:
Oh well thought it sounded too good to be true, last thing I want is a shattered hardened lumps running around in the motor.
Ive read with interest your modded rockers/ rotax adjusters, I’m going to get in touch with a guy that does KTM motors that run those adjusters. My top end was awash with oil so I’m not worried about oil starvation.
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The oil has to get to the cam lobe via the hole in the rocker, via the spindle. The inlets rely on the channel across the head that the studs can block. Can be oil everywhere but the right place.
To fit the Rotax screws I had to tip a bit from the valve, and relieve a smidge from under the rocker.
 
Tippie said:
The oil has to get to the cam lobe via the hole in the rocker, via the spindle. The inlets rely on the channel across the head that the studs can block. Can be oil everywhere but the right place.
To fit the Rotax screws I had to tip a bit from the valve, and relieve a smidge from under the rocker.
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Thanks for that- How much did you remove from valve tip? Not sure how deep hardness goes.
 
The GT I owned some years ago had a horrible ‘chinging’ rattle at about 3000 revs. You could hold the throttle at the appropriate revs to make the noise - many but not all of 750’s seem to do this. At one Amicale rally a very nicely presented sf passed by and it was worse than mine. Steve Winterton said fitting a Rita electronic ignition would cure it but I never tried that. In the end I started wearing ear plugs after a bad hearing test at work and that hid the noise.
 
Normski said:
The GT I owned some years ago had a horrible ‘chinging’ rattle at about 3000 revs. You could hold the throttle at the appropriate revs to make the noise - many but not all of 750’s seem to do this. At one Amicale rally a very nicely presented sf passed by and it was worse than mine. Steve Winterton said fitting a Rita electronic ignition would cure it but I never tried that. In the end I started wearing ear plugs after a bad hearing test at work and that hid the noise.
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I’m actually thinking about my Earlier post where I thought the noise sounded “ almost like pinking”, it does coincide with that high load 3-4000rpm. I don’t know if the Rita advances more smoothly or at higher revs or even if my Auto advance springs are weak and it’s advancing too early- I’m still on points . Very interesting point you’ve brought up.
New valves, guides, springs are going in- soon see if noise is better/ same then I can go down an ignition route, although I have a dislike for Rita ignitions.
 
Exmoor beast said:
I’m actually thinking about my Earlier post where I thought the noise sounded “ almost like pinking”, it does coincide with that high load 3-4000rpm. I don’t know if the Rita advances more smoothly or at higher revs or even if my Auto advance springs are weak and it’s advancing too early- I’m still on points . Very interesting point you’ve brought up.
New valves, guides, springs are going in- soon see if noise is better/ same then I can go down an ignition route, although I have a dislike for Rita ignitions.
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If you really want to stay with points it is very easy to adjust the advance rate and modify the max advance of the mechanical advance unit. There are also numerous electronic units to choose from besides Rita.
 
Tippie said:
If you really want to stay with points it is very easy to adjust the advance rate and modify the max advance of the mechanical advance unit. There are also numerous electronic units to choose from besides Rita.
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Exactly- I’m going to run it with existing ignition post rebuild then start playing with advance unit , I restricted the Bob weights on an XL500 once to make it run better. I will probably secretly fit electronic ignition but still tell Paul Marx that it’s on points- so don’t mention it to him…
 
Finally fitted new valves, springs, Tappets and put it back together. New tappets had a rough ground finish so I gave them a polish on a piece of corrugated cardboard with Autosol , the grooves were same as radius so I didn’t polish a flat. Three from the left are polished- far right is as out of packet. They are a lot longer but seem to miss the cover caps.
Daughter gave me a hand threading cam chain through head, whole lowering it, fiddly job.
 

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Exmoor beast said:
Finally fitted new valves, springs, Tappets and put it back together. New tappets had a rough ground finish so I gave them a polish on a piece of corrugated cardboard with Autosol , the grooves were same as radius so I didn’t polish a flat. Three from the left are polished- far right is as out of packet. They are a lot longer but seem to miss the cover caps.
Daughter gave me a hand threading cam chain through head, whole lowering it, fiddly job.
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Where did you get your "tappets"?
Paul
 
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