Help with 79 GS750 rattle appreciated - please have a listen!

[Andyjwatson]

Hello All,

Please help diagnose this rattle / knock / pinging which seems to be getting slowly worse and is driving me mad!

Engine ticking over when hot:

https://www.youtube.com/watch?v=K56-5-39E2I

Main rattle almost disappears when pulling away under load:

https://www.youtube.com/watch?v=L384t_FU2fc

It is slightly quieter when cold and also makes more of a distinct 'ringing' tapping sound. When filming the youtube, the main rattle seemed louder on the clutch side, but pulling in the clutch in neutral makes no difference. No louder with the oil filler off.

I'm pretty sure it's not the 'cam walk' issue although it does seem to become less obvious above 2000rpm. I've tried the winding back the camchain tensioner described in the factory manual to reset but this makes no difference and wheel returns quick.

It's not really noticeable when riding(until you stop), quiet under acceleration , doesn't seem to be any vibration with it.

I've heard loads of rattly GSs on here and youtube but no-one mentions the quieter under load bit - In the back of my mind this seems significant like maybe rod bearings or piston slap - what do you think?

Regards

Andy

 

[sam000lee]

Yup, cam walk. My GS750 does the same thing. Mine goes away at anything above idle and also seems to happen more in the fall when the temperature drops a little (even after engine warms up completely).

 

[Andyjwatson]

Thanks for reply.

I'm sure there is some top-end rattle in there but what's worrying me I'm sure is from lower down. I've had another listen and gone round with a long screwdriver stethoscope on a cooler engine.

https://www.youtube.com/watch?v=xDAAC66NN6M

https://www.youtube.com/watch?v=C6wG2EC-n-g

To the naked ear it sounds to be coming from the rear of the cylinders, with the screwdriver it sounds loudest on the crankcase under the crank and to the rear of the timing cover / front of clutch cover.

Could there be anything on the primary drive / clutch causing this?

I've not had the clutch cover off but peering through the filler hole, the clutch basket will rotate a couple of mm by turning the rear wheel in gear, turn a bit harder and it will rotate another 2 or 3 mm with an audible crunch - is this normal?

Regards

Andy

 

[hannibal]

I've tried the winding back the camchain tensioner described in the factory manual to reset but this makes no difference and wheel returns quick.

i think it's a cam chain rattle.

 

[allojohn]

Your videos shows the cam chain tensioner to be static, it should be moving back and forth. I don't think you set the tensioner correctly.

The plunger isn't moving, did you back out the set screw 1/4 to 1/2 turn, then tighten the lock nut.

 

[Guest]

I have a similar issue to Andy and I thought it must be cam chain so I checked the tensioner as per the manual and it was OK. I have never seen my tensioner move is that correct. If so how much should I be seeing. I have thought about fitting a manual one like the race boys do.

 

[Steve]

Your videos shows the cam chain tensioner to be static, it should be moving back and forth. I don't think you set the tensioner correctly.

The ONLY time you should see the knob move is when you install it, then release the set screw. OK, you might see it move just a bit more when you first rotate the crank (by hand) a couple of turns to make sure nothing interferes.

.

 

[Andyjwatson]

Oooh I'm glad you said that -I did check the tensioner as per the factory manual and it does seem to be operating correctly.

I have a bit of a confession to make however...

The last job I did (see post in carb/fuel/exhaust) was to replace the inlet stub o-rings, I had no idea they could be so bad but it struck me a few days ago that I couldn't remember if I'd re-balanced the carbs afterwards, I'd done them not long before, after doing the valve clearances.

Anyways, last weekend I put the gauges on again and they were not just a little out, they were as much as 10cmhg between them. You could hear the difference as each carb was adjusted back in to line and it's much smoother now.

Don't get me wrong, it still rattles like a rattly thing but most of the random clatter has gone. The pickup hesitancy has gone although it's still a bit lean on no.3.

Regards

Andy