Engine tapping while braking 1979 GS750

[Guest]

Hey guys,

When I jam the brakes on my 79 750e and close to stopping Im getting an engine tapping when the engine hits around 1400 rpm. Sounds like oil starvation to me. But Im not sure how that could happen? Oil pickup clogged? The oil light never comes on so Im confused on what it might be. If you keep the revs up under decel it wont do it. If I let it coast to a stop, it wont do it. Bike has 20000 miles on it. Clean and full oil, fram oil filter. The tap is steady and sounds like one cylinder and drops with the engine revs.

[Brendan W]

Could it be the cam chain tensioner ?

[andy10889]

I guess, I just did the valves and the chain seemed nice and tight. Ill try the manual recommended chain tensioner adjustment. It only happens when the bike dips forward.

[geol]

You may be able to hear the "tapping" only when the rpms are low enough. Does this bike have an automatic cam chain tensioner? It might not be a bad idea to remove it and rebuild it while it is out anyway. There are a couple orings in there and an oil seal. You might want to replace the spring at the same time (the one that causes the plunger to push out against the cam chain guide). If that doesn't work, take off the valve cover and ensure the shims are all in the buckets... although unlikely, there isn't a whole lot more it could be unless something is broken.

[andy10889]

Ill check the cam chain tensioner tonight. Valves are all good and the noise sounds like its from the bottom of the case. I hope its not a bearing. I might pull the oil filter too and check for particles.

[hillsy]

Strange noises like this sometimes come from places you don't expect them to.

How tight / loose is your final drive chain? Might be some noise at the front sprocket as the chain loosens up top......maybe you only hear it when the revs are low.

Does the noise happen with the clutch either engaged / disengaged?

[hannibal]

I agree with hillsy. It might be time for a new chain/sprockets.

[andy10889]

Clutch in or out, stopped or going. Not the chain. Its in the engine somewhere.

[TxGSrider]

Maybe an exhaust leak? I know on a car if the gasket fails they can sound like a lifter tapping.

[andy10889]

Negative. Its in the engine somewhere. Ill try to lift the rear end up and see if I can recreate it in the shop.

[geol]

If you can get the noise to happen when the bike is on its stand in the shop, you might want to go to Harbor Freight and pick up an inexpensive mechanic's stethoscope to help pin point where the tapping is coming from.

[Brendan W]

Is the clutch nut tight ?
Don't know if you bike has the straight cut primary gears but if not the clutch gets pushed out when the drive is reversed.
If you open the oil filler and pull the clutch you can sometimes see the basket moving.

[andy10889]

Ill take a look at that tonight, thanks for the tip.

[andy10889]

Okay, basket is okay. I reset the timing chain tensioner. Synced the carbs, and did the valves. Now the sound is gone. No idea what it was. I do have some of the upper head cam walk noise as noted on other threads on this forum.