Topic: knocking noise under load.

[mcpuffett]

i think i already no the answer to my question but i guess i need a second opinion  ,i have noticed a knocking noise coming from the alternator case on my 750 f1, it does it mainly when setting off under load (louder knocking) and also at tickover(idle)but not as loud, if you lift the revs to say 2k at idle it goes away?, but if you put your hand on the case and rev the engine you can feel the knocking  , thing is bike runs great just done 160 miles on her today, i reckon it is my main bearing going , what do you fellas think?   mick.

[TwoTired]

Alternator rotor loose?

[spitfire]

Hi Mick,
          Think TwoTired could be right, long time since I played with bike engines but big ends knock under load and the sound is unmistakable, mains rumble all the time, seems strange that the noise goes under revs. My BSA went great with gone big ends until it siezed at Ballaugh Bridge.

Cheers

Den

[mcpuffett]

ok took casing off and alternator rotor not loose , starter clutch cog has some side to side play in it? , put it back together and took it for a run knocking noise still there under load ?,did about 100 miles or so about 10 miles from home started to make like a whining noise from the same area? the faster i went the louder it got and the slower the quieter?, i have heard similar noises from car alternators when the bearing has packed in?, will order a rotor puller of dave silvers in the morning then i can have a look behind my rotor.

[Jerry Rxman Griffin aka MuthaF'er]

Hope you don't have a rod bearing going. Take it very easy until you find out what it is to minimize damage. Rebuilding a blown engine is very costly. Replacing the engine is generally less expensive but then you may inherit another's problems. Knockin ain't good! It's a major issue.
Jerry

[mcpuffett]

ok heres the latest update, got my rotor pullin tool from dave silvers and got the rotor off , everything looked ok,  only play i could find was on the back of the rotor there are 3 cross head screws that hold all those springs and weights etc, they are good and tight and line up with the punch marks from the factory, but there is still a bit of movement there, so i pulled another rotor and starter clutch off another engine and there is no play on this one , put it on and put the bike back together took it for a ride and the noise has gone  ;)did about 10 miles and tried hill starts etc and still no noise  so it seems as though the knockin noise was coming from the back of the rotor and the starter clutch mechanism ? , will post a pic tomorrow , anyone else had a similar experience ?   mick.

[spitfire]

Great news Mick, I like it when it turns out like that ! and one for the memory bank.

Cheers

Dennis