Clattering Minarelli

I could use some advice from those more experienced with Miarellis than I am. I have a Concord XKe that I'm fixing up for a roommate, and it has a disturbing high speed clatter. The one and only obvious problem of the engine is that someone in the past dumped the bike, hard. This resulted in severly bent pedal arms, pedal shaft, and breaking off a piece of the case, in a four square inch area around the left side pedal shaft exit hole. The broken case piece was JB welded back on, and leaks oil when running.

Other than that, it seems fine. Starts, idles well, goes about 30. Except at around 22MPH, the engine develops a loud clattering noise, in time with the engine speed. I believed it had something to do with the top end, but upon tear down I found everything satisfactory. Both rings unbroken and not worn excessivly, intact piston, not hitting the head, smooth bore, adequate crank, good bearings, no play or noise, correct timing, etc.

Any guesses? Could the bent shaft be causing a problem? Should I just run it until is explodes, and then rebuild it, or rebuild it now? I'm willing to split the case and replace the internal components with new bearings and seals, but it would delay the project and add cost.

Re: Clattering Minarelli

in time with engine RPM? Examine the flywheel and everything in it and around it...

Re: Clattering Minarelli

Already done, and except for nonstandard screws, all is in order.

Re: Clattering Minarelli

run it till it blows up, and then re build it

Re: Clattering Minarelli

why only around 22MPH.. not above and not below? i dunno .. maybe harmonics set it up at that rpm .. or at that road speed..

i'd guess that whatever is making the noise rotates .. Aside from the engine, wheels, sprockets / chains / pulleys / belts... But then it could be a fender rattling. If you feel it in your hands it may be the front end.

a bike takes a hard dump and lots of things can happen. Isolating a source of noise or vibration is often difficult.

Re: Clattering Minarelli

case broken, probably a chunbk of it still in there.

Id just get another engine

Re: Clattering Minarelli

Well, BenJammin is going to supply me with the cases and seals to rebuild it, so I'm going to do that and hope it goes away.

Also, I meant that is starts at 22 MPH, and then just gets louder as I go faster.

Re: Clattering Minarelli

Could it be pre-ignition? If your timing is too far advanced, you could be slowly burning a hole in the piston. This is also known as detonation. Check with a timing light to see if the marks on the flywheel align with those on the case. Adjust the stator if needed.

Hope this helps.

Also sounds like a worn and loose wrist pin bearing. They can get noisy just before they cause problems.

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