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TECHNICAL MOTOBRICK WRENCHING In Remembrance of Inge K. => The Motobrick Workshop => Topic started by: John Lang on May 10, 2026, 04:23:46 PM
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The attached audio file is labelled 'pushrod noise' but that is an assumption. Reading through the site I see various other possibilities. Have a listen. The knocking noise abates somewhat when the clutch is disengaged. I hope that makes worn monkey nutz, faulty valve clearances or something dreadful inside the engine less likely.
Will visible inspection of the pushrod thrust bearing -- aka throwout bearing or 'puck' (Chris Harris) -- reveal whether that easy solution will solve it? If so, I would like to take the part from my 1987 K75C parts bike. I understand, however, that there was a change in pushrod design that might disqualify this attractive option.
My 1992 K75RT has about 100,000 km on it, the 'parts bike' has about 225,000 km on it but no knocking sound..
Advice welcome. - John L
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Extracting the push rod bearing assembly for inspection may help lessen the suspect pool. If you're ok with contortion, by crawling under the Brick—if you don't have a lift—you should be able to extract for inspection: a) the piston, the piston bearing, the spring, and maybe even the push rod bushing (#2 in the drawing) if it is the old style assembly, or b)the one-piece piston/bearing assembly (photos #2 and #3).
A problem with an alternator bearing cannot be ruled out yet. Remove the plastic shield covering the alternator, place the tip of a long screw driver on the alternator body then put your ear against its handle to determine if the alternator is the source of the noise.
old style clutch piston assembly
(https://motobrick.com/gallery/4/1601-100526170053.png)
clutch side
(https://motobrick.com/gallery/4/1601-190524122817.png)
boot side
(https://motobrick.com/gallery/4/1601-190524122608.png)
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Thank you for the prompt response, Laitch. I will listen to the alternator, inspect the clutch rod piston as you suggest and report. - J
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To locate the clunking noise at idle I listened to the alternator with a screwdriver stethoscope as suggested. Not the source. Then I noticed a split in the crankcase ventilation ("S") hose. Replacing it smoothed out the idle, reducing the volume of clunk to a level below the threshold of my being sufficiently concerned to bother investigating the clutch rod. All is well.
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Surprise! Surprise! That's a cake-taker. Good work, John and thanks for the update. icon_cheers