Engine knocking


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v340
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Engine knocking

Post by v340 »

Hello. Does anyone know what could be a reason of that knocks in the engine (https://drive.google.com/file/d/1MepSeS ... sp=sharing)? The noise is loudest around the gearbox. Switching the clutch does not change the noise. I was thinking about crankshaft bearings, but there are no filings in the oil.

steve murdoch icoa #5322
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Re: Engine knocking

Post by steve murdoch icoa #5322 »

The smart guys will be along but it sounds similar to a knock i had in an engine, although not near as loud.
Turned out to be a connecting rod bearing.

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Re: Engine knocking

Post by jnnngs »

Hi,

As a pretty quick / crude test to see if crank / rod bearings have gone:
- take all plugs out, then for each cylinder:
- turn it to TDC (using a screwdriver / rod down plug hole to feel when it gets there)
- then turn engine a few degrees past TDC so piston is travelling down the bore
- then push down on the piston (thro' the plug hole) with the screwdriver / rod - if you can feel the piston move down the bore you have (a lot of) free play in the bearings

Only works if a lot of play, but when the bearings go, they tend to go big time.

Paul.

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Re: Engine knocking

Post by daves79x »

I'd say a lot of the noise is the clutch basket. As revs build, it sounds pretty normal. A good carb clean and sync might do wonders.

Dave

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v340
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Re: Engine knocking

Post by v340 »

I'll start with the simplest things (Paul), then check the clutch basket and carburetors (Dave). Eventually, I will dismantle the engine and check the bearings (Steve). I have little free time, so it will take me some time, but I will let you know what I checked. Thank you.

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Re: Engine knocking

Post by daves79x »

An additional thought - in the video, it almost seems like there is a miss-fire at idle. This is often carb-related (partially plugged low-speed circuitry), but could be electrical too. If you do not know fore sure the health of the carbs, that's the first place to look. As you likely know, rebuilding the clutch basket with new rubber cushions is fairly straightforward.

Dave

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Gearheadgregg
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Re: Engine knocking

Post by Gearheadgregg »

Does sound like carb issues , Rod knock will increase with RPM , when you raised your RPM on this video it sounded better.

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v340
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Re: Engine knocking

Post by v340 »

I checked the engine as Paul wrote. Good news - I don't feel any slack, but I know that 0.1 mm is terrible, and I don't think I will feel it. Dave - I checked the sparks on plugs and indeed, on the first cylinder the spark is very weak. On weekend I will check the ignition coils and look into the clutch basket.
Although the carburetors were cleaned and adjusted six months ago, but I think I'll do it again.

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Re: Engine knocking

Post by daves79x »

You may have a bad spark plug, bad cap, bad wire, bad coil output, or much more common, a failing set of spark units. Spark unit failure can be intermittent at first, before one totally fails. It would be a pair of cylinders, however.

Dave

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Re: Engine knocking

Post by NobleHops »

Yoicks, that sounds terrible, and way too loud and sharp for a clutch basket issue, to me.
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Nils Menten
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v340
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Re: Engine knocking

Post by v340 »

I checked the ignition coils. They showed different resistance. I removed them - each had a broken casing. I ordered new ones with wires and spark plugs. I haven't looked at the clutch yet.

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