How to silence that recent camchain startup clatter

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CycleRob
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How to silence that recent camchain startup clatter

Post by CycleRob »

I have been reading here-n-there about the F800 Rotax motors developing a cold engine start-up cam chain clatter noise after some 25K miles. Well, mine started doing it at about 22K miles. It quickly got louder over just a few weeks time and lately the clatter was lasting about a full second. Highly motivated now by the abnormality of the situation, I decided to remove the tensioner and see what was happening. Only the seat and lower left body panel has to be removed for access. A full sized 22mm box wrench and a really heavy hand tug loosened it up. Loosened it the rest of the way and it popped out as expected. Everything looked OK. Nothing scored or even worn looking. What I found was a 13mm free length tensioner spring (new=15mm) and what appeared to be a hydraulic lifter type assembly with a non removable center piston showing its very tiny check valve ball at the bottom-center of the piston's recessed backside. I thought maybe the check valve ball was not sealing the oil in, but compressing the oil filled piston showed a near rapid release of oil between the clearance between the piston OD and its housing bore. It compressed quickly and with a lack of an expected heavy resistance from just a manly thumb-n-finger squeeze, as if it was worn out or defective. The tensioner parts are precision machined thick steel parts, so wear did not appear to or seem to be the cause. It had to be intentionally designed that way, relying on oil pressure to both actuate the tensioner without creating any dynamic over-tight spots and lube the cam chain whizzing by as the chain tightly slides against the lengthy, synthetic chain guides.

Not having any replacement parts yet, I decided to try a shade-tree mechanic's fix to isolate the probable cause of the noise problem. Is it the hydraulic piston assembly, worn chain guides or just a sagging spring? As always, you should make the easy shots first. No, the fix would NOT include stretching the tensioner spring! That would only weaken it further. The plan was to insert a spring spacer washer to reclaim some of the spring's lost 2mm of pushing power and the combined minute wear of the 3 cam chain guides and dozens of cam chain link pins. The available solution turned out to be a used, often discarded, brake Banjo bolt sealing washer. It was the same outer diameter as the tensioner spring and thick enough to matter, but the washer's ID was too small. An easy fix with a few strokes of a Rat-Tail file after it was clamped in the bench vise. Smooth off the burrs and it was ready to be added to the dead end of the spring. Next is what I thought would be the easy part . . . putting it back together.

Getting the tensioner body threads started is only for strong hands, cautious patience and perfect axiality. There was a LOT of spring tension to overcome before the mating threads even touched the engagement point, most likely caused by a camshaft lobe that stopped in the wrong random position. I should have put the bike in 6th gear and turned the engine while pressing on the tensioner bolt to find the camshaft position that would use a valve spring working on a cam lobe to slacken the cam chain on the tensioner side span of cam chain, but with talk radio playing and other distractions, it did not occur to me at the time. Oh well, next time no mistake. I used a screwdriver handle with the bike's frame member as the center fulcrum, it's plastic handle end contact point eyeball centered on the bolt head face as I incrementally, carefully tightened it slowly with the 22mm open end. Once the threads engaged the wrench was needed to run it down into place. Then I socked it down tight with the box wrench end and got the ignition key from the seat lock.

Prior to engine start-up, I wasn't expecting much, so it was a real surprise. The clatter was completely gone! The stock spring gets fatigued over time, usage and sags just enough to cause the almost alarmingly loud start-up clatter. So . . . BMW has again manufactured another bike (Rotax engine) with a noisy cam chain tensioner problem. There are many dozens of very different Japanese bikes over the past couple decades that have NEVER had this sort of problem!! It's a good thing it has an easy fix. Shim it with 1 (or 2) modified brake line banjo bolt washers -or- just replace the tensioner spring. I bet they are in stock at the dealer. Just be extra careful that you do NOT cross thread those Aluminum tensioner threads machined into the cylinder head!

.
`09 F800ST

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RBrider
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Re: How to silence that recent camchain startup clatter

Post by RBrider »

Great post, CR. Thank you. Hopefully, I'm some years away from dealing with that. Hopefully, my '13 has a new, improved spring.

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Re: How to silence that recent camchain startup clatter

Post by Boxer »

I need to do this for Lil Chubb. She clatters like crazy at startup. When can I come over for the procedure? :biggrin:
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CycleRob
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Re: How to silence that recent camchain startup clatter

Post by CycleRob »

Boxer,
Anytime it isn't raining, this Wednesday to Friday (25th--27th) when half of the garage will be empty. With just over 24,200 miles mine has just started clattering a little bit again, indicating the washer thickness needs to be thicker, by adding another one or by looking for another easy solution.

I'll E-Mail you now and we'll talk tomorrow (Tuesday) between 10:30---Noon.
`09 F800ST

Member since Sept 10, 2001

"Talent, On Loan, From God" --Rush Limbaugh--
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