MK1 primary (?) knock I can't nail

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camstevens
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MK1 primary (?) knock I can't nail

Postby camstevens » Sun May 03, 2020 2:54 pm

Hi all
I have a nasty knocking when under accelerating under load on my MK1. It occurs only when putting power on, or sometimes when giving it a rev on stand. It was present a while back and seemed to abate away, and I've since done 400 miles, but assumed it was the clutch contacting casings.
I decided to nail the problem and have tried every possible clutch and outside cover shimming and position option, but sadly the noise has returned with a vengeance......and I just cant pinpoint where it's coming from. In a attempt to contain the clutch movement I reduced the BA gearbox input shaft float to .010, and replaced gearbox grease. I've looked at the BA drawings (and Mr Moore's YouTube video,) and struggle to to see where in the BA such a noise could propagate. I wondered if it was drum wobble ( also attached video), but attempted to lock drum movement by jamming drum tight against inner ...but sound remained.

It kinda sounds like a big end but not......sounds more like a cyclical contact. I checked to see if the big ends had run doing screwdriver test, and they are tight. The shock absorber spring / cam are also new.

I can make the noise by revving the engine stationary and out of gear (video also attached) but the noise is much much harsher when taking off in gear.

Apologies for the rambling email, but I'm just attempting (badly, I know) to outline the problem.

Cheers
Campbell

[ Play Quicktime file ] 20200503_122926.mp4 [ 36.39 MiB | Viewed 659 times ]


[ Play Quicktime file ] 20200503_114926.mp4 [ 24.84 MiB | Viewed 659 times ]


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Re: MK1 primary (?) knock I can't nail

Postby will_curry » Sun May 03, 2020 6:27 pm

The coupling gears can make quite a racket, especially when they're worn.
Even when new there was enough noise for Ariel to tell owners in the Owner's Guide
not to worry.

I had to ran my Mk 1 for a few weeks in the early '70s without the fibre discs fitted to the coupling
gears until I could get replacements. What a row!

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Re: MK1 primary (?) knock I can't nail

Postby Paul_Linden » Sun May 03, 2020 6:49 pm

That is a lot of play in the clutch in the video where you move it around by hand. Is everything that should be there, present? I’m thinking about both thrust washers in the clutch. If everything is there, is it all clamping down correctly when you tighten down the clutch centre nut? Is the end of the mainshaft flush with the clutch centre nut when the latter is tightened down? Or is the clutch centre nut sticking out a bit further than the end of the mainshaft?
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Re: MK1 primary (?) knock I can't nail

Postby camstevens » Sun May 03, 2020 9:24 pm

Hi Paul
I'm pretty sure everything is there, and there are shim washers either side of the drum. With regards to the clutch centre, there is some thread still protruding when the nut is tight. I'll take another look at it, but I did grab the splined clutch centre after the nut was tightened and checked for play.....it felt rock solid with no play.

I was thinking about replacing the brass/needle roller bearing with something like a modern nylon-type material like teflon impregnated PETP. Assuming that's the root cause!

Cheers
Campbell

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Re: MK1 primary (?) knock I can't nail

Postby will_curry » Sun May 03, 2020 11:05 pm

In over 50 years of Arielling I've never found the need to replace this
clutch free-wheel bearing. I've always thought that a bit of wobble in
the clutch basket relative to the clutch centre helped the clutch plates
to free, especially when going from neutral into first.

While the bearing isn't turning while the clutch is engaged it is loaded
by the tension in the chain - probably not insignificant with the 35bhp
of a Mk1.

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Re: MK1 primary (?) knock I can't nail

Postby simon.holyfield » Sun May 03, 2020 11:10 pm

I don't think that's coupling gears - mine rattles (quite a heavy rattle) from the coupling gears when it is very hot - it's quite a distinctive sound and it is a constant sounds that appears at tickover - your sound suggests it is moving something as the revs rise.

Again, I'd expect a big end to manifest as a constant knock while it was running.

Are all the splines in good shape, on the crankshaft and gearbox mainshaft? what about the clutch centre splines? have you had a look at the clutch centre nut and the six basket screws recently?
cheers

Simes

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Re: MK1 primary (?) knock I can't nail

Postby john.whiting » Mon May 04, 2020 1:20 am

Check the primary chain for damage .

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Re: MK1 primary (?) knock I can't nail

Postby nevhunter » Mon May 04, 2020 2:19 am

Big end will get worse as the oil thins and you can pick which one by shorting out plugs individually at about 15oo rpms. When it fires again you get a sharp single noise. I don't think that is the problem. I'm inclined to think it's the coupling gears fit on the mainshaft(s) which should be Bl***Y tight or you rely on the key(s). BAD!.... The backlash due wear is not even. There will be a place where it's greatest and as you say the hotter the engine the MORE the effect. It's relatively easy to check backlash. Nev

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Re: MK1 primary (?) knock I can't nail

Postby camstevens » Mon May 04, 2020 7:49 am

Hi All
I'll look to elimiate the clutch as cause first (easiest to get to)......some time ago Peter Kemp did suggest an "old school" apprroach to quieting down a noisy clutch was to file the tabs off an old plate an open un the plate inner to act as a buffer between the drum and discs (put in first ahead of other plates). I'll put this back in to see if it makes a difference. With regards to coupling gears, I imagine one could check for backlash by looking at the timing side...I remember checking this when I first put the engine together and didn't spot anything untoward.

Could such a noise come from the gear box? Perhaps I'm going loopy, but I think I notice a correlation between new gearbox grease and the noise.....the main shaft and output bearings feel sound, but perhaps the lay shaft is flailing about?

Cam

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Re: MK1 primary (?) knock I can't nail

Postby john.whiting » Mon May 04, 2020 12:01 pm

My vote goes to the coupling gears loose on shafts or badly worn (backlash) ...this is the likely cause of the loudest knock..What about the crank flywheels ,is it possible for one of these to come loose?..I think you already eliminated big end looseness.....Clutches sometimes rattle at idle in a single ,dont think a four would rattle the clutch,as the idle is so regular...............However there is another phenomenon with motorbikes ....a .small noise becomes louder and louder ,until its deafening ,but strangely no-one else notices it ...Any vehicle repairer is quite familiar with this .


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