I have just put my barrel on and was setting up the timing when I noticed a metal to metal clicking sound as the exhaust valve comes up. I have one of those little inspection camera things so put it between the cams as I slowly turned the motor over. The click happens exactly as the cam goes over the cam follower two clicks as it gets to top and goes over.I could actually feel the click through the cam. The inlet is not making any noise so I swapped the cams over and the exhaust still makes the same noise. Would this be a problem with the cam follower? It seems to be the only thing that makes sense. According to my manual to change the cam follower the cam spindle must be removed. So if I have to change it is there any way to take out the cam spindle (and reinstall) without having to strip the engine back down again and split the cases.Any help is appreciated.

Cheers,
Mike

email (option): jamik@westnet.com.au

Hi Mike,

In order to take the cam follower / Tappet out,
You do not need to take the engine out or to split the cases,
But you would need to take the barrel off, to unscrew the tappet guide from the top,
(where it goes into the barrel’s valve adjustment “case”)
Unless you can figure out how to release it through the small space you have around it. usually impossible.
I have heard of people who tightened it with a chisel and hammer when it opened by itself, trough this hole,
But I do not think it can be normally released this way..

Anyway- then you would like to disassemble all that’s in the way on the timing system-
The cams, cam spindle, the idler (Big middle sprocket ) and so on.

My be it would also help to replace the tappet guide.
It rarely worn, but if it is noisy, may be..

Note that though looks the same, there are 2 different part numbers for
Inlet and exhaust tappets. (And spindles)

Could be that the noise come from the top section?
The valve, valve guide and so on?...


Noam.

email (option): Noam10@gmail.com

I dont mind if I have to remove the barrel again. I have put brand new valves and guides in and the guides have been reamed to suit and the seats redone. Probably will take the barrel off and apply pressure to the top of the tappet to see if noise is still there when engine is turned.
Cheers,
Mike

email (option): jamik@westnet.com.au

Mike, could the clicking be the backlash in the cam and pinion teeth? The pressure on the teeth changes direction as the cam changes from pushing the valve to the valve pushing the cam.....for want of a better description.

It has been discuses on this site before, as to why some M20 engines, even if rebuilt with all new parts, have more timing gear clatter than others. Apparently the gears were all picked at the factory to give the minimum of backlash clearance. I suppose all the parts were made with a plus or minus tolerance. Two parts together at opposite ends of the tolerance would be unacceptable on assembly.

Just a thought. Ron

email (option): ronpier@talk21.com

Hmmm I never thought of that. I'll check tomorrow.The inlet valve and guide are nos and the exhaust are repro not sure if that would do anything. I just dont want the engine to sound like a battered up tin can rattling down the road. If I take out the cam pinion how do I replace it with the cases still together. Heat case with a heat gun and freeze pinion and knock in with a soft mallet? or is that just dodgey.

Cheers,
Mike

email (option): jamik@westnet.com.au

Mike the pinion is the one that is keyed onto the end of the crankshaft and needs a puller to remove it but should tap on easily. No need for any heat and not worth removing unless you are going to replace it. I think Ian told me, when re-building an engine, he would go through his stock of cams to find the ones with the least backlash. This is OK if you have a box full of cams. I don't think there is anything too detrimental with excess backlash.....just a bit more clatter. I really don't think you need to be replacing your cam followers just yet. Ron

email (option): ronpier@talk21.com

Hi Mike...This is not uncommon and there are a couple of possible causes.
1) wear in the crankshaft pinion and/or cam wheel teeth..
2) crankshaft alignment outside of tolerance.
What happens is that as the cam opens the valve it is compressing (or driving) the valve spring. As it goes over the highest point of the cam the spring then 'drives' the cam..At this moment it will take up any slack in the drive train causing the cam to 'jump' forward..and that makes the noise.
The most common cause is the crank. The crankshaft should run true to within .002" when measured at the mainshafts..If it has not been set up within tolerance the shaft runs eccentrically, varying the gear tooth clearance between the crank pinion and the cam. If the largest period of clearance includes the cams maximum lift position you get the noise. Strangely,this doesn't seem to affect the inlet cam in the same way...maybe because it runs in the opposite direction and maybe because the intermediate gear, mag drive gear and the mag have a 'damping effect'...I haven't really looked into the reason for that. Every time I have come across this problem it is the exhaust cam that is affected.
Although you have already swapped cams around and got no improvement it may be that the teeth on both cams are equally worn...or the teeth on the crank pinion..or both. So you will need to look at that again.
Also you will need to establish whether the crank is running true. If it isn't you can usually pick it up by 'feel' initially as the clearance between the gear teeth at different crank positions varies. If you are unsure using this method a clock gauge will be needed to confirm whether the crank is within tolerance or not.
I would say it is most unlikely to be a cam follower/ guide related problem..Finally, a reduction in the tappet clearance settings will help to quieten things down...I have never really worked out why the M20 has such large clearances..I have always set mine at a 'tight' .008" on the inlet and a 'slack' .008" on the exhaust (after initially checking the clearances a few times when the engine was hot), with no apparent detrimental effects after years of use with various bikes....Ian

email (option): ian@wright52.plus.com

Hi,
Thanks everyone for your help. I will check everything tomorrow.

Cheers,
Mike

email (option): jamik@westnet.com.au

Had this problem with a AJS,turned out to be the cam bushes that were worn

They both have a direct pressure oil feed on the M20...I've yet to see a really worn set and they are rarely worn badly enough to need replacement...Ian

email (option): ian@wright52.plus.com

I think Ian hit the mark with his discussion of the gear lash and eccentric rotation of the pinion.

One other cause not mentioned is a broken cam follower. I found one on a B34 running Goldie cams. The follower broke at the neck of the shaft, inside the guide block. The top portion, with the adjustment nuts, can then be lifted out of the guide block leaving the lower half with the foot in place making this an easy diagnosis.

I assume the fierce cams caused more side loading on the follower leading to the failure. Gold Star followers are solid and do not have the narrow oil-retaining neck ground into the shaft, even though great pains were taken to lighten the valve train for high RPM. Roland Pike and his chaps must have had the same failure.

Have any of you chaps found a broken follower in an M20?

Jeff

email (option): jjbandoo@aol.com

I checked the exhaust cam gear and it does seem to have backlash. I put some engine assembly lube on the teeth and it quieted it done a lot. So thanks again for everyones help. I think I can live with a few rattles as long as I know its not serious. There is a cam on ebay at the moment so may bid on it to try it out but depends how high the price goes.
Cheers,
Mike

email (option): jamik@westnet.com.au

Hi Jeff..I've never had a problem ref. broken followers and have routinely run B33 engines with scrambles cams up to 6500rpm and to 7000rpm for very short bursts on the dyno in one case. The Goldie went another 5-700rpm beyond that though...and had to do it intermittently for 250 miles or so in a Clubmans TT race...
You have got me thinking (worried) about the sprinter now though. That has a cam that is more fierce than a Clubmans inlet and it will also have to rev to around 6500-6750 rpm.. I'll have to check that the guide is as long as possible to support the follower. (the inlet guide had to be shortened to allow clearance for the cam)...Ian

email (option): ian@wright52.plus.com