Timing idler pinion noise

[bikerbob]

 I fitted a toothed belt drive for the dynamo some months ago and have recently become aware of a noise coming from the timing case sounds like a noisy chain, on investigation with a mechanics stethascope the noise is coming from dead center in the timing case the probe being on the BSA logo no noise at the mag or dynamo or in the area of the oil pump. Dismantled the timing side and found that there was excessive end play on the idler pinion removed the inner timing case and fitted a shim to take up the play now only a few thou play with the inner case fitted, thought that was the problem but the noise is still there. Took the outer case off again and the only thing not fitted was the cork seal as there is not enough clearance to fit one. I carefully measured the distance between the pulley and the inner timing case there is only 1mm gap. so I have some 2mm cork so made a new seal and to give it more room I put the pulley in the lathe and machined a recess in the back of the pulley so that when fitted the seal is just lightly pressed against the inner case. Refitted everything and started it up and the noise is still there you can hear it on tickover anybody got any ideas as to the possible cause of this noise, I can't remember it being there when the chain drive was fitted.

[muskrat]

Backlash from the cam pinion. If you remove the plugs and wind her over by hand, every revolution you will hear a little "click clack". At low speeds the valve spring pressure back tracks (for the want of a better term) and puts reverse pressure on the cam pinion (try's to spin it backwards) so any clearance between the cam/idler/crank pinions is heard.
Cheers

[bikerjohndavies]

Must be something contagious. I also have noticed a strange noise coming from my A10 SR motor the last few weeks and finally, following a ride last Friday, I went round the engine trying to work out where it was coming from and decided it was the timing cover. Took the cover off to find excessive play in the timing pinion. I also have a belt drive that has been on there for years. On taking the large drive sprocket off I noticed a small hole in the inner cover just next to the bush and it looks as though the inner case has partially fractured so allowing the bush section to move out. This engine has been together for a number of years and I am unsure why it should now decide to fracture though I guess at some time in its life it had been weakened when trying to get the dynamo drive sprocket off and has now just had enough.
So I am now looking for a inner timing cover with a tacho drive take off from the oil pump part number 42-154 if there is one out there.
Cheers, John

[wardleybob]

If you can't get a cover I can convert one for you.

[bikerbob]

Thanks for that tip of yours Muskrat, I tried it but could not hear anything so not being able to find anything wrong I have chosen at the moment to ignore it and wait and see if it gets any worse. I have been out for a few runs and it does not appear to be getting any worse.

[duTch]

 I also have a Dynamo-Belt, and given the belt tension is greater than the chain tension, I wonder how much extra load/wear there might be on the outer idler bush, and increase the wear rate?
 The way I see it, the timing gear arrangement loading, though minimal and equal, will inherently already have an outward/forward force on the bushes, but the extra with the belt on the outer bush...?
 At least one other British marque has the exhaust cam at the front, so I think would even out the bush loading..., just a thought 

[bikerbob]

You may have a relevant point there Dutch I will run the bike until the winter lay up and then have a look at the outer bush and see if there is any significant  wear. If there is I will post on this site and let people know. Thanks for pointing that out.

[duTch]

 Yo Bob, I hope it's not actually valid, will save a lot of hassle. But if it is valid, and thinking it further the only way I can think of to make it last longer is to use needle rollers in place of bushes, but sealing it is another story 

[rocker21]

needle roller conversion works well, you can buy them with an oil seal at one end, shaft has to be ground to 18mm and you need 2 old bushes to make the thrust  faces from, ie cut the top of the bush by the oil hole and put a slight taper on the end so it will press in ok. i also have a notched belt drive from SRM which has been modified for an Alton alternator. been like that for years with out problems, main thing with a belt is not to over tighten it as the alloy pulley's expand like mad when hot.

[bikerbob]

Took the bike out for a run today on start up I could not hear anything but after 30 miles the noise was quite distinct coming from the timing case where the idler pinion is. According to the instructions that I got with the toothed drive the correct tension is you should be able to turn the belt to 45 degrees at the midway point that is quite tight so rocker21 could have a point if as he says the alloy pulleys expand quite a bit when hot so making the belt even tighter.

[rocker21]

personally i think that is to tight, you need to double that, those 2 alloy pulley's expand a lot when hot, the belt does not, the old chain drive being all steel did not have the same problems, also they ran in grease , the belt drive is dry, i also have a bob newby belt primary drive and clutch and that needs a fair amount of slack for the same reason.

[Dynamo Regulators Mike]

A couple of points about the Dynamo Regulators Belt Drive Kit.

The Data-sheet advises: "The Correct tension is such that it is easy to twist the belt at the middle of the lower run by about 45 degrees each way."

This tension was arrived at after a considerable exercise looking at a number of drives on different bikes. If any thing many think this initially seems too slack.

But we also caution "note that belt tension will increase in a hot engine so some slack when cold is
important. Better to have the belt seem slack at this stage than it be on the tight side."

As Rocker21 says the alloy of the pulleys expands with temperature and so does the distance between drive centres being mounted in the alloy cases. Not a problem as such but this must be allowed for.

There is not extra sideways force on the pulley for the toothed belt compared with the chain. The precise nature of the machined pulleys in fact means there is less variation in tension than with the chain. (V belt drives are different in this area, as some tension is required to prevent slipping.)

[Greybeard]

Does a dynamo belt make much difference to engine noise?

[bikerbob]

Thanks for those comments I am busy this weekend but one day next week I will take the timing cover off and slacken the belt off a bit  and see what happens with it being a toothed belt it should run okay with a bit more slack. Greybeard I have not really noticed any  less noise than the chain. some years ago I had a Gold flash and I fitted  a vee belt drive to the dynamo and that had to be quite tight to avoid slipping and it was no quieter than the chain the advantage with the toothed belt is it runs faster and gives better charging at lower speeds I can be under 30mph with headlight on and still not show a discharge on the ammmeter unlike the chain drive where to show a charge you had to be  above 30mph.

[muskrat]

I had trouble with the belts when I first started to use them. 1/2 turn (nearly 1/2" up and down) slack fixed the problem.
Cheers