Is that addition to the large idler meant to decrease the thrashing noises going on in there?
E: Engine Timing Gear Noise
- Thread starter Cyborg
- Start date
Is that addition to the large idler meant to decrease the thrashing noises going on in there?
Yes, that was an exercise on the large idler. I once read about someone who had lead weights on the idler for reducing any noise. Actually I don´t expect much noise in my engine, all gears no play in cold engine, lapped with diamond paste for good tooth finish. But sure, with warm engine there must be some play when having steel gears in an alu case. Don´t know if any noise will be transmitted outside, not very much I guess. Anyway, not a complicated mod on this idler : The idler is squeezed between two alu plates pressing on fat o-rings in the five holes , threaded tophat alu spacers inside. So you can tighten the countersunk screws with very mild Loctite. The rubberlike O-rings dampen any dings completely, without them it´s like a steel bell with a ding.
There are some more places inside the box of troubles that can be noisy - old cam shapes with too much valve clearances , or steel pushrods in an all alu engine - gets you more valve clearance when hot , more than you´d like and clatter from that. All theory, I can only tell in a year or so.
Vic
There are some more places inside the box of troubles that can be noisy - old cam shapes with too much valve clearances , or steel pushrods in an all alu engine - gets you more valve clearance when hot , more than you´d like and clatter from that. All theory, I can only tell in a year or so.
Vic
Vic, I am in awe of your mechanical ability, but one question, when your are lapping gear tooth engagement into perfect mesh with diamond paste I can only assume that you are are removing eccentricity from the metal of the timing gears, how do you achieve this, and how many rotations does it actually take to remove perhaps 1/10th thou of eccentricity, and then as you say, when the engine warms it must introduce a running clearance again, I am not being critical of what you do, your workmanship looks to be beyond reproach, I just find this level of perfection and precision extremely interesting.
Peter, hard to say how much of run-out of gear form one can lap with paste on gear teeth. You´d have to set up a machine for gear lapping as is done on spiral bevel gears for milling machines or so. I just mounted cam gears and large idler in the engine case with that amount of preload as you can do when bolting up the idler and its three nuts. By turning the lot with fingers you can feel and hear any tight spots so I tried the lapping exercise and after some time things got smooth, mainly getting smoother finish on teeth flanks after lapping off any light preload. . The gear on the crank end was machined to size later after measuring centers of crank to idler shaft. Same with the alu gear for the magneto, home made for the Beetle mag, made by Ronco, Vertex, Scintilla and its cam mod for 50 degree engine.
The cams with gears came from Andrews and were quite good and the idler modded for a standard needle gear. In every case best to check over pins in the lathe what runout the gear cutting may have and try to rectify accordingly as good as you can. It is a gamble anyway, you never know what you get when having spare parts. In machine tools - lathes - gears are precision ground after heat treating - would be nice for the large idler too , as with that size it will be out of shape most likely. Well , somebody in retirement can spend all his time on things like here, the project has started 30 years ago, so not a quick job really . . . .
Vic
The cams with gears came from Andrews and were quite good and the idler modded for a standard needle gear. In every case best to check over pins in the lathe what runout the gear cutting may have and try to rectify accordingly as good as you can. It is a gamble anyway, you never know what you get when having spare parts. In machine tools - lathes - gears are precision ground after heat treating - would be nice for the large idler too , as with that size it will be out of shape most likely. Well , somebody in retirement can spend all his time on things like here, the project has started 30 years ago, so not a quick job really . . . .
Vic
With my Comet when turning the engine over by hand the permanent magnets in the Alton generator would cause the large idler to ring like hell’s bells if any backlash. I’m assuming it won’t make that much noise when and if it’s ever running and under load. I can see your modification making a fair amount of difference.
I hope you are installing a tach on your bike, otherwise you won’t know if it’s running.
I hope you are installing a tach on your bike, otherwise you won’t know if it’s running.
So maybe you could try the o-ring mod to see, it is not a big deal to do, provided you got a lathe - or someone to help. I´d think a magneto would be even worse on the timing gears regarding smooth operation. One reason I did not lighten the cam gears like often seen as I believe some more mass on them could smoothen out changing load directions from cam lobes when followers riding up and coming down and all that rattling from this in case of any backlash in the gears. I don´t think your Alton will add a lot of noise to the engine in normal operation, it got a number of poles so more or less smooth load on the valve train, my guess. Are you still busy with a restoration so no road test yet?
Vic
Vic
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Two main areas for noise........in the timing chest, it is better to have clearance in the gears than running them too tight as this will cause a wining noise..........eccentricity in the gears will cause a hunting noise, either hot or cold depending on which ones and how bad they are. Worn out cams and followers are an obvious problem, as per worn cam bushes.......all pretty common on these old girls. Tapping and rattles are usually from the top end, if the original floating rocker bushes are still in use, best fixed with the locking ET 100/1 mod........however if the rockers themselves have any noticeable side play or slop in the pin/bush then the engine will always have a constant tapping sound coming from the engine, no matter how many times you adjust the tappets.
I believe you are correct and the Alton will be smooth enough even at idle. I was surprised at how much noise it makes just turning the engine by hand.
Not a restoration... it’s a Comet powered abomination. It’s close to being finished. Just needs wiring, paint and a few minor details. My attention deficit disorder keeps getting in the way.
Is that a Vertex magneto you have on there? I have a few extras of those VW flat four ones.
Nigel
Nigel
