E: Engine Are Alloy Idlers a Problem?

Generic Beardy

Generic Beardy

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I have opened up my timing chest and been greeted with alloy idlers. I'm a little surprised at this as everything I have seen this far has shown steel ones...... I would guess that these are an aftermarket thing from yesteryear. My gut feeling is that these would be a recipe for oil full of aluminium. Am I being pessimistic?
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vibrac

vibrac

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No they were original fitting and steel ones were racing only. I may be in the minority but if the idler is correctly meshed and shows no real sign of wear I would be happy to use it after all I guess Tony Rose had one on his 100K journey. I think during the years when twins were sub £100 and Comets were sub £25 they got abused and hence their reputation.
Having said all that my alloy (and Bronze) Idlers hang on the wall
 
Generic Beardy

Generic Beardy

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vibrac said:
No they were original fitting and steel ones were racing only. I may be in the minority but if the idler is correctly meshed and shows no real sign of wear I would be happy to use it after all I guess Tony Rose had one on his 100K journey. I think during the years when twins were sub £100 and Comets were sub £25 they got abused and hence their reputation.
Having said all that my alloy (and Bronze) Idlers hang on the wall
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Ah, well that is comforting. Everything looks in good order so I shall cease panicking. Thank you!
 
royrobertson

royrobertson

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Hi, in the late sixties, when I was new to Vincents, I had the alloy idler in my then road Norvin start to shed alloy filings from its teeth and these clogged the annular groove feeding the big end which failed. The expense at the time and the lack of transport to work and back was devastating. I realise this was a twin and perhaps there was more loading on the teeth but may I suggest that if you can afford it a steel idler gives peace of mind.
roy the racer
 
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chankly bore

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Yes, and a related "cause or effect" problem is the original alloy/steel Idler Gear Shaft assembly, ET51/1. After 70 years the originals are untrustworthy and Loctite is not a cure in my opinion. A one- or two-piece all steel replacement is available. Now a couple of small details: The H.T. lead should be 28 1/2" long and go around the back of the head as per engine photos in "Richardson", your gear position indicator looks a little close to the gear lever- it should never touch, as it prevents top gear from fully engaging and that can be noisy and expensive. Saying that, you're lucky to have a good unmolested engine, mate. The A.T.D. gear must have at least .008" backlash.
 
b'knighted

b'knighted

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I did have a Comet breather pinion break up and a fragment got caught between the large alloy idler and the steady plate. This shaved the idler and aluminium swarf travelled through the lubrication system. The first I knew of this was when my left boot slid off the brake pedal. When I stopped to see where the oil was coming from I found that the rubber return pipe had been forced off the steel pipe to the RFM banjo. There was a golf ball sized mass of aluminium shavings between rubber and steel. I replaced the alloy with a steel idler. Had it been replaced earlier it wouldn’t have released swarf.
 
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oexing

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Hmm, alu chips in the crank pin ? That would mean the filter did not do its job ! I´d think a good paper filter will get anything bigger than 0.05 mm - well, two thou - or maybe even smaller ?? Anyway, no felt flter for me, E-types had them too. So better find a paper type with rubber seal in its through hole, not at the plain ends. So you just slide them onto a piece of tube coming from the timing side , sitting in the 1/4 BSP. I found some at Aliexpress, a bit shorter, but there is not a huge oil flow on Vincents.
Alu gears in timing sides can be found in other engines but straight cut gears are not overly great, only two teeth in contact at any time. So with softer alu flanks will have wear in time. Better design would have gone for spiral gears, like Earles fork BMWs. These do not fail in a bang but get noisier in time with sloppy mesh. Check flanks all around the gear, at valve lift in two or more places there will be more wear from forces on cams.

Vic

alu gear on R 69S, with timed breather on camshaft in front of alu gear:
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