Cam thrust washer

I've just bought a new cam from a reputable cam grinder in the UK but on fitting it there is no end float, in fact there's negative end float and the cam locks up when the sprocket is tightened up. I'm using the normal chamfered thrust washer.
On measuring the cam, it seems that the timing side journal is 0.5mm too short to fit through the timing side bush.

My options are either send it back and wait another couple of months to get it replaced, or get a thinner thrust washer made.

The last option seems easier but I'll need to know what material the washer is. I guess it's a kind of hardened steel. Anyone know?

The washer is case hardened steel. You could grind it thinner. Or you could remove .5 mm from the end of the tach drive teeth on the cam. The cam is soft enough to machine easily. I would want to make sure the cam lobes are still safely centered under the lifters. Jim

Strange finding unless wrong type cam drive end, they did vary that end, but I'm not expert enough except to know some cams can't switch straight out for each type.
But if cam drive is secure to turn and lobes line up good under lifters when turned the right way CCW to crank, the tach drive sucks it fully to TS, so might just get away with nibbling off the flat face of factory steel thrush washer. The secondary flat ring washer is bronze material - never install that kind with an tab sticking off, remove that and then ok to use.

So like what bike is this ? 72 was the most questionable for bronze retainer thrust washers.Never experienced a tight fitting cam re:lack of hoizontal travel. Most are a tad sloppy if anything. Peter.

comnoz said:

The washer is case hardened steel. You could grind it thinner. Or you could remove .5 mm from the end of the tach drive teeth on the cam. The cam is soft enough to machine easily. I would want to make sure the cam lobes are still safely centered under the lifters. Jim

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I've just spent the past couple of hours doing dummy builds putting the barrels onto the timing side crankcase so I can see what's going on inside. The lobes don't line up properly with lifters when using the chamfered washer either, so shifting the whole cam along by 0.8mm will fix it.
It seems the whole issue would be fixed by your suggestion of machining the tach drive gears. However, this is an aftermarket cam and and it's made of nitrided EN40 b steel so I think it might be hard to machine.

I had a couple of washers that I played arouund with just to check clearances, and it needs a 2.2mm thrust washer. The chamfered one is 3.1mm. Anyone know how thick the bronze one with the tab is? ( Yeah I know I should break the tab off if I use one.)

One other question. If I ground the chamfered washer down by 0.8mm, would that penetrate the case hardening?

pommie john said:

One other question. If I ground the chamfered washer down by 0.8mm, would that penetrate the case hardening?

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Actually I think you would find the nitrided cam was easy to machine. You would want to use a carbide tool. You would go through the nitiding on the edge of the gear teeth. Nitriding is very thin.

The washer could be ground on the tapered end [ the end that goes against the tach gear]
and I don't think you would bother the hardening enough to be a concern. I think this is what I would do. Jim

comnoz said:

pommie john said:

One other question. If I ground the chamfered washer down by 0.8mm, would that penetrate the case hardening?

Click to expand...

Actually I think you would find the nitrided cam was easy to machine. You would want to use a carbide tool. You would go through the nitiding on the edge of the gear teeth. Nitriding is very thin.

The washer could be ground on the tapered end [ the end that goes against the tach gear]
and I don't think you would bother the hardening enough to be a concern. I think this is what I would do. Jim

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Thanks for your help.

I think that's what I'll do.

Torontonian said:

So like what bike is this ? 72 was the most questionable for bronze retainer thrust washers.Never experienced a tight fitting cam re:lack of hoizontal travel. Most are a tad sloppy if anything. Peter.

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Sorry, just realised I never answered this.

It's a bit of everything! '64 Atlas but the timing side cam bushes are the latest flanged type so the run with a chamfered washer. The old cam was fine with a tiny bit of end float.

Somehow the thrust washer was left on the bench when my Combat cases were last apart over 80,000 miles ago. With mushroom-headed tappets many valve-adjustment intervals go by without the need to touch anything. Any reasonable clearance will probably be fine


Tim Kraakevik
kraakevik@voyager.net
'72 Combat, '74 RH10 850 E-Bay chopper