E: Engine Exhaust Tappet

Peter Holmes

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VOC Member
I have probably had a lucky escape, I am not sure when I last rode my Comet, but it was probably towards the back end of last year, wherever I went I got home without a hint of trouble, well none that I noticed anyway. So with nothing better to do today I thought I would check a few of the usual things, when I get to the exhaust tappet it is loose, and I mean loose, I immediately started to think savage cam or follower wear, probably both, but then I find the bulb on the end of the pushrod virtually worn away and the tappet adjuster snapped in half, but somehow hanging into to rocker by just a single thread, has anyone experienced this before, should I investigate further down or just replace the pushrod and adjuster and see how we go, any suggestions.

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davidd

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Peter,

I would guess that the pushrod may have started to shorten first, which it will do if the end of the pushrod does not match the the adjuster really well. The shortening of the rod caused the hammering that snapped the very hard adjuster.

It could have happened in reverse. The adjuster may have snapped causing the rod to shorten over time assuming that when it snapped it created enough clearance to do some hammering.

As far as I know, it is not wear. The metal has collapsed. It can happen quite fast.

Pushrods pb_1.jpg


I had this happen at a race. I had to adjust the tappet every time I went out. Big Sid told me that I had not lapped in the shape well enough prior to assembly. He suggested that I use a drill press to do it.

The cam and follower, in my case, were fine.

David
 

brian gains

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coo!, dodged a bullet there.
so just to confirm, every time an adjuster or push rod is replaced lap the items together?.
 

Albervin

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Was the break above the tappet/rocker? As someone who tries to get to the bottom of these issues I would certainly have a look at the cam follower. Not a big job (especially in these days of crap TV, and nothing better to do) and you get to check a few other potential problems. The spindle may be loose?
 

Bill Thomas

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I have never seen that before, But when fitting a worn pushrod it sometimes get very close to the edge of the tappet hole, Because an you get away from the top the rod gets thicker.
What I mean is there is limited swivel in the hole when the valve is fully open,
If the tappet is brittle, Maybe that would snap rather than bend the rod ?.
It would also depend how deep the valve seat was ?.
 

Marcus Bowden

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VOC Member
The last four years of my career I joined three ships on the East Coast of America at different intervals with a gang of two or four Philippines fitter / motormen purely to overhaul generators. Some times we would join and the generator was already stripped down with all pushrods in one rocker cover (little larger than Vincent covers) nine or five cylinder 18 or 10 rods respectively. When overhaul completed and started twenty thirty hours later tappets would be rattling, adjusted, 100 hours again 200 again, 500 again. When something has been running together for extended service they all wear differently. If my gang and I did an engine the pushrods would be marked at the top with a centre pop mark for inlet and two marks for exhaust and placed in the individual rocker covers along with the matching rocker assemblies. When started it would run to the next service interval 1,500 hours.
With my bike pushrods, they are marked 1,2,3&4 put into a lathe on top speed and lapped into each follower & tappet sockets gyrated with fine past then jewellers rouge. The test is, rod into a socket with a dab of oil and rod should stay there with it gyrated around for a few seconds hanging on surface tension. very seldom do I adjust tappets.
bananaman
 

greg brillus

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Whilst I have never done this, I do check the fit of the pushrods into the follower cups and the tappet adjusters themselves, often grind the OD of the ball so it will sit fully down the hole. Like lapping in the teeth of timing gears, again which i have never done........It does sound like a good idea, but i seriously doubt the factory did it. We have just made a small batch of shortened pushrods from silver steel and hardened the ends, these fit nicely in the cups both ends.
 
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