Engine: 2.0 Carb B200K/B200F: Lumpy running engine

[Velorum]

Originally Posted by Clifford Pope

That raises the question of course, at what mileage would it be advantageous to change a belt?
We always focus on the over-riding need to avoid the risk of a belt breaking from age or use, hence the figure of 50,000 miles which I think is the official one.
But if an engine is noticeably smoother and better-running with a new belt at 40,000 miles, then presumably fuel economy would benefit too? And possibly other longer-lasting factors - a "dithery" camshaft might wear faster ?

Timing belts after all are very cheap and its an easy 1 hour DIY job. Perhaps routinely changing at say 25,000 miles would make sense?

Good point

I change mine at 38K

This is what someone advised me to do some time ago - cant remember when this was or who, might have been Mike


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[rusty244]

Originally Posted by Clifford Pope

My 240s have always had a tendency to a lumpy idle - it seems to be inherent in the design. I have eliminated all the usual causes, as discussed above, but then this weekend by chance stumbled on an unexpected cause.

I replaced the timing belt - it was 2 years old and had done 40,000 miles, which is when I like to change mine. The slightly uneven idle has miraculously disappeared. Also the car pulls better at low speed, and curiously, the burbly exhaust note has diminished.
There was nothing obviously wrong with the old belt - not worn, not shedding rubber, not stretched, tension was adjusted properly, and the timing was correct. All the same, a new belt works better.

I can only conclude that belts gradually beome more stretchy, allowing a bit of resonance in speeds as between the crank and cam shafts. Does that seem feasible? Anyone got any other explanation?

+1 my 240 seems to pull better after a new cambelt towards the end of last year. Thought I was imagining things! Noticed a very slight improvement in idle too but the engine mounts were changed at the same time so difficult to say if there was any change there (was pretty good before in any case).

Again with mine the old belt looked fine visually although slightly ashamed to say it was over 10 years old

2-3 yearly changes it is then going forwards - as you say very easy to change / cheap to pay someone to change.