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MG MGF Technical - Cam belts and Tensioners

As some of you will know, Lynn and I should have just returned from Sweden and Norway after a 2 week trip that would have included the Swedish Annual MG meeting at Falkenberg.

We didn't make it! In fact we only got as far as the Clacket Lane Service Station on the M25.

Stopping for a natural break, it was obvious something was wrong with the engine as we pulled into the carpark. At 10mph it was possible to hear a dreadful whirring sound from the cam belt side of the engine, which then stuttered and cut out, just allowing us to coast into a parking slot.

In short, the tensioner had disintergrated, the belt jumped, and the valves crunched. We had driven the 90 miles from home in the rain, at 70mph, fully loaded, hood up, case on the luggage rack, and with the wind noise, no obvious sign of anything amiss.

Nor had I heard anything over the previous days, though over time, unless there is a dramitic change at one go, slow changes in noise are not always obvious.

The Rover MG recommendation is to change the cam belt every 60,000 miles. The general concensus of opinion on the web and covering all makes of cars, (this of course is hindsight) is that tensioners, on average, last twice as long as cam belts. This of course means that some will not! They may go just before the 120,000 mile service.

When I had the 60,000 service done, I insisted that the water pump be changed as well. But not the tensioner. It only costs about £45 plus fitting.

Have a look at http://www.mgfcar.de/cam_belt/preventive_70345_E02.pdf

Don't wait - get it done and save a new head!

Tony
Tony Thompson

Tony did you have the automatic or manual tensioner ?

The manual tensioner is supposed to be more robust.
Jon Baker

The manual tensioners do fail - I'd probably make a point of changing it at the cam belt service - exactly what Tony suggests.

Autotensioners have a plastic tensioner wheel - which presumably makes them less suitable for high performance engines with higher rev-limits - but I haven't yet heard of one failing?

Unfortuantely, it is no easy task to convert a manual tensioner engine to an automatic tensioner - and is definitely not recommended for VVCs.

Tony, is the head recoverable?

PS for those of a morbid disposition and want to see the consequences of a tensioner failure, see Don's engine pictures here: http://www.mgf.ultimatemg.com/group2/common_problems/CoH/tensioner_failure.htm
Rob Bell

Rob,

Yes, it's currently having new valves fitted - as far as I know, the guides were okay. Hopefully I'll be back on the road by the week-end.

Of course, the pistons are now enhanced, with symetrical and aesthetically pleasing patterns. :-)

Tony
Tony

Phew - that's a relief! :o)

Hopefully you'll be back on the road soon! :o)
Rob Bell

I would remove pistons and check ring lands for damage.
mike

Mike,do you have an estimate on how much extra clearance that is needed to make the "K" an safe engine ? / Carl.
Carl

Tony

What a disaster!
I dread this type of trip/nigtmare. You
get the car out, prepare as well as you think you should and then on the way to a holiday bang!

I would have had SO much grief from the wife of it were my car!

Always get the tensioner changed at cambelt time. I have seen the results of a engine killed at 85mph by the tensioner letting go. and was it REALLY bad!
The lady owner just thought it was just making a funny noise and charged on regardless! she ended up selling the car for a song.

I understand that you can change all the parts in the eventuality of this catastrophe without taking the engine out though. Nightmare nevertheless.

Neil

This thread was discussed between 28/06/2006 and 30/06/2006

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