Rough cold running

[Tanz]

I think this long running saga is finally sorted. It was always going to be something simple. Convinced there was not a vacuum leak, I advanced the ignition so it would start and run. Then when warm adjusted the ignition to 10 degrees, turned the engine off and set the crank at 10 degrees BTDC. Removed the distributor cap and marked the position of the rotor arm and the plate the sensor sits on to see if anything moved as it cooled over night. Nothing did move then it occurred to me the timing belt drives the distributor perhaps I should check in that area. I was surprised to find that when checking the tension of the belt using a Kri-kit that the belt was very slack. (told you at the beginning of this thread that the Excel had been neglected ) According to the Tim Engel post I printed out a few years ago a used belt should be at 50 - 52 LBS . Mine was less than 40. Anything less than 45 he says 'park it or drive at your own risk'. So I reset it to just over 50 (hard to be more accurate than that with a Kri-Kit) and the car started with the ignition set at 10 degrees and ticked over - it hasn't done that for a while!
So I can only guess that as the engine warmed up the belt got tighter and moved the ignition into a drivable window?
Moral of the story is check your belt tension on a regular basis and don't assume it won't move.

[Pete Boole]

Well done Phil!! I've also seen wear in the slot that the woodruff key sits in in the pulley - may be worth checking when you replace the belt.

Pete

[Lotus-e-Clan]

Thinking outside the box ... or should that be thinking outside the dizzy cap?

Brings a new set of possibilities to the diagnostic table.

Well done Phil!

[Tanz]

Well done Phil!! I've also seen wear in the slot that the woodruff key sits in in the pulley - may be worth checking when you replace the belt.

Pete

I might change the belt soon as its 3 years and 3 months old - done over 5000 miles. Hope it hasn't stretched because its about to break I never thought that a belt being slack would have such a strange effect on the timing. Doing the twist test it didn't feel that slack and sounded normal when running. It was only noticeable when i did the Kri-Kit check . Guess I took my eye off the ball concentrating on the M100. How do people look after multiple classics Pay someone I suppose

[Hawaiis0]

One thing to note, is the concentric belt adjuster position ( or whatever it's called).

It should be fitted so that the belt rotation is applying tightening force. get it wrong and the belt rotation could be undoing it.

[Tanz]

One thing to note, is the concentric belt adjuster position ( or whatever it's called).

It should be fitted so that the belt rotation is applying tightening force. get it wrong and the belt rotation could be undoing it.

I'm pretty sure it is in the right position but will check when fitting the new belt. When I bought the car in 2007 and came to change the belt the previous owner had fitted the tensioner the wrong way round.

For any new owners who are wondering what we are on about see diagram below

[bash]

I havnt got any pictures but when my belt tension changed some years ago it was because the plate that the tension bearing is mounted to had developed some stress fractures and it was close to letting go so make sure you check that carefully when you do the belt, I was lucky.
Bash

[bash]

SJ sell the mount, mine had two fractures one of which was halfway across the plate.
https://www.sjsportscars.com/parts-and- ... E2275F.htm
I suppose the clue here is they actually sell the mount, so logically they must fail. From memory the stress fractures developed from the base of the welds.
Bash

[Pete Boole]

There are also two versions of that mount depending on whether a/c is fitted or not.

Pete