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MG MGB Technical - Timing Light - varies between 10 and 15 degrees

Hi all - my first post. Great site by the way.

I have a 69 'BGT mostly original and i'm nearing the end of a full rebuild/restoration. The engine is back in and running fairly well but not as smooth as I'd like. It won't idle comfortably below 1000 rpm.

I'm happy that valves are set correctly, static timing is spot on and carb tuning/balancing is fairly close (using a colortune) - fine tuning will follow when the dynamic timing is sorted out.

I've followed the usual instructions, removing the vacuum pipe etc. However, when I shine the light on the timing marks the pulley mark fluctuates between 10 and 15 degrees BTDC erratically. Surely this should be steadier?

I suspect wear in the distributor but not sure if this would cause that effect.

The distributor shaft seems to have a lot of rotational play when twisted back and forth - but not sure how much is 'normal'.

Ideas and suggestions very welcome.

Regards
p j podesta

I'll await responses from others to see how close I am, but this used to be the standard indication that there was too much play internally in the distributor. You indicate the vacuum has been disconnected from distributor, I'm asssuming you plugged the source of the vacuum.

My bet is currently on a worm bushing/bearing creating too much slop in the dizzy.

I'm heading to AdvancedDistributors with mine for other problems.
R.W Anderson

It would appear that the centrifugal advance springs, after all these years, have stretched and are causing the timing to wander about. These springs are next to impossible to source new, so sending the distributor off to be recurved by someone like Jeff Schelmer (?) would be your wisest move. RAY
rjm RAY

Can I hijack this thread slightly to ask how you attach you timing light. With the battery behind the seats and the timing marks under the pulley (1968) the cables on my timing light aren't long enough. Also I have four 'teeth' to the timing marks and the Haynes manual only document three and five teeth. I assume that each of mine are 5 degrees? Seems like adjusting the timing could be a two man job!
Steve Church

Steve,

I attach mine to the brown on the fuse box for positive and then to any earth point. There should be one just below the fuse box.
I have the 18V with timing marks on top of the pulley

This guy is good for distributor parts.

http://www.distributordoctor.com/

Andrew
Andrew Horrocks

Ideally the rotor should return under spring pressure fully clockwise when released gradually, but used distributors almost certainly will have some slop. Don't confuse slop with the light initial spring. My V8 always had some jitter but on replacing the timing chain and gears it was steady as a rock. Any wear in the cam, drive gear, drive dog and weak or misplaced advance springs can cause this jitter.

Correct springs for 25D distributors (which a 69 should have) are available from http://www.distributordoctor.com/distributor_advance_springs.html

The timing light can be connected to any 12v and earth points, e.g. brown, purple, white or green on the fusebox or even the coil +ve of chrome bumper cars. Earth from any convenient point such as coil bolt or alternator body. I suppose it's too late to advise getting an adjustable timing light, with those you set the advance you want on the light and adjust the distributor to give TDC :o)
PaulH Solihull

Paul,
My timing light does have the dial in advance feature. Unfortunately as the timing marks are under the car I can't adjust the distributor and see the timing marks at the same time as my arms aren't long enough! Possibly with some arrangement of mirrors maybe.
Steve Church

Steve, set your engine on TDC using the timing marks, then put another mark on the crank pulley where you can see it from on top, mark the timing cover with another mark so they line up, i use a bottle of tipex for this type of thing,that way you can move the distrbutor and see the timing marks at the same time,A.T
andy tilney

I changed my dizzi because of slop in the top bearing. It seemed a bit unfair to expect the car to run well when it didnt know when its next spark would arrive. I was able to set it a lot more advanced as advance was predictable and consistent across the cylinders. This is different to being able to turn it against the advance springs.
Stan Best

Steve - a lot of upping and downing maybe unless you paint additional marks but the principle still applies. I more had in mind you not knowing the distance between the pointers, but you can work that out as well by setting it to say 10BTDC on the light and adjusting to TDC, then turning the dial back towards zero and see what it reads when you are on one or more of the marks. Less easy if the mark is leaping about though ...
PaulH Solihull

This thread was discussed between 12/10/2010 and 14/10/2010

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