Moss Motors, Ltd

Hi,

I've been having a bit of trouble trying to time my '74 MGB. Problem is, the timing mark seems to drift by about 3-5 degrees when at a constant idle speed. Is this normal? It's been 25 years since I last timed a car using a light, and I don't remember encountering this before. Could it be indicative of a sloppy timing chain?

Thanks for replying,

Micawber

Could be the chain, but I'd more likely vote for wear in the distributor housing or assembly. If the engine speed is consistant then I'd rule out a vacuum leak that could alter the vacuum advance. If the bushings in the housing are worn the shaft can move from side to side effectlvely altering the clearance between the points and the cam which will alter timing. Sounds like it's time to get Jeff up at Advanced Distributors to rebuild it for you. Highly recommended work and at a very reasonable price. http://www.advanceddistributors.com/

---

'73 Midget (V6)
'59 MGA (I6) under construction
'73 Lotus Europa

"There is a fine line between a hobby and mental illness"

I concur absolutely with Bill Young. Forget the timing chain. Overhaul the distributor.

---

Motorbill
From Lola to Land Rover, If it's British and has wheels, it's likely I've bloodied me knuckles thereupon

I should have pointed out I just installed a spanking new Pertronix distributor, hence my need to set the timing!

Wow, that does change things a bit. The pertronix system isn't that sensitive to changes in distance between the pickup and reluctor magnet as far as I know, so even in a worn housing they are usually more accurate than points. I'm going to shoot in the dark a bit now. Timing light, is it a set back type? If so it might be variying a bit electronically. I have seen a loose ring on a harmonic damper before but that's really a reach so don't put much faith in that being the cause. I will assume that you got a new rotor and cap with that new distributor, perhaps the rotor/cap gap is changing enough to cause the spark to be delayed a bit, again a bit of a reach, but the new distributor really takes away a lot of the more likely causes. Try unhooking the vacuum advance line and pluging that just for grins, that might cause a bit of spark scatter. Let us know what you find, it's a real interesting problem.

---

'73 Midget (V6)
'59 MGA (I6) under construction
'73 Lotus Europa

"There is a fine line between a hobby and mental illness"

Micawber-

My vote is to try another timing light if you can if plugging the vacuum line doesn't calm things down. I'm curious, is the timing light the one you used twenty five years ago?

 

LCJUTILA 

Thanks for your suggestions, guys. Seems I had a dodgy timing light. I borrowed a neighbours and had no problems.

BTW, the timing light was new, so back to the store it went.