Distributor - incorrect but does it matter

[StevedTR4A]

Can any of our technical members please advise?

Many of our cars have "incorrect" distributors. My TR3A with standard spec engine (86mm)bore has a distributor from a Mini Moke! It runs very well, starts easily and doesnt miss a beat.

Last April TR4AGeoff started a thread by informing that his engine had been damaged by the use of an Austin A40 ditributor with a 16 deg cam. - too much advance.

Another thread provided a list of "correct" distributors used on TR3s and 4s. The Lucas specification list provides the following;

 

TR 40480 - 15deg@2700rpm

TR 40698 - 14deg@2700rpm

TR 40735 - 10deg@1200rpm

TR 40783 - 14deg@2500rpm

TR 40795 - 10deg@1200rpm

Mini Moke - 13deg@3000rpm

A40 - 17deg@3200rpm - this is the one that caused internal destruction

 

Although I might be missing out on lower rev performance the advance figure on my Mini Moke distributor falls within the figures of the correct TR distributors - so am correct in assuming that my "incorrect" distributor is not causing problems?

 

At what level of advance would you expect damage to occur?

 

I am out of my comfort zone here so clarification would be much appreciated

thanks

Steve

[stuart]

Suggest you give Martin Jay (Distributor doctor) 01398361678 a ring and have a chat with him.

Stuart.

[Don Elliott]

I don't have any ideas as to what is right or not. All I know is that the distributor on my 1958 TR3A is the one that came with the car brand new. Also, after 183,000 miles or more, it still has the original bushings, springs and counterweights.

 

It starts and runs super.

[vivdownunder]

Hi Steve,

 

A four pot TR engine will run OK over a wide variation in timing, but it's essential to avoid pinking under load. (low speed acceleration in top gear)

 

That tells you it's too far advanced and firing the charge before TDC. In simple terms it's trying to force a piston down when it's still travelling up.

 

That's probably why the A40 distributor wrecked an engine.

 

Pinking is easy to hear in the cabin, and the first thing to do is retard the timing in small increments via the distributor vernier, until hopefully it disappears.

 

As soon as an engine is modified in any way such as a larger bore or hotter cam, the distributor usually needs to be re-curved to suit.

 

For instance an 83mm standard TR3A engine is fitted with distributor 40480 or 40698*. An 86mm engine needs either distributor 40735, or an 83mm distributor re-curved to 40735. *(40480 is screw on vacuum pipe/40698 is push on).

 

That said, providing there's no pinking with the Moke dizzy, you can apply the old adage - "if it ain't broke don't fix it".

 

Regards,

 

Viv.

[StevedTR4A]

Thanks guys

I have never heard any pinking so I guess everything is OK.

Thanks again

Steve

[david ferry]

Steve,

 

The numbers on the case may well be totally meaningless by now.

 

It's what's going on inside and how it's calibrated that is important.

 

Perhaps yours has previously been set up for your car.

 

David

[Richardtr3a]

My 3A was often a failure at starting when hot and this was when the whole car was worn out and used every day. I had the distributor rebuilt by a well kbnown name in 1986 and it was bette.

Finally I sent the unit away to Martin Jay and he reported different springs and the wrong weights. He rebuilt my unit and the car has never run and started so well. I can switch off in traffic jams and it will restart just like a new car, instantly. No embarrassing engine grinding away before firing up.

It was the best improvement I ever made to the car, after the replacement chassis.

[StevedTR4A]

Thanks David and Richard

You may well be correct David. It could have been set up for the car way back in the 70's when it was fitted.

I think as it is running so well I will leave well alone.

I guess at some point I could delve further and have a look at the weights to see if they have been changed but for now I will leave it.

cheers

Steve