Ignition timing too far advanced

[eng622]

I have now replaced the cracked I. searle head with the replacement. A PO fitted electronic ignition and did not get the timing right. With the engine idling, vacuum plugged it was a good 30 BTDC. No idea how many miles ran like this but I was the unlucky one to get the head cracked or maybe it was already on its way. Would that much advance cause that damage. Now set to 10 at idle and advances another 20/30 on revving. The vacuum housing is now very close to an oil pressure pipe union so can only be retarded a fraction more.

[svenedin]

That is an absurd degree of advance. I would have thought that the engine was pinking (pre-ignition) under load.

The mechanical advance starts at quite low revs (roughly 400 rpm distributor which is 1/2 engine rpm so 800 rpm engine speed). Slow the engine down to 800 rpm before checking with a strobe. You already blocked the vacuum advance.

6 BTDC dynamic is the book figure but each engine is different and the book figure does not take into account modern fuels. ESM told me they DO use the book figure when I was there with my car a while back.

If you cannot retard any more by rotating the distributor because there is an obstruction to the vacuum housing you can move the HT leads around on the distributor cap. So to retard you would move lead 1 anticlockwise I position on the cap and likewise all the others. Mark the leads if you are likely to get in a muddle and remember the firing order is 1,3,4,2 in an anticlockwise direction. The rotor on the Morris Minor 25D4 moves anticlockwise so moving a lead anticlockwise is having the effect of retarding. Alternatively, if you are already close enough you can use the micrometer adjuster on the distributor (marked A/R advance retard). I am not exactly sure how many clicks per degree on the Lucas 25D4 but I have previously posted 11 clicks per degree! The range of adjustment that is possible is fairly small though, only a few degrees.

Stephen

[eng622]

My hearing is not the best but never heard any pinking (is it a high pitched noise) or other engine noises, only when it started chugging when running on 2 cylinders. The distributor is one of these electronic ones, maybe Accuspark, no adjustment and the vacuum cannister is much closer to the body than the standard one. Can rotate 90 as suggested but will road test as is first.

[svenedin]

I don’t like those Far East distributors. I think the advance curve is suspect as well as everything else. MMOC spares can sell you a proper Lucas distributor.




Stephen

[liammonty]

The pinking test isn't always the best. I DO have good hearing and of the several Minors I've owned over the years, some just haven't pinked audibly even with ludicrously advanced timing. The engines are relatively low compression which makes pinking a little less likely.

The critical thing to check, if you're unsure about the distributor advance curve, is maximum mechanical advance. You should make sure that doesn't exceed about 30-32 degrees. Advance at idle is less important but is na easier way to set things up IF the distributor is advancing correctly, which is not necessarily the case.

I agree regarding the cheap electronic distributors. I would be tempted to fit a NOS one from club spares or a rebuilt one from Distributor Doctor, which is what I have on both my Minors. They aren't cheap, but there's a reason for that I guess.