The 'E' Type Forum

Some years ago I restored my 1963 E-type roadster and had the pleasure of getting many good advise from this forum.
The car is finished and approved, but other events has taken my time so this year is the first year I actually use it. The car had been "upgraded" with a 4.2 ltr engine so I had a 3.8 ltr built from scratch and installed to bring it back to original. I had all carbs overhauled too and put in a 123 electronic distributor. I wasn't satisfied with the way the engine was running and it wasn't until I found a good old certified Jag mechanic that it was tuned into a smooth Jag.
However, even then, I found that it backfired the cylinder from time to time and some (black?) smoke then poffed out. I continued to use it, but then suddenly it started to come blue smoke out of the left exhaust pipe. I have followed the spark plugs and they have never had the nice brownish look. The two front tends to be a bit "oily" while the rest are soothed black.
I guess this means only one thing, oil is coming into the cylinder of either one or both the two cylinder in front.
I checked the compression and this is fine. The engine running OK.
What is the likely cause? Oil coming down a valve? Other thoughts?
Thanks in advance for advise.

Hi,
Are you still in the ‘running in’ stage with your new engine - I.e it’s not yet covered more than a few miles?

My thought for what it's worth is that blue smoke associated with poor valve seals normally occurs when you are coasting downhill with the throttle closed. Because the engine can only draw a limited amount of air through the induction system, more vacuum is applied to the valve seals, and if the seals are poor, oil will be sucked past them.

No valve stem oil seals on a 3.8 head (unless its modified) . Rich running may cause your smoke on that pair of cylinders.

Barrie

No Valve stem oil seal in original cylinder head of course but the leak of the valve guide are commun.

Short answer: There is something wrong with your brand new engine. Take the car back to the engine builder and get them to fix it.

Long answer: You describe two different problems.

The first is your car occasionally backfires with a puff of black smoke coming out of the exhaust when it does.

This first problem of itself might well simply be related to fuel mixture still being incorrect despite tuning, or might be an intermittent failure of spark, causing unburned fuel to detonate in the exhaust. Or it might be related directly to the cause of your second problem.

The second is that you now have (I assume) constant blue smoke coming out of the left exhaust pipe and the front two plugs look oily.

As you say, blue smoke suggests you have oil entering the combustion chambers. While plug colours are not reliable with lead free fuel the presence of oil on plugs in the 2 front cylinders might add weight to this idea.

It's really impossible to correctly diagnose this across the internet but I'll list a few possibilities that come to mind.

Assuming you do have oil coming into the cylinders, it is coming from one of 3 places.

1. Past the rings.
2. Past the valves.
3. Through a crack in the block or the head.

1. If your engine is newly rebuilt, has sat for a while and hasn't really been fully run in it is possible that your rings have failed to bed in properly or that you have a ring/rings stuck. Either may allow oil into the combustion chamber. In addition this may pressurise the crank case. Should your crank case pressure be high, excessive oil vapour may be pumped back into your air plenum via the breather pipe. This would potentially make your front two cylinders oily and misfire.

If you have a stuck ring a "spirited" drive may free it. Get the car thoroughly warm and drive it hard, with full throttle to maybe 4000rpm and ensuring that you vary the rev range. Do not let the engine labour. Again, this might help bed rings in too although if your bores are glazed honing them is probably the only fix.

2. A "normal" compression test doesn't entirely exclude leaks. It just tells you that the pressure in the cylinder can momentarily reach a peak that is recorded on your gauge. It doesn't tell you that once the peak pressure is reached that gas does not leak past the valves or the rings or elsewhere.

Do a leak down test. If you have a leak that is allowing oil into the cylinders a leak down test should not be normal. If you have a valve leak you may well be able to hear gas hissing as it passes the valve. If you have leaky rings and you squirt oil into the cylinder it may temporarily seal the rings, allowing cylinder pressure to be maintained. As above ring leak should pressurise the crank case too. Head gasket leaks (not likely in your case given what you have told us) will cause bubbling in the cooling system.

3. A crack would be a diagnosis of exclusion. Personally I think it's unlikely that this is your problem, but if nothing else was to turn up you'd have to exclude it.

If I had to put a bet on, I'd say that you have a stuck ring, but as I said above this is purely conjecture based on my subjective interpretation of your post.

Bottom line. Take the car back to the people who built your engine and get them to fix it.

Thank you so much for a comprehensive answer. I will Give the guy a try and if it doesn’t work see what to do.
Thanks again. Highly appreciated.

You wrote:
“ ...I had a 3.8 ltr built from scratch and installed to bring it back to original.”

“ I had all carbs overhauled too and put in a 123 electronic distributor. I wasn't satisfied with the way the engine was running ...”

“...it wasn't until I found a good old certified Jag mechanic that it was tuned into a smooth Jag...”

Then you describe a series of problems, which could be costly to repair.

If I had rebuilt your engine and even your carbs I would be unlikely to agree to do free repairs if you have been washing oil from the bore of two cylinder due to faulty setup, including fitting a different distributor.

If I built and installed everything but you went to someone else for setup and the 123 that has damaged my work - same thing perhaps.

If I was the guy who last worked on your car setup and it runs smoothly, I may refuse to take the blame for symptoms or repair due to previous damage.

Decide which person you trust if Andrew’s advice doesn’t work and give them full responsibility if you can’t DIY. Good luck!