Bewildered

[AustinWood]

We have reviewed the engine in our 1929 fabrid saloon. It was getting very noisy and leaking a great deal of oil.
The work incuded replacing the rear main lip seal, new piston rings, adjusting camshaft end float, enlarging oil pump adusting connecting rod balance and fitting a silicone block base gasket.
This has been successful in that the engine is quieter, smoother and oil tight however we are struggling to get it running properly.
With many years working on Sevens I've never encountered this before.
There were a number of faults.
We replaced the electronic distributer with a DK4. Repaired some carburettor (22FZ) issues.
The engine started easily and ran well untill it was warm. It then lost power and started misfiring and running very rough. This was eventually traced to a sticking exhaust valve. This has happened before and was a built up of carbon on the stem.
   
Cleaning and grinding valves improved things but the engine had a very bad flat spot. Opening the accelerator had no immediate effect but after a delay it was OK. It was spitting back as well. I took this to be weak mixture. That would also explain the sticking exhaust valve.
Today I replaced the jets. Now fitted 7.5 to both main and compensating. An immediate improvement. Running very well. But as it warmed up then started to bog down. Pick up now 100%.
Removed the plugs. Nos 1&2 look fine, Nos 3&4 are sooty. ie Mixture rixh on two cylinders, both on the same port. What can cause that?
   

All idea welcome

[stuartu]

As a naive suggestion, an air leak on nos 1 & 2? Fix it and revert to the former jetting. Surely it can't be that easy?

Good luck,

Regards,

Stuart

PS which exhaust valve was sticking?

[Austin in the Shed]

A tooth out on cam timing ?

[John Cornforth]

Hi

The only thing I can think of that would consistently give weaker mixture for 1/2 compared to 3/4 is an inlet manifold air leak on the 1/2 branch, usually at the gasket between manifold and block. If you alter the carb to get the weak mixture cylinders correct, you end up over rich on 3/4.

[AustinWood]

Manifold gasket's my thinking but I fitted new gaskets to the manifold and downpipe. These are made of a gasket material I've had for a very long time, 'Hallite' I think. Its a fibre heavily impregnated with graphite.
I'll try going back to the weaker main jet and see what happens to Nos 3&4.
It seems unlikely that the valve timing's out as the car runs very well until it's run for a bit. It's very lively for an almost standard 1929 with the 22FZ carburettor.

[falcott]

Cracked inlet manifold?

[Ian Williams]

For what its worth I would say Stuart is bang on the money, you have an air leak somewhere.

[John Cornforth]

I guess it's possible that an over-large clearance between an inlet valve stem and its guide could allow uncontrolled air to enter, though you would hope that there would be enough of an oil film to fill the gap. Is there any noticable side play in the valves ? Any small inlet air leak will have most effect when the throttle is nearly closed at idling and slow speeds.

One test for air leaks is to spray WD-40 in the suspect area and listen for any change in engine speed/sound as it gets sucked in and temporarily displaces the air.

[Ruairidh Dunford]

I was getting false mixture readings in the summer, because of sealing issues with the plugs.

We were away at the time and my roadside remedy was to seal them with high temp silicone. Once home I fitted insets and changed the plugs to 14mm, all has been well since.

I don’t expect this to be your issue, the cause for me was a poorly machined head.

[AustinWood]

That's interesting Ruairidh.
The plugs in the engine were NGKs and I can't remember when they were fitted, but within the last 30,000 miles. No 3 plug was fouling so I tried some KLGs that have been around for ages (KLG wentout of business in 1958 I believe) which were much the same. We invested in new Champion D21s. The cause was actually the sticking No3 exhaust valve.
The Champions do seem to work loose. I find that after a short run two usually are not as tight as I had left them. I might try the KLGs again. Seems unlikely as you say, but so does everything else.
I shall try changing the main jet back to 7.0 as it was, but leave the compensating jet at 7.5. I suspect that won't help.
The next step is to remove and check the manifolds and check the tappets which may have settled.
The really irritating thing is that when started from cold it runs very well indeed. Tickover with choke is perfect and performance excellent - until it starts to warm up.