Plug Number Two Overheating

[The_Doc]

Hi All,

A problem I’ve been trying to diagnose for a while. Weirdly, plug number two is showing all the signs of overheating - the electrodes appear white, with no brown or black colouration. I have checked the ignition - swapped over the coil, new plugs, I have run it on points and with Luminition optotronic ignition and the advance seems to be a few degrees BTDC. I have done a compression test and all cylinders are showing 150 psi after a few turns of the engine. And the valve clearances look good at 10 thou. I doubt it’s a fuelling issue as plug number one is running rich, and this points to ignition, however I’m struggling to think what’s left to check. However, it could be that the problem is actually with cylinder 1, and the fouling of the plug is coming from something other then the two much fuel, and running lean on plug 2 would cause overheating.

Is it now worth taking the cylinder head off and checking the state of the valves and to see if the waterways around cylinder two are clogged? At the next opportunity, I might check to make sure the valve lift is consistent.

Weirdly, I have noticed a potential new knocking noise coming from the engine, but this might be me tuning into random noises, as the sound softens once the engine is warm. I worry, I am just looking for issues now.

Thanks in advance,

Adam

[ctc77965o]

+1 for valve lift - this could expose a cam problem.

[Waldi]

Do you loose cooling water?

If so, it is worth checking the head of the pistons with an endoscope for comparison.

Waldi

[RogerH]

Have you tried replacement plug leads and plug cap?

 

Roger

[The_Doc]

6 hours ago, Waldi said:

Do you loose cooling water?

If so, it is worth checking the head of the pistons with an endoscope for comparison.

Waldi

I don’t seem to be losing coolant, I think the head gasket doing it’s job.

 

3 hours ago, RogerH said:

Have you tried replacement plug leads and plug cap?

 

Roger

Yep, tried that. It didn’t make a difference to the problem.

My current thought is that it could be that cylinders 1&2 are actually running lean and I might have a small leak through the valve stem to number 1 of oil. I’m just trying to think about the way to diagnose this.

 

[Motorsport Mickey]

Did this problem start just after you removed the inlet manifold in the past, and then replaced it. ? Think back, sometimes you don't connect the two occurrences. It sounds like an airleak into the manifold of cylinders 1 and 2, normally this is caused by the inlet manifold not seating correctly when replaced. Run the engine and spray brake cleaner or other flammable mix around the inlet manifold at the front and mask the carburettor from ingesting any at the front. The leak if there will show up as an increase in revs temporarily as the inflammable mix is sucked in and burned increasing the richness there.

Mick Richards

Edited September 16, 2023 by Motorsport Mickey

[The_Doc]

2 hours ago, Motorsport Mickey said:

Did this problem start just after you removed the inlet manifold in the past, and then replaced it. ? Think back, sometimes you don't connect the two occurrences. It sounds like an airleak into the manifold of cylinders 1 and 2, normally this is caused by the inlet manifold not seating correctly when replaced. Run the engine and spray brake cleaner or other flammable mix around the inlet manifold at the front and mask the carburettor from ingesting any at the front. The leak if there will show up as an increase in revs temporarily as the inflammable mix is burned increasing the richness there.

Mick Richards

The inlet manifold hasn’t been disturbed, but I’ll double check using some kind of flammable spray at the points where the Janet manifold mates with the cylinder head when I get a chance.

my gut feeling was point to ignition side, but the only thing I can think of left is a worn distributor that isn’t firing on 2 properly.