Update on sooty plug, No 2 cylinder

[1969Mk3Spitfire]

My new cylinder compression tester has arrived so opportunity to check plug state.  I'd previously swapped No 2 spark plug, the sooty one, with another cylinder. Despite only doing 20 or so miles since their clean, No 2 is already sooty while the others are fine.  That's ruled-out the plugs.

I can only check compression on 3 cylinders, frustratingly, as the tester fouls the dizzie on No 3. 

No 2 has the lowest reading at 11.2 bar.  No 1 reads 11.7 and No 4 11.8 bar.  Engine cold.  Is this approx 5% difference significant?

There's nothing visually obvious looking at the cap and leads.

As I said in the previous thread, I'll probably buy a Club ignition service kit and replace everything.

Car starts and runs well.  Acceleration (I don't drive hard) is smooth and progressive.

Any additional thoughts, opinions and recommendations most welcome. Thanks in advance. 

 

[Pete Lewis]

the tests are all close enough to be ok   is this soot  or an oily deposit ??   

this could be oil from an inlet valve guide rather than any ring problem  do check youre breathers are all clear 

some rocker covers have a gauze inside if so this needs a wash in petrol or such like  , they can be completely blocked 

you can prise the retaining plate and withdraw the mesh (if one is fitted)  

other ideas  are turn the dizzy to point rotor at no2 and check the points gap produced 

double check  tappets are at 0.010"  cold    &  spin the pushrod to check for any bend 

Pete

 

 

[1969Mk3Spitfire]

Thanks, Pete,

Fairly sure its soot as it has a mat appearance, not shiny oil.

Breather is clear and I cleaned the gauze filter earlier this year (but I'll check again).

Just done the tappets, that's how I found the problem, didn't spin the pushrod to check for bend but the engine sound is good, no hint of a tappet noise.

A good tip to check points gap, I'll measure all 4 to see if there's much difference.  Not sure if it's relevant but dwell angle is very stable on Draper digital multimeter.  From memory, it's 1 degree out of spec, so close that I didn't adjust it (especially given that the car runs well, if it aint broke, don't fix it syndrome).

[Pete Lewis]

good   if its soot and it doesnt self clean after a choke start given a good few miles of hot running 

then its the burn thats in trouble  

low or late spark 

rich mixture and manifolding makes no 2 susceptible 

reverse that thought and is it No 1 thats  weaker than no 2 

just thinking outside the box  

Pete

 

[1969Mk3Spitfire]

Pete, I found around 0.001 inch difference between the points gap on each lobe, possibly measurement or more likely operator error. I put a DTI on the shaft and it was around 0.04 to 0.05mm different between each lobe. Again, with operator error I’d say that the shaft is turning symmetrically and that there are no irregularities between lobes.

Still open to other suggestions?

[Pete Lewis]

strong tea soumds a plan 

out the box   have look at the valve guide height   should all be the same is there a loose one  ???

Pete

[1969Mk3Spitfire]

Everything about the head seems in order, at least as far as I can tell without removing it.

I’ll fit the new condenser, points, arm, cap, leads and plugs when I receive them but in the interim I was thinking about giving the car an Italian tune 😀

My trips out tend to be between 5 and 10 miles, max speed 50 mph, mostly a lot less as some of my route is on a congested A road.

I don’t think that I’ve ever taken it over 60. Albeit a revvy little engine, I’m happy to drive it with a little mechanical empathy, it is 52 years old, after all.

There are plenty of motorway and dual carriageway options near home so, what do you guys suggest as an Italian tune (distance and engine speed cycle)?

 

 

[Iain T]

6 minutes ago, 1969Mk3Spitfire said:

what do you guys suggest as an Italian tune (distance and engine speed cycle)?

Anything that makes you smile! I would avoid motorways. When I try out any tuning I leave it in 3rd or 4th (I have a 5 speed) to keep the revs up it saves getting a speeding ticket. 

Iain 

[Pete Lewis]

to get a clean plug you just need a nice smooth cruise around the50mph  , no hard acceleration , no standing starts   off the lights  

a fairly fast light throttled cruise for 20minutes    coast into a layby   switch off and pull the plug 

Pete

 

[Mjit]

21 hours ago, Pete Lewis said:

to get a clean plug you just need a nice smooth cruise around the50mph  , no hard acceleration , no standing starts   off the lights  

a fairly fast light throttled cruise for 20minutes    coast into a layby   switch off and pull the plug 

Pete

 

Yea, but then you've got the cost fo the ferry crossing to France and Covid tests out and back to find a piece of road where you can do that!

[Chris A]

3 hours ago, Mjit said:

Yea, but then you've got the cost fo the ferry crossing to France and Covid tests out and back to find a piece of road where you can do that!

I can give you dozens of stretches of road where it is possible around here 🇨🇵