Rapid (very) plug fouling

[IanHood]

Thanks for the reply Colin. No, I haven't extracted the guide o rings yet but, in any case, the valves have no discernable 'slop' and so I can't believe enough oil is getting by them to oil the plug as quickly as it happens.

Ian

[IanHood]

The plot thickens. Although there is an o ring in the inlet valve guide, there isn’t one at all in the exhaust guide. Once again though, that shouldn’t make a lot of difference on the exhaust side should it?

Ian

[Duccout]

Hi Ian,

I wonder if it could be unburnt fuel fouling the plug and leaving an oily residue? Just thinking out loud..... Or maybe the oil is not draining from the cam box fast enough? Hopefully Nigel or Eldert will look in and comment.


Colin

[IanHood]

I think it’s definitely oil but right now, I’m stumped

Ian

[blethermaskite]

Ian, how oily was the combustion chamber and piston crown when you removed the head? were they as oily as that exhaust port? there has been a lot of oil in that exhaust port......are you sure that those valve guides are tight in the head? that combustion chamber looks like it has been welded up to me, the squish around the exhaust valve seat looks wrong and the combustion chamber looks like a grinder of some sort has been at it plus some pock marks. I would lightly grind in both valves until valves are seating well, degrease and dry out the rocker chambers, fit the valves with heavy grease on their stems(seals the valve guides) and the springs (no rockers) fill each port in turn with petrol and see if you get a leak somewhere..........Cheers, George.

[IanHood]

Hi George,

The combustion chamber was very oily. I was thinking I’d do exactly what you describe. The guides are tight in the head, valves have no slop in the guides and the piston and rings are new. It has to be coming from somewhere which is why I’m suspicious of the casting right now.

Ian

[Jordan]

Perhaps you can test to see if the suspicious hollow is allowing leaking?
Lap the inlet valve and Install valve gear with new stem seal. Make a flat metal plate to attach to inlet port face with a good seal.
The plate will be provided with a threaded tube to attach to a pressure line with gauge. Pump up and see what happens.
Suitable pressure testing tools are available at low cost.

[IanHood]

I've decided to have the head vapour blasted first which should make it easier to see any areas of concern. Will let you know.

Ian

[Eldert]

Hi Ian

are you sure the problem is in the cylinderhead ?

did you check the piston rings ?

Eldert

[IanHood]

Hi Eldert,

Yes, pretty confident because it ran well with a previous springer head on it so unless something strange happened during the or shortly after the head swap, it shouldn’t be piston rings.

Ian