Anyone know about checking spigot to head clearances?

[stinkwheel]

It's on my fairly highly tuned 612 enfield bullet. I'm getting oil blowpast round the head gasket which I think is either because pressure is escaping an excessively wide spigot gap OR the spigot is to high and the head gasket isn't being compressed enough.

I'm pretty sure it's the former because there is no pressurised oil passing through the head gasket, only the return from the rocker box (which has an atmospheric breather fitted) or anything which has made its way up the studs from the bottom end (which has a negative pressure breather). The high pressure oil feed to the top-end is external. In either case, there's no pressurised oil there so I can't see how it would be blowing out unless assisted by cylinder pressure.

I'm running a modern cometic composite head gasket with a fire ring.

There's very little out there on how to measure it, I'm thinking pop the head off, plastiguage the top of the spigot and re-torque. Then the question is what gap to shoot for? In an ideal world it would be zero but if it is, how do you check the head gasket is sufficiently compressed. If there is a gap, what gap is acceptable or do you skim it for zero?

The head can be skimmed to close the gap and the spigot can be skimmed to widen it.

Or am I barking up the wrong tree and there's an easier way to do this?
____________________
“Rule one: Always stick around for one more drink. That's when things happen. That's when you find out everything you want to know.”
I did the 2010 Round Britain Rally on my 350 Bullet. 89 landmarks, 3 months, 9,500 miles.

[Robby]

What do you mean when you say spigot? I'm trying to understand the problem, but google just shows me fuel taps and the fiche doesn't show any obvious reason for head gasket to allow oil out but keep compression in.

Could it be leaking from the rocker covers and working its way down? I assume you have a higher output oil pump, but the drain holes from the rockers would be standard size.

I mention this because there still appears to be no way of persuading a Honda CB250RS rocker cover to seal, but the oil pools around the head gasket and on my left boot.

[stinkwheel]

The cylinder liner stands proud of the cylinder surface and sets into a recess in the head. In theory, the spigot seals the combustion gasses and the head gasket seals the oilways.

There's little out there on exactly what the clearance should be and how you check. In theory, the spigot should seat against the head at the exact point the gasket is fully compressed for proper function. In reality, it appears nobody actually does this or if they do, they aren't saying how. It's also probably why nearly every spigotted barrel you see is leaking oil round the head gasket.

I'm pretty sure it's leaking round the head, the sides of the rocker covers are clean and I fitted a bunded breather in one of them so there shouldn't be any positive pressure in there.

Cylinder barrel with spigot:
https://lh3.googleusercontent.com/pw/AP1GczMYsWvff3GlMST8I6urHqvFLysqp9onlqI80EoRV-ppOxY5OkFrO27E3Xcfw2iglQpqq7UIEQmpYn4q96XvCHtPOE6xTYWt2ShqBd6GhRBFsmVQVBzQF4amzVlXViI3pWZWa-dTFOJjKN457x-a1aRb=w657-h876-s-no

Cylinder head with recess for spigot:
https://lh3.googleusercontent.com/pw/AP1GczMjSSWw9Jzkpm-16LRYOkBvy9XBsk6J2AzrTxk49BPKpwaXfm6BSg6jh2RDPyVExJYy7IoO6cpEGhlZ6ST-bpwvFGh-urrzwkFCmh2K4WF1noCwMxlARlQuWpx14LfLSJ75GQ33V8GoJkFDN0M6A2Su=w1168-h876-s-no

The head gasket fits round the outside of the spigot and is sandwiched between the head and barrel in the normal way.
____________________
“Rule one: Always stick around for one more drink. That's when things happen. That's when you find out everything you want to know.”
I did the 2010 Round Britain Rally on my 350 Bullet. 89 landmarks, 3 months, 9,500 miles.

[virus]

I think your about right in your plan there. Id be looking at going down the same path, possibly using spacers to vary head gasket thickness to suit if its not holding back compression, on account of it being easier to throw another spacer in than do the afformentioned machining.

What I would suggest is deffo try and get the plastigauge measurement with it hot / as close to running temp as possible, test with spacers til you get the 'right' measurement then machine to suit. For something like that i'd aim for a 0-0.1mm clearance at operating temperature.


The other option ofcourse if the spigot deals with all the combustion and the head gasket is just for oilways, is to machine a small countersink into the top of the barrel and fit an O ring for the oil ways and do away with the head gasket entirely.
____________________
own: 81 xs1100g...
owned: 85 rat CG (sold), 91 GS500e (stolen), 84 gsx400f (scrapped), 81 z250 (siezed, siezed, scrapped), 83 cb250rs (sold), 84 gpz750r ratfighter (killed) 84gpz400 (sold), '80 cb650 ratfighter (wrote off) 95gsx6/12f ratfighter (killed) 91 xj900 (sold)
stinkwheel Well I just had my hands up a pigs fanny. Which makes your concerns pale into insignificance.

[stinkwheel]

[Pete.]

Is this a viton coated MLs gasket or a more traditional type? The MLS gaskets won't have any discernable amount of compression IMO. If truly the spigot seals on the head with no gasket then IHow else ar you going say it will have to do that at the exact same time that the gasket is clamped up solid. This is the only way that you can be sure that the top face of the spigot is fully seated with the recess face in the head. With the four bolts outside the sealing ring it would be all too easy to pull it down cocked otherwise.

I think I would build it up dry with no gasket and clay/plastigauge the gap under the head where the gasket would be. If the clay mic's out the same thickness as the gasket then you wil be pretty sure. If the clay is thicker then it's riding on the spigot. If the clay is thinner then it's riding on the gasket.

Another method is if you could find an old very large micrometer you could turn a plug for the bottom of the cylinder and mic the distance to the spark plug land with the gasket fitted and not fitted. if the distance is appreciably less with the gasket fitted then it's not sealing on the spigot.

If you were nearby to me I would fit them up in my lathe and measure the distances with the DRO and a dial gauge.
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a.k.a 'Geri'

132.9mph off and walked away. Gear is good, gear is good, gear is very very good

[virus]

[stinkwheel]

[sickpup]

The traditional thing to use would be solder, a line laid around the head to be compressed by the liner but anything with a low surface tension so low springyness or low memory could be used.