[High On Octane]

This question is directed at ACE and BW:

I think I am going to order a set of head gaskets and lap all my valves, remove the base gaskets and set the spigot height correctly.  My question is, should I order the 1mm head gaskets or the .5mm gaskets?  I want to see how much compression I can make now before the new heads without doing any machine work to cylinders.

Scottie J

[Bullet Whisperer]

I think I sort of went over this as an aside recently in another post, but as the result of a lucky mistake, I once received a set of 1mm thick solid copper head gaskets for a 700 twin. Except, that in real life they were for a Meteor Minor Sports 500 twin and the holes for the bores were not big enough to pass over the spigots of the 700 barrels. Careful work with a flap wheel in the drill soon sorted this and a bit of filing at the pushrod holes got me a perfect fit.
 I think this gave a good advantage, as, usually, the 700 twins have a 'sandwhich' type of copper head gasket which can be prone to blowing - the inside edges of the head joints, where they are right next to each other seem to generate hot spots and the gasket faces of the heads can warp, so look out for this, too.
 I would try to get and modify these solid gaskets and anneal them before fitting to make them more compliant to any surface undulations and irregularities, although, ideally, your gasket faces need to be flat, especially if the machine is to be ridden hard.
 B.W.

[High On Octane]

That is exactly where mine blew the first time with the solid copper gasket, and then a second time on the other cylinder with composite gaskets.  The studs have been replaced with 3/8 studs with SAE threads, maybe I should pull one out and get replacements for those too.  The 2nd time I replaced the gaskets with solid cooper again, I hand torqued them because I didn't trust the threads I want to torque them by "feel".  I torqued the heads, went for a 20 minute ride and then torqued them again while hot.  Other than not setting the spigot height and leaking a bit of oil, I haven't had any other head gasket problems since.  Also, when I did the gaskets the first time I used my hard sanding block and used 180 grit paper over the top surface of the barrels and had a local respectable head shop inspect the heads and trued the mating surfaces for me.  And I noticed when I did the gaskets that they didn't fit the cylinder bore very well with my +.040 bore or the studs.  Do you think maybe I should just order the Interceptor gaskets instead?

Actually, I just looked at Hitchcocks and it doesn't look like the Interceptor even used a head gasket?   

[High On Octane]

I called Cometic Gaskets in Ohio today, they are the makers of the composite gaskets I had ordered from Hitchcocks before, but shortly failed.  After speaking with the guy in the tech department, he said that their composite gaskets are actually really good and use the same style gaskets on high performance V8s with great success.  We came to the conclusion that my gasket failed because the flame ring was likely damaged due to having a +.040 bore and the gaskets being made for a standard bore, thus the piston making contact and breaking the seal.  Bad news is that they no longer have a listing for the 700 twins.      BUT  They DO have a listing for pretty much every other type Enfield made from the 500 twins up to the new G5/C5 line up, including a composite gasket for the Interceptor.  But they do not stock them and will take 3-4 days to produce on top of shipping and is going to be about $50 after shipping.  So it doesn't look like I will have the bike fixed in time for the Distinguished Gentleman's Ride. 

[Bullet Whisperer]

The Interceptors used things called 'Cross rings', they were a bit like a chamfered piston ring which were crushed between the heads and barrels. You needed different sizes if the cylinders were rebored, just like piston rings.
 B.W.

[High On Octane]

Cometic sells actual gaskets for the interceptor instead of the cross ring or whatever.

[ace.cafe]

I recommend settling on some form of head gasketing that works for you, and getting the spigot set right, and then leaving it.
Compression tuning is best done by adjusting the barrel base gasket thickness, or even shaving the bottom of the barrel if necessary to get the piston height where you want it, in relation to the combustion chamber.
On a hemi chamber like these vintage engines have, it is easy to move the piston height around for compression tuning, because we don't have any matters of squish gap to be concerned with. You can move that piston height around with relative impunity, as long as it doesn't hit a valve near TDC, or actually hit the head.
This way, once you have set all the sealing factors at the head gasket joint, you don't have to mess around with that anymore. Get it right, and leave it be, and tune compression under the barrel joint.

[High On Octane]

What are the chances of pulling the head to lap the valve and reuse the head gasket that is there?

[ace.cafe]

What are the chances of pulling the head to lap the valve and reuse the head gasket that is there?

If the spigot seals the compression properly, then the oil should be abe to be sealed with a used gasket and some joint sealing compound. If the compression is not properly sealed at the spigot, then no kind of gasket is going to remain intact.

[ERC]

There isn't any spigot on the cylinders I have for the 700s and there isn't any recess cut into the heads to accept one.The Bullet cylinders have them not the 700 twins that I have. The 500 twins I have do have a spigot on them.  ERC

[High On Octane]

ERC, my motor does have the spigots.  I had to remove them when I resurfaced the cylinders last year.

[ace.cafe]

ERC, my motor does have the spigots.  I had to remove them when I resurfaced the cylinders last year.

Well, if your engine has no spigots, you need a fresh head gasket.

[ERC]

The motor must be a 736 cc. I think on those they had a piece called a cross gasket ring. I've never had one of those apart. Have you ever had the serial # checked to see exactly what motor it is.  ERC

[High On Octane]

The motor must be a 736 cc. I think on those they had a piece called a cross gasket ring. I've never had one of those apart. Have you ever had the serial # checked to see exactly what motor it is.  ERC

When you ran my numbers thru Graham the motor came back as a '57 Trailblazer.

[ERC]

That's interesting the cylinders if stock should be flat with no spigot. All the  ones I have are flat. Maybe someone else can shed some light on this.  ERC