Returning My G3C to 350cc

[jimh]

Knut, thanks for the info. regarding the Alfin barrel and head on the CS models, I hadn't seen that before, I've had a problem with the head not sealing for a quite while now and have the barrel off at the moment, I will lap the joint in again but am thinking of also fitting the gasket (013793) to try and cure the problem, any thoughts?
Jim

[RichardS]

Jim,
I would start by cleaning everything off so you can see bright metal surfaces - the spigot on the top of the barrel in particular, then put some dense black 'magic-marker' ("Sharpie") all over the top of the spigot. Then place the head on top and pretend to lap it a bit, but with no paste. Lift it off to see if the black marker has been damaged and scratched off anywhere. If so, the spigot is bottoming out before the outer area is sealing and you need to reduce the spigot or possibly add a gasket to make the seal.

If the black marker remains intact you should just lap more to get a proper seal and correct whatever is the current problem.

[jimh]

Hi Richard,
Thanks for the suggestion I will be in the garage later today to have a go at it, will post the results later.
Jim

[jimh]

The marker didn't rub after after 'trial' lapping the Cylinder spigot into the head joint so decided go ahead and properly lap the area around the spigot and then measured at various points, the recess in the head is 2.3mm deep, the spigot height above the barrel 2.2mm so the spigot is close but not bottoming out.
Still of a mind to use the standard road model gasket which is 1mm thick as apart from slight loss of compression I cant see what harm it would do or alternatively use the standard 1mm gasket and make a 1mm thick circular gasket to fit in the recess in the head as well.
Knut mentions ensuring the top of the spigot and the recess are flat and level to each other I don't have the facilities to do that unfortunately.
Cheers Jim

[Joker_Bones]

I lapped the the head to the barrel of my ally short stroke twice, the spigot it wasn't bottoming out and I thought I had made a good job, both times it leaked.
I fitted a copper gasket, new and annealed of course, it leaked.
I fitted a composite gasket, it didn't leak.

This ally long stroke engine I have gone straight to copper gasket.

gasket.jpg

As far as I am aware there is not a composite gasket available for the ally long stroke engine, if there was I would have gone straight to that.
Not a recommendation or anything, just the way I felt about it at the time.
It's not been run yet, will it leak? I've no idea.

[jimh]

Hi J-B,
Am I right in my understanding that the Al-fin barrels fitted to the CS models sealed at both the spigot into the head recess and the 'lapped' area around the barrel spigot?
Jim

[Joker_Bones]

Not according to Knut's extract...

"Cylinder head and barrel joint. Normally there is an annular space between the spigot on the
cylinder barrel and the small face on the cylinder (head), when the cylinder head is assembled."

it goes on to describe how the small face on the cylinder head can be made into a mating surface as well. Perhaps to help with a sealing problem? I don't know.

There was clearance between the barrel spigot and head recess in both my engines, that is what I expected and checked to make sure there was. To get both surfaces to mate at the same same time, both surfaces would have to be perfect.

[jimh]

Thanks for pointing out the head to barrel sealing reference, with regard to gaskets there's a company in Stourbridge who say they make their own gaskets in any material, all done inhouse, obviously don't know about cost etc. - motorcyclegaskets.co.uk

[Andy G]

Thanks for pointing out the head to barrel sealing reference, with regard to gaskets there's a company in Stourbridge who say they make their own gaskets in any material...

So do I...as long as the material is the side of a cornflake box

[Joker_Bones]

there's a company in Stourbridge who say they make their own gaskets in any material

Good intel