Kingfisher / Osprey

[Arbian]

What changed to require a different head gasket between 1988 and 89 on the K & O?

[Charles uk]

I was hoping somebody else might answer this one, so sorry for the delay.

On the later model 102cc QUB models the bore was level with the outer edge of the water jacket so used a head gasket that only a few thou thicker at the bore compared to the outer reaches.

On the early head gaskets (which I understand are no longer available) this was about 10 or 12 thou thicker, so it looks like the bore was recessed about 8 thou below the water jacket edges, so if you have a QUB that requires the early gasket, get the cylinder top face machined enough, so that you get a machined clean surface from the bore to the edge of the water jacket.
As long as the piston doesn't project any, before the head gasket is fitted you will be OK for piston to head clearance.

Use a small wipe RTV head gasket sealant on the bore edges & outer edges of the water jacket on reassembly.

Are you in Scotland or W.A.?

[Arbian]

Thanks Charles, I held a steel rule on edge across the bore but couldn't even get a 2 thou gauge in between, the motor is a 1987 KL. On a related point the outer edge of the top of the bore is thinned down to a couple of millimetres due to corrosion within the jacket ... will this be enough of a face to make a seal or is there anything I can do to restore it?
P.S. I am in Perth Scotland.

[Charles uk]

Measure the distance from the clean flat top of the piston to the top of the water jacket, at top dead centre.

Take a picture & post it with the measurement.

[Arbian]

Charles, Not sure what measurement you mean but have attached photos .... as you can see there was a fair bit of corrosion within the jacket with the top part of the cylinder greatly thinned. Inside surface of bore looks fine and piston running smoothly.

[Charles uk]

I need the distance between the top of the piston & the top of the cylinder wall at TDC, so that I can make an educated guess how much to skim the head face of the cylinder.
The cylinder looks like it's getting near the end of it's life, but as they're no longer available you've not got a lot of choice.

Your piston looks like it's running hot, give the carb a real good cleaning including the main jet & float chamber & give me the number stamped on one of the flat sides of the hexagonal main jet, it should be a 115.

[Charles uk]

Arbian did you get the piston to head distance without the head gasket measurement & the main jet size?

[Arbian]

Sorry Charles not had a chance but will do it Fri night or sat and post. Thanks.

[Arbian]

Seems to be 32 thou. Jet is a 115.

[Charles uk]

Can't skim much off that, try 12 thou off the top of the cylinder, anyone with a mill could do it.
Remove the head studs using double head nuts before you take the cylinder in for the work.
Is there any sign of a paper gasket between the cylinder & crankcase?

Did you measure the compression before this?

[Arbian]

Couldn't measure compression when I got it as head was off ... and goosed. I think I have sourced an early gasket so hopefully skim wont be necessary. Still worried about thinness of outer top of cylinder .... could I repair with chemical metal just to get surface area for gasket seal back?

[Charles uk]

Try you've got nothing to lose, doesn't the chemical metal require a clean metal surface to stick to?

[Arbian]

I guess I could brush the surface with rust remedy first? As you say nothing to lose. Thanks will give it a go.