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Since I suspect I've managed to pop the head gasket trying to keep up with CBR6RR's and ZX6s round cadwell a few weeks back, I've borrowed a compression tester from a mate.

Manual says it ought to be 99-156psi. I've got:

Cylinder 1: 170psi
Cylinder 2: 140psi
Cylinder 3: 120psi
Cylinder 4: 190psi

A little bit random .

Engine's coming out and getting a new head gasket anyway, but I'm surprised by the two high values.

Comments?

Test was done with the coils disconnected, all plugs out, throttle held wide open, engine cold - I've read that it should be done with the engine warm, but that was on a car site. Seems bloody difficult on a bike cos I'd have to warm it up then get the tank and airbox off.

if its coked up you'll get a higher than specced reading.. i wouldnt worry about it

the carbon build up in the combustion chamber can easily reach 1mm thick, same if not more on the piston crown.

#2 and #3 run hotter (leaner) so build up less than the others.

guess she's popped #3 then.

what were/are your HG symptoms ?

spat a bit of coolant out of the breather after the last session at cadwell. Passed it off as just being a bit hot. Went out the following friday for a ride with some mates, was running hot and smelling of coolant before I even got to the meet (15 miles away). 20 miles later was getting very very hot at anything less than 60mph, and again, blowing coolant out.

I've not entirely ruled out some sort of blockage in the coolant system, or even a duff thermostat, but thought I'd comp test it first as that's relatively simple to do.

Might test the thermostat before I drop the engine out, but those pressures seem to say it's coming out anyway. Can't quite see coking making a 50psi difference - and if it is bad enough to, then I probably ought to have the head off and clean them up anyway!

fuel in the cylinders will up the readings too, turn the fuel tap off and run it till it cuts out then do the test again.

rover220 wrote:fuel in the cylinders will up the readings too, turn the fuel tap off and run it till it cuts out then do the test again.

good point there chap !

yeh, classic HG failure symptoms im afraid Deviant.