Knuckles Pans Shovels
I have a 1990 kx250 that i have just rebuilt the engine, i checked the piston to head squish and it has only 0.43mm including the gasket, i had the cylinder bore re plated and they refaced the cylinder deck so that must have decreased the clearance a bit, also the head has been planed at some stage in its life.
Dose anyone know a good place in auckland that could re mrchaine the combustion chamber?
Anorak
Put in a thicker base gasket..... sorted.Originally Posted by rudolph
Kinky is using a feather. Perverted is using the whole chicken
has made a bo-bo in his nappies
Dunno 'bout Auckland Rudolph, but if you want a reusable custom thickness copper gasket, Lani is a great guy..
http://www.coppergaskets.us/index.htm
Or, for machining the comp chamber, Dave is worth a call.. http://www.twostrokeperformance.com.au
Knuckles Pans Shovels
Thanks for the replys, a thicker base or head gasket is out of the question, it turned out my head had been planed way too much, I bought the bike in parts, I don't think the last owner had any luck with it the way it was.
I may have found a 2nd hand head. but otherwise I will talk with that 2 stroke guy in the link
Anorak
Why are they out of the question $1 worth of gasket material some grease and a pair of scissors.Thanks for the replys, a thicker base or head gasket is out of the question, it turned out my head had been planed way too much, I bought the bike in parts, I don't think the last owner had any luck with it the way it was.
I may have found a 2nd hand head. but otherwise I will talk with that 2 stroke guy in the link
Its how a lot of factory bikes set the squish. we are only talking an extra 0.4-0.5mm here at most.
Kinky is using a feather. Perverted is using the whole chicken
Forum whore
As he said "the head has been machined at some stage of its life" I would guess that means that the original squish area has now been machined to almost nothing, and it is now left with a sharp edged bathtub head dome, and a narrow squish area.
If so, no amount of base or head gasket thickness will fix the problem.
Anorak
But that is a guess from you. As he has just said the squish is now .4mm rather than about 1mm only .6mm at most has been removed are you not able to follow that?
Unless it was an idiot that machined the head the squish step would not have been removed at all. He has not stated that this has occurred he said he had had he had machined the cylinder deck. As it was running before then without any incidents As he never mentioned any it only needs the height relationship corrected.
The head on a 1990 KX250 is not bathtub shaped at all regardless, its a very conventional squish with a width of about 50%.
I note Eric Gorr actually recommends to use two head gaskets on this era bike with permetex sealer. But what would he know...........
Kinky is using a feather. Perverted is using the whole chicken
No8 Wire Extraordinaire
So you've checked it with solder on an assembled engine? Another head would be easiest option, but anyone competent with a lathe could fix it and probably improve upon the shape. About 0.9 or so is ideal for a 250. The problem is that that clearance will make the compression too high. So some will need to come out of the bowl.
A cleaner running bike will be the result. But a 1990 will likely have a groove worn in the carb slide which will have more bearing so save to replace that.
Plenty of articles to read but you probably just want to ride it.
If you do find the Eric Gorr 2 dirt bike book it is well worth the money.
Don't you look at my accountant.
He's the only one I've got.
Knuckles Pans Shovels
This is my head, you can just see the step from the gasket face to the squish band on the upper right
http://i354.photobucket.com/albums/r...ps2sinuirq.jpg
This is an un planed head, it has a much bigger step
http://i354.photobucket.com/albums/r...ps567jcnlv.jpg
The KX uses a steel head gasket,
No8 Wire Extraordinaire
Yeah my GG needed almost 2mm planed to get it the right clearance, not uncommon. So you measured it on the bike with some solder down the plug hole?
Don't you look at my accountant.
He's the only one I've got.
Knuckles Pans Shovels
Yer I poked solder down the plug hole, then removed the head and layed a bit across the piston and put the gasket on and bolted the head down and turned the motor over.
No8 Wire Extraordinaire
Is that a central straight plug? If so real easy to turn more of a step and take some area out of the chamber to get the comm to where it should be. But you should really measure the chamber with the piston held at the top, a burette and some light oil (fork oil is good).
Don't you look at my accountant.
He's the only one I've got.
Knuckles Pans Shovels
The spark plug is at an angle so carn't hold it with a mandrill in the lathe.
But yes the chamber would need to be CCed with a burette but if this new head mesures up ok with solder I will run with it.
Knuckles Pans Shovels
I have been talking to Gaudenz Gisler at Gisler Moto and he says don't put extra gaskets under the cylinder and I should aim for 1.2 to 1.5mm squish.
Anorak
Did you tell him you had Decked your cylinder too much?
I wouldn't suggest extra base gaskets just a thicker one. IE to correct the additional clearance you had created.
Eric Gore suggests two head gaskets for these models.
https://books.google.co.nz/books?id=...%20250&f=false
PS. 1.5mm is not a squish clearance. Its the width of a bus. (1.2mm seems about right though)
What puzzles me is you said the head was modified before you got it so it obviously ran well enough before you decked the cylinder.
Kinky is using a feather. Perverted is using the whole chicken
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