Maintenance & Technical > KDX (KX step child)

KDX Leakn Head Gasket

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Hillclimb#42:
I've had an issue with my old 86 Kdx 200 with the head gasket leaking. The first head, I had was a custom deal fabricated from a solid piece of aluminum. It was more like a solid block, without all of the cooling fins that are stock. It looked like a pretty good design at first, but after close inspection, there were several little dings in the gasket surface area. Looked like it got banged up in the box that I got the bike in. I tried a two different gaskets before giving in and reinstalling the original stock head. It didn't want to seal either. During a top end refresher over the winter, I had them flatten out the head's gasket surface. That did the trick so far this year, but now its leaking again, in the same spot as before. I tried tightening up the bolts, a new gasket, really tightening up on it. Still leaks. It seems to be shooting out towards the back of the cylinder, after it warms up. I get little puffs of smoke during a high rev.

1st question
  Is it just as easy to flatten the cylinder surface as the head?

2nd
 If it was leaking from a bad casting or cracked cylinder how could I tell the difference?


3rd
Is it going to crater, if I keep riding it like that?

Hillclimb#42:
Nobody has had an air-cooled bike with a head gasket issue? It worked for I'd say 3-4 hours of actual ride time, then started spitting smoke again(towards the back). I saw one of my engine builders spraying the copper gasket with something that helped. Cometic gasket did not fix it. Leading two districts in hillclimbing (30 pts=1 race) kinda in a pinch. need some experienced advice.
thanks, Hillclimb42

don46:
first off you should lap the head and cylinder together, one may be true the other may not.

I wouldn't think it would be fom a bad casting or a cracked cylinder, but then who knows.

You don't say how bad its leaking, I doubt that it will crater, but it will hurt performance if it is leaking severly, and you could damage the mating surfaces with a severe leak.

I've had some off the wall motor combos and have used products like High tack and copper cote in rare circumstances, in fact I ran a snowmobile motor without head gaskets only copper cote, not reccommended.

so heres what I'd do, your in the middle of a points battle and can't not run it, pull off the head and cylinder and lap them together, use a new head gasket and spray it with copper cote aand make sure you torque the bolts evenly, that should get you through your next two races.

Good luck.

Friar-Tuck:
 Sorry to have taken so long to get back,
but I really don't know of anything more than Don recommended.  Pull the cyl and remove the studs, lap the head to the cyl or take them to a shop and have them surfaced. 
  (You may also have to contend with an increase in compression if the shop has to take off too much material.) 
  You could try to make a copper gasket, however I don't know exactly how to cut it cleanly.
Surfacing and or laping them in together should cure the leak.
  Be careful torquing down more than the specs account the aluminum will start to distort the fit and the gas will find a
way out.
  Maybe you could get the pieces to Larry W. after the season and see what he can do with it.
  Tuck\o/

greencannon:
My K5 cylinders leaked coolant badly even after all the above remedies mentioned here. one wa an 87 and the other 01.
no matter what I did, they would leak. I decided to one more time to resurface the head and cylinder at the machine shop and this time goop up the gasket with Yamabond 4.
They both have been leak free for 3 yrs now.
i know your not dealing with coolant, bit the problem is similar and the fix may be worth a try.

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