KDX Leakn Head Gasket

[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.

[Hillclimb#42]

I have yamabond. How do you lap them to gether without total disassembly? Wouldn't the compound be everywhere? Do you just rub in circles, 1/4 turn the head then more circles?
It barely has smoke coming out and only during a high rev. I put the gasket on dry, do you guys oil, grease or adhere head gaskets normally? Thanks for the tips, guys, I'm listening.

[Friar-Tuck]

 Yes Kyle you have to pull the cyl, head & remove the studs from the cyl. And yes it will get in the water jackets, cyl etc.
    Look up a glass shop near you and ask for a piece of scrap around 12" square or so, the thicker the better (without getting crazy.)
 I taped on sandpaper and use acetone to wash away the filings.  The tape came unglued on the bottom of the glass so I held the bottom of the paper with one hand and worked the cyl and head w/the other.  This is also messy.  I kept the tape dry on the top (furthest away from me) by putting two pencils under the glass.  this way the acetone & filings run down away from the top edge.     

 I guess you could also lay some paint stirrers on the bottom of the sandpaper and use "C" clamps to hold it down,
 (let the clamps overhang the workbench) 

  I move the pieces in a figure 8, I don't push down on the piece, just the weight of the part was enough to see it working.
The other reason I don't push down is to not "Influence" the cutting in any one place.

After you think you've gotten the parts flush, use some prussian blue to verify you got all the imperfections out of the mating surfaces.
 Hope this helps some...

  Tuck\o/

Maybe Larry or Jerry have a better way or Idea, I'd be interested in their opinion too.

[barryadam]

Check for surface plates (granite) in used machinery places, or at machinery stores.  Usually a bargain and much less flexible than glass, and if you get a more precise one, it's flatter than glass (unless you are paying for optical quality glass). A surface plate is pretty heavy and solid, so there's no need to hold it like a piece of glass while working.

Attach sanding sheets using 3M contact spray adhesive.  Remove any "price tags" from the back of the paper, or it'll affect the  surface.  Vacuum metal dust off the sheets on a regular basis.  Remove sheets when worn and clean up the granite with acetone.

[Larry Wiechman]

 A granite surface plate is the hot setup! A 12" x 18" import plate can be bought for less than the shipping costs. Great for checking flatness of cases, clutch plates and brake discs.
 http://www.jtsmachine.com/jtswebshop/measuring/PM036.asp
 Good supply house. They used to knock 10% off the price of all orders placed on Tuesdays. It never hurts to call and beg.

 Chamfer the tops of the threaded stud holes. This relieves local high spots as the tension from the stud distorts the sealing surface. 
 
Larry

[Friar-Tuck]

 Thanks guys!
  That's the kind of Insight that separates the amateur from the pro's 
I have that adhesive...why didn't I think of that!....( insert Forehead slap here) 
  Tuck\o/

[Hillclimb#42]

Very Good tips. Thanks Guys. Sounds like a plan. Also talked to Freddette. he said that was a common issue with the ol' air cooled KDX's. He suggested running the bike without the head stay. Said that he had no trouble with his air cooled heads after running them without the head stay. 

[Friar-Tuck]

Hey HC, that guy is like a quiet super hero,
(list of accomplishments http://www.frpoffroad.com/aboutus.htm#aboutus )  very cool you were able able to speak to him!
  More insider secrets, (run the air cooled bike without the head stay)...
Thanks for posting the results of the conversation.
 Tuck \o/

[wierdo]

Hillclimb, you might want to have a real good look at the cylinder studs where the leak is coming from. I recently had an issue with a leak at the RH side of my kx500's head, tried all the bonding agents, lapped both surfaces and cometic gaskets but still leaked.
the studs torqued up fine, but after start up and a couple of revs would start to leak again, so after pulling apart a couple of times the stud broke off in the barrel, turns out that the stud closest to the leak had stretched slightly, and when i looked at the rest of the studs 2 more were in the same condition.
I replaced all the studs and  while torqueing down the same 3 stud holes pulled they're threads.
I installed time-serts into the barrel with the new studs, a lick of permatex aviation gasket goo onto the metal head gasket and haven't had a leak since.
If it wasn't for the stud breaking i wouldn't have found the source of the problem, and after the third teardown i was really getting P O'd with it all.
Hope this helps........Wierdo.........