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Hey guys,
Since I have had this bike I have had a leaking head gasket out of the rear of the head. At first it dripped down the cylinder. I replaced the head gasket, then it moved just a tad but still close to the same spot. It also got a bit less. I then took the head and cylinder off and sanded the head and cylinder until my permeant marker wore off. I put it back on with a new head gasket. I now rode it again for 2 days and rode a pretty tough trail with lots of being stuck and spinning and pushing and boiled over a bunch. It has the slightest amount of coolant out of the back of the head. Is this a problem? I dont think it happened on day 1 with normal riding but it did on day 2 with gnarly riding and boiling over. I am wondering what I do now. Thinking of adding some copper gasket sealant. I also wonder if it is even a problem because it is so small and so little coolant.

I am trying to fix the coolant boil over issue also. Starting with a kx500 1.6 cap and probably going to wire up a Rad Fan.

How exactly did you sand the head and cylinder? Those are machined surfaces, so hand sanding them is not the course of action I would have taken. you would need to pull the studs out of the cylinder and then lap the surfaces on a perfectly flat surface, like a plate glass with compound. better yet would be to take it to a machine shop and have them surface it. Any leak is an issue that needs to be addresses, no matter how small. The higher pressure cap may help some, also Engine Ice or a similar wetter will help.

bufftester wrote: 03:35 pm Jun 01 2022 How exactly did you sand the head and cylinder? Those are machined surfaces, so hand sanding them is not the course of action I would have taken. you would need to pull the studs out of the cylinder and then lap the surfaces on a perfectly flat surface, like a plate glass with compound. better yet would be to take it to a machine shop and have them surface it. Any leak is an issue that needs to be addresses, no matter how small. The higher pressure cap may help some, also Engine Ice or a similar wetter will help.

Thanks
I should have been more specific. I pulled all the studs out and sanded the cylinder on a piece of glass. I then did the same for the head. New gasket and torque to spec. I actually went out and looked and it was more leak than I remember.

I probably should just take it to a shop and have them do the cylinder and the head to get it perfect.

might be worth it to have a dye inspection done, could be a micro crack or casting defect causing the leak if you are sure the mating surfaces are perfectly flat.

What is a dye inspection?

Edit just looked it up. I will ask the machinist to do this also.
Thanks.

I’m not sure they are flat. I did it the best I could but I’m no pro. I will prob take it in. I want it just fixed right.

Are you tightening the nuts in a criss cross manner?

new head gasket each time?

Beyond that, it does sound like a trip to a pro to have them check for flatness.

lcgordon711 wrote: 08:54 pm Jun 01 2022

bufftester wrote: 03:35 pm Jun 01 2022 How exactly did you sand the head and cylinder? Those are machined surfaces, so hand sanding them is not the course of action I would have taken. you would need to pull the studs out of the cylinder and then lap the surfaces on a perfectly flat surface, like a plate glass with compound. better yet would be to take it to a machine shop and have them surface it. Any leak is an issue that needs to be addresses, no matter how small. The higher pressure cap may help some, also Engine Ice or a similar wetter will help.

Thanks
I should have been more specific. I pulled all the studs out and sanded the cylinder on a piece of glass. I then did the same for the head. New gasket and torque to spec. I actually went out and looked and it was more leak than I remember.

I probably should just take it to a shop and have them do the cylinder and the head to get it perfect.

Its quite easy to check this yourself.

First, you need a true flat surface. A Machinist's surface plate is the ideal choice, but a piece of thick plate glass, not common window glass, or ground granite counter top will work too.

Next, you need a tube of Prussian Blue marking medium which you can get at any auto parts store. Common lipstick works pretty good too.

Using the Prussian Blue, make a real thin smear over the true flat surface. Next take your cylinder, head joint face down, placed on the marked flat surface and rub it around a little bit and lift it off.

Next do the same with the cylinder head.

The areas where the Prussian Blue has transferred to the joint faces are the high places. The surfaces with no blue markings are the low places.

Very careful work with a scraper to removed the blued high spots will result in a true flat surface to each joint face. Minute occasional low spots are okay so long as they aren't too extensive.

Thanks I will try this but honestly I’m tired of taking it on and off. Sick of buying new gaskets everytime. Probably just best to get a machinist to fly cut the head and cylinder and be on my way. Hopefully no crack.

If it were me, I'd get a florescent dye penetrant kit w/ developer, like Bufftester stated. Before having it machined.

Molly's 70 = E. F. Hutton

I will have him check it. Stuff is a bit expensive to buy for myself. Not sure how much I would use it.

Hey guys I was wondering since I have one ride with the fresh top end and I’m already 80 bucks into gaskets. Can I get away with running the same head and base gasket. Head would be nice because it is 30 bucks. If it’s important to go new I will but just wondering before I buy 40 bucks in new gaskets. I know a lot of times they are 1 time use.
Thanks

I would never re use a head or base gasket.

lcgordon711 wrote: 02:34 am Jun 10 2022 Hey guys I was wondering since I have one ride with the fresh top end and I’m already 80 bucks into gaskets. Can I get away with running the same head and base gasket. Head would be nice because it is 30 bucks. If it’s important to go new I will but just wondering before I buy 40 bucks in new gaskets. I know a lot of times they are 1 time use.
Thanks

Do not reuse.

Yeah I have heard this by 99 percent of ppl and always have. But then I hear some ppl say especially with the kdx because it’s a metal head gasket that you can reuse if it’s not damaged.

I’ll buy new. I’m planning on not opening this up for a long time.

lcgordon711 wrote: 01:46 am Jun 12 2022 Yeah I have heard this by 99 percent of ppl and always have. But then I hear some ppl say especially with the kdx because it’s a metal head gasket that you can reuse if it’s not damaged.

I’ll buy new. I’m planning on not opening this up for a long time.

You've got it backwards. Metal head gaskets are the ones that can not be reused. Once they're compressed, that's it. O'ring heads can have the gaskets reused sometimes.

Oh yeah I know orings can. I have reused mine. I was meaning paper. Those can get messed up when removing. Yeah I’ll just go new.

I’m gonna have 300 bucks into this stupid cylinder.

lcgordon711 wrote: 06:05 pm Jun 13 2022 I’m gonna have 300 bucks into this stupid cylinder.

It’s an expensive sport.

Yeah this bike has too much money in it. Oh well it’s fun. Took the cylinder off and inspected it closely. It had a horizontal line on it. Looked like a crack. Cleaned it with a wire wheel to see if it was still there and I can’t quite tell. Should have it to the machinist Thursday and he is going to check it for cracks. I nicked the top of the cylinder with my vice grips when pulling the alignment pin out so good thing he is going to cut it. That was stupid.

Edit
One question might shed some light on the issue. It seems to happen when he bike gets really hot. I rode a 40 mile trail that was a bit tough but not bad. A bit quicker and I think I boiled it once at the beginning on the one tough section. It had the slightest drip leak at the end but not much at all. Next day we rode 13 miles of hell. Super slick, still snow in places, downed trees, super hard trail , slow and getting stuck and spinning. I boiled the bike over constantly and it was leaking big time. I mean not crazy like dripping or anything but a decent chunk of blue. Would this indicate a crack because when the cylinder gets super hot it expands the metal causing it to leak? Could the head do this as well? When you pull off the head gasket there is no mark of any thing that looks like coolant is getting through. It looks perfect. Not sure how a leaking head gasket looks.

Any thoughts on this?? Thanks