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jameskiehl

Head gasket, valves, pistons, rings? Oh my.

27 posts in this topic

Guys,

Had a bit of a meltdown in the desert a couple weeks ago. Lost compression completely. The valve cover gasket was visibly damaged, but that would not change the compression (right?).

Is there any way to determine if it is just a bad head gasket or if there is something more serious (rings > valves > cylinder) before i disassemble the entire top end? There is no compression at all right now. I can depress the kickstart by hand with little to no resistance. I'd love to just throw a new head gasket on there, but if i go through all of the work of removing, checking and reassembling the cam assembly, i might as well fix whatever's wrong down there the first time.

Thanks a lot,

Jim

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Cylinder leakage test!

Apply compressed air through the spark plug hole with the valves shut (you may need to think about that) and see where the air escapes. Take ther radiator cap off , check the crank breather hose, the exhaust pipe, and remove the air filter. After you detect where the air is escaping then you have a good idea of what needs to be done next.

Option two. If you have no compression take the cylinder head off and find out what is going on. Since it may be time for service anyway.

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OK, thanks. The valves are closed at a certain positioning of the cams, which i can change by taking the cover off and rotating the crankshaft, correct?

And if i force air into the chamber, and it leaks out through the gap where the head gasket sits, then it is at least the gasket, possibly more.

The one thing that bothers me is having to mess with the valves. I have read some horror stories about folks trying to check the tolerance, seeing that they are within specs, replacing them and ruining their engines.

Any other words of wisdom before i jump into this?

Thanks so much,

Jim

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Yes Read the service manual. if you do not have one you can download one from the "sticky notes" at the top of this forum.

Yes your are correct in your assumptions.

You will now need to be brave and carefull. If it does not seem perfect then do not proceed until it is perfect.

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1. check for colling water condition (changing in the level).

2. check the oil condition-color.

3. remove the valve cover, bring the cam that all valve supose to be close and check clearance- if you find no clearance in one valve that means that one valve is opend allways.

4. in my bike, the valve bucket (the cap that sits on the shims) was stuck pressing the valve (exhaust) little bit. there were no compression, kickstart moves with hand freely.

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Pull the valve cover off and check if there's a valve hanging open. If there's no compression at all there's a good chance that's what ithe trouble is. When you say "meltdown" what do you mean? These engines are pretty easy to tear down, it's worth your effort to learn how to repair things yourself.

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Guys,

Thanks for all the tips and questions. This is a 1998, and by 'meltdown' i mean that when i was riding in the hot desert environment, my coolant leaked out completely as i was riding (not sure where... or if it didn't just boil off from being low in the first place). I did not notice soon enough, and as i was riding along the motor started sputtering and died. By the time i rolled to a stop and tried kicking it over, there was no compression at all.

OK, i checked the valve clearances. the exhaust ports were both just one gauge step out of tolerance (a .254mm gauge wouldn't fit either, but a .229 did fit). the cam bearings are still fine, there doesn't seem to be any damage or scoring on the cam lobes.

Now i have pulled the entire head off and i am puzzled by what i see.

I expected the combustion chamber to have black carbonized residue which could be removed with some spirits and a soft brush. What i found is that the chamber has residue that looks grey and has a hard consistency. Solvent will not loosen the gunk, and it mostly resembles what happens if you melt solder and let it drip onto a surface and harden up.

The engine is not siezed , i was and still am able to turn the crankshaft and move the piston up and down.

QUESTIONs: How to i take the next step in cleaning this stuff if solvent is useless? are the cylinder, piston, rings and head all toast because of this stuff?

I am trying to post some pics on a website and insert the links here, but my computer hates me. Will post if available.

Thanks again,

Jim

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Sounds like the piston got cooked and the grayish hard stuff will most likely be the aluminum piston skirt material. If the engine got that hot then the rings are probably siezed into the ring land and no compression could be built up. I think you are in for a teardown, why was the coolant that low in the first place. You may what to find that out before you rebuild the engine and cook it again. WR Dave.

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ok, thanks for the advice. i guess at this point i start to consider the 426 or 450 upgrade. i've got the head off now, can probably pull the cylinder and piston today and have a shop take a look by tuesday.

i know it's hard to say for sure, but what do people do at this point? that stuff is cooked on, seems like a pain to clean it up. i know i can't, but i'm sure somebody could sandblast it. in theory, anyway.

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Guys,

Here is a link to some photos of the damage. looks like the walls of the cylinder are cracked through. the piston is really screwed. now i guess i just put a new cylinder, piston and head unit on.

my next dilemma is: do i go OEM , or upgrade to a bigger bore? i suppose i'll figure it out.

photos are here.

Enjoy.

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Guys,

Thanks for all the tips and questions. This is a 1998, and by 'meltdown' i mean that when i was riding in the hot desert environment, my coolant leaked out completely as i was riding (not sure where... or if it didn't just boil off from being low in the first place). I did not notice soon enough, and as i was riding along the motor started sputtering and died. By the time i rolled to a stop and tried kicking it over, there was no compression at all.

OK, i checked the valve clearances. the exhaust ports were both just one gauge step out of tolerance (a .254mm gauge wouldn't fit either, but a .229 did fit). the cam bearings are still fine, there doesn't seem to be any damage or scoring on the cam lobes.

Now i have pulled the entire head off and i am puzzled by what i see.

I expected the combustion chamber to have black carbonized residue which could be removed with some spirits and a soft brush. What i found is that the chamber has residue that looks grey and has a hard consistency. Solvent will not loosen the gunk, and it mostly resembles what happens if you melt solder and let it drip onto a surface and harden up.

The engine is not siezed , i was and still am able to turn the crankshaft and move the piston up and down.

QUESTIONs: How to i take the next step in cleaning this stuff if solvent is useless? are the cylinder, piston, rings and head all toast because of this stuff?

I am trying to post some pics on a website and insert the links here, but my computer hates me. Will post if available.

Thanks again,

Jim

Was there any damage to your piston top like pitting? Could be small flecks of aluminium. Are the piston ring glands intact? Also remember on 4 strokes the deposits should be hard compared to say a 2 stroke where everything is oily. I would say if there is no scoring on the cylinder walls you are okay. The valves are another topic. Will the head if upside down hold liquid without leaking thru the valve seats? Need to see some pics to narrow down your problem.

Doc

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Was there any damage to your piston top like pitting? Could be small flecks of aluminium. Are the piston ring glands intact? Also remember on 4 strokes the deposits should be hard compared to say a 2 stroke where everything is oily. I would say if there is no scoring on the cylinder walls you are okay. The valves are another topic. Will the head if upside down hold liquid without leaking thru the valve seats? Need to see some pics to narrow down your problem.

Doc

Dude, did you miss his link to his pics? The top end is toast.

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Great timing for an upgrade. It's pretty obvious where all the coolant went, right out the tailpipe where it can sometimes be hard to see depending on the severity of the cracked cylinder. I may have missed it, but how did the oil look? What ever you do, don't try to salvage any of those parts. Start fresh and don't forget to rebuild the coolant pump and install new, quality hoses. Also make sure to give the entire cooling system a pressure test prior to starting for the first time. Take your time and do it right. A few extra minutes thinking it out will save alot of heartache. Good luck and keep me posted. Cheers.

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Guys,

one more thing. is there a good bolt-on solution? Or will i have to change the connecting rod along with the piston, cylinder and head? i'm a little hesitant to split the case if i don't have to.

Thanks,

Jim

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OK guys. got all the parts put together, and am now installing the old cams. this is a WR, and it looks like the cams are not lined up exactly like the manual stresses. i have a picture of the original timing, sort of. i can tell that the lobes were 180 from how you install them, but i'm thinking it tells the same story.

does anyone know:

1) are the YZ and WR cams the same? (thus making the timing choice of 12 or 13 'links' between the top of each cam determine if they line up exactly)

2) since there are two cam settings that people use for the same cam set-up, which side shoud be aligned perfectly at TDC? which should look slightly off?

something tells me this boils down to advancing or retarding the timing, and could use a little education on what is doable and what is disatrous.

thanks.

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Id completely rebuild the engine if it were me. If you are going to spend the money, why not go all-out and start with pretty much a brand-new engine?

As was said, it sounds like the engine ran itself out of coolant and then ran until it got so hot that the inside of the motor just melted to the point where the engine didnt have enough compression to run.

I think its pretty impressive that the engine ran as long as it did.

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basically, the bottom end is probably fine. the engine didn't sieze, and i didn't drop a valve, so there's no real reason to think the bottom end is bad. i've rebuilt the top end, and its already been expensive enough. thanks for the suggestion, but i am at the point where i am wondering about my cams. anybody have any idea about the timing?

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