1982 KDX 175 rebuild HELP!

[KDX Dan]

New to the forums! New to me KDX 175.
Bought this bike about two months ago, cherry condition all original pieces in great condition. She had great compression when I purchased and ran like a raped ape. 10-15 hours later she lugged out up the hill and died. I haven't ran compression test yet, but just by "feel" I can tell its gone. I'm guessing its safe to assume that a rebuild is necessary. I'm also typically a 4-stroke guy, so if my 2-stroke questions sound dumb... it's because they are. Now that we have that established, i'm looking for some positive feedback and "constructive criticism"
Questions:

1) Is it necessary to replace reed valves, Piston and rings or both?
2) If necessary to bore, any recommendations on bore size?
3) Any recommendations on parts. (Brands, Locations, Stay the hell away froms.)
4) Is this bottom end compatible with a larger head and piston?

All info. is greatly appreciated.
Thanks in advance
Dan

[KDXGarage]

Welcome to kdxrider.

Does it kick over?

What are you "feeling"?

Without pictures it is quite difficult to diagnose, but if something broke inside the engine, it could be top end, bottom end or transmission / clutch.

If the piston broke, then one would need to examine the damage.

It could be bad or real bad.

Stock form, the cylinder was plated, so a replate would be best instead of installing a sleeve. No boring on plated cylinders.

There are no power valves or liquid coling, so that will be less to worry with.

Do you have the owner / service manual? That is a HUGE step in the correct direction. Get one off eBay for cheap if you haven't already bought one.

[ohgood]

Pull the head and look inside

[KDX Dan]

Just for clarification, are power valves and reed valves the same? You said there are no power valves. What kind of magic is this? lol What kind of valve system is in this bike?
By feel, I mean that when I kick it over I can feel that everything inside is moving like it should. There is no grinding or any indication that there is internal damage. Just minimal resistance on the compression stroke.

[KDXGarage]

Intake is controlled by a reed valve system.

Power valves adjust exhaust flow to alter the power band.

No power valves in that engine.

I suggest you do a compression test. Report back. Do not disassemble yet.

If you want to do a vacuum or pressure test, this needs to be done before disassembly

[KDX Dan]

OK, Compression is at zero... Pulled the exhaust pipe, to look at piston.

Severe piston damage

Piston ring is folded up over the top of the piston and there are large chunks missing. I think that it is safe to say the cylinder is damaged as well.
I know parts are hard to come by. So a new cylinder is probably out of the question. There is a very large motorcycle salvage yard not far from here, and i'm going to call and see what they have. Are there any years or sizes that are compatible that I should know about?

If I have to go the replate route. Any suggestions on where to start? How much $ is reasonable?

Also, what are the chances that piston fragments have damaged the reed valves?

Again, I apologize for the newbie questions, and I really appreciate you guys taking the time to comment back to me.
Thank You
Dan

[KDXGarage]

OOOPS. NOT GOOD.

Look at Power Seal USA or Millenium for cylinder repair and replating. Wiseco for piston kit.

You might have crankshaft damage as well. All those pieces flying around usually hit everything. Crankshaft bearings don't like shrapnel, either.

[david]

Also, what are the chances that piston fragments have damaged the reed valves?

Reed valves are cheap and are a wear item, so plan on replacing them anyway.