[Vykn]

Hey guize, I've been on the forum for a couple months now and know the bunch of you could give me some help.

I grabbed a '99 YZ80 before my brother had a chance to short change it for pennies on the dollar.

I stripped it down to frame, painted it a nice Yamaha Blue, and did some other repairs.

I rebuilt the engine as it didn't run; new crankcase seals, shifter seal, and top end gasket & o-rings. Piston wasn't in terrible condition, and the ring wasn't seized in the sides.

Cylinder itself had wear, but nothing worth mentioning.

I replaced everything to spec torque, and even did a leak down test. Only lost about 1-3 PSI a minute. I only could get 60PSI off a tester at WOT up to 8 kicks.

It has spark when tested outside of the cylinder, but won't start up. I've tried bump-starting, and removed the closed-circuit shorting of the kill switch out of the equation. New spark plugs, properly measured 32:1 mixture as stated in the book.

Starter fluid doesn't start it either; verifying it isn't a fuel issue.

Any ideas? Thanks!

 

[grtfast]

Compression is low. It should be ~130 psi minimum with a tester.

 

[Vykn]

Any tips on how I can find the loss of compression? The piston was a pain to get into the cylinder. I didn't measure clearance maximums but I had to mess with it and use oil. It only has one piston ring.

 

[SVS]

Did you change the ring at least?

Sounds like it might not be a bad idea to get a new cylinder, piston and ring. There really isn't much else to go wrong on a 2-smoke when it comes to compression and they can go wrong fast...

 

[Vykn]

I didn't. :frantic

I wouldn't mind putting a new cylinder, piston and ring in there. I was hoping i'd have some way of knowing she has some life before I throw munney at her.

:dunno


I'll look at some deals for it.

Edit: I'm not going to look for deals. $250 for a new cylinder. :nono :nono :nono

What about resleeving?

http://www.bikebandit.com/aftermark...s-sleeves/l-a-sleeve-cylinder-sleeve?m=145970

How much would a shop cost to resleeve it? (I never like resorting to a shop.)

 

[03SlowZ06]

Why would you need to re sleeve it? It's a 2 stroke. Put factory rings in it. Takes an hour and half to do.

 

[Vykn]

 

[grtfast]

Holy shit. The cylinder is junk. Re sleeving is a bad idea because the heat transfer from the cast iron liner to the aluminum sucks. Either get it replated or get a new one. You need a new piston and ring as well.

 

[03SlowZ06]

Yep. It's toast. Get online. You can find a new over bore jug and top end kit for a reasonable price.

 

[Vykn]

I'm going to measure the cylinder and take it to a shop to see if it's possible to get it bored over.

They want $250+ for a new cylinder which isn't worth it for the bike. I'll be getting a new piston as well.

 

[grtfast]

It's a plated cylinder. There is no liner to bore. It is possible to get replated, but those gouges will need to be repaired via welding once the old playing has been removed. That will likely cost more than a new cylinder but you can check. This company does replating:

http://www.mt-llc.com

For what it's worth, if you're thinking about a dirtbike from an investment perspective, your never going to get out of the gate.

 

[nitrous36]

Wow those cylinder walls are damaged. Your best bet like the others said is to get a new cylinder. Not sure you can bore the one you have.

 

[SVS]

 

[XCSEDAN]

holy shit that is fucked.

if you think thats ok, you got no idea what your doing. i had a mate with a YZ250 in the same condition (cylinder was worse actually) we slapped it back together with a new ring and traded it in the next day, he too thought it was ok.

anyway, what can you do, its fucked. either look for another motor (probably gunna be fucked) or have fun and modify it, aka big bore time.

forget trying to rebuild it on the cheap, wont happen, it'll cost twice as much.

 

[Vykn]

I got a used cylinder & piston. It's running, but in reverse. :nono

I've set timing with the marks on the case and the magneto, but no luck.

 

[grtfast]

How are you spinning the engine backwards to start it?!

You need to take this thing to someone who knows what they're doing.

 

[Vykn]

I'm not starting the engine in reverse... You're a bit of an asshole.

The kick start spins the crank in the CORRECT direction. When I release the clutch, it rolls in reverse.

I've set timing with the coil plate & the case. But I'm unable to set the magneto in time with the case due to the woodruff key. Any suggestions?

 

[Vykn]

For those with the "if you think that's a good cylinder..." I wasn't saying it was good to go run against 500's.

I was trying to at least get it to combust a few times to know that everything else is sound. I know what I'm doing.

 

[grtfast]

I'm not starting the engine in reverse... You're a bit of an asshole.

The kick start spins the crank in the CORRECT direction. When I release the clutch, it rolls in reverse.

I've set timing with the coil plate & the case. But I'm unable to set the magneto in time with the case due to the woodruff key. Any suggestions?

:flipoff

How exactly is the engine running backwards if you're starting it by spinning it forwards? Explain that one and we can go from there.

Have you tried pushing starting it?

The reason I infer that you don't know what you're doing is that no one who does would put that engine together with that cylinder and try to run it.

 

[grtfast]

.... I know what I'm doing.

Not really. You can take it apart and put it together (although you've likely done something wrong there with this whole running backwards mess), but you didn't think the cylinder damage was a problem, and didn't even recognize that the low compression was from the large gouge in the cylinder once you had it together. An engine is a precise machine, it's not a water faucet or a table leg that you can duct tape together and hope for the best. There is one way for it to be right. One way. your explanations aren't enough for me to determine what you've done wrong, so I am left to tell you to take it to someone who knows what they're doing. You don't know enough to know what you don't know. They can tell you what you've done wrong and you will know for next time.

Have you verified that the crankshaft is turning backwards when the engine is running? You can look at the ignition rotor to see.

Push it through with the kickstarter and look at which way the crank turns. If you're starting it with the kick starter, then I'd bet my paycheck that it's spinning the same way when it is running. I can't see how the crank could switch directions during starting. That makes zero sense.

You likely have something assembled incorrectly and the engine is being spun backwards to start, but I can't imagine how that could be. One thing for certain, you don't really know what you're doing or you wouldn't be on here asking these questions. :dunno