Hi, new to this forum, pretty awesome resource. I bought a used engine for my daughters 2002 LT80, (eBay), shockingly it arrived with about 50 PSI compression. After getting the cylinder bored/honed, new piston and all, it still has only 50 PSI compression, after adding oil it gets up to 120 PSI or so.

I installed the Boyesen reeds when I put it back together. It did start and I drove it around the block for a couple minutes, with good power, the night I finished the rebuild, but it hasn't started since.

At first I thought there was a fuel issue and rebuilt the carb, however it wouldn't/won't fire up even after pouring a little gas in with the spark plug out, so I bought a compression tester. I realize the compression test indicates the rings are not right.

Can some one recommend a reference for rebuilding the top end. I'm going to pull the head back off and see what's going on in there but I don't have a great deal of experience with rebuilds.

I didn't check for ring gap when I installed the new piston, uh, is that critical? Other than that it was pretty straight forward. Would a leaking head gasket issue be 'temporarily "fixed" by pouring oil in, or is that definitely rings?

I apologize for the rambling message, it's getting late. Thanks in advance.

 

Welcome to the forum. Lt80 are a 2 stroke engine and require gas and oil in the cylinder. You said that you use gas in the cylinder? Was it premixed with oil? If you run straight gas it will wash the cylinder walls and possibly damage the cylinder and rings. You mentioned that you replaced rings and pistons. Did you do a break in procedure? This mean to run the machine at idle until heads get hot to touch. Turn off machine and let completely cool down and repeat again 2-3 more times. This is to allow the rings to seat true to the cylinder. Compression around 120-125 is good. As far as having the head rebuilt i would strongly suggest getting in touch with LT80! Jack is the most knowledgeable guy on this forum and he is very reasonable with prices. He would be the man to get in contact with. He know everything and anything about there little machines he is great. Keep us posted on what you find.

Rob - KFX80Dad

 

Welcome to the forums.
I rarely check the ring gaps. Being too tight isn't the problem.
The rings only fit one way in the ring grooves. If you had to push hard to get the cylinder on the piston, they might be incorrect. The lil numbers on the ring ends go up.
Arrow on the piston goes toward the exhaust.
Take the head off and see what's going on (if anything).
Let's go from there.

 

Thanks for your replies, I do pre-mix the gas, so that shouldn't be an issue.

I removed the head and the cylinder, everything still looks brand new, most of the crosshatch from the boring/honing is still visible on the cylinder wall.

I rotated the rings to check for broken pieces without checking first to ensure the ring gaps were lined up with the pins in the ring grooves. I don't think that was the problem, it didn't take a lot of effort to install the cylinder down over the piston.

I don't remember little numbers on the rings, it seems to me there was either a dot or a letter 'T' stamped on each ring near the gap, which I did place up.

They are Suzuki OEM piston and rings, 1.0 over, the arrow was/still is pointing towards the exhaust port.

Full disclosure: My torque wrench ranges from 20-120 ft/lb, so I just tightened each head nut by feel. I guess I will head down to Sears and buy a smaller torque wrench before I re-install.

1. The head gasket can't be reused?
2. The head gasket (when new) had a raised rib that went all the way around, was that supposed to be installed rib up towards the head or down? (I installed it rib up. I think.)
3. Would pouring a little oil in through the spark plug hole cause a leaking head gasket to seal?
4. It seems like the crankcase seals aren't the problem because the problem was fixed when I poured some oil in the cylinder for the compression test...?
5. Since the rings were never fully seated would that have caused the compression test to be low?

I really appreciate all of the help from you guys, I'll probably be going through this again with my nephews 80 when I get this one going.

 

By the way, one more question- how do I know if the head has already been milled the .030? Thanks!

 

All seems good.
To Answer::
1) The head gasket can be re-used.
2) Either way is fine.
3) Temporarily....Maybe.
4) I agree.
5) Certainly. Rings really don't seat for a long time. Especially if you use a synthetic oil.
6) If the head isn't marked, I'd bet it's stock. I mark all the heads I do.
7) You can put it together with your ft/lb wrench... 9.5 or so ft lb. (100-115 inch lbs.)

 

Hey LT80, thanks for your help, I will re-assemble and go back to looking for a fuel issue, more to follow on that. The spark was consistent and blue. Thanks again

 

Update: re-assembly delayed while I'm getting the head milled... should be back together this weekend...

 

Ok, got the engine back together, and it runs... apparently there was a bad seal with the head gasket... I bought a smaller torque wrench, torqued it down 10ish ft/lb, and ... it runs. Pretty good. However...

...it only runs when I pour gas directly in the cylinder through the spark plug hole. Then it dies.

1. Does it matter which way the wire clip on the needle attached to the float goes?
2. I changed the petcock to the off/on/res version... the carb is definitely being supplied gas through the fuel line.
3. What is the "boiling the carb" technology? Something you get from harbor freight? I bought the gallon can of Berryman carb soak, but it leaves a sticky residue all over the parts being soaked.
4. I think there is a new carb (from evilBay) in my near future, but I'm willing to try any suggestions first.

Just a side note, I'm wondering why leaving the gas petcock on to the carb floods the carb... isn't the float and needle supposed to contriol that? I rebuilt the carb using the Moose kit.

5. With the 1.0 over piston, .030 milled head, and Uni-filter custom intake, what size jets do y'all recommend? I ordered that 'Power Up' kit from Mid-west Mini, they sent a different-than-stock jet, I assume smaller to lean it a lil, but I've lost track which one is which. The one in it right now is the stock size that comes with the Moose kit.

Thanks, any help offered is greatly appreciated.

 

i noticed the same thing with my berryman carb soak can, it leaves a real nasty residue on the parts, its as bad as just cleaning it, i used 3 cans of brake cleaner and a brush to get it off.

the power up kit comes with a 90 main jet, its smaller then the stock one, i ordered just the main jet from midwest mini since i'm not interested in a "power up kit" and i personally didnt notice a night and day difference in power, but it seems to have crisper throttle response.

you said a custom intake? why remove the stock intake? is it the stock carb at least