Recently bought and old LT80 for 100 bucks to fix up for my son. Had been sitting in the back of a shed for a couple years. It had all the engine plastic removed, but looked to be pretty much complete. Previous owner said it would need rings. I was assuming the worst when I bought it and figured If I couldn't get it going I would just sell it or part it out.

Got it to turn over fairly easy, but wouldn't start (no big surprise). Had spark, so I did a compression test... 60psi. PO said rings were bad, so no surprise. However, when I tore into the motor, I found a brand new standard bore Wiseco pison... Cylinder looks to be in good shape too. So, what could be causing such low compression? Metal gasket between head and cylinder looks new, base gasket between cylinder and case looks new but they lathered it up in orange gasket sealer goup (even saw a drip in the case ). Could that be causing the issue?

 

Love that red silicone. Possible po just stuck a new std piston in a worn cylinder. One that needs to be measured and bored to the oversize piston it needs. I've seen this plenty of times. Measure the piston at the skirt and also the bottom of the cylinder and see what's the difference. If over .004 difference or more,could be the problem why it wont run. http://www.wiseco.com/ProductDetail....Year=&ModelID=
Member "LT80" should show up later and get you straightened out as to what to do..

 

That's what I was thinking OPT (piston size)
New piston but I don't see any crosshatch in the cylinder.
Even at .007+ clearance it should have more than 60# comp.
After measuring to make sure, I'd be getting a new Suzuki piston kit (.5 over) and have the cylinder bored to the cylinder.
OR you can get the ebay el-cheapo kit for 15 bucks less than a stock piston. For a stock application, they should be ok.

OPT...what's wrong with red silicone??? It does so much good on the sides of the gaskets.. LMAO

 

LT80 does that look like the wrong rings for a wiseco piston, those don't look like the keystone style on the two lt 80's I have that have wiseco's in them.
GldRubi03 look at the rings and see if it looks like a silver ring is bonded to the outside.

 

Looks ok to me. Suzuki rings would not fit in a wiseco.

 

Thanks guys. I will take some measurements tonight and double check the rings but they seemed to fit like they should. I did try to take some measurements before I posted and if I recall the piston was 50.5 and the cylinder was 49.5. So I think I was doing it wrong lol. It's hard to measure the piston with the studs in the way.

Could the low compression have anything to do with the gasket goop, or reeds (sorry still learning about 2 strokes)? I remember seeing you post somewhere that the only way to get that low of compression is with a blown head gasket.

 

Not the goop or reed.
Surely a blown head gasket would do it but IMO you would have seen that.

 

So, here are the numbers I cam up with. 1.966" on the skirt of the piston and 1.970" at the base of the cylinder (pic shows 1.967 but I was able to get the larger reading). Am I measuring these correctly, and these are within in spec correct?



I noticed one side of the piston had some scratches. I checked the inside to verify that they are not cracks going all the way through. Is this something I should be concerned with?


About the rings, I thought you were supposed to position the gap at one side of the pin and the gap for the other side directly opposite? These Wiseco pistons seem to have a small key in each of the ring slots that holds them in place, and are only spaced about 30* apart and on the intake side. Does this seem correct?

Lastly, I reassembled everything, and tried the compression test while adding some oil through the spark plug hole. I would add about a tsp at a time and each time the compression would go up about 20psi. I stopped when it reached about 110. Could this have been the problem all along that the cylinder just wasn't lubricated enough to get a good test? Or, does this indicate some other problem?

 

Micrometer and inner bore gauges are a better method of measurement,but if you have .004 clearance with calipers,just my I'd go to the first oversize Wiseco and have the cylinder bored and honed to finish. Manual should tell you the proper clearance,but most of the little ones usually are .002 or less std piston to cylinder clearance. Max piston to cylinder clearance on a Sportsman 90 is .0047,then time for a new top end.

 

OPT::"I'd go to the first oversize Wiseco and have the cylinder bored and honed to finish"
I agree with the exception of:: I'd rather see a Suzuki piston in it. I don't use Wiseco's in LT80's.
I set cast pistons (Suz/pro-x) at .0025 clearance. A Wiseco is set at .0035 clearance.
I'd be happy to help you out if you feel the need.