1988 LT80 low compression after rebuild

ggaspo13

ggaspo13

Member
Jan 20, 2013
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2
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S. Jersey
Hey guys,

So I sent my sons '88 lt80 cylinder out for rebuild and now it's all back together with 70psi compression. I checked for spark, fuel, then compression after it wouldn't start. It has spark, was getting fuel, so I checked the compression and got the low reading. I then squirted a little oil in the top of the cylinder and got a reading above 150psi....what does this tell me? I have heard to try this to test the rings, but they are brand new and seated correctly on the piston groves. Any thoughts? Thanks !!!
 
then it just needed to lubricate the rings.

sometimes they get stuck in the piston and allow blow-by or they are dry and wont form a seal

this usually only happens to brand new or sitting for years
 
That can totally happen. With the oil in there. Start it up. Run 1 heat cycle. Check compression again. If good. Do rest of heat cycles. If compression low. Check the builders work.
 
Is it a new piston?

What was done to the cylinder?

Who assembled the engine?

Was ample oil used in the piston fitting?

Was the ring gap checked?

Were the rings free in the piston grooves?
 
So I just took off the cover that sits over the top end and investigated a bit more to find some of that oil I put down the cylinder working its way between the base gasket. I then took the cylinder off and there was a tear in the paper base gasket. Not sure how I didn't catch that during reassembly but I'm pretty sure that's the culprit. Thanks for all of your responses and I'll update when the new gasket arrives.
 
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Base gasket leak should not produce a low compression reading!

While you have the cylinder off do some measurements and check the ring gap.
 
Just noticed that the crankcase is filled with gas....I'm at my wits end with this thing. I am going to attempt to drain the gas out, but I can't seem to find a crankcase plug. Maybe standing the quad upright....
 
There is no drain plug!

Remove the spark plug, drain carb of fuel.

Hold throttle wide open and kick until your leg hurts.

Hold a white rag over the plug hole and when it stops spitting it should be right.

Oops just remembered you have the cylinder off, stand the bike on end.

Before you put the cylinder back on put a little 2 stroke oil into the case and a little down the main bearing feeds.

All that fuel may have washed the oil off the bearing surfaces.
 
Thank you blaaster. Drained all of the gas out by standing the bike on end. I am now going to attempt to answer your previous questions. The cylinder was sent to out for top end rebuild. I assembled the engine when the fresh cylinder and top end kit was returned to me. Yes ample oil was used in piston fitting. I did NOT check the ring gaps, but the rings were free in the piston grooves.
 
I am pulling off the carb shortly to clean it up and check things out. I am planning to put in a fuel shut off valve too because the petcock on these does not have an off position.
 
?
should be able to shut it off.

lt80.gif
 
I have a lt50 with the same petcock. The motor always got flooded. I found a petcock on ebay that has off, on and res. after you get the new petcock just plug the vacuum line on the intake manifold. With that petcock won't allow fuel into carb.
 
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The float setting may be incorrect, the needle and seat may be varnished up, the float could be sticking.

I never turn my fuel off for personal safety reasons and never have any problems.
 
LT80s have funky petcocks & brass on brass float valves. they will leak & they will fill the case with fuel till it runs out the carb :) .. I put a cheap lawnmower type inline shutoff valve in the fuel line and leave the petcock on prime .. I pull the plug, stand the bike up on the grab bar, hold the throttle open and spin the starter for awhile to drain the fuel down through the pipe. If this works for you to get it started it will still need to run a bit to clear. It will smoke like crazy for a long time as it burns the mix oil out of the pipe :)

Just for fun a pic of LT80 carb I modded for alky
Lt80alkycarb013.jpg
 
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