what happened

redneckchicken · Post by **redneckchicken** » Thu Nov 17, 2005 12:58 am

alright guys i got a new compression tester so i was going around testing it out right i figured lets go check the compression my baby my 73 jdx8 (my first sled) the fan side test a hair over 120 but then i went to the pto end and here lies the problem my it only had 30 lbs compression so i pulled off the head and i have a dibit burnt in the top left corner. Now last year i was riding and the engine locked up but after i pulled the plugs and let it sit a while it freed up and i rode it home. I have had it running many times since then. but what do you think caused the dibit?

400brian · Post by **400brian** » Thu Nov 17, 2005 2:56 am

It got too hot.

Lots of posibilities as to why.

First thing I'd suspect is the pto crankshaft seal.

With the correct action, the jug may be salvagable. I'm guessing the piston is toast from your description.

redneckchicken · Post by **redneckchicken** » Thu Nov 17, 2005 2:39 pm

yeah the piston is shot but the cylinder looks fine so i need to replace the seals

Danzig · Post by **Danzig** » Thu Nov 17, 2005 3:27 pm

did it lock up while riding or after you shut it off and came back to it a day later or so and then you found it locked up?

harleysportster · Post by **harleysportster** » Thu Nov 17, 2005 7:17 pm

redneckchicken,
I would wash the cylinder with meritic acid to remove any aluminum deposits and then hone the cylinder lightly so the new rings seat properly and then, REPLACE both crank seals. Since one side caused a melt down, the other side will soon also.

JDXsand00s · Post by **JDXsand00s** » Fri Nov 18, 2005 12:36 pm

I've had about enough of blowing up pistons. Last year my X8, after about a mile disintegrated the pto piston. I did the same thing about a month later in my 500, and though I haven't tore it apart yet, I'm pretty sure I fried my 500 again this morning when I was out cruising. That engine was hot, good thing I have 2 spares in my basement.I'm pretty sure I rebuilt that engine with a used oil seal, obviuosly a bad idea. At least my 400, is reliable: 300+ miles without engine or carb problems.

harleysportster · Post by **harleysportster** » Fri Nov 18, 2005 10:31 pm

JDXsand00s,
When rebuilding a 2 stroke engine with a burn-down or melted piston, the engine should be pressure tested to assure the cause was corrected before putting the engine back in service. This test will check all crankseals and all gaskets for a leak which could cause a lean condition.

Bad crankseals is the most common cause for a piston melt down.