melted PTO piston.. let's find out why!

thanks for all the posts everyone, and Sideshowbob, i will be ordering the new needles and boots.

now....
i took the sled out today for some test runs with the new rebuild.
took it real easy on her, 1/4 to 1/2 throttle. brought my plug wrench with me and checked the plug color often. made a change to the needle clip to richen the mix a little and the plug color changed to a light brown (was much lighter before this change).

drove around a little longer then started to head back to my truck.
3/4 throttle for a little ways then BANG.. it happened again!
loss of power and change of engine noise... this time i hit the killswitch right away. rolled to a stop. pulled the plugs and the PTO side was white/grey.

towed it to the truck and brought it home.
took head off and saw a very whitish piston...... with a little melt near the exhaust port.
pulled the jug off and WHOA!!! bottom of the piston skirt is missing!!!!!!! exhaust side.


now. it would seem i'm having bad luck with this engine.
i did use used parts for the top end... i did not measure to see if they were worn too much. and i'm guessing they were as what else would cause the bottom of the piston to break off.

the magneto side piston, you could wiggle it in the cyl quite a bit before we took the cyl off. my nephew noticed this as he was helping me remove the topend. he believes there was too much slack and that caused the piston failure.

i am open to all suggestions.

currently, my plan is to buy a piston kit from royal, probably 0.20 and get the cyl's bored to match the new pistons. also buy the newer needles and 2 new boots off a 91 exciter as suggested above.

2 pic's of the damage. cyl's look fine!
there is about an hour run time on this engine since installed.

0207001726.jpg


0207001728.jpg
 
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IMO:

Even if your clearances were fat...that mag cylinder is lean! Black is lean it can fool you. There is something seriously wrong causing it to go lean that must be sorted out before you break more part$.
Post some pictures of the carbs on that sled. Because this sled seems to be a combination of years, it could have 4 different type carbs.
1/ butterfly carbs [original exciter carbs]
2/VM38 Power Jet Carbs
3/VM38 Non power jet carbs
4/TM 38 flat slides [came on the Exciter SXs]

Before you order new needles check yours to see if they are already the updated version.

Has the cylinder head been cut/modified for a higher compression ratio?

JM.02c
 
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i agree. serious problem.

my first step, i took my carbs off and brought them to my local sled guy. he worked on my older cat and did an awsome job. asked him to look over the carbs, give them a good cleaning and let me know what he finds.

i will post pic's of the carbs when i get them back.
they are not the butterfly ones.
they are not the flat slides either.

unsure about the power jets... i know mine does have a large sensor type thing that screws into the side of both carbs near the air screw. i believe these are some sort of throttle safety switch and they are disconnected.

the cooling lines to the carbs are also bypassed. have seen a few exciters including my nephews which have them disconnected.

when i was inside the carbs i know they have a 320 for a main jet, can't remember the other jet sizes... and the needle clip in the slide is set to the middle position. unsure of how many turns out the air screws are set at.

no aftermarket exhaust. air box is in the sled and looks to be in good shape. boots between carbs and air box are good.

will post back when i know more.
 
Phazer burn downs...

Big-Kid sent me a post on the nozzle updates for the carbs, check out next to my post about my burn down, click on his link for to me for carb info!
 
very nice day outside in my area so decided to do a little work

first off, i will be picking my carbs up tomorrow (friday) evening. will post a pic of the carb's when i get them.

pulled the engine out of the sled. took both pistons off and snap'd a few pic's.

dumped this out of the y pipe, exhaust side.
0218001318.jpg


exhaust y pipe. you can see how white the PTO side is!
0218001318a.jpg


PTO piston
0218001336.jpg


PTO piston, another shot
0218001336a.jpg


magneto side, no melting but upon closer inspection there is mild cracking on the carb side!
0218001336b.jpg


so. safe to say these pistons are trash.

i also checked the vent line for the fuel tank and it is clear. i can blow easily through the line and hear it exiting out the fuel tank filler hole.
i did not speak to the fella that worked on my carbs as he was suposed to let me know if he found anything that would have caused this melt down.

will be checking my slide needles tomorrow to see if they are the updated ones.

NOW. what would you's suggest.

i still have a good spare bottom end so...
1. buying 2 used cyl's, 2 new pistons and rings going this route?
2. have my cyl's bored over and 2 new pistons and rings?
3. search for a good used engine?

as always, thanks for any advice.
 
I have 2 used jugs and pistons if you pick up the shipping. I do not know if the pistons are usable. I can send pics and you can make a decision. Kind of learning as I go with the sled repairs.
 
i know of 2 good used jug's that i can get for $60 (CAN) a piece locally. but i'm undecided which way i should go yet. i want something that will be reliable but also don't want to break the bank!

i appreciate the offer Theo125 and wil keep you in mind.
 
Ok let me know if u change your mind. These are free if you pick up shipping. My zip is 12061 if you figure out the weight.
Good luck
 
haven't done anything with this sled since the last meltdown but i'm always thinking why?

as mentioned this is a mix of 2 different year sleds/motors.

would using the CDI box off the 1992 with the 1989 engine cause any problems?

i looked online and they call for different part numbers.
 
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