02 Viper meltdown help needed

S

Sailopus

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Jan 10, 2012
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NorCal
A little background first....

I bought this project sled for my wife for cheap last year. It had a center piston melt down and I rebuilt the entire engine. Had the crank rebuilt and all new gaskets and pistons, etc.

Got it running last season and it ran fine through an entire rank of gas. Took it out this season and ran through a half tank of gas. It ran rough at idle so I figured the carbs needed cleaning. Sure enugh when I took them off the pilots were clogged. Put everything back together and it purred like a kitten.

After the carb cleaning I didn't really bleed the cooling system, which i think may be the issue, but is what I am looking for some expert opinion on...

Anyway, took the sled out last weekend and while riding fairly easy, the sled comes to a stop and shuts off. Seized. Get it home and take it apart and the mag side piston is melted down. The other two look fine.

So, I am hoping it is due to not bleeding the coolant and having no circulation in the coling system. Do you think this is likely the cause, or should I be looking for some other reason for the meltdown? I have a new piston and jug on order but I don't want this to happen again.

The sled ran great after the rebuild and this season until I took the carbs off and didn't bleed the coolant system.

Let me know what you think and point me in the right direction!

Thanks!
 
Post some pics of the pistons, will give everyone a much better idea on what happened.... I am going through through the same thing and mine was a lean meltdown at part throttle with stock viper with good gas or so it was supposed to be anyways...
 
Send some pics of ur piston and jug if you can. The guys on here will want to see that. Just to verify why she blew. Are you saying you didnt bleed cooling system after rebuild or carb cleaning. If you didnt bleed cooling system after rebuild I can see that being a problem but you dont have to bleed system after carb cleaning.
 
I was saying I didn't bleed the system after cleaning the carbs. There is a coolant line that runs through the carbs. Though the switch is in the off position at the PTO head. Does that mean coolant wouldn't be flowing through there anyway?

Now I am really starting to wonder why it melted down.

One other thing, there was never an overtemp light on the guage or any other indication on the guages.
 
If the knob was on off, then yes, no coolant would be flowing. Did you clean the top hat filters in the carbs? How many miles are on the sled? Could be a crank seal also.
 
No I don't think I have done anything with the top hats on the carbs. The chassis only has 600 moiles, but I rebuilt the motor about 100 miles ago. All new seals and rebuilt crank as well.
 
even with the knob off it will still flow coolant from the mag side hose when you pull the carbs off. I usually stick something in the hose (a 1/4 drill bit, not the business end, works well as well as a golf tee) you can lightly clamp the hose with a small pair of vice grips before removing too. I wouldnt think you'd get enough air in there to lock up the engine but I wouldnt say it's impossible.
 
Needles ben moved per specs on many threads? Vipers are prone to lean burn down in mid range. Moving the needles helps alot. Opticool head gasket with original engine rework? I seriously doubt not bleeding coolant system had anything to do with it. The sled rental places had a high amount of engine failures due to inexperienced riders renting vipers and cruising 1/3-1/2 throttle all day.
 
I would put an opticool gasket on and consider raising your needles and or changing pilots. But really before you raise needles or change pilots you need to do plug checks in the mid range and high range to see how it's burning.

After cleaning the carbs did you change out your tank gas? Because what may have been a bad tank of gas might have re-clogged your jets after the cleaning. Just a thought.
 
Needles are most likely stock. I will check them and move them to the #4 position??? I just ordered an opticool head gasket for added insurance. I will also start using octane booster.

Is there a trick to check the rod bearing? I sure hope it is okay as I just spent $500 having the crank rebuilt.

I am also having trouble getting the stuck piston pin out of the burned down piston. Any tricks?
 
There's three basic checks for the rod bearings. First and most important, If you pull away from the crank or push toward the crank is there any play? Play there is bad.

Second, is called big end side clearance (.01 to .03 in). It's essentially the slop between the big end of the connecting rod and the side wall of the crank shaft. You'll need a thickness gauge.

Third, is called the small end free play (.03 to .04 in). It's the amount of play the small end of the connecting rod has parallel to the length of the crank shaft. Maybe I should say "side to side" play. I used a dial indicator to measure this.

There's also the common sense check. Make sure they move without grinding and they should be real smooth.

I'm thinking you may want to either buy a service manual or become a VIP member on this site. If you do the VIP route, a lot of the electronic manuals are available for free with the VIP membership.

I would have guessed that whoever rebuilt your crank would have maybe checked your rods? Not sure.

Not sure about your piston problem. I have some ideas but they're not proven. So, I'll let someone else pipe in. Are you using a piston pin puller?
 
Last edited:
Suprx125 said:
If the knob was on off, then yes, no coolant would be flowing. Did you clean the top hat filters in the carbs? How many miles are on the sled? Could be a crank seal also.
Click to expand...
Where are the top hat filters located? I've had the tops off to adjust the needles, but haven't cleaned any top hat filters. Cleaned the pilots, jets, other passageways, but don't even know where to look for these filters.
 
They are located behind the needle seat. Need to remove the pin for the needle first carefully with a spring punch. Don't break the bridges that the pins go in.
 
SRX_700 said:
They are located behind the needle seat. Need to remove the pin for the needle first carefully with a spring punch. Don't break the bridges that the pins go in.
Click to expand...
Alright, I've had the float and needle out before. Must have missed the screen. Thanks for the help!
 
Ok, here are some pics of the piston. I already sent the jug off for replating so I couldn't get any pics of it unfortunately.

Conditions were maybe around 30F out and easy riding on the trails. A friend was riding this sled and she was probably keeping it around low to mid throttle most of the time.

Let me know what you think and any questions.

Thanks!
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I did bleed the oil pump after I rebuilt the motor.I also ran the first tank of gas with extra oil in the gas during break in.

The carb boots look good and were nice and tight.

I just took apart the carbs and the needles are all set at 3.0 (clip on the number 3 slot from the top and both washers below the clip). I will make sure I change it to the 4.0 position to make it a little richer.

Do you think the needle position and not adding octane boost would cause this lean burndown?
 
I'm guessing that the burn down side is the exhaust side of the piston but I can't tell from the pics.

I suppose it could have been from the needles. Do you know what jet setup your running? Pilots, mains?

I had a burn down where an exhaust manifold leak was the culprit. I hadn't known it but the guy before me had a cylinder reworked and I found that out when I sent it in and they told me it had been in before. I figured out the cause by noticing he had stripped out the exhaust studs and even replaced them with bolts. The manifold ports were not straight across and if you put a ruler across them the mag port was low. So he was giving those studs hell trying to pull that manifold port down and stripped them out.

Not sure if this was the cause but you might want to put a straight edge across the exhaust manifold ports.

Just an idea.
 
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