New to the "connection". I have a 1994 400L that I bought as a basket case. The oil injection pump had failed - the roll pin that holds the drive gear on the bottom of the shaft broke. The gear would no longer turn the pump and without lubrication the piston rapidly welded itself to the cylinder. The roll pin is a poor design with serrations at the split providing multiple opportunities for stress riser failures. I had no experience with these engines but have rebuilt various engines in the past so I gutted this thing down to the crankshaft and started over. During the process I bought the spanner socket for the odd nut on the right side of the crank and fabricated a puller to remove the counterbalancer. No expense was spared to do it right. I bought a new oil injection pump and replaced the factory roll pin with a hardened spring steel roll pin and installed the gear on the shaft with stud and bearing mount to insure the same type of failure could not re-occur. The engine was assembled with all new bearings, seals, etc. Based on all the horror stories I had heard about the factory cast pistons cracking I put a forged wiesco piston in this so I would not have to worry about the skirt coming off and ending up in the base. The cylinder was so torn up it had to be bored to 0.060 to clean it up properly - it was already at 0.020 when I got it. Wanting more performance I cleaned up the ports - the liner to cylinder fit was particularly bad. I corrected the loss in port timing that occurs on these cylinders with overboring by raising the roof of the transfers and exhaust port back to stock dimensions. Having little experience with aftermarket pipes on these machines I ended up with the Hot Seat pipe and clutch kit ( at the time it was the only one I was aware of that would fit this model). The piston to cylinder clearance was set to 0.004. After rejetting to a 260 main (34mm stock carb) and changing the jet needle from a 6DH29(stock) to a 6CEY6 ( more taper and more fuel at part throttle) the unit was gently broken in by my wife. I did not trust myself to keep from pinning it right away. I have owned engines with wiesco forged pistons before and understand the difference in their expansion characteristics versus cast pistons and have always allowed the engine temp to get up to at least 100 F before really getting on the throttle. I put about 250 rather troublefree miles on it in mixed conditions with many drag races as well as towing the kids around on a sled in the winter. The performance was vastly improved over stock and the thing would easily outrun my buddies stock 660 grizzly. After the 250 mile mark it seemed to be slowly losing power (compression was down to 100 psi) so I pulled it apart again. There was evidence of a mild seizure with scoring of the piston and the cylinder. All of the damage was in the section of the cylinder where the rings travel. Very little damage down low on the piston (no marks in the piston skirt). The rings were partially stuck in the ring grooves. Clearance was up to 0.009. To me it looked like I might have cold seized it when I was towing the kids around on the sled. In winter conditions it is not easy to build heat in the engine. I am committed to putting the thing back together and solving it's current problem. I have discussed this with two different reputable Polaris dealers with different results. One dealer refuses to use stock pistons due to the cracking issues. The other swears that the factory piston is the finest piston you can buy for the Polaris engine and that the cracking issues do no show up until piston to cylinder wall clearance exceeds 0.007. At that point this dealer says the harmonics resulting from piston slap are what cause the skirt cracking. I have one more bore left in this cylinder but have considered buying a new style cylinder (98 and up type) and going back to the stock piston. I ride in all types of weather conditions down to about 20 degrees F and do not know if the inherent thermal expansion characteristics of the forged piston will tolerate the vast difference in temeratures. And yes I went up one jet size to a 270 and raised the jet needle one clip position for winter conditions. I would appreciate feedback from people with experience with this engine with trail pipe combo in particular opinions on tuning/setup and stock versus forged pistons.
Thanks,
Mech

 

Welcome to the forums.....I would go with a Wisco piston. They say that the polaris piston is bad for breaking the skirt off.

 

Welcome again,I have always used a Wiseco in my 02'400.I used the stock piston and two wiseco's on the stock bore.They were always replaced when the jug came off for various engine mods.I finally bored it 0.10 to clean it up last month.My engine builder(Rick Ritter)told me that I must use good oil and keep the air filter very clean.There was no scoring what so ever.This bike is used for drag racing only.I generally ride it wide open all day.Never had any problems.This is on a 75-85 hp engine.Again,welcome to the forums.[img]i/expressions/face-icon-small-smile.gif[/img].

 

Wiseco Baby! [img]i/expressions/face-icon-small-smile.gif[/img]

 

You didn't say what oil you're using but, as 401 mentions Rick Ritter telling him, good oil goes a long way. Definately use synthetic. I use nothing but Amsoil although other synthetics are also good. Synthetics are especially helpful at temperature extremes as they flow better when cold and don't break down when hot. Also be sure the injector pump is adjusted properly. These things use very little oil so you can err on the rich side a little. And of course use premix as well in the first tank on a fresh motor.

 

go w/ Wiseco, stock Polaris pistons suck

 

Forgot to say what oil,Polaris Gold mixed at 32:1,premix.

 

I read some where that if you overheat the motor the cast iron sleeve could become softer thus shorting the life of new rings and piston. i had a neighbor with a 250 trail boss and he had a similar problem fresh rebuild only lasted a few months. He rebuilt again and now were waiting to see if it holds up. If not were going to resleeve it. And he did use a wiseco piston the first time second time he went with something made in china. I have a wiseco in my scrambler and 2 in my ski doo no problems yet.

 

Thanks to all for reply. I am running Polaris "gold" oil and ran the first ten gallons of 92 octane gas pre-mixed with "golden spectre" at 50 to 1 in addition to the oil injection. As I said in my initial post there is virtually no damage to the piston or the cylinder above or below the region of ring travel. When I got the machine as a basket case with non functional oil injection there was severe damage to both piston and cylinder- not just in the area of ring travel. For me that kind of rules out lubrication or dirt injestion as the cause of the malady. It looked as if the top of the piston swelled from excessive heat growth in a cold cylinder. The rings show evidence of damage where the ends butted together as if clearance was insufficient. I feel certain that I hurt it towing the kids around at less than 5 mph at less than 1/4 throttle in 20 degree weather. If this occured as a result of cold seizure that would mean I would have to limit or give up using the beast in the winter or go back to a stock cast piston. If not it means my set up is not tuned right. I am confident that if I don't change something in the set up and just put it back together with new parts it will kill itself again in cold weather. Is 0.004 piston to cylinder clearance proper for a wiesco forged piston in one of these engines? With the current stock 34mm carb jetting of 260 main(summer) 270 (winter)/jet needle 6CEY6 (clip in 2nd from top)/needle jet 0-6(480) the engine if anything is on the rich side from 1/4 throttle through wide open. It seems very happy when on the throttle. I have run it wide open for extended distances approaching 70 mph and it will not even run hot. The part throttle from idle to 1/4 throttle has been another matter. I have tried to run various needle profiles at different clip positions in an attempt to get it to carburate cleanly. All of the needle profiles I tried appear to be very similar in taper from the starting point to 1/4 throttle and get different from there. I have been forced to run every needle I tried with the clip in the second from the top position (one lean from center) just to get it to run clean enough to be rideable. If I burnt it up because of the set up it was because it was too lean in this throttle range. The only thing I can think of left to try would be a different needle jet to meter more fuel in the idle to 1/4 throttle range or shim the needle position in the slide barrel to be able to split hairs between the 2nd and 3rd clip positions. Has anyone out there sucessfully run a similar combination with forged piston in the cold weather? Any suggestions in altering the set up to make this thing live?
Thanks,

 

The very first top end that i did on mine i found the stock piston skirt was cracked ,i have been running the hell out the wiseco pistons since and never had a problem with the pistons.I was using polaris gold mixed at 32:1 and i now run alky with maxima 927 mixed at 28:1.