TA 5.7
Guest
I am woundering if anyone, or are there any different types of pistons I can use in this engine. I am using Wisco 73 mm, but not having much luck with them. I do not like these pistons. Even with proper break in, proper warm up, they are not reliable. I use, and race other big bore sleds, and have no trouble, including full mod sleds. Just woundering if a arctic cat 73.4mm piston would work, and should I get the cylinder sleeved.
staggs65
Moderator
what kind of problems are you having exactly?
they are reliable but theres alot of things that can make them not reliable, like piston skirt to cylinder clearance. Whats that spec your using?
be a little more specific on your problem and we can help.
There isnt another piston for the bore unless you run a cat piston but youll need a spacer plate made up because the compression distance on the piston is differnt, youll also have to reset up the cylinder heads.
there would be a need for a sleeve on anything more then 73mm in my opinion, beyond that your just too thin on the material left. Then going to a steel sleeve its not going to wick the heat away from the piston as quick, so youll need more jetting(richer) and correct ign. timing will be more of a concern. Stepping backwards in my opinion.
be a little more specific on your problem and we can help.
There isnt another piston for the bore unless you run a cat piston but youll need a spacer plate made up because the compression distance on the piston is differnt, youll also have to reset up the cylinder heads.
there would be a need for a sleeve on anything more then 73mm in my opinion, beyond that your just too thin on the material left. Then going to a steel sleeve its not going to wick the heat away from the piston as quick, so youll need more jetting(richer) and correct ign. timing will be more of a concern. Stepping backwards in my opinion.
TA 5.7
Guest
The problem I am having is that the piston skirt will have some skuff marks and the piston rings will slightly stick. I am wondering when this happens if the engine is actually getting to hot. The top of the piston is ok. Not at all lean. I had the cylinder redone with matching piston and when this happens it will put a hair line crack in the exhaust port on the pto side. This has happened twice to the same cylinder. When I rebuilt the engine I even let it heat up and cool down 3 times before using. When this happens it seems it does it on 1500 to 2000 feet runs, regardless the temp. These sleds are reliable for long than that, but most races are only 1000 feet. But now I am affaird to go any further than that. I have tried bigger jetting, big enough it would bog off the line. It's also running bored carbs and different cdi box. Its all from CPR. When it works the sled runs great I am pleased, I am just nervous it wll happen again.This is not like these reliable srx's. Stock form they are great, It was raced 3 summers on ashault without any problems, its a 2002 and I bought it new. What water temp should it run and what piston clearance should I have?
Rings sticking is a sign of heat. cracking at the triple port is heat and light seizure related.
just a bigger main jet usually doesnt fix the problem, you usually always need to address the needle.
you need to remember that added timing in a 2 stroke adds heat to the piston, so this is adding to your problem, again, you likely need to address the needle. bored carbs will flow fuel differntly then stock ones will.
Its not likely the problem, but dont run a lean oilpump with a 780, stock is good or slightly lean if your running very good synthetic oil like amsoil, etc. I only go about 1/2-3/4 a mm leaner then stock on a 780.
I like to see water temps of 70-80 degrees before you go out whoopin on the sled. The wiseco pistons expand quickly and they are harder then the cast cylinder is, any little bit of detonation rattling the piston and they will break off the skirts, or if temp is cold they will cold seize easily. A 780 needs to owned by a disciplined rider for sure.
I believe most of your problem lies with the needle settings in the carb and the cdi box. If your doing 1000ft speed runs, it will go faster with the stock box. The other box is a viper box and the added timing is good for drag racing 500-660ft after that its actually not helping you. Again added ign timing adds heat to the pistons, retarded ign timing adds heat to the pipes... you need the pipes to be at "X" center core temp to have the engine pull the correct top peak rpm/power.
just a bigger main jet usually doesnt fix the problem, you usually always need to address the needle.
you need to remember that added timing in a 2 stroke adds heat to the piston, so this is adding to your problem, again, you likely need to address the needle. bored carbs will flow fuel differntly then stock ones will.
Its not likely the problem, but dont run a lean oilpump with a 780, stock is good or slightly lean if your running very good synthetic oil like amsoil, etc. I only go about 1/2-3/4 a mm leaner then stock on a 780.
I like to see water temps of 70-80 degrees before you go out whoopin on the sled. The wiseco pistons expand quickly and they are harder then the cast cylinder is, any little bit of detonation rattling the piston and they will break off the skirts, or if temp is cold they will cold seize easily. A 780 needs to owned by a disciplined rider for sure.
I believe most of your problem lies with the needle settings in the carb and the cdi box. If your doing 1000ft speed runs, it will go faster with the stock box. The other box is a viper box and the added timing is good for drag racing 500-660ft after that its actually not helping you. Again added ign timing adds heat to the pistons, retarded ign timing adds heat to the pipes... you need the pipes to be at "X" center core temp to have the engine pull the correct top peak rpm/power.
TA 5.7
Guest
This is very helpful info. Yes this is something I planned on trying by putting on stock cdi box. With my 1000 hooper timing and hot pipes are very imporant like close to 20hp and pulling different rpm's. My needles are as rich as they can go from day one. Almost to rich for trail riding. The slelf is out of the air box as will, it was recommed by Jeff. I did put it back in to see if it made a difference. I think my problem is to do with heat. What shoud be a operating temp, piston clearance,and how much timing does this cdi accually give me. 2 to 3 dergrees can mean alot.
like to see .004-.0045" piston to cylinder clearance.
water temp should be around 125-128 operating for your run, the stock thermostat opens at 112-120. Theres guys who will remove the stats to make the engine run cooler but with wiseco's the cylinders need to be warm, not hot but warm. I am assuming you have a water temp guage, whats your average temp?
you can always change the needles, go to a differnt taper(richer) and then you can likely back off the main jet.(lots of racing set ups will be a large pilot jet, big needle with small main.)
timing is like 9 degrees at 8500rpm with stock srx cdi, the viper box is 18 degrees at 8500rpm.
does your cdi box have the letters 8EK on it? or just hand engraved simons cpr on it with all else ground off?
one thing I will say is just the change to differnt ign timing will change the ENTIRE fuel curve, the sled will go instantly over rich with less timing and have better topend. check the box and report back.
water temp should be around 125-128 operating for your run, the stock thermostat opens at 112-120. Theres guys who will remove the stats to make the engine run cooler but with wiseco's the cylinders need to be warm, not hot but warm. I am assuming you have a water temp guage, whats your average temp?
you can always change the needles, go to a differnt taper(richer) and then you can likely back off the main jet.(lots of racing set ups will be a large pilot jet, big needle with small main.)
timing is like 9 degrees at 8500rpm with stock srx cdi, the viper box is 18 degrees at 8500rpm.
does your cdi box have the letters 8EK on it? or just hand engraved simons cpr on it with all else ground off?
one thing I will say is just the change to differnt ign timing will change the ENTIRE fuel curve, the sled will go instantly over rich with less timing and have better topend. check the box and report back.
I wouldn't run that box over 660'.Been there done that.
TA 5.7
Guest
Yes, I really think this could be one of my problems. If this is the right timing than that is way to much for longer drags. This would create more heat than needed. By looking at the plug readings the jetting should be safe, especially when I replace the cdi box. I did have to change the wires going into the cdi box. My temp did read higher on different trails but I would put snow on the running boards. I have a new gauage for this winter. Would case porting work on this machine? I still use it on the trails sometimes. It is still running stock or close to stock compession.