What is everybody running for pistons in the 800 doo. I have to rebuild one for a guy and was reading alot on this site(3 hours) about single ring or two ring design. Brand x , BRand y, OEM. This guy is not heavy on the throttle just a easy trail rider. The sled was given to him ( family deal) , only 900 miles and this weekend driving at 60 km/h he took out a cylinder and piston. Plugs looked good. From what I can see through the plug hole it might have been a ring caught a port on the exhaust side. This is the PTO cylinder. Haven't ripped any further into it. He would like to get a rough price as to parts and labour cost first. I know there is talk about ring related issues with some of these engines so I was thinking of tearing the whole engine down and going through everything. Just need some input on OEM or aftermarket pistons.

Thanks in advance.

Alot of people us Wiseco but there seems to be some Cold Seize factors with them ( not properly warming the sled up and takin off ) Alot of the guys/gals on this site tend to use Bill Cudney Pistons..OEM..or SPI ive used SPI and Wiseco and had no problems. Also SPI has teflon coating so when the pistons go agian it should help from not scoring so bad. hope this helps.

Grant

Try cudneyracing.com, quality parts and exceptional after sales service.

nitris, lots of ways to build a 800 but from what you've stated, in Canada, order a set of spi's from Royal Distributing. They aren't marking em up as much as some of the shops. Also get a couple wiseco b-1031 wrist-pin bearings and make it easy on yourself (the stock uncaged rollers can be a pita if your not used to them). Order a base .7 gasket from doo. If there is no other damage your looking at about 150-160 US$ for parts to do the whole thing. Canadian dollars?

Thanks guys. I am going to go through the whole engine. Seems like 2003 was a poor year for skidoo. I also read about a mid range lean between 4800 and 6300 RPM, anyone confirm this. I want to check the bearings, seals, carb boots. I am going to tally the cost and give him the worst case possible. I don't want this guy going out and getting another 1000 mile and the same thing happen. His wife looked so depressed, she was looking forward to this winter. Hell if I had my two sleds serviced I would of gave them as a loaner. I guess I have to pinpoint what caused the problem in the first place.

Thanks Again

Nothing wrong with 03's IMO, best carbs and they got the improved pto end seal and some other minor changes. Lean midrange isn't really a problem either, the guys with egts just kind of got freaked out when they saw temps higher than they were used too. If you were to hold it in the midrange under heavy load like breaking 3' of new for miles then it might get hot and you'd want to raise the needle a bit or use the throttle more. The timing is at the peak of its' advance + the clutching (read stiff secondary spring) creates a situation where your running higher rpms at lower throttle setting, this is why they get hot on the mid, for the most part not the carbs fault.

1. Get the Wiseco B-1031 wrist-pin bearings and make it easy on yourself
(the stock uncaged rollers can be a pita if your not used to them).
2. Order a base .7 gasket from doo.[/b]

hillpounder :

1. Do you know of any other make of the caged roller bearing ? ( Here in Sweden we have a bit of trouble getting other stuf then pistons from Wiseco ! :confused: )

2. On different Forums I have read that it exist warious base gaskets for the Rotax 793 / HO mill,
for example that it exsist different shaping of the base gasket and different thickness of them.
Can you tell me some more about this and were to get them.

Which way to go and which not to go..... :whatever:



SWRules

lasse, they are 20x25x23 caged bearings couple others that work:

Yamaha 93310-32009 (think it 98 up srx)

doo 99 formula 670 Z ( that year and model only)


They use different base gasket thickness's to set the squish clearance to a desired measurement at the factory. Variance in parts (mainly the top case 1/2 machining) may have a slight difference that can be adjusted for. How much effort they spend doing this is questionable from what I've seen, but nonethe less.

Rule of thumb is to replace with the gasket it had on it. Think most 800's I've seen had .7 gasket (7 holes). If you want to be technicle on the 800 doo each base gasket thickness will reduce the squish clearance .004", and with change the compression ratio .16:1, and the head volume .53cc.
So you can see where one mayalso use the gaskets to adjust the compression a tad. IN theory there is change in port timing also, but not on a 800 doo, it takes more than a few thous.

lasse,

they are 20x25x23 caged bearings couple others that work:

* Yamaha 93310-32009 (think it 98 up srx)
* Ski-doo 99 formula 670 Z ( that year and model only)

They use different base gasket thickness's to set the squish clearance to a desired measurement at the factory.
Variance in parts (mainly the top case 1/2 machining) may have a slight difference that can be adjusted for.
How much effort they spend doing this is questionable from what I've seen, but nonethe less.

Rule of thumb is to replace with the gasket it had on it.
Think most 800's I've seen had .7 gasket (7 holes).
If you want to be technicle on the 800 doo each base gasket thickness will reduce the squish clearance .004",
and with change the compression ratio .16:1, and the head volume .53cc.
So you can see where one may also use the gaskets to adjust the compression a tad.
IN theory there is change in port timing also, but not on a 800 doo, it takes more than a few thous.[/b]


:) THANX for the information !



Just of curiosity, Why just the 1999 Rotax-670 ? :rolleyes:

It would be very helpful if someone could suply me whith the OEM # for the different base gaskets
for the 793 engine and what thickness they are !

SWRules