SPI vs. Wiseco Pistons

[Arctic37]

Do any of you guys use SPI pistons. It's time to do a rebuild on my 900 Thundercat and I want to get the most reliable pistons and rings for a stock engine. I'm torn between saving a little money on SPI's or spending a lot more on Wiseco's, but when it comes right down to it I want a good strong engine. Thanks, have a good one.

 

[powderpusher]

Id recommend weisico as ive been using them on all my rebuilds and they have never given any problems my theory is that a lower price is probably lower quality product when it comes to engine parts

 

[maxwell]

forged vs cast

wisecos are a way better piston. way less imperfections being forged

now they are a little tight.

so..

you need to take your clys and pistons into a machine shop (motts/cydle works)

and have them properly fit and clipped

other wise it will squeek on you if you use wisecos

ive built countless motors with wisecos and not one has blown yet 6000+km so far on some.

 

[Arctic37]

forged vs cast

wisecos are a way better piston. way less imperfections being forged

now they are a little tight.

so..

you need to take your clys and pistons into a machine shop (motts/cydle works)

and have them properly fit and clipped

other wise it will squeek on you if you use wisecos

ive built countless motors with wisecos and not one has blown yet 6000+km so far on some.

Are you talkin' about having the ring ends gapped properly when fitted into the cylinder? Not quite sure what you meant by "fit and clipped"

 

[maxwell]

well your cyls will need to be honed or bored to remove any damage or uneven spots

not sure what they do to the rings..they call it clipping i dont know

either way from the 1010324098324 posts about wisecos letting go it was from not having a machine shop take a look and makign them fit properly

 

[ZRrrr]

Wisecos expand at a different rate than the cylinders. Hence the need for proper cylinder wall to piston clearance. Proper engine warm up is critical and a slow beginning when finally on your way. Many guys drop in Wisecos, fail to warm up properly or hammer the throttle when time to ride, only to squeek.

I have used SPI pistons several times with no issues whatsoever.

 

[Modman]

Wisecos expand at a different rate than the cylinders. Hence the need for proper cylinder wall to piston clearance. Proper engine warm up is critical and a slow beginning when finally on your way. Many guys drop in Wisecos, fail to warm up properly or hammer the throttle when time to ride, only to squeek.

I have used SPI pistons several times with no issues whatsoever.

Go to this link and read in the information supplied. Get the SPI's IMO, wiseco's are just not worth the few $$ saved. They are not a better piston.

Why do you pay $150 each for cast pistons compared to $90 each for a forged? - you know the answer.

https://www.snowandmud.com/forum/f55/king-cat-pistons-5848.html

Cast vs forged - forged not as dimensionally stable, hence the greater piston to cylinder wall tolerance.

You can run Wiseco's (or any other forged piston) and make them last for years, many people have. But they need to be warmed up properly each and every time. Just remember that if you get them.

 

[maxwell]

they are more expensive than spi?

 

[YellowMissile]

Go to this link and read in the information supplied. Get the SPI's IMO, wiseco's are just not worth the few $$ saved. They are not a better piston.

Why do you pay $150 each for cast pistons compared to $90 each for a forged? - you know the answer.

https://www.snowandmud.com/forum/f55/king-cat-pistons-5848.html

Cast vs forged - forged not as dimensionally stable, hence the greater piston to cylinder wall tolerance.

You can run Wiseco's (or any other forged piston) and make them last for years, many people have. But they need to be warmed up properly each and every time. Just remember that if you get them.

(This has been borrowed from another board)

Forged pistons are more durable than cast pistons will ever be. Cast pistons are very brittle, and are prone to skirt breakage as a result.

For riders that will take the time to do a proper break-in, and will discipline themselves enough to fully warm their engines before each and every ride, Wiseco pistons are a superior product to OEM. They are more durable under high-heat high-load conditions, less prone to skirt breakage from piston slap if the bore has a bit too much wear on it, and longer wearing than any cast piston will ever be.

Cast pistons don't require much in the way of special break-in, that's part of the reason they come as OEM equipment in two-strokes. Forged pistons, on the other hand, are a different story. A forged piston must be heat-cycled before it can be run hard, or you're playing roulette with your engine.

A new forged piston has to be heat-cycled several times to relieve the internal stresses left over in the metal from the manufacturing process. If this isn't done properly, the piston will distort and become out-of-round, causing it to wedge itself into your cylinder, more commonly known as a "seizure". A seizure with a two-stroke isn't a very dramatic occurrence, usually the engine just stops running. You re-plate the cylinder, rebuild the top-end again, and you're back in action. On a four-stroke, however, a seizure is often catastrophic. The four-stroke has more rotating mass, which creates additional inertia. So, when the piston seizes, the rest of the engine tries to keep spinning. The result is, more often than not, a snapped connecting rod, broken crank, and destroyed cases. A big bill usually follows.

To better understand why forged pistons are more seizure prone, you need to understand what makes a forged piston different than a cast piston.

A cast piston is manufactured by pouring molten metal into a mold. The final shape is machined to it's final exacting tolerances.

A forged piston is made by taking a chunk of metal, and beating it into shape with a die-press under enormous pressure. Like casting, the final shape is achieved through precise machine work.

The main difference between a cast and forged piston is the grain structure. A forged piston is beaten into shape, and as a result the metal stretches and compresses as the piston takes shape. The varied, elongated grain structure is like fiber reinforcing, and it makes for a very strong piston. Microscopic cracks don't readily propagate through the structure of a forged piston due to the high density and the irregularly spaced and sized grains. A cast piston, on the other hand, is made up of grains that are all the same size, because it starts out as a liquid that, after being poured into a mold, undergoes a controlled cool-down process that allows the metal to reach a near-perfect equilibrium right out of the mold. The highly regular grain size and distribution makes them more prone to crack propagation and failure.

The break-in of the two types is very different, because the metal properties are very different. The forging process produces a lot of internal stress from beating the metal into the intended shape. The stress is trapped in the metal of the finished part. A cast piston has lower internal stress, because it was able to seek it’s own internal equilibrium as the liquid metal flowed around inside the mold and then underwent a controlled cool-down. Since a cast piston has lower internal stress, it won’t distort nearly as much as a forged piston will when heated to a high temperature. The forged piston's propensity to distort when heated is the reason they require an elaborate break-in procedure.

To relieve the internal stress, and maintain it's correct shape, the forged piston has to go through a series of heating and cooling cycles. As it heats up, the grain structure will re-distribute itself into alignment to relieve any trapped stress. As it cools, the cylinder will contain and restrain the piston, maintaining it's shape. After a few heat/cool cycles, the internal stress reaches equilibrium, and the piston will no longer distort when heated in the engine. It will maintain it's shape for the rest of it's life.

Forging produces a higher grain density than casting, making the part much more durable under high-heat, high-load conditions. As long as you are patient enough to break a forged piston in correctly, you will have a piston that is more durable under extreme conditions.

Problems with Wiseco pistons are almost always caused by one of these three issues:

1. Improper break-in-This can be a death sentence for a forged piston.

2. Improper warm-up-A great way to cold-seize the engine. This also kills crank and rod bearings, not just forged pistons.

3. Cylinder-to-piston tolerances too tight-You can't just slap a Wiseco piston into a brand new engine with no time on it. Forged pistons require about .002" more cold clearance than a cast piston. Once it's time for the first top-end job, a cylinder will usually have loosened up enough for the forged piston to have enough clearance. Most Japanese two-strokes spec .002"-.004" clearance for the OEM pistons. Wiseco specs .003"-.005" clearance.

Another less common cause of problems with all pistons is when the person doing the top-end work doesn't drill the lube holes in the piston for an engine with a central exhaust bridge. A forged piston will actually tolerate this better than a cast piston.

Anytime you rebuild the top-end, you have to measure the ring end-gap, and file the ring ends if neccessary. I rarely have a set of Wiseco rings that don't need to be relieved slightly. If the end-gap is too tight, the ring ends will hammer the locator pin right out of the piston, with devastating results. Wiseco specs .004" per inch of bore size for their ring end-gap clearance.

All of these problems are caused by the mechanic that does the work, or the rider that's too lazy to perform a proper break-in or proper warm-up. You can't blame the product for your own incompetence (although that's usually what people do).

 

[Arctic37]

Thanks for all the info everybody. I learned the hard way with a '94 Wildcat I have how important warm-up time is. Now, when I start my sleds I let them warm up while I put my ridding clothes on, usually by then the tops of the heads are starting to get pretty warm. Even then I try not to get on it hard until I'm sure it's nice and warm. Have a good one, again thanks.:d

 

[tom29]

go with cast.
forged is softer material and expands easier which causes it to squeak and with softer aluminum it smears all over the cylnder wrecking nickasil. even with the proper machining my buddies bike burnt down after 15-20 hours of riding had a more than sufficient break -in. Have seen MANY wisco piston motors burn down in a couple hundred miles. true enough about cast being more brittle, but just like any piston, if there is too much piston clearance its gonna rock and bust the skirt. cast will outlast the forged and you wont have to do a 35 hour break-in period haha
i run cast SPI and gave my motor maybe half hour-hour idle and 5miles with lots of oil. after that ride er hard. try that with a wisco and you'll be calling the chopper after lunch time. factories run it for a reason, it WORKS

 

[maxwell]

factories run it because its dummy proof. for warranty. if they knew damn wel they could get more miles out of there motors going forged they would except for....

NO ONES GONA BREAK THEM IN PROPERLY = WARRANTY ISSUES

i dont know that i agree with you...my wiseco motors are outlasting stocker motors...im talking 08 and 09 sleds here to.

5000km beat to death with nitrous and overrev. pipe the works

155 psi still? within 1 psi of eachother. cant beat that.

 

[Modman]

(This has been borrowed from another board)

Forged pistons are more durable than cast pistons will ever be. Cast pistons are very brittle, and are prone to skirt breakage as a result...............................

.......All of these problems are caused by the mechanic that does the work, or the rider that's too lazy to perform a proper break-in or proper warm-up. You can't blame the product for your own incompetence (although that's usually what people do).

That post sounds like it was borrowed from the Wiseco website. Like I said, run whatever you want, just make sure that if you use Wiseco's you warm them up.

Personally, I'm not a big fan of Wiseco's. They are not a superior product IMO. Anything that requires more clearance to accomodate a larger expansion of the piston means more chance of seizure and more chance of things going wrong. They are not as dimensionally stable as a cast piston which means they will not maintain their shape as well, they will distort, even with a proper break in procedure. Forging a piston - you cannot forge the intricate webbing into a piston that you can into a cast piston. So cast is more brittle - this only becomes an issue if the piston to cylinder clearance becomes too great, then you risk the chance of snapping a skirt. This is not a function of the piston, its a function of the operator and neglect to inspect the motor. Any piston will fail if subjected to this. Wiseco's just don't snap the skirt off, they will just bend the skirt of the piston or wear more in that area.

My cast pistons have 7000 + km's on them and only now am I thinking about swapping. Not because they are worn out completely but they are getting close to the tolerance limit, in reality they might go another 2000 kms though if I wanted to push it. I will end up swapping them before next season as I already have the pistons on my bench though. Run hard with twin pipes and lean jetting all the time. I have seen more motors fail with Wiseco's than any other piston manufacturer. This is just my thoughts on it.

Run what you want.

 

[maxwell]

i think it was a post on doo talk

i was looking for it actually

 

[Scrambled]

I just got back from Sicamous were I chatted with quite afew guys about this subject and most recomended not useing Wiseco's,most recomended stockers unless you boring it out,this surprised me since in my dirt bikes they worked great.but they figured it was because snomobiles have alot of heat cycles in one day compared to bikes,just thought Id pass that on to you.

 

[maxwell]

once again

in the morning WARM IT UP WELL make sure it does not idle high, flip the choke or wahtever

if you stop for a minute or 2 let it run for a couple seconds before booting it!!

most people "OH I LET IT WARM UP REAL GOOD"

takes 20 minute break....

HAMMERS ON THE THROTTLE

seizes

go figure


you need to be carefull with them but they are BULLETPROOF

 

[YellowMissile]

I agree run whatever you want.. but a cast piston is in no way more "dimensionally stable" (stronger) than a forged piston. I am new to the 2 stroke game and cannot comment on the reliability of wiseco vs stock argument, but have been building high horsepower small/big block engines for years and it is universally accepted that forged components are stronger and more durable than cast. This does not only apply to pistons but also connecting rods, cranks and pretty much anything that can be forged versus cast. It has to do with the stresses of the manufacturing process that the inherent strength is created, in fact certain parts can be further strengthened by "shot peening" them, (a process of adding stress into the metal by compressive force). Manufacturers like ski-doo do not use these processes as they are more expensive and the extra strength is deemed unnecessary for the application. Like everyone is saying.. run whatever you want but in my opinion a cast component is inferior to a forged one in terms of strength and ductility.

 

[summitx]

Rebuilt my last sled with WISECO's and wouldn't hesitate to do it again. Like everyone says though.... WARM IT UP properly. This is the case with any engine but how many guys do you see pull the cord in the lot then wheelie away from the trailer / pin it up the trail. After my build the sled had better compression and pulled a lot harder. Took my time breaking it in and never looked back.

 

[tom29]

sometimes they work sometimes they dont. guess it all depends on the rider and how they ride. i my self would run a forged piston in a smallblock v8 or big block. but in a car/ truck motor you arent holding 8100 rpm for a 30-45 second pull. motor is going to build alot of heat in that much time which is where i think the forged piston will expand and sqeak. they probably will fell slightly better cause of the lighter forged piston, but i wouldnt trade reiability issues for a .5hp
if the wiseco's worked for you then great, nothing better than strong running motor. but i dont think id rather spend the extra time and money on a piston which IMO, is no better than a stock one. i would rather break it in for an hour or two and few miles up trail then 2 or 3 tanks of fuel.
Run what you want, as long as it works

 

[summitx]

Wiseco rebuild cost me just over 400.00 for parts. Pistons, rings, bearings. Stock pistons were over $200.00 more for same thing. Again like most things in life it is personal preference. I'm not sure one is any better than the other and you will always find someone on both sides of the story. My opinion do what you are doing, research ask what other riders experienced and then make a decision on what is best for you.