Super Jet Stroker Cranks

[masterblaster]

I'd like to point out that you can't really compare the life of an OEM crank with a stroker. Why?
Because you don't check the health of the OEM crank every season or every other season. You just run it until it breaks. And you get lucky for seven years.
th
The stroker crank you consciously check after every season of riding because it was freaking expensive. So you find you should probably replace the bearings after two seasons, just to be safe.

I really don't think you can say that the OEM crank lasted 7 years while the stroker lasted 2 years, and I am pretty sure you can see why.

Ive had a few 6 mil cranks rebuilt and just ran them until they gave up the ghost,riding every other weekend at the time and on average once during the week,they went about 1.5 years at 180 to 195 psi stock timing or tl 30 deg didnt seem to make a diff.I foged them if they swallowed substantial salt water,other wise just flushed on trailer.

Ive also had myself and known many othes with SS big bore high comp motors blow cranks in less than 2 yrs time.almost all fail on the main bearings,for both above mentioned motors. when you start using really large pistons on SS the rod end bearings fail before that.

The only long term motors ive ever owned or seen are close to stock bore,mildly ported under 190 psi,ive got one pushing 8 yrs now and still gets ridden hard time to time.no real power there though,imho with the cost of buying and rebuilding strokers coming so far down in price with adr,there is no point in messing with SS cranks anymore especially with so many having cheap crappy rods that break before the crank bearings even wear out,just plan on rebuilding a stroker every 2 yrs min.this wasnt the case a few yrs ago,they use to be way more expensive than oem SS,now the oem SS has increased crazy high and the strokers are now coming down in price ALOT. its minimal price to pay for this level of power and kinda a no brainer....

4 mill is alrighttttt i guess,better than SS but for a couple hundy extra you can go 8 to 12 mil and keep comp lower and make real power that will last a while,the case work is not that expensive and only has to be done once as long as you dont grenade the motor....things dont get to expensive until you press comp though the roof and start messing with race fuel,everything wears out way faster and god forbid you ingest ANY water at all,crank is toast,maybe everything else too including cases in some scenarios

 

[powerhouseperformance]

Stroker cranks are probably the most misunderstood upgrade parts for our skis. There is more to it then what others have posted, ie if 4 is good 10 is great right? Well that's not really the case. The rod length itself plays a large role in the way the power is delivered. The rod to stroke length ratio is the term used to describe this. If the rod to stroke length is small the piston will experience extreme acceleration velocities and high side loading which leads to early piston failure and rod fatigue. Honda saw it prudent to put a 144mm long rod on 79mm stroke cr 500 to keep piston speeds in check on an engine that peaks rpms in the high 6000's . Contrast that to a similar 78mm stroke 10mm stroker Yamaha crank with kawi based 133mm rods on an engine that commonly has an msd rev limiter set at 8k = piston speeds that are very excesive. Stroker cranks also make port timing more radical. If we have an engine that was ported optimally for a stock 68mm stroke crank and decided to throw a 4+ into it the port timings would get whacked out enough that everything we gained from the stroke would probably be out weighed by the poor porting...especially in the transfers. This is why we use a different cylinder between our ss and our 4mil even though it would fit.

Another element to consider is vibration. Vibration is hp. The violent shaking that those rubber engine mounts are absorbing is energy - all which never makes to the prop. The less vibration that you can make the more power that gets to where you want it and less of it that goes into shaking rubber and beating up bearings.

Bottom line a common 10mm+ stroker 133mm rod crank will have a shorter life span than the smaller strokers will with higher piston side loads and more vibration. For those looking for every little bit of power they can get at any concession the 10mm may be the best choice. For those looking for some longevity there are better choices.

 

[CameronPerdue]

anyone put hour meters on there skis? i come from dirtbiking so when i got my new superjet i put a hour meter on before even starting it

 

[Mentzel]

Yamaha did that,its called the 66E

Dasa Racing Engines

 

[wanderer1]

Dasa Racing Engines

? Can you explain please. Also I'm on my 3rd DASA but I don't see how they apply to the question that was asked that I responded to. The quote you used was in response to a question asked about OE manufacturers. Yet I still don't see where DASA comes into play.

 

[LimitedSlip7]

Who has the best prices on 10mm stroker cranks right now? How much does it typically cost for a crank rebuild?

 

[KTM434]

ADR cranks are reasonably priced
rebuild costs can vary

 

[LimitedSlip7]

$700 to rebuild a crank?! Dang, I was figuring it would be more around the $300-400 range. I guess it depends on what bearings you go with. I might have to figure out how to do it myself if I'm going to be doing it once a year, it can't be that hard.

 

[KTM434]

Shouldn't need to rebuild it every year. Prices will vary budget bearings are for budget cranks and budget engines. What engine are you going with?

 

[N-D-Red]

GroupK.com has great info on strokers and 2-stroke engine theory. Harry has been building engines for a very long time. Whether you agree or not is up to you but it is good reading for gear heads.

 

[scottie mac]

Best post on here.

SM

Stroker cranks are probably the most misunderstood upgrade parts for our skis. There is more to it then what others have posted, ie if 4 is good 10 is great right? Well that's not really the case. The rod length itself plays a large role in the way the power is delivered. The rod to stroke length ratio is the term used to describe this. If the rod to stroke length is small the piston will experience extreme acceleration velocities and high side loading which leads to early piston failure and rod fatigue. Honda saw it prudent to put a 144mm long rod on 79mm stroke cr 500 to keep piston speeds in check on an engine that peaks rpms in the high 6000's . Contrast that to a similar 78mm stroke 10mm stroker Yamaha crank with kawi based 133mm rods on an engine that commonly has an msd rev limiter set at 8k = piston speeds that are very excesive. Stroker cranks also make port timing more radical. If we have an engine that was ported optimally for a stock 68mm stroke crank and decided to throw a 4+ into it the port timings would get whacked out enough that everything we gained from the stroke would probably be out weighed by the poor porting...especially in the transfers. This is why we use a different cylinder between our ss and our 4mil even though it would fit.

Another element to consider is vibration. Vibration is hp. The violent shaking that those rubber engine mounts are absorbing is energy - all which never makes to the prop. The less vibration that you can make the more power that gets to where you want it and less of it that goes into shaking rubber and beating up bearings.

Bottom line a common 10mm+ stroker 133mm rod crank will have a shorter life span than the smaller strokers will with higher piston side loads and more vibration. For those looking for every little bit of power they can get at any concession the 10mm may be the best choice. For those looking for some longevity there are better choices.

 

[masterblaster]

Stroker cranks are probably the most misunderstood upgrade parts for our skis. There is more to it then what others have posted, ie if 4 is good 10 is great right? Well that's not really the case. The rod length itself plays a large role in the way the power is delivered. The rod to stroke length ratio is the term used to describe this. If the rod to stroke length is small the piston will experience extreme acceleration velocities and high side loading which leads to early piston failure and rod fatigue. Honda saw it prudent to put a 144mm long rod on 79mm stroke cr 500 to keep piston speeds in check on an engine that peaks rpms in the high 6000's . Contrast that to a similar 78mm stroke 10mm stroker Yamaha crank with kawi based 133mm rods on an engine that commonly has an msd rev limiter set at 8k = piston speeds that are very excesive. Stroker cranks also make port timing more radical. If we have an engine that was ported optimally for a stock 68mm stroke crank and decided to throw a 4+ into it the port timings would get whacked out enough that everything we gained from the stroke would probably be out weighed by the poor porting...especially in the transfers. This is why we use a different cylinder between our ss and our 4mil even though it would fit..

always enjoy reading your posts,informative. The cr 500 after the brief run of air cooled 84 85 when no one could track them was developed for top end 100 mph plus long sustained desert racing,from 87 on they were looking to make it work better for that purpose and made the rod longer by a 1/8 inch.Even still many used 5.5 stroker cranks in them.cp developed the liger cylinder for that stroke and made it a 630. I had a cr 500 for a while,most people dont realize the power to weight they generate.To this day that motor is used in many competitive carts and sprint cars for its top end performance and torque.We are using stroker cranks in freestyle/freeride applications with little to no top end sustained use so it doesnt seem relevant. I doubt many are ever seeing that 8k tl rpm even with a pfp or sim pipe im sure with your history with the cr 500 motor you already knew that.

I see your logic with the smaller strokers possibly being less maintenance and vibration,guess my question is why 4 mill if your building them from billet and lightening them at a cost of 1k plus.I can see maybe if your making them from stockers for economics as art does. Ive riden many 4,5.6 mill motors,and it seems the 6 mill long rod is the sweet spot for power and less vibration best long term wear. the case work is minimal,im sure if someone is buying a crank over 1k a couple hundred in case work is of no concern,its a easy diy really. would be nice if crank balancing could be done with the flywheel being used to help with vibrations.

 

[623pwr]

Is this why OEM Yami cranks tend to outlast Kawi OEM cranks, due to stroke? I've always heard 68mm cranks are very reliable. Or is it just a bearing issue with the kawi OEMS?

 

[masterblaster]

both use koyo,the kawi is a lil longer stroke

ktm..adr will rebuild their stroker cranks for alot less than 700. you can buy them for that much new

 

[623pwr]

I'm guessing when you get into a bore to stroke ratio above 1.25 its time to stroke for more reliability, due to piston speed? I'm sure there is more to it then that, just curious.

 

[scottie mac]

Speaking as someone who has had stock stroke, 5mm, 6mm and 8mm strokers (all lameys) built by Tim Judge, thery is very little noticeable difference (in fact, I'd doubt anyone would be able to tell he difference) in vibration between a stock stroke to the 8mm. Especially if they are both trued and welded by someone who knows what they are doing.

As for the cr500 rod cranks, both my 6 and 8mms had cr500 rods. My race blaster motors revved in the 7800-7900 rpm range and had as much bottom end hit as anything south of 1000ccs in the free ride community. Just because you are a free rider, doesn't mean you want your motor set up to rev lower. Rpm should be controlled by your index finger, not your ignition or pump set up. Two skis with identical set ups, one revs 7500. The other revs 7850. The one revving 7850 will hit harder because it revs faster with a dry pipe.

Reliability on any crank from stock to 16mm is 50% how well he crank was built and trued and 50% owner maintenance. I've got more time on strokers than probably 99% on here and most of that time was at 7800rpm plus I've never had a crank failure. Wonder why?

SM

 

[Matt_E]

B...b...b...but race motors don't have bottom end!

 

[scottie mac]

^^^^lol^^^^^

SM

 

[623pwr]

So a stroker is going to give the same reliability, just depends on users riding habits and builders quality? If so its good to know, thanks for the feedback.

 

[scottie mac]

Strokers have higher piston speeds, so that can compromise piston life. BUT, longer stroker motors like 8mms have less sidewall stress than a shorter stroke crank. So, in that scenario, they are better for piston life, lol.

Long story short, if you want performance, you are going to have to pay for it either way. Either in rebuilds of cranks or top ends. The way I look at it is, get yourself a good, reputable builder, follow that persons directions and take care of your $hit. ANY motor can have a failure, but user error or hack builders are usually the biggest reason why riders have them.

SM