Opinions on stroked 426


43 replies to this topic
  • yz454

Posted February 16, 2005 - 04:45 PM

#21

Ha guys there is no spacers and long cam chains needed , unless you go long rod.

  • YZDAD1

Posted February 16, 2005 - 04:53 PM

#22

I would think if you wanted to go economically the stock head is fine. Also, are you looking to bore and stroke? Poweroll did not recomend the both of them together but being the "adventurous type" that I am I went with both since I was looking for the best bang for the buck. Poweroll likes to clip the lid of the stock piston 1mm (crank goes up 1mm and down 1mm = 2mm increase in stroke) Anyway, I thought that to be more of a reliability issue than an increase in bore and a good piston. By the way, the cost from Poweroll for the work is the same price with or without the piston machining!?!That part I was a little unhappy about, I guess they machine the piston for free :) ! Anyway, Cometic gasket company made me a thin aluminum spacer that I sandwiched between 2 base gaskerts and it created a leak free factory like installation. You really have to look hard to see the shim between the gaskets. It will make all your riding buddies with there newer 450's really twist their throttles to keep up! :)

p.s. PM me for my low buck recipe to make this happen for minimal $$ :p

  • 642MX

Posted February 16, 2005 - 05:05 PM

#23

when you go with a hi-comp piston, 13.5:1, do you need to do any jetting changes?


I didn't change my jetting. I just wish the piston slap would go away.

Has anyone else used a Wiesco 13.5:1 and heard more piston noise than with the stock piston?

  • grayracer513

Posted February 16, 2005 - 05:28 PM

#24

Poweroll likes to clip the lid of the stock piston 1mm (crank goes up 1mm and down 1mm = 2mm increase in stroke) Anyway, I thought that to be more of a reliability issue than an increase in bore and a good piston.

I took that approach with a Chevrolet V8 that I did a quarter inch stroke on some years back, having .112" cut from a set of forged dish tops. It worked out fine.

There are two things to consider in using that method to correct the deck height. The first and most obvious is whether there is enough material available in the piston crown to support that reliably, and whether the valve clearance cutaways will have to be deepened. This can be rather difficult to determine absolutely, and ends up being a sort of educated guess.

The other issue is that doing this moves the top piston ring closer to the top of the piston. Part of the reason the top ring is positioned as far down the piston as it is is so the piston crown can shield it from direct exposure to combustion gases by virtue of the tight space created between the piston and cylinder above the ring. Moving the ring higher increases its exposure, and can result in carbon or sludge deposits in the ring groove. I doubt that 1mm would have a very big negative effect, though.

  • cowboyona426

Posted February 17, 2005 - 09:46 AM

#25

So, judging by this I'm guessing you did not have them machine the top of the piston down? Economical is always better! :p I wonder what the difference would be in the bored/stroked motor with a stock head? How much time did you have on your bored/stroked motor? This is something I may look into seriously this summer :)

Sent you a PM YZDAD :)

  • YZDAD1

Posted February 17, 2005 - 02:13 PM

#26

No, I did not machine the stock piston down, I used a JE in this particular engine. I had plenty of time on this engine, my Son raced it in the 250 / Open Novice class and practice rode it on our practice track. If it was unreliable, we would know by now! :)


"642MX" your "piston slap" may not be as much piston to bore slapping as much as "piston to head" hitting with your high compression setup. There real close, check it out.

  • HyBridYZ426

Posted February 17, 2005 - 03:47 PM

#27

lots of good info...I just took my motor out and am going to clean it up/refresh it..i was thinking of going with new rings till i seen this...I think I will have to save more b4 I get in to it now....Please post more info on any thing else thats bang for the buck! :)

  • bushy

Posted February 17, 2005 - 03:54 PM

#28

Makes me wish I had a job + money.

459 cc with the same reliability? I'd be there in a heartbeat :) :) :p

  • ISBB

Posted February 17, 2005 - 05:59 PM

#29

No, I did not machine the stock piston down, I used a JE in this particular engine. I had plenty of time on this engine, my Son raced it in the 250 / Open Novice class and practice rode it on our practice track. If it was unreliable, we would know by now! :)


"642MX" your "piston slap" may not be as much piston to bore slapping as much as "piston to head" hitting with your high compression setup. There real close, check it out.



I thought the higher compression pistons just changed the shape of the domes and not the size of the piston??? if this was true then he should not be slapping the head w/ his piston unless its a stroker... please do correct me if im wrong..

  • YZDAD1

Posted February 17, 2005 - 07:09 PM

#30

I thought the higher compression pistons just changed the shape of the domes and not the size of the piston??? if this was true then he should not be slapping the head w/ his piston unless its a stroker... please do correct me if im wrong..



Your partially correct, the domes are "bigger" (more volume) and take up more of the combustion chamber space. But, the aftermarket parts that we install in our "hot rods" are small production run components that may or may not match entirely to factory specs (even though they are high quality parts). I know that if a base or head gasket is a little thinner or a piston has a slightly different compression difference you can have the flats of the piston (or dome) smacking, tapping or "kissing" the head. This make an audible sound , mostly at idle that most take for granted as piston slap. And sometimes it goes away when the engine warms up because the piston swells up and stabilizes in the bore (less rocking) and the aluminumn engine itself can slightly grow and the noise subsides. Most hard core race engines have the piston to deck "cozied up" and will actuall touch slightly or be close enough that carbon never forms on the deck surface of the piston and head. The actual touching usually occurs during the overlap stroke as this is when the piston dome is unloaded, when the piston is on compression the actual compressing of the oil film, bearing clearance, rod deflection etc. allows the piston and head not to touch. Whew! :)

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  • 642MX

Posted February 18, 2005 - 02:28 PM

#31

Your partially correct, the domes are "bigger" (more volume) and take up more of the combustion chamber space. But, the aftermarket parts that we install in our "hot rods" are small production run components that may or may not match entirely to factory specs (even though they are high quality parts). I know that if a base or head gasket is a little thinner or a piston has a slightly different compression difference you can have the flats of the piston (or dome) smacking, tapping or "kissing" the head. This make an audible sound , mostly at idle that most take for granted as piston slap. And sometimes it goes away when the engine warms up because the piston swells up and stabilizes in the bore (less rocking) and the aluminumn engine itself can slightly grow and the noise subsides. Most hard core race engines have the piston to deck "cozied up" and will actuall touch slightly or be close enough that carbon never forms on the deck surface of the piston and head. The actual touching usually occurs during the overlap stroke as this is when the piston dome is unloaded, when the piston is on compression the actual compressing of the oil film, bearing clearance, rod deflection etc. allows the piston and head not to touch. Whew! :)



The noise happens at low idle and then at mid throttle. Hot or cold makes no difference. I checked the rod, it seemed tight. I also went with a hot cams 450 exhaust cam when I did the rebuild. I had to reshim the exhaust side after the cam install ( yes, the valves are all in spec) and I replaced the cam chain.

I have no clue what this noise is, I'm guessing piston slap (Weisco quality :) ) I thought it could also be the tensioner not holding the chain correctly or the auto decompression device in the cam?? What do you all think it could be?

  • ISBB

Posted February 18, 2005 - 02:41 PM

#32

so whats a good way to ensure that they wont touch...... Im sure prolonged KISSING of the head cant be a good thing...

  • YZDAD1

Posted February 18, 2005 - 06:56 PM

#33

You can "static" measure the piston dome protrusion or how far down in the cylinder it is with an indicator either with the base gasket you want to run or without it and measure the base gasket thickness along with head gasket thickness and calculate what the minimum piston to head will be.

"642MX", have you had the head back off since you put it together? If not, and it sounds like you've exhausted a lot of other potential problems you may want to pull it off and check for piston to head contact. Or if you know of someone with a borescope you could borrow, this would enable you to look through the spark plug hole and check. By the way, I ran Wiseco's this year in my boy's 450 (+2mm High Comp 53 RWHP) and 250F (+2mm High Comp 37 RWHP) and the pistons look absolutly perfect after a good season of racing/riding (pin bores,skirts,lids) I'll zyglo them and check for cracks, but they look like they have plenty of service life left in them. :)

  • ISBB

Posted February 20, 2005 - 01:10 PM

#34

YZ dad do you feel its safe to run a wiseco high comp piston?? You seem like a guy w/ a lot of knowledge in this area and was just curious about your opinion..

  • 642MX

Posted February 20, 2005 - 02:00 PM

#35

Good question. I can tell you that the bike has more snap of idle, but the noise still (maybe piston slap, maybe its going to explode?) bothers me.

YZDAD, Satch, GrayRacer and FFR seem to know alot about the YZF.

  • YZDAD1

Posted February 20, 2005 - 04:01 PM

#36

YZ dad do you feel its safe to run a wiseco high comp piston?? You seem like a guy w/ a lot of knowledge in this area and was just curious about your opinion..



I have no issues with running or recommending Wiseco pistons, either in standard or high compression. They will give you good performance and service life at a good price too. I'm not sure but does'nt the "R.P.M.s & Eric Gorr" Kits use Wisecos? I've had real good performance & quality with JE pistons also. It's really your choice or stock OEM for your rebuilds, but they are only available in standard compression. I hear the new "Vertex" pistons are real good quality too, but I have not tested them yet.

  • FFRacing79

Posted February 20, 2005 - 04:38 PM

#37

I didn't change my jetting. I just wish the piston slap would go away.

Has anyone else used a Wiesco 13.5:1 and heard more piston noise than with the stock piston?


Wiseco pistons for the 450 come with .003" clearance. I replate and tighten up to .00015"

Falicon has a stroker kit(505) that uses the stock length rod. They reposition the crank pin on the flywheels...no spacers, stock cam chain.

  • FFRacing79

Posted February 20, 2005 - 04:40 PM

#38

I took that approach with a Chevrolet V8 that I did a quarter inch stroke on some years back, having .112" cut from a set of forged dish tops. It worked out fine.

There are two things to consider in using that method to correct the deck height. The first and most obvious is whether there is enough material available in the piston crown to support that reliably, and whether the valve clearance cutaways will have to be deepened. This can be rather difficult to determine absolutely, and ends up being a sort of educated guess.

The other issue is that doing this moves the top piston ring closer to the top of the piston. Part of the reason the top ring is positioned as far down the piston as it is is so the piston crown can shield it from direct exposure to combustion gases by virtue of the tight space created between the piston and cylinder above the ring. Moving the ring higher increases its exposure, and can result in carbon or sludge deposits in the ring groove. I doubt that 1mm would have a very big negative effect, though.


Another alternative is to use copper base shims. You can get them from Cometic. You should have at least .060" squish clearance.

  • Crf450ex

Posted February 20, 2005 - 07:43 PM

#39

642mx, just wondering do you run race gas. If not then what you are hearing is probably pinging, not piston slap. 13:1 is a bit high to not run race gas. From what i hear 12.5:1 is the max you would want to run on pump.

  • 642MX

Posted February 21, 2005 - 07:38 AM

#40

642mx, just wondering do you run race gas. If not then what you are hearing is probably pinging, not piston slap. 13:1 is a bit high to not run race gas. From what i hear 12.5:1 is the max you would want to run on pump.



Citgo 110 leaded. I've had real good luck with this fuel, I even ran it with the stock piston.





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