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4Mil Crank kit

This is a discussion on 4Mil Crank kit within the Yamaha YFZ350 Banshee (1987-Present) forums, part of the Performance /Technical category; I just twisted my stock 02 crank and messed up the top end too darn needle bearing washed it out... so i'm lookin at a ...


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Old 06-25-2008, 11:40 AM   #1
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unhappy 4Mil Crank kit

I just twisted my stock 02 crank and messed up the top end too darn needle bearing washed it out... so i'm lookin at a 4 mil crank kit.. what sould i look out for or what will i need to change over what i was runnin with the stock crank... I have stock carbs jetted for fmf fattys and v-force2 reeds i have a cool head with 21cc domes a K&n filter and my timeing is +4 advanced.. I'm goin to get stock bore juggs and run that 4mil stroker crank set up what do i need to know???? Thanks Matt
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Old 06-25-2008, 02:33 PM   #2
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A year ago, I was in the exact same situation that you were. (needle bearings on the rod let loose)

I bought a hot rod 4-mil crank from Cascade Innovations that included the important TZ bearing. I then had my mechanic bore my sleeves to the next size and installed some Wiesco 795 series pistons. He then custom cut dome blanks for my cool head to get the clearance and compression I wanted (185psi).

I ran this set up with stock carbs for a year and was happy. Then I bought some 28pwk's and I am even more happy.
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Old 06-26-2008, 10:26 AM   #3
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Thanks dextreme for the info where should i start jettin if i'm goin to use my stock carbs for now with these mods...The kit comes with a spacer plate for the crank do i still need my domes cut like you had??? i'm goin to run 21cc domes for pump gas... And what are the tz bearings this crank is a hot rods welded and it comes with everything i need to do the whole motor seals, gaskets, pistons everything...Thanks
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Old 06-26-2008, 12:31 PM   #4
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Quote: Originally Posted by banshee440 View Post
Thanks dextreme for the info where should i start jettin if i'm goin to use my stock carbs for now with these mods...The kit comes with a spacer plate for the crank do i still need my domes cut like you had??? i'm goin to run 21cc domes for pump gas... And what are the tz bearings this crank is a hot rods welded and it comes with everything i need to do the whole motor seals, gaskets, pistons everything...Thanks

You need to run one or the other. The cut stroker domes or the cylinder spacer plate. I would highly recomend running the cut domes over the cylinder spacer plate. When you move the cylinders up and it advances the port timings. They opean sooner because you physicaly moved the cylinders up 2mm by putting the spacer plate inbetween the cylinders. A 4mill stroker crank will cause the piston to fall 2mm farther down in to the cylinder at bdc and it will pop up out of the cylinder 2mm at top dead center. So that is why you need to run cut domes or a spacer plate. To keep the pistons from hitting the head. With a stock stroke banshee when the pistons are at bottom dead center the piston stops at the bottom of the transfer ports. With a 4 mill stroker the piston stops 2mm below the transfer ports. 4 mill stroker and 2mm spacer plate the piston stops 4mm below the transfer ports. Not the best situation for performance.

The best option is to have the cylinders ported for running a 4mill stroker crank with cut domes. That will make your banshee an animal. Porting changes when ports opean up and how long they stay opean. You do this by changing the size and angles of the ports.

Porting a 2 stroke engine is like putting a Camshaft in a 4 stroke engine.

A TZ or Max Load Bearing is a heavy duity bearing.

You should talk to Jeff at FAST he has the cheapest parts around. Probably could save you a few bucks and you wont have to run that spacer plate. You cant order from his web site you have to call and talk to him.

www.farmandsandtoys.com

josh
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Old 10-21-2012, 01:21 AM   #5
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grin 4 mill banshee question

hey there have a quesyion about 4 mill kits. you seem to know what u are talking about. now i got a weisco 4 mil kit with the long rods. this kit require that u space the head for the 2 mills of the piston that comes out. therfore it requirs u 2 use the 795 series pistons. the have bigger ports i guess shorter and raised the wrist pin. ports line up perfect but iffy about that big gasket. does this sound right? i put it all together thinking its not going to run. 60 over and a pretty heavy port. sent head out and got trinity cut. replaced all studs and nuts put it together run it on 110 and this damn thing RIPS so suprising . can u explain this? got v force 3 trinity 2 into 1 with 41 mm kehin with k&n im runnimg a 70 thousands jet. 35 pilot no advance timing (stock) trinity stage 4 pipes

THANK YOU SO MUCH FOR THE HELP!
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Old 10-21-2012, 03:30 PM   #6
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1. This thread is over 4 years old man.
2. Im not sure I follow. I would get your domes cut so that your dont have to run a spacer plate. They are gheto and the're another place for a possible air leak. Check your squish and compression before you run it. Do you even need race gas? Was it ported for the 4 Mill or was it ported for the stock crank? Ditch the 2 in 1 carb set up. Get 2 PWK 35's or 33's.
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