4MM strokers

[Hightempsilicone]

I purchased a used banshee yesterday. I was told it was a 4MM stroker. Being new to the banshee I am not sure if you can visually tell that this is true or not. So how can you tell if this is true?

 

This is what I know so far.

 

35MM PWK

CPI Inframes

Lock Up

 

It has no spacer plate so that rules that out. Any other way to tell?

[fixitrod]

Pull the head and see if the pistons go 2mm above the surface of the clylinders

[Ducman]

It doesn't need a spacer plate to be a 4mm stroker. The only way I know how to tell for sure by looking at it is to take the head off and look at the #'s on the pistons. If its a 4mm long rod crank it should have 795 series pistons so the # on the pistons will contain the # 795 and the piston size, probably 64.5mm = 06450 or 65.0 = 06500. Also if it doesn't have a spacer plate it will have custom cut domes so if you look at the undersides of the domes side by side with standard domes you will see the there will be an approx 2mm larger lip before the squish band begins rather than the sqish band nearly comming to the bottom of the dome. The piston top will also come 2mm above the top of the cylinder.

[fixitrod]

Not all 4mm strokers use long rods. Some builders like how the stock length rods rev out compared to the long rods. Long rods are suppose to be a little bit more reliable but aren't necessary until a 7mm stroke increase over stock.

[fixitrod]

Oh, and welcome to bhq. Sounds like you have a nice shee from the get go.

[Hightempsilicone]

Oh, and welcome to bhq. Sounds like you have a nice shee from the get go.

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Thank you! I found my front brakes from a member here. I will be getting ride of the twist on it due to my past history. 43 broken bones, 4 of which I can blame on a twist LOL

 

I am going to drop it off and have it dyno'd because I want to know what I have. I am not a fan of buying used because you dont know the "TRUE" history. I have turned every bolt on my YFZ so I know exactly whats on it and what else needs to be done. This Banshee is just a mystery for me right now.

 

What should I make on the dyno? I am also going to check the compression tonight. The heads are currently stock (I think) so where should the compression be? I was told it has 4 rides on the new top end but who knows.

[fixitrod]

The head may look stock, but if it's a 4mm stroker it's been cut and domed. Check your compression for sure. It may be higher than you think and may require race fuel.

 

Who did the porting for the stroker crank?

[Hightempsilicone]

Well the previous owner was using straight F&L 111 mixed 32:1 Klotz

I even got 30 Gallons of fuel with the bike.

 

He said it was ported but how I have no idea. I did get a bunch of receipts though.

 

I can see that the crank was welded and trued.

 

There is also a line item Port X2 and here it is "Mill Head"

 

It looks like Scribbs did the milling and porting.

[fixitrod]

I'm not sure who that is but sounds like you have a nice machine. Maybe you can get a hold of scribbs and see what they did. Your receipts may reference a 4mm some or a part number for the crank. You can look at wiseco's web site and match the part number to the crank. I can't guess what your compression should be since it's modded.

[SDD]

Well the previous owner was using straight F&L 111 mixed  32:1 Klotz

I even got 30 Gallons of fuel with the bike.

 

He said it was ported but how  I have no idea. I did get a bunch of receipts though.

 

I can see that the crank was welded and trued.

 

There is also a line item Port X2 and here it is "Mill Head"

 

It looks like Scribbs did the milling and porting.

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Hightemp do you live in San Diego? Scribbs is in El Cajon. The crank could be a long rod and use 795 pistons. The only true way of telling what crank you have is to measure the actual piston stroke. I'm hiding a 7mm stroker in stock cylinders and the head could be any old bolt on aftermarket head. If you bought it from a guy that didn't seem like he was pulling your chain you probably do have a 4mm stroker.

[r6rider04]

i just got my 4mm stroker together and it goes great (now that i figured out 300 main jets were way to small ) any way, i have stock head right now with a "stroker" head gasket, not sure if that is what you guys mean by spacer plate, but it was $52.00 i checked compression before i started it ,about 152psi for both sides haven't checked since rings have seated, very happy with it i can stand it up in 6th with no clutch love my shee

[Wallrat]

If you don't want to pull the head you could just pull of the tank and stick something long down the spark plug hole until it touches the top of the piston. Measure the difference between the top of the stroke and the bottom of the stroke. Stock stroke is 54mm so if its a +4 you should have 58mm.

[Hightempsilicone]

I dont think he was pullin my chain, but I do know how people tend to stretch the truth when trying to sell something. The bike is beautiful and I cant wait to get it out in the dunes next week. I guess I just like to know the history of whats in it. Nothing beats building it yourself or at least choosing what you want done to it.

 

So you can infact have a stroker motor with no plates. Is the stroke achieved on the piston? Wrist pin re-located?

 

I am new to 2 strokes but have been building my YFZ this past year.The interesting thing is there is not a big hitting powerband on the bike like the other banshees I have ridden. A few that I have been on before if you are not holding on tight you will get bucked. This just doesnt have that hit.

 

I am going to check the compression tomorrow. I can only assume that it is a higher compression because the previous owner was running straight 111 octane. But I also know that people think more octane = more power which is not always the case. At what PSI should I need to run 100% 111 octane?

 

I will also at least pull the jets to see whats in there now.

 

2 strokes are still a mystery to me so thanks for all the help!

[Wallrat]

The added stroke comes from having the pivot point on the crank placed further from the center. The 795 series pistons do have the wrist pins located closer to the top of the piston in order to accomodate the added stroke. I would check the compression and see if he has his timing advanced any before I thought about running a lower octane. The timing advance can be in the form of a different stator plate or an offset woodruff key on the flywheel. You'll need to pull off the left engine cover and use an impact to get the flywheel nut off. After that you need a Yamaha flywheel puller to get the flywheel off. Pick up a Clymers manual ASAP and it'll show you how its all done.

Edited January 20, 2005 by Wallrat

[Hightempsilicone]

The added stroke comes from having the pivot point on the crank placed further from the center.  The 795 series pistons do have the wrist pins located closer to the top of the piston in order to accomodate the added stroke.  I would check the compression and see if he has his timing advanced any before I thought about running a lower octane.  The timing advance can be in the form of a different stator plate or an offset woodward key on the flywheel.  You'll need to pull off the left engine cover and use an impact to get the flywheel nut off.  After that you need a Yamaha flywheel puller to get the flywheel off.  Pick up a Clymers manual ASAP and it'll show you how its all done.

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The seller said the timing was advanced 4 degrees. But I do have a question on that as well. On my YFZ I put a Dyna CDI on and advanced the timing 4 degrees. So if the timing is already advanced (Mechanically) on the banshee is there any benefit of running an aftermarket CDI or should I keep the stock one?