SLORYDER

I'm not a pro, but I believe the main ddifferences are the powervalves and the ignition system. IMO RZ cylinders are much more desirable than banshee cylinders because the powervalves give you a much wider powerband and you can go more radical on the exhaust duration because at low rpm's the valve keeps the timing in check

Oem gaskets

I'm thinking it is .080" but I'm not sure..

Bill nye gots nothing om mr. wizard

I believe the stock piston to head clearance is about .080" with a .020" deck height BTW I made my calculations using 1 and 2mm combined thickness of the gasket plus plate so it should be correct

HA! Got it. 2mm spacer would give you too much transfer timing in most all applications. No spacer would be better for trails but the bd would be a little low w/ no porting. Seems like decking the bottom of the cylinders with some minor porting and custom domes would be a killer woods machine with a pipe such as the fmf gnarly. 4mill, 1mm spacer and some minor porting would be my cup of tea though.And it appears i could leave my head bone stock;)

You can get within 2-3 degrees. Good enough for me to get a feel for if there are any big changes in duration.. I would definately use a degree wheel for my final cuts

I had one of those by the time you machine the cover weld it a but the plexiglass you could have bought the nice one

Yeah my crank did the exact same thing. I've heard of others doing the same-I wonder what could be causing this? I sent mine to HJR I believe it was $75 to fix. Might as well send your jugs toget ported while you're at it.

What I do is make a graph two line horizontally the lines are 58 mm apart the top line is my theoredical tdc, the bottom bdc then I measure down from the top line the distance form tdc to the top of my exhaust, then another from the top line to a point where my transfer roof would be next I draw a line 110 mm long from the top line down and this point will be the top of a circle 58mm in diameted. next I draw a line 110mm long from the theoredical top of my exhaust port and make a mark on the circle where the end of the line falls. If I measure f4rom the top of the circle to the line goig to the exhaust it will give me the degrees atdc. Same goes for the transfer. I can't be accurate tho w/o a protractor

I try not to either. I have a good method problem is I don't have a protractor handy. I will also add that my ghetto fabulous ideas will work IF you have the knowledge understanding AND foresight to make every cut and calculate every angle duration ect correctly. It is not something that anyone can do, but, like I said if you have the right guidance I believe something like what I explain can be done by almost anyone. I know I've made some dumb (apparently) topics but rest assured I was probably trying to get something out of it that I couldn't have got by asking directly. And I believe I have done a fair job. In a woods or play application where max performance doesn't matter I wouldn't hesitate to try something myself, but make no mistake if I wanted something competitive I would definately send my engine to a builder.

You know you're alright B I really don't know for sure, I don't really have a scientiffic means of doing it right now, just a ruler and a compass....I came up with like 136/ 195 but that doesn't seem right.. I you give ma a formula I would be happy to try and figure it out, even though my math is rusty at best...

Gotcha

Heathen, If a performance oriented engine (some trails, more duning and dragging) is what you are after, then IMO a 4mm with a spacer is the most economical way to go. Theory: This is assuming the plate gives you around 124 transfer, 190 exhaust. If you have pipes such as T-5's just the durations gained from the spacer and the displacement gained from the stroke I would guesstimate a gain of around 12-14hp, as compared to 5-7 on the bottom end and a loss on top with crank no spacer. From this point you can raise your exhaust port another mm or so and widen to about 75% and you will have gained I'd say another 8 or so hp in the upper mid range, and lose a couple hp down low. So 20+ hp gain from buying the crank, porting it yourself which most anybody can do as you don't have to touch the transfer roofs AT ALL. Yes if you were looking to NOT use a spacer, buy the crank and send it to a builder he could port it for you and get maybe 5 more hp than you did but you'll pay 300 or so plus shipping; the additional crankcase volume would be compensated for 20 fold by the extra free hp you got out of your engine. And about the air leak from the spacer-c'mon you gave the same non'leaking case and jug surfaces you did BEFORE the spacer, and two brand new shiny surfaces and gaskets to add. If it was not leaking before it will not leak after. You can call it shadetree all you want but there are just ZERO reasons not to go for it as long as you know where to cut

First you said that the crank/spacer would result in stock port timing, now you say that the timing would be more radical..Do you have any clue what it would put the timing at? If you do please share as I am very curious... Op stated that he really wants a 421 cub. The powerband created by port timings depressed from stock will definately not be satisfying if that is the what is desiring. I took it literally perhaps he meant he just wishes he had money for a project like that...

Like I said I have never ported 2 stroke cylinders, but have done a full rebuild of a four stroke engine including my own combustion chamber work and a full port and polish. All one needs is a little intelligence and the right guidance and they can do anything they set their mind to. You are much quicker to offer ridicule than guidance so if anything you are adding to the problem. Actually blowit finally admitted I was right. And I still believe he is wrong because if you add a 2mm spacer and a 4mm crank your durations should be a few degrees more radical. A 4mm with a spacer no porting will run circles around a 4mm no spacer no porting. I have yet to hear anyone tell me specifically why my plan won't work, just a bunch of people telling me I'm not a builder therefore have no right to state my opinion. 4mm crank lower ports to top of piston 70-72% bore width on the exhaust Raise exhaust 1mmIF blowit was right and durations are stock raise the intake ports 3mm Chamfer all ports Bump compression Probly under $700 with old crank exchange and a solid 60+ horsepower and a wider powerband than stock I'm still waiting for someone to tell me why this won't work The only problem I see is the spacer would add to the crank case volume a little but I believe the added duration would make up for it ten fold

OK sweet. So 4mm crank, no spacer custom domes for lot more bottom end due to the longer power stroke and more work being performed at a given rmp. This is of course at the expense being able to rev due to the shorter durations. If tight trails is all you ride, and you already have a shee, this would be the way to go. I would still open up the exhaust port some too. At least to 70%. The spacer will give you close to 10 hp up top due to the increased durations and a bottom end as good as stock thanks to the power stroke being stock. With the cool head you wil sweeten the bottom end even more and this is why I would recommend the spacer. Good addition of all around power. You might stay in the trails but one day you'll want get out into the clear and let her rip.I would actually raise the exhaust at least 1mm if the crank + spacer puts your duration back to stock. And BTW papa smurf I was way out of line calling you out like that and I apologize. Each to his own.

No the 4mm with the spacer. Could you possibly give me some timing numbers with the 2mm spacer since you are so willing to help?

So I see you refuse to state the flaws in my theoredical build...

Sir I am simply offering my opinion and letting the guy know what I believe would be the most cost effective way to go. A builder would also inform them of the same (although it would be the most cost effective for them) The guy stated that his ideal engine would be a 421 cub with 34mm carbs. I believe that my route will be along those lines but cheaper and obviously less powerful. I bet that 4 out of 5 guys would prefer to do the job themselves and save some money. Problem here is that the majority of people on here don't have enough faith in themselves or others, and only trust what they hear from builders ect. So you end up with a socialist forum that is a mass oppressor of the truth. Two strokes are easy to modify (and equally easy to mess up) IF you have the right guidance. I have been into two strokes for five or so years and only in the past few weeks have I really gotten curious and learned a lot. And I can assure you that I will not touch my jugs further until I feel completely comfortable doing so. I believe I have outlined an ideal diy build for this guy if he decides to do some research and go for it. I was getting ready to dump 5 g's into my banshee, then realized i could sell it as is and use the money to buy a pre built banshee with 125+ hp for the money i was going to spend on mine. Then I realized I could mod mine myself, still be very pleased with my results, and use that remaining 4500 to buy a sweet 2 stroke ski boat. Which I can become obsessed with and mod. If this guy does not believe in doing things himself I have nothing whatsoever against him and he can disregard my posts. If anyone has a problem with my plan I would love to discuss it further.

Sweet I have a fan club!

I tend to disagree that you need to read all those books to gain the knowledge needed to port an engine. You gan gain much in a two stroke by doing fairly simple modifications if you are properly guided. And I plan on fixing that divider as well as a few other things. Tell me what flaws you see in my theory. I would like to learn.

If you do not port you will lose your top end. If you run the spacer plate plus drop the port floors (which almost anyone can do since these are not c critical area that you must get perfect)you gill gain in the mid-top end which is where the banshee shines. The spacer plate adds crankcase volume which makes the engine slightly more inefficient, but the added durations will more than make up for it and that's a fact. I'm not advising him to bllindly follow my advice, but with some research and planning I believe he will realize this is his best bet. Your engine is good for what, 80 hp? That's with around $3,500 in work. I would not hesitate to say the engine I decribed would be close to 65 and he will spend less than 1,000. You could have sold your bike for say $2500, put that 3 g's in and had a 10 mill cheetah bike with all the goodies. Please don't blindly attack me sir; I think you need to learn to use your brain a little more.

What did I say in my post? A BUILDER WILL TELL YOU TO RUN NO SPACER AND PORT TO THE CRANK. This is ideal if you have unlimited funds, but if you are on a budget you can do it my way, save 250-350 bucks on a port job, and still have a MAJOR increase in power. You will need to have someone more experienced than me verify that the port durations will be ok, but I don't believe anyone will disagree that my method is much more cost effective and will probably be the the best bang for your buck. And blowit, I said it would be a bottom end motor due to mellowing out the durations. This is wiithout having to send the jug to a builder. You guys have peoples minds on here warped into thinking that only a rocket scientist can port an engine. Ii am not trying to brag simply stating a fact but I went from NEVER touching an atv engine to doing a full rebuild on a 730cc vtwin, including cams, valvesprings, new JE pistons and relieving the valve pockets on the heads as well as doing a full port and polish; all by gathering knowledge on my own and feeling comfortable about what I was doing and then going for it. This site is like an internet tourist trap and you will be lesd into believing that you are not smart enough to do anything yourself. And by the way that 730cc Vforce ran HARD for more that 2 years in the hot southern Louisiana weather and many people told me it was the hardest running Vforce they had ever seen. If I can do it I think anyone can with the right guidance and determination. You will be hard pressed to find the former on this site. Good luck

I think your best bet, if you have to take out your crank anyways, is to go ahead and get a 4mill crank (RDZ sells tham with a TZ bearing for 425) and get 2mm base plate spacers. NOW, some people (mainly builders or nut swingers) will tell you to not run tha spacer and cut the dome and re-port. This is good if you want to have loads more bottom end to midrange, due to having a much longer power stroke...However if you use the spacer, you will make your port timing more radical (essentially adding a more top end oriented cam) and gain a lot of midrange to top end. If you do this you will need a dremel with a 90 degree but to lower your transfer port windows to the top of your piston at bdc (not completely necessary but you will get a big bump in port area) and lower your exhaust port floor to the top of your piston at BDC (necessary because the gasses trying to escape will catch that lip and cause all kinds of turbulence. So which way you go depends on whether or not you want the more agressive bottom end. I'd send the stock crank to get trued and welded and get them to send you back both cranks, then sell the old one. Oh yeah and while you have your jugs off I would widen the exhaust port to 72% of your bore and also raise your intakes a couple or 3 millimeters and also smooth out the entry way. Do this and add a generous chamfer to the top of the exhaust port and even more so (1/8" on the sides and you will be good to go. If I had to guess you would gain close to 20 hp by doing this and you could use the stock carbs. Also get your squish (piston to head clearance) to .035 (absolute minimum) to .040" by shaving the stock head. Again not necessary but it will get you close to 5 hp To me this will be your most cost efficient way to bump your power and you will have a 4mill crank for if you ever want to co 421 cub.