big bore help... hybred 2-stroke port timing pistons

[woodsracer144]

i need help with a polanda... ok i know i've posted like 3 of these now, i'm doing this build i dont care about the money, its the cheapest thing for me right now... i got a good start, i still need to pick up a piston, the only questions that i had are the following,

are the wrist pins and all that the same, the polaris 400L and the 250r OE...

does the OE polaris 400 piston need any work? the skirts trimmed? hole bored? i know over the years there have been different things done, some have helped and some havnt, what are some of the better ones... duncan bores another hole in theirs or makes a bigger one...

port timing, how could i judge this? i think i'll send it out to CT and have him do all the port work for me, but would i have to send the whole motor out there then? i dont want to have to pay him 900 on the pork and puttin the motor together and taking it apart( not sure if he would have to touch the bottom end I.E. take alittle off on the cases)
what will it do if its off a little and i run it? i know its not going to run like it should but im not going to loose a piston or something like that over it right away will I?

I have the bottom end ready to go, all i have to do is get a piston and cyl and get a carb picked out. then only expence i will have is

25 on cases to be bored
40 bucks on a Oe polaris piston and rings (thats what they were the last time i got one)
and then a head gasked

so im looking at about 70 bucks and i have a big bore... not with the port work on it...

I'll be posting pics of this as i go along, the cyl needs a little work done to it...

[woodsracer144]

any one, anyone at all? come on theres gotta be some one out there...

[Derrick Adams]

Well, first let me say that I have never had a Polanda engine, however I would like to try one out.

BUT... It's my understanding that the Polaris pistons are junk. They literally fall apart, so stay away from those. That puts your piston cash up to $150 for a decent one.

I also know from reading that either the cylinder or the cases have to be modified to line up the studs to bolt down the cylinder. It would stand to reason that you would also have to machine the cases to accept that large of a cylinder sleeve, which is going to put you out another $100 at least. Not to mention that if your dissassembling your bottom-end your going to want to throw in new crank bearings and seals and gaskets. Firgure another $175 for that.

Just trying to point out some things you may have missed. Keep us posted on how this goes. I would like to try it myself some day.

[derby]

Originally posted by Derrick Adams
Well, first let me say that I have never had a Polanda engine, however I would like to try one out.

BUT... It's my understanding that the Polaris pistons are junk. They literally fall apart, so stay away from those. That puts your piston cash up to $150 for a decent one.

I also know from reading that either the cylinder or the cases have to be modified to line up the studs to bolt down the cylinder. It would stand to reason that you would also have to machine the cases to accept that large of a cylinder sleeve, which is going to put you out another $100 at least. Not to mention that if your dissassembling your bottom-end your going to want to throw in new crank bearings and seals and gaskets. Firgure another $175 for that.

Just trying to point out some things you may have missed. Keep us posted on how this goes. I would like to try it myself some day.


Of all the places you would send it why to ct? Why not send it to someone who has built a few of those? You should talk with dave moore about it. He was big into those setups a few years ago. As far as a piston goes you may be able to use a cpi designed 250r/banshee piston depending on the bore/rod combo you use.

[woodsracer144]

I do all my own milling and welding, i take my own motors down and all that, all i would have to pay for is parts, i just had all new bearings in the bottom end,

when you said moving the studs or else doing it to the cyl, i am doing this all to the cyl, for more then one reasons, 1) this way if i would like to go back to a TRX top end i can, its not just for this one, and 2) it will be alot easier if ( i hope not) but if i loose a left case half. just use any 250r case and go no messing around re doing the studs...

the piston that i had from polaris was pretty good...

i think the piston for a STD. bore polaris is 83 mm...

another thing i wasnt really sure about is what size carb to run, i would like a PWK or Air Stryker... i didnt know if a 38 would cut the cheese or if i would need a 39 or something in the 40's, im not makin a drag quad, im looking for a good strong mid range... with 389 i can use the CC's to get the top speed i want and the low end also... im not looking to a 120 mph quad, even though im sure i could get it with this...

i got my cyl and cases at a buddys place and im goin to get them tomorrow and im going to get started on it...

[86 Quad R]

contact tim at titan racing. he will be able to help you with known issues and has a compiled list of the varying combo's of pistons and their applications. :cool:

[woodsracer144]

can you pm me his info? thanks

[machwon]

What are you going to do with the cylinder base nuts by the intake. If you move them in on the cylinder I'm thinking your going to cut into the intake reed area. I might be interested in doing some porting (much cheaper than $900 at CT) if the situation for the doing the motor right is there. You will be fine with a 39mm carb, probably right around what the cylinder used stock.

[86 Quad R]

HERE (http://www.titanracinginc.com/) you are.

[woodsracer144]

Machwon thanks for bring that point up, i totally for got about it! i'll have to check it out tomorrow so i know for sure... i think i will be ok though...

thanks for the link also!

i'll have some pics tomorrow for an up date...

[woodsracer144]

Alright boys and girls! let the building Start!

first off i sarted off with cleaning and cleaning and cleaning some more and i still dont have the hole things clean but i can work on it now...

i get it mostly cleaned up and now i got it welded up half way. i have alot of milling and sanding to do and i also need some input on some porting stuff...

[woodsracer144]

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[machwon]

Ok Kiddies, all kidding aside. I wouldn't worry too much about cleaning, porting stuff, etc at this point. You will still need to clean it again after all the milling,grinding, etc. How far did you go with the crankcase halves? I think you have more work involved here than what you realize.

[woodsracer144]

UPDATE!!!!!
Yester day i workd on getting the guessets made for the exhuast side base studs... it took me 4 hours to get both of them done but i ran out of the alum filler so i couldnt weld them in yesterday, i picked some up and to day i went to town....

I worked on it all day at school today... it was a total of...4 hours and i got the cyl decked and the gussets welded in, and i built a total of 3 jigs, one didnt work cause it was too big for the Vice in the mill so i had to pull 2 of the studs and make it down sized...

Now my problem is with getting the holes to all match up. i got an idea for a jig, i just hope it works...

Im going to run a tube threaded in to the spark plug hole on the cyl head and the tube will run the length of the stroke and it will be flush with the bottom of the cyl skirts, then i will use a piece of pine board and lay it flat across the bottom of the cyl and hit it with a hammer so it will mark out the center of the bore and the OD on the skirts, after i find that center i will do pretty much the same thing with the cases to find the studs. lay a board on top and hit it once and then it will make a print where i have to drill it out, i have already have the case bolt patten found along with the center, i just have to get the center of the cyl done...

its might be hard to understand but i'll post pics, its not the most to the dot spec but i think its the best i can do, i had my teacher helping me and he said this is would be the easiest way to do it so i'll see how it turns out...

[woodsracer144]

1

[woodsracer144]

decking

[woodsracer144]

the exhaust side, you can tell where the little pocket is that i filled in if you look really really close to the color of the metal..

[woodsracer144]

update!

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[woodsracer144]

UPDATE! didnt think it was gonna take this long but i got the cyl on the cases, im waiting on a few things but its on there...

http://i374.photobucket.com/albums/oo185/mornin151/DSC01157.jpg
http://i374.photobucket.com/albums/oo185/mornin151/DSC01159.jpg
http://i374.photobucket.com/albums/oo185/mornin151/DSC01158.jpg

[Langbolt]

Have you given this guy a call ?

http://www.rtrperformanceengines.com/apps/photos/photo?photoid=43646734

:devil:

[woodsracer144]

Originally posted by Langbolt
Have you given this guy a call ?

http://www.rtrperformanceengines.com/apps/photos/photo?photoid=43646734

:devil:

nope i havent

[machwon]

Have you put a piston in it yet and tried to roll it over? Might be your next step, but looks like you got the cylinder mounting figured out.

[woodsracer144]

Originally posted by machwon
Have you put a piston in it yet and tried to roll it over? Might be your next step, but looks like you got the cylinder mounting figured out.

im waiting on my piston should be here monday or tuesday...

i still have to check and make sure that it will go through the whole stroke and all that...

i hope i dont have to mill more on it but i think will be good on that, main this is if i would need a bace plate... i was told people use a 3/8ths inch plate, i didnt understand that i've seen these with out them and im seen very few base plate motors.