is the bottom end the same on a 340 nd a 250 can i just bolt 340 jugs and piistons on my 250 with out chngeing rods and crank 1980 gemini

what first comes to mind is a bit NO ... it seems like there would be too many variables for that to happen, for example the stroke of the 340 and the 250 would have to be the same. i think you would be better off with a full engine swap, or better yet a new sled. a vintage model with the 340 you are looking for could probably be had for the price + headaches a swap is gonna cause you.

does anyone know the stroke of each motor

this guy is selling his 540 for 500$ (http://www.snowmobileworld.com/forum/index.php?showtopic=36260)

the point i'm trying to makes is that if you leave the 250 as a 250, sell it and look around a bit, you could probably find a sled with a bigger engine for the ammount of money you got for the 250 + what you would have spent on a new engine for it, or jugs/pistons/rings assuming that swap was possible ( which i doubt). i would advise to you now to drop the idea of this "jug swap" and at least consider a full engine swap (which in my opinion would still cost more than a different sled). you have to keep in mind as well that the crank of the 250 is only made to handle the power of that engine and with the 340 pistons/cylinders in there it might make too much power for it to handle. Also, new carbs/jets would be required as the 340 would want more gas than the 250. if the electrical system is already failing (and judging by a few of your other threads on this board it is) it may not have the power to ignite a larger ammount of fuel, or the plugs for the 340 might have to be gapped differently than the 250 thus making it harder on the system to jump the gap. go with a new sled, your wallet with thank you. it seems like a lot of cash out front but start thinking what new pistons + jugs + rings + various other parts will add up to and you will realize you arnt saving the cash you thought you were.

look at what pistons + sleeves cost at royal distributing (http://www.royaldistributing.com/servlet/MiddleRedirect?page=index1.html)

granted these are canadian prices and i dont know if that applies to you or not but a piston kit + 2 sleeves is gonna cost you AT LEAST $250 and thats low balling it. plus you still need the cylinders! i would imagine that if the 250 is running you could squeek $200 out of it with a little bit of effort. now this leaves you 50$ away from the 540 i posted at the top of this post. with a little looking around you should easily be able to find a similar deal in your area.

as it is rihgt now i have like $100 into my sled and a 340 that needs one cylander (wrist pin)came out and cant find the clip i am thinking its in bottm end
weak spark problem is fixed (electronics of 340)
i would use the 340 bottom but mine on my 250 is in perfact shape (all brand new as of last year
i just need to know if its the same stroke it will all bolt together but if the stroke is different it will have low compression or beat the piston into the head cover
so all i will have to buy is a gasket set

a gasket set isnt gonna save you if the stroke is too short and you're not getting compression. and if the stroke is too long you're gonna have to stack up A LOT of 1/8th inch gaskets to overcome it

i am not gonna try it if the strok is different thats why i need someone to tell me if it is

What is the model number of your 250 motor and what is the model number of the 340 motor? You should have an EC25PM, which has a 55.6mm stroke. Depending which 340 motor you have it could have 55.5, 55.6, or 60mm stroke.

:sleepy: yes mine is a EC25PM
what 340 modle numbers would ahve the same stroke (55.6)

and thanks for the help i am really looking forword to gettting a 340 in my gemini as it will only go 47mph right now

I'm getting this out of a specs book and it makes sense that the one you want would be an EC34PM. All ignition and timing specs are identical. 61.8mm x 55.6mm. Good luck.

than ks alot i will keep ya posted on how it works out