I believe with the 170 kit you have to bore the cases, the big bore kit already comes with cylinder bored. you might as well get a stroker crank while you have the cases apart, I went with the 4 valve head also. this engine will smoke a stock 250. _________________ 2006 carter gx150llr lots of goodies
2007 JOYNER250 lots of goodies looking for more
2004 yz85 dirtbike
2003 pw 80
2006 50cc pitbike
2006 117 stroker pitbike
2 1996 yamaha 600 snowmobiles
2 1980 yamaha 340 snowmobiles
1997 wolverine 350 4x4 quad
Yes you have to disassemble the engine and split the case, then the case needs to be bored. Some people have ground the block with a dremel to enlarge the case so the large cylinder will fit it. It can be done this way but I personally would not recomend doing it this way, thats my opinion. When I do a big bore job I bore the case using the mill with a boring bar this way you have a precise cut without removing any more material than is needed. This is important cause of the oil galley and studs which hold the cylinder and head to the case. If too much is removed this can weaken the block in the stud area. Now you can go with the 59mm bore kit which requires no machining where as the 61mm and 62mm does. TOM _________________ GUNNUT
SYCARMS;Blade Karts,ATV's Parts,Service,Performance Parts & Accy's
You are talking about an engine that was designed as 125cc. Do you want to risk reliability for that little bit of extra, it's not fun splitting the case either, you run the risk of oil leaks down the road as well.
Also, look at your piston, you are talking about adding 4-5mm in the diameter, that is not a whole lot of change there, 20cc "may" sound like a lot for a 150 but again, I like reliable.
One last thing, I would suspect that the biggest difference in power when going to a big bore kit would be the increased compression ratio. These engines are pretty low compression and respond really well with bumping the CR up.
More cc's + same size combustion chamber = higher compression, that higher compression will probably give it more power than the extra 20cc's will (in my opinion of course).
But if you are dead set on it then go for it, it is dirt cheap compared to those ridiculously overpriced exhausts and clutch sets. just my 2-cents, I definetly lean towards the get in, turn the key, and start everytime type though, not much of a risk taker I guess! Good Luck!
Kell _________________ Honda 300ex
Dazon Raider Mini 90 (busted transmission )
I did the 170cc big bore kit as well. Yes you have to spilt the case in order to do it. After I split mine I had a guy who worked at GM bore it out with one of those fancy machines where he works. After it was all said and done..... O man I've got some power now. There hasn't been a hill yet that I cannot climb. If you do decide to do it and you have any questions along the way feel free to PM me and I'll be glad to help you out.
Articles
)
