Thoughts on 61mm big bore kit for gy6

Posts: 205

im thinking about putting a 61mm piston and rings in my gy6. i see alot of people selling new jugs with the rings and piston,some even with a head and cam.

why cant i just take the old jug off my engine and have a machine shop bore it out?

what is the benifits of having a different cam. high and low torque?

im guessing the head has bigger valves. but again couldnt i buy new valves and port and polish the old head?

you just dont see many people having the machine work done most buy the bolt on kits. looking at over 250$ for the complete kit and 180$ for jug and piston.
you can buy a 61mm jug and piston for about 110$ but you still have to bore it. i can get a 61mm piston and rings for $40.00 and $30.00 to bore the jug why not go that way?

Keep in mind these are the cheapest prices i could gather they may be less or more elsewhere. cheaper is not always better so you may be better off buying from a Buggynews dealer!

Posts: 200

The 61 and 62mm big bore kits require the engine casing to be bored due to the cylinder being a larger diameter.If you were to try to bore the stock cylinder you would have no cylinder left because the other big bore kits have a larger diameter sleeve which again is why you have to bore the casing.The exception is the 155 kit which does not require the case to be bored,but beware I have seen some 155 kits that were cheap and so I ordered one only to find that the sleeve was considerably thinner than the higher priced cylinder,it was as if the cylinder was an origional 150 sleve but bored to a 155.This will work I guess but for how long who knows.These are air cooled engines and run quite a bit warmer than a water cooled engine.You would not want the cylinder to be to thin.This is why I will not use a 63mm big bore kit because the sleeve is so thin and knew of one person who installed the 63mm only to have to replace it after a short perion due to the cylinder being so thin.Like the 155 kit I mentioned earlier it was quite a bit cheaper and true you would save quite a bit of change but in the long run it would cost you.Beware you have good suppliers and bad suppliers in Asia,so you need to see what the average prices are cause when you find one much cheaper there is usually a good reason for it.In other words you get what you pay for.Now you have several cams available for the GY6 and they all fit a different purpose so you will need to know how you will be driving it eg. do you want more low end torque,or top end speed or a combination of both.I see many advertise big valve head which is misleading but not necessarily on purpose for things get mixed up in translation.What I found with the large valve heads is that the valves are no bigger but the ports instead of being the normal24-26mm they are the large 30mm and also you need to know what chamber the head has for you have large port heads with the stock 58mm chamber and also 61mm,62mm,and 63mm chambers you would not necessarily want to use a 58mm chamber with a 62mm bore. And I have seen some big bore 62mm kits come with a 58mm head.

Posts: 205

sycarms what do your prices run on the 61mm kits. i agree about the 63mm thats why i was just going to get a 61.

that makes perfect sense on using a stock jug the walls being too thin. i want a cam for low end torque only. i still dont know what head to get or if my stock head would be better

Posts: 200

I will PM you with info TOM

Posts: 19 · Newbie Joined: 18 Apr 2008 Posts: 19 Pictures: 0

I cant see changing to 61mm bore unless you are ready for new piston/rings.

I wish these kits were tested more, like on a dyno with HP specs, so you know what to expect as far as gains. has anyone seen any HP numbers online?

if you change to a 61mm bore, 30mm carb, intake and Uni filter, you would go from 10HP, to maybe 11?

Posts: 205

i know someone on another post was trying to get his 250cc faster. because his son with the 150cc bored to 170/61mm was smoking him. said the 250 could be wide open and the 150cc would come up beside him,laugh and pass him

Posts: 273

Guys with 170cc bore kits please chime in. Motorheads please chime in. I stripped the theads for my spark plug and a Tap and helix coil kit cost 50 bucks. So I called baja and was quoted $75 for a new head. and ordered it. I received it today. But while I was waiting for it I thought, with the work invalve changing the head coupled with my desire for more speed and torque why not get the big bore kit and send back the stock head. The $75 is already spent , and Baja will take the part back as long as I don't use it, So $175 for a Kit sounds really good to me compared to an engine swap which I'm not qualified to do, not to mention finding a complete transplant.

Greg

Posts: 273

Guys with 170cc bore kits please chime in. Motorheads please chime in. I stripped the theads for my spark plug and a Tap and helix coil kit cost 50 bucks. So I called baja and was quoted $75 for a new head. and ordered it. I received it today. But while I was waiting for it I thought, with the work invalve changing the head coupled with my desire for more speed and torque why not get the big bore kit and send back the stock head. The $75 is already spent , and Baja will take the part back as long as I don't use it, So $175 for a Kit sounds really good to me compared to an engine swap which I'm not qualified to do, not to mention finding a complete transplant.

Greg

Posts: 200

You do know that the 170 bore kit will require you to bore the casing? TOM

Posts: 273

The machine shop will take care of that right? I'm the remove and replace guy. I want to know what this kit can do for the cart. Will it hit 40mph can i climb steeper inclines from a dead stop, and more power out of turns.

greg