Splitting the crankcase

The GT-5 engines are a little harder to find if just looking for a new bottom end but you could try gasbike.net or send Roger a Pm and ask where he buys most his parts from. Roger knows his stuff quite well and he prefers the GT-5 engines over the PK-80 type so he may know a few sources that most of us don't know about.

Blm25super said:

Thx dave i just emailed him

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didnt get your e mail... just pm me and i will list my parts source.....

http://custommotoredbicycles.com/ga..._piston_kit_49cc_parts_for_motorized_bicycles
well most of the single pieces are ordered from

aas you can see you can seperatly order a 38mm or 40mm full circle crank with ether a long or a short rod, and you can order the rods seperatly ... this allowes you to build what you want in whatever case ... this site has a lot of good parts and a great variety of them too including 40mm spaced intake jugs !

other than that if i want to order a full all together GT5 its through gasbike or whereever i can find one LOL

but if you know how to punch out the bottom end bearing on the crank and remove the con rod or your dareing enough to DIY then you can convert a GT5 crank to use a standard PK80 pisston and jug by swapping con rods and pistons thus making the future procurment of parts mutch easyer.

if its a new crank and con rod your after then they have it it will be a...
38mm sroke full circle crank, with the long 115mm rod, and you will need a high wrist pin piston, and i sugest you run a better needle bearing since you mentioned your gonna run a fred top end !!!!!!

you can get the needle bearing through treatland its a puch moped bearing i forget what number though .... a quick search should bring that right up.

just do not buy a grubee unless it comes with the CNS V3 carb !!!! this is not me saying it, to get you to use that carb its actually because those that came with that carb are the better quality ones, beter bottom ends !!!and large bore long Z intakes!!! and if you can get through the cns v3 tunning you will get more responce from it than an NT and more top end also in my opinion.

Mainly the rod and piston, but there are a few subtle differences in the cylinder as well... Gotta go GT-5 all the way or PK80 all the way for the rotating assembly and top end.

there is also a differance in stroke !!!

the dax f80 has a crank thats ground for 40mm stroke and all others are 38mm

so if the biggest motor is what your after then make it a dax kit

but you can get the other 66cc motors anywhere

if you want ease of parts availability then get a dax or pk 80 you will have a true 70cc motor that has standard parts

i like the grube gt5 personaly though to build apon i just seem to be able to extract more power from the stock factory port map than any other motor even though its only 66cc vs 70cc. the gt5 has differant and parts are hard to come by so be warned
IE: the jug has differant porting and the rod is longer and the piston has a differant wrist pin location

MotorBicycleRacing also sells the 40mm stroke engine and parts. His "GenV" is every bit as good or better than Dax's best. PM him for availability and prices

maniac57 said:

MotorBicycleRacing also sells the 40mm stroke engine and parts. His "GenV" is every bit as good or better than Dax's best. PM him for availability and prices

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Very True... Dax or MotorBicycleRacing are the only places I'll buy a complete engine from... very noticeable difference in smoothness and quality. Not sure which one is best, or if they're both the same in quality, but you can't go wrong with either engine.

That measurement is the distance from top dead center to bottom dead center, or the distance the piston travels in the cylinder. I measure it with a pocket ruler, its easy with the head removed.