piston hitting head. wrong piston ? cylinder ? what is going on here ???

A

abefroman

New Member
Ok, a while back I ordered a 'cut-on' piston and ported head from JNMotors. I finally got around to installing it and the piston HITS the head !!!!! attached is a picture of the cut on piston and a stock kit piston. you can see that the wrist pin hole is MUCH lower on the cut on piston. also, I included a link to a short video I did of the piston hitting the head.

did JNMotors send me the wrong piston / cylinder ??? maybe for a 49/50 cc engine instead of a 66/80 engine ?? maybe the piston they sent was for a different stroke than what I have (stock kit) ??? I've read that there are two strokes - 38mm and 40mm. the wrist pin holes look like they might be 2mm difference but I'm not sure.

wtf is going on here ??? I think I'm just going to have to cut on my stock piston using the JNMotors piston as a guide. I also dont think that the cylinder they sent me has had ANY work done to it. I feel like I wasted $102 (with shipping... that they got wrong !) !!!!!!!!!!! AAAHHHH !!!

see pic, and youtube link.... http://youtu.be/O_vhszzltMA
 

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Re: piston hitting head. wrong piston ? cylinder ? wtf is going on here ???

Either you ordered the wrong parts or they sent the wrong parts. The piston on left is a "Type A" piston with a hole height of 15/16". The one on the right is the "Type B" piston with a hole height of 1 1/16" and bigger transfer windows. THe type a piston is what is widely used. I've only heard of the type B piston being in grubee engines, but then who knows they are from the land of china. PK80 style engines use type a pistons with a 110 con rod and 40mm stroke. Grubee engines use the type b piston with a slightly shorter con rod and 38mm stroke. I'd say just use the modified piston as a blueprint for your stock parts and see what you come up with and send the parts back to where you got them from. Get an expansion chamber! I strongly recommend you do not interchange engine internals unless you really know what your doing...

Frank
 
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Re: piston hitting head. wrong piston ? cylinder ? wtf is going on here ???

F_Rod81

Thanks for the reply. evidently I've been buying kits (7 kits off of ebay from rose326a.... and 2 from Gasbike.net) with the type 'b' piston. All of the 10 kits i bought are the same. It suprises me that you said the type 'a' is standard when all I've seen is type 'b'

I plan to cut my stock pistons using the one I bought as a guide. One more question tho... should I cut back the piston skirt on the intake side ?

I have the SBP expansion chamber on my micargi puma stretch cruiser and it's awesome. I plan to buy more of them. the SBP exhaust seems to be the most popular.. and at around $75 not too expensive. However, I've seen a LOT of other expansion pipes.. the banana, x pipe, etc. are any of the other ones better than the SBP or should I just stick with the SBP ???

Thanks a bunch !!!
 
Re: piston hitting head. wrong piston ? cylinder ? wtf is going on here ???

abefroman said:
F_Rod81
7 kits off of ebay from rose326a.... and 2 from Gasbike.net) with the type 'b' piston. All of the 10 kits i bought are the same. It suprises me that you said the type 'a' is standard when all I've seen is type 'b'
Click to expand...

Like I said made in the land of china... and supplied from vendors that only care about $$$ not the product, and have proved to be inconsistent at best. Either way with all them spare parts laying around you should be good to experiment. There is plenty of information pertaining to pistion modifications all over the forum that will come up with a basic search. All the expansion chambers you mentioned are good for the entry level motorbiker, and tuned right they do there job.

I prefer to use modified KTM expansion chambers. Looks good, pulls good, sounds good! However they need to be custom modified to each bike. If your looking for a different bolt-on type of chamber then get a Torquer II pipe from Arrow Motorized Cycles. I have had both sbp and arrow pipes before, and they worked great once properly dialed in. SBP sounds more like a MX, and the arrow sounds more like an Italian moped.
 
Re: piston hitting head. wrong piston ? cylinder ? wtf is going on here ???

Yup, you got hold somehow the wrong part there.
 
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Re: piston hitting head. wrong piston ? cylinder ? wtf is going on here ???

i run grubee gt5's if your willling to trade lol

but yeh that piston you got is for the 38mm crank and long rod combo that grubee uses in there gt5 motors . the dax f 80 has a 40 mm stroke and a differant rod than the grubee and yes you can run that piston if you have the skill to make a 3-4mm thick jug spacer for the base but its not wrth the effort.

you need the low wrist pin piston for your motor

ss far as i know the only motor that usses the high wrist pin piston is the 38mm stroke crank grubee gt5 with the ZAF-60 con rod .... i made a video of a hi breed motor i am making in the performace section where i am useing a gt5 38mm stroke crank and zaf60 rod with a type b piston and running a ciilynder from a 40mm stroke motor and decking it down for a zero deck hight
basicaly the oposite of what u have going on now . i like the 38mm cranks with the #60 rod and type b piston cause the whole assembly is a lot lighter than the 40mm stroke is that and the type b piston alone is a few grams lighter that all the others stock ! i find it produces a bit more midrange and a higher reving motor
 
Re: piston hitting head. wrong piston ? cylinder ? wtf is going on here ???

for the x chamber question u had....

there are realy only a few that work out with our motors despite all the claims
the arrow torquer pipe
the JNM fatty pipe or snake pipe also seen on arrow racers
or make your own torque pipe plans are all over here just type torque pipe

the best one for high rpm race riding would be the fatty pipe but it requires some fab work
the arrow torque pipe bolts up and adds midrange
and the custom torque pipe plans can be tweeked to your needs buthas to be hand made and takes a lot of work
 
Re: piston hitting head. wrong piston ? cylinder ? wtf is going on here ???

You sound like you have tried most of the x chambers on the market. Me I have only tried 4 , Every one I've tried has been better than a stock pipe. The pipe that stands out for me was the SBP X chamber, I haven't read a bad word about one. I'm not saying its the best pipe out there .ITs a nice improvement over a stock.
 
Re: piston hitting head. wrong piston ? cylinder ? wtf is going on here ???

I have tried a lot of differant pipes but . Only one setup i have foind is best for ulra high rpms and sped for wide open drag racing . . . Its a 3-4 FT LONG 3/4ID strait pipe! !!

Man is it loud and obnoxtious but lol it lets the motor rev as far as your carb will let it!
 
Re: piston hitting head. wrong piston ? cylinder ? wtf is going on here ???

spanners said:
You sound like you have tried most of the x chambers on the market. Me I have only tried 4 , Every one I've tried has been better than a stock pipe. The pipe that stands out for me was the SBP X chamber, I haven't read a bad word about one. I'm not saying its the best pipe out there .ITs a nice improvement over a stock.
Click to expand...

correct me if im wrong, but SBP only makes one pipe, right? the multi piece adjustable pipe, correct ?
 
Happened to me- just throw on a few extra head gaskets and that will do the job. That is, if the piston is barely hitting the top.
 
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