66/80cc Pistons

kdaddy1980 · Oct 1, 2013

a guy brought me his bike and I discovered there was a little piece of metal bouncing around inside the cylinder and pitted the top of the piston and the head and caused the piston to jam up into the cylinder, i dont know what the piece was but it looked like the tip of a spark plug.

the bottom end of this motor seems fine it spins free and has minimal play, so im going to attempt to put a new cylinder, piston, and head on it but the problem is,im realizing that there are differences in motors. even though they are both 66/80cc the one has a shorter crank,(or longer, im confused) i found that out when i bottomed out the piston skirts on the piston on the right.

i need help to identify the one on the left, it has the wrist pin hole lower than the other one, I think its a gt5A but im not sure. they show a picture on gasbike.net but its hard to tell what the differences are, they have 3 different sizes for the 66cc including the "super rat" which im not farmilair with either, can anybody tell me what the differences are? the left one seems a little taller too, but only about a 32nd of an inch or so.

mapbike · Oct 2, 2013

kdaddy1980 said:
a guy brought me his bike and I discovered there was a little piece of metal bouncing around inside the cylinder and pitted the top of the piston and the head and caused the piston to jam up into the cylinder, i dont know what the piece was but it looked like the tip of a spark plug.

the bottom end of this motor seems fine it spins free and has minimal play, so im going to attempt to put a new cylinder, piston, and head on it but the problem is,im realizing that there are differences in motors. even though they are both 66/80cc the one has a shorter crank,(or longer, im confused) i found that out when i bottomed out the piston skirts on the piston on the right.

i need help to identify the one on the left, it has the wrist pin hole lower than the other one, I think its a gt5A but im not sure. they show a picture on gasbike.net but its hard to tell what the differences are, they have 3 different sizes for the 66cc including the "super rat" which im not farmilair with either, can anybody tell me what the differences are? the left one seems a little taller too, but only about a 32nd of an inch or so.

Piston on left is a typical PK-80 like what most of the china girls use, The one on the right is the typw that the Grubee Skyhawk engine uses, im no expert on the Grubee engines since I never wanted one or owned one, there may be another that uses the one on the right bt I dont know whatever engine it would be.

Looks lile the one on the left come out of a completely wore out engine.

Map
.wee.

crassius · Oct 2, 2013

seeing so many changes in these things (and not sure why)

best is to get good measurements and see what they match up to - I've no idea how many diff pistons are out there now

kdaddy1980 · Oct 2, 2013

mapbike said:
Looks like the one on the left come out of a completely wore out engine.

yes, this engine was toast. the guy he bought it from told him it was the clutch cable that was out and thats all that was wrong with it. yeah right. the piston was siezed, the ring broke in half ,the piston had scores about 1/16 inch deep on each side , not to mention it was burnt.bad..it probably overheated and made an awful sound when that piece of metal bounced around in there and the thing finally locked up.

bllboyd · Oct 16, 2013

I have an 80cc china girl and just tryed the right piston and it don't work properly you loose a tone of power and rpms because the wrist pin sit in a different position it don't work you can only replace it with the one on the left I BELIVE it's a gt5a where as the one on the right is just a gt5 I think could be wrong but that's my personal experience

mapbike · Oct 16, 2013

Piston on left is the typical PK-80 piston, almost all engines you will find on ebay with exception to Skychickens uses the piston on the left in the first post.

The pix posted here on 10/02/2013 look like what happens mot of the time when these engine suffer a catastrophic failure...... ding ding ding.... and the answer is.... upper wrist pin bearing flies apart and one or more pieces of it gets hurled up by way of the transfer ports and ends up on top of the piston until it get s caught between piston and upper edge of one of the porst in the jug and then Ka-Pow...! burrrrr burrrr burrrr... puh...! and thats all she wrote dear John...LOL!

Sorry for the silliness here but I been down that road and it aint a good one, I upgrade my upper bearings religiously now..... I dont take that risk because it just aint worth the trouble and expense of replacing the entire top end of the engine over a $6 part that could have prevented the whole things.

Map reddd

bllboyd · Oct 17, 2013

Yep that's exactly what happend to my engine although way way more DAMADGE lol pics attached I DO HAVE A QUESTION THOUGH !!!
I ordered a new piston rebuild kit the included the following
( jug / piston / cylinder head cover / wrist pin / rings ) ALSO AND I HIGHLY RECCOMEND THIS !!!! I ordered the ( juice motor parts ) " bronz bushing " instead of another needle bearing ( it'll just blow up again rite ! ) now my china girl a " boy go fast " engine off eBay uses the pk-80 now the kit I just mentioned was a gt5 but like I said it don't run rite ( low power / rpms ) it came with the piston on the right ! If I use this jug and cover but put in a pk - 80 would it work then could it be I shoulda ordered the gt5a rebuild kit ?????
Thanks

kdaddy1980 · Oct 20, 2013

so where do i find the pk- 80 piston? i looked on ebay but what they have says a pk-10 and a pk-13.

mapbike · Oct 21, 2013

The pistons listed as PK-13 on ebay is the correct piston for the PK-80 type engines, the ones listed for skyhawk and flying horse engines are differnt.

Best deal I seen is to order direct from china on ebay for $14.99 piston, wrist pin, clips, price is right if a person doesnt mind waiting 7-10 days for shipment.

Map

kdaddy1980 · Oct 21, 2013

ok the next question is, will my skyhawk (skychicken lol)jug and head work on a pk-80 bottom end, with that pk-13 piston?

i know it sounds like im creating a monster here but im just trying to get some use out of these old engine parts i got layin around and help this guy get his engine built. if it would work i would do it. but im a little apprehensive since my last mishap bottoming the piston skirts out. ill ask questions first lol

kdaddy1980 · Oct 22, 2013

mapbike said:
I upgrade my upper bearings religiously now..... I dont take that risk because it just aint worth the trouble and expense of replacing the entire top end of the engine over a $6 part that could have prevented the whole things.

Map

do you also use the bronze bushing from juicemotoparts.com that bilboyd was talking about? if not what kind or bearings do you usually use?

mapbike · Oct 22, 2013

kdaddy1980 said:
do you also use the bronze bushing from juicemotoparts.com that bilboyd was talking about? if not what kind or bearings do you usually use?

I have a couple of the bronze bushings from juicemotoparts but I haven't used one yet so I can testify to how they hold up.

I have bought upper caged needle bearings from motion industries in the past but lately I have got what I think is a better bearing from www.bearingsdirect.com I by KT101415 bearings for $6 and some change the ones I got from motion industries were 2milimeters narrower and I'd rather use the 15mm wide bearing rather than the 13mm.

You can also enter the bearing demensions into the searxh box on amazon.com and find the bearingdirect bearing, they sell on there also.

Hope this helps ya

Map

FMB42 · Oct 23, 2013

Piston Bikes might have the piston(s) you need:

http://www.pistonbikes.com/product-p/epcc25-66.htm

mapbike · Oct 23, 2013

FMB42 said:
Piston Bikes might have the piston(s) you need:

http://www.pistonbikes.com/product-p/epcc25-66.htm

The A Type is correct piston, problem is that $11.00 for piston only and then high priced shipping...

The same piston with rings etc on ebay with free or cheap shipping and you get other new parts that you might as well also replace while you're at it, why pay more than you have to for the same thing is what I say.

http://www.ebay.com/itm/330921139747?ssPageName=STRK:MEWAX:IT&_trksid=p3984.m1423.l2649

http://www.ebay.com/itm/130993281578?ssPageName=STRK:MEWAX:IT&_trksid=p3984.m1423.l2649

Map reddd

FMB42 · Oct 23, 2013

mapbike said:
The A Type is correct piston, problem is that $11.00 for piston only and then high priced shipping...

The same piston with rings etc on ebay with free or cheap shipping and you get other new parts that you might as well also replace while you're at it, why pay more than you have to for the same thing is what I say.

http://www.ebay.com/itm/330921139747?ssPageName=STRK:MEWAX:IT&_trksid=p3984.m1423.l2649

http://www.ebay.com/itm/130993281578?ssPageName=STRK:MEWAX:IT&_trksid=p3984.m1423.l2649

Map

Ya, the shipping along with the "rings not included" are a pain in the wallet. But nonetheless, sometimes it's good to know that you've got options.

A case in point is that just yesterday one of the retailers that I like had the Type A #2 piston that's used in my engine. So, today I thought I'd get one as a spare and yep, you guessed it, they're currently out of stock.

kdaddy1980 · Oct 23, 2013

i read the description on piston bikes,and it said that the diameters are all the same on 80/66cc engines only dif is the wrist pin hole. so if the piston diameters are all the same then are all the jugs/cylinders the same? is there variations with ports? or is there a variation in the cylinder height?

FMB42 · Oct 24, 2013

kdaddy1980 said:
i read the description on piston bikes,and it said that the diameters are all the same on 80/66cc engines only dif is the wrist pin hole. so if the piston diameters are all the same then are all the jugs/cylinders the same? is there variations with ports? or is there a variation in the cylinder height?

Well, the "A" pistons, or most of them anyway, have numbers stamped on them (i.e. 2, 3, and 5 IIRC). Not sure if these numbers denote the diameters of the pistons, the dia. of piston pins, or the factory they were made at. I'm not sure if you can "mix" these numbers around so to speak, but I do know that when the time comes I'll do what I can to replace my #2 piston with the same.

As for your jugs/cylinders question; I really don't know (but I'm very sure that other, more knowledgeable, members can answer this...

kdaddy1980 · Oct 24, 2013

FMB42 said:
Well, the "A" pistons, or most of them anyway, have numbers stamped on them (i.e. 2, 3, and 5 IIRC), but I do know that when the time comes I'll do what I can to replace my #2 piston with the same.

thanks, i would try to match the numbers if i could but the top of that piston was obliterated and no number is recognizable.

mapbike · Oct 25, 2013

All the 66cc pistons are 47mm and there are two different wrist pin heights, there were some older flying horse engines that had a larger dia. Wrist pin but as far as I know those are all obsolete now and wrist pin dia. Is same on all of them as well as bore size for the 66/80 china girl engines.

Map

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66/80cc Pistons

kdaddy1980

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