grubee gt5 cylinder differant port map than others ???

rogergendron1

rogergendron1

New Member
hi everyone, i have a grubee gt5 that needs rebuilding and i have read that the grubee gt5 66cc jug has a differant port map than the standard pk80 or dax balanced motor.

my question is can i run a pk80 jug on a grubee gt5 ?

i know the pistons are differant as in the location of the wrist pin hole is lower on the grubee gt5 motor or is it higher lol i forget..... any way are all the jugs the same and the grubee just uses a differant stroke crank arm and thinner base gasket and higher wristpin hole than others to achive the same port timing or are the jugs differant as well ?

for instance i know the grub33 gt5 has a differant piston and stroke than my dax does

dax has a 110mm con rod and is 85mm hole to hole i think
and the grubee is 100mm and 83mm hole to hole ?? i am unshure here.

can i use a pk 80 jug on a grubee with some modifacation if i have to ?

for instance with a thicker base gasket and a differant piston ?

my dax has a 1.6mm base gasket and the grubee gt5 was far less like .5mm so right off the bat the dax has 1mm taller ports and the piston is differant also so w.t.f. ???

where can i get a grubee jug lol ? the only place i know of is arrow and they are all modded, i plan to save money and do the moddin and porting myself so spending 70$ on a grubee jug is out of the question ! all i can seem to find is pk80 type jugs for sale where can i get a stock grubee gt5 jug ?

or can i just use a pk80 jug and mod to get the correct port timing by raising or lowering the jug via gasket thickness and raising and lowering the piston via wrist pin location ?

the ports need to be fully open at BDC and the piston needs to come to the top of the jug for correct squish clearance at TDC, can i achive this with a pk 80 jug on my grubee gt5 motor using gaskets and piston swapping? or do i need a grubee gt5 jug ?
 
Last edited:
I could be wrong but from my understanding the jugs are all the same .the area that's diferent is piston con rods if I reamember right from another post on here thers 3 or 4 diferent conrods and pistons or something like that. ohh and if I am wrong on this please someone correct me. thanks
 
Bill's right...I verified this recently by making a veritable "brass-rubbing" of some jugs' interiors using a strip of loose-leaf and a pencil: the jugs are identical.
 
bill2781 said:
I could be wrong but from my understanding the jugs are all the same .the area that's diferent is piston con rods if I reamember right from another post on here thers 3 or 4 diferent conrods and pistons or something like that. ohh and if I am wrong on this please someone correct me. thanks
Click to expand...
PK 80 style motors and SkyHawk motors use different jugs or cylinders.
Different pistons too.
 
you can run a pk piston in a gt5 as long as the con rod has z-l on it or zaf 50 not the zaf 60 tho. and yes the jugs are different the biggest visual difference is the gt5 usually has a tapered transfer port window..
 
the gt5 piston is the b style the pk is the a style the wrist pin is higher up the skirt on the b piston.. you can get a gt5 jug at bikeberry or gasbike whoever sells grubees. ive always had good luck with a Skyhawk lower ends matched to a pk top end
 
flybytaco said:
the gt5 piston is the b style the pk is the a style the wrist pin is higher up the skirt on the b piston.. you can get a gt5 jug at bikeberry or gasbike whoever sells grubees. ive always had good luck with a Skyhawk lower ends matched to a pk top end
Click to expand...

so running a pk 80 top jug on my grubee gt5 will esentialy raise all the ports ? given i use the grubee gt5 con rod and piston ? what size base gasket an even 1mm or should i use the 1.6 ?

if its true this setup would get better tranfer port timing and an nicely raised exhaust port that can be ported out a bit lower if desired, but i would have to lower the intake a lot with a good amount of port work to make it happy right ?

seems like a preformance mod for a grubee gt5, would be to add and mod a pk80 jug ?

so a gt5 lower and gt5 piston with a pk80 jug would need a lot of port work to correct the port timing

but a gt5 lower with a pk80 piston and pk jug would have ideal timing but the piston deck hight would bee to low due to the rod length and the jug would need to be decked ?

fly by taco.... can you elaborate some more on the combos of parts you have used with the gt5 lowers ? i have a spare gt5 motor with a scored up jug and piston and i am looking to do a long term full out high rpm racer build using the gt5 bottom end, think home brew arrow street racer.....
 
Last edited:
Roger, I was having good luck running a gt5 lower end with the zaf60 rod and a pk complete top end. There is modification needed though. Using the type a piston on that rod requires a spacer under the jug. Just search my name and check out some of my posts... how about this sheet weather were having? Lol gotta finish my motor swap and get my nokian tires on..
 
you will have super low compression, because the gt5 endiges have a 38m stroke, while pk80 motors have a 40mm stroke. I recently ran into the reverse of your problem, I bought a super cheap crankshaft from gasbike.net (a super grubee affiliated supplier) and they sent me a crank with a 38mm stroke. when I went to install this, the stroke was much too short, the piston did not reach the top of the cylinder, and the piston hit the crank on the downstoke. i guess you could machine down a pk80 cylinder to work, which it *might* - but why?
just buy a grubee cylinder: http://www.gasbike.net/cylinder-body-gt5-60cc-80cc-3456-prd1.htm and then port that for high performance.

good luck dance1
 
hey taco your right ! i do have the 38mm stroke full circle crank and the zaf 60 rod and with the pk 80 piston it does not work the piston comes out of the pk 80 jug but if i run the type b high wrist pin piston on the 60 rod and 38mm stroke crank it port maps perfectly to the pk 80/ f 80 40mm stroke top end but the jug needs to be decked down a bit to get the right deck hight as the f80 jug is a bit taller than the grubee gt5 jug

so with the zaf 60 rod and type b piston you can run a standard jug as long as u plan on decking it down a bit
 
I've done all the measurements on both bikes, unless the dax PK80 has a new version out, in which case I've merely heard claims of it being 40mm stroke (I'd like verification because if it is, I'd be going for it, I want a longer stroke crank), but to my knowledge noone's actually taken the time to measure. The GT5 cranks are ALL 38mm stroke (37.66 actually but hey, whos keeping track?), and the con rods are 110mm and 115mm (80mm eye-to-eye and 85mm eye-to-eye). This is why the wrist pins of the Type A/D and type B motors differ by 5mm (Type A/D has a 115mm [85mm] rod with the wrist pin center 21mm from the crown, the Type B has a 110mm [80mm] rod with the wrist pin 26mm from the crown). This sets both the pistons at exactly the same height at TDC and BDC. a 2mm longer stroke (40mm stroke) will give you 1mm lower at BDC and 1mm higher at TDC. This also means the jug needs to be at least 0.4mm taller (to make a deck height of 0.1mm), and the ports need to be separated more to achieve the same timing. That said, the port maps are identical last I saw, the only difference is the Type A/D motors' ports are 1 or 2mm LOWER than the grubee's. That means the transfers arent nearly as open as they should be, the exhaust is never fully opened and opens later (good for low-end power! this is what gives it it's grunt!) and the intake opens more fully. I've seen both types of cylinders on the same bike and I can confirm the Grubee (Type B) ports are at least 1-2mm higher up (I ordered a type D cylinder from speeddemon.com, and noticed I had a lot less power on my GT5a, took the head off and checked the ports, the transfers BARELY opened at BDC, my roommates motor [completely type D, top and bottom] has the same problem).
 
The setup i am running now is the grubee gt5 38mm stroke with a juv from a dax, the jug ports are fuly open with a stock base gasket on the exhaust and transfers
 
66sub said:
the complet gt5a is a brute in stock form when head is corrected.
Click to expand...

I have to agree, with some pedalling it launches harder and faster than most cars. Without pedal assistance it still launches about as hard as an old pontiac firefly (so not fast, but respectable for such a tiny engine).

With a proper carb, it's even faster. Easily the best mod you can do is the wider manifold and bigger carb, aside from the pipe.
 
im all about GP PIPES now and i dont even know where to begin. when i try googling etc i get no where fast. seems they like economical cylinder timing with non excesive transfers? ask me in 2 months maybe but i think im going to come up short looking for answers.
 
Last edited:
going fast with piston ports means likely the gt5a is a poor choice with the eyebrow transfers. the top end rpms will only be messy and loud. for lowend stump pulling it should be the best by a long shot.
 
Last edited:
Yeh the grubee jug i have seen all had angled transfers where as the dax and pk 80 style had a levle top

i do like the grubee motors and despite all the hoo ha about the dax and the gen v i have run all 3 i can say i stil like the grubee gt as a base motor for a fully moded engine
 
But damn its a pain in the ass trying to find a high wrist pin piston lol

I have ordered 2 high wrist pin grubee pistons now and bolth times got sent the low qrist pin lol

one had no maekings and one had a #2and an arrow however bolth pistons were exactly the same despite the markings

now if i can just get the right piston i can finnish my stuffed high comp midrange stump puller!
 
You must log in or register to reply here.
Back
Top