Issues with Grubee GT2 Frame

BikeSmith · Nov 28, 2015

Hello. I just picked up a Grubee gt2 frame from a company called Piston Bikes. The frame looks the same. but the fuel tank filler is a push and turn like on all the kit tanks, and it is really hard to open and close. but the one on the grubee site and other sites, look like a spin on type. also my fuel petcock from my grubee 4g engine kit will not thread in. Has anyone ordered from this company before? are they good? did I buy a KNOCK OFF? Or am I doing something wrong. Any help would be great. :-||

wing nut · Nov 28, 2015

hello ,
sounds like you got what ever petcock hard ware they had laying about that day ....but imho ive found most of the "stock " & "kit"petcocks are severly lacking ...
intsead what you can do is go to your local lawn & garden center & get yourself a much better fuel valve / petcock..nappa carries one that threads right in & its fuel out let is at a 90 degree angle ...perfect for directing the fuel line

dbledsoe · Nov 28, 2015

Many of the photos on the Grubee web site are old, very old. Years back the GT2 frame from Grubee did have a threaded screw on gas cap. Not so anymore (as best I can tell). Now they all use the "quarter turn" gas cap the same as what comes with the engine kit 1.5 l gas tank. If it is hard to install spray it (on the underside, to include the rubber gaskets) with WD40.

As to the built-in frame tank fuel outlet, mine was threaded to accept the standard bike engine kit supplied pet cock. It was a wee bit difficult to get started but it fit and does not leak.

BTW, some here will tell you that your frame is not a Grubee frame even though the Grubee frame may look identical to your frame. My suggestion? Ignore them who say such.

BikeSmith · Nov 28, 2015

Thanks for the Frame info dbledsoe. I will try to look for a new petcock, wing nut. Do you guys know what the standard thread size on these frames is. or the standard thread size of most petcocks. I looked but can't find my thread gauges right now. Just a note. I have hundreds of bikes. but this is my first motorized bike build. So this is all great info for me. Thanks again.

wing nut · Nov 28, 2015

i do believe its 1/4 npt

BikeSmith · Nov 28, 2015

Thanks. wing nut.

dbledsoe · Nov 28, 2015

I just checked my spare GT2A frame against a threaded brass tube I bought at Home Depot and the fuel petcock boss of the frame is 1/8" MIP (NPT).

Don

crassius · Nov 28, 2015

I'm a bit confused about whether we're talking about the petcock or gas cap. A hard to turn gas cap can be fixed by making sure it is nice & straight, then filing as needed on the edges of the lock slots.

dbledsoe · Nov 28, 2015

Actually I thought we were talking about both.

Filing on the locking edges is a way to fix the tight fitting gas cap, or as I did, just try another gas cap (I have about five spares of the funky little 1.5 liter gas tanks with caps so I can easily juggle gas caps).

You also asked about thread size of the petcock. I checked my spare GT2 frame (build in progress so no petcock has been fit yet) and the thread size is 1/8" NPT.

Don

BikeSmith · Nov 28, 2015

Thanks Don. I will try the 1/8th npt. the petcock I have looks like a fine thread pitch of some kind. Crassius. I will try and file the edges. the cap hardly even go's in the hole. and one of the two "teeth" on the cap gets hung up when you try to pull it out. if that will not work. I may just have the machine shop weld in a new thread-in style from an aluminum motorcycle tank or oil overflow tank. that way I have some cool options later on. I need to build a new engine mount anyway. because I am putting a 4stroke kit in the 2 stroke frame. and the mount is too short.

wing nut · Nov 29, 2015

sorry for confusion, i was talking about petcocks , my frame came with a plastic gas cap that didnt vent right

dbledsoe · Nov 29, 2015

BikeSmith said:
Thanks Don. I will try the 1/8th npt. the petcock I have looks like a fine thread pitch of some kind. Crassius. I will try and file the edges. the cap hardly even go's in the hole. and one of the two "teeth" on the cap gets hung up when you try to pull it out. if that will not work. I may just have the machine shop weld in a new thread-in style from an aluminum motorcycle tank or oil overflow tank. that way I have some cool options later on. I need to build a new engine mount anyway. because I am putting a 4stroke kit in the 2 stroke frame. and the mount is too short.

1/8" NPT is a rather fine thread.

The petcock that came with the engine kit 1.5 liter gas tank works just fine in the GT2A frame gas tank fuel outlet boss... not that the Chinese petcocks are all that great, but so far they have worked ok. As to their service life, well that may be an entirely different matter. If you can find a better quality petcock with 1/8" NPT thread you might want to go for it. Or, alternatively drill and tap the GT2 frame tank for a small motorcycle type petcock.

I bought a couple of brass petcocks with 1/8" NPT thread size from gasbike.net that seem to be of a bit better quality (but still not all that robust), but I do consider them a better alternative to the pot metal petcock that is standard in the typical bike engine kit. Unfortunately I fear that just about any petcock you elect to use is going to be a Chinese sourced item... not that that is all bad. I know for a fact from first hand/hands on experience that China can make some really good top notch stuff, and I have several higher end Chinese telescopes sporting superb optics, along with my iPad, iPhone, and MacBook Air that prove it.

Don

BikeSmith · Dec 1, 2015

Thanks again for info on this subject. I am probably going to go for a motorcycle type valve. Finally found my thread pitch gauges. an it seems to be 1/8th npt. but it looks like they might have tilted the tap on the last couple of threads when they pulled it out. So I am going to have to re tap anyway. so might as well go to a better one I guess. I did get the fuel tank cap to work smoothly today. just a little filing goes a long way

but now I found that my bicycle chain sprockets don't come even close to being inline with each other. I have a single on the wheel and the frame is set up for a caset. so I gues I will be rebuilding my rear hub.

but it will come together in the end. I am still having fun building this bike. so all is good.

dbledsoe · Dec 1, 2015

BikeSmith,

This will make you cringe but it worked for me. I was in the same predicament as you, single speed rear wheel frame too wide at the drop outs. I opened my bench vice nearly all the way, put aluminum vice jaw blocks in, slid the GT2 frame rear wheel drop outs in-between the vice jaws, the frame in a vertical position (with the steer tube axis parallel to the ceiling of the garage), and proceeded to crank (tighten) on the vice pressing the drop outs toward each other until my single speed rear wheel fit as I wanted it to (drop out width inside to inside 4 1/4"). I had to squeeze it down to about 3 3/4" to allow for frame spring back, which brought it to 4 1/4" once the vice pressure was released. Pedal side sprocket aligns perfectly with the crank sprocket.

Like I said, it is cringe worthy but it worked and the frame looks like it was made to fit the single speed rear hub, no bends or kinks visible in the seat or chain stays. Something to think about.

I've done the same to two GT2 frames now.

Don

wing nut · Dec 1, 2015

id like to see some pics , are we ready to discuss the gold stuff on the frames?
http://motorbicycling.com/showthread.php?t=44299&page=2

dbledsoe · Dec 3, 2015

wing nut said:
id like to see some pics , are we ready to discuss the gold stuff on the frames?
http://motorbicycling.com/showthread.php?t=44299&page=2

Pics of what, my squeeze frame? I can do that... when the outside temps get above 20 f here.

As to the gold stuff coating the frame, I thought you addressed that to your satisfaction in another thread? As for me and the mysterious gold, my powder coater dealt with it. How? I do not know, nor do I care. I quizically pointed it out to him (as in WTF is that?) and he simply told me not to worry, they will deal with it. His response sounded good to me. All I know is that two GT2A frames I have that were once gold are now painted black, one of them anyway, the other is British Racing Green.

Don

wing nut · Dec 3, 2015

yes the squeeze frame , and any other pics
i figured id link that post to this in order to share my experiences
i also had my powder coater remove it

BikeSmith · Dec 4, 2015

Well everything seemed to come together after rebuilding the rear wheel. got it outside today. and fired it up for the first time and took it for the maiden voyage around town. I LOVE this thing. all I can say is that I now UNDERSTAND!!!.

will have to blow it apart and paint it after it snows. the body shop said they would glass media blast the frame for $35.00 and it will be clean and ready for paint. dance1

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