Help with ordering piston, grube gt5

[rogergendron]

Hey guys I am new to the forum but a very experianced mechanic.

I have a problem here. It seems like there are at least 3 dif piston types for the same style engine.

I am doing a rebuild ... Port polish port matching exe .... And I am litteraly done, all I need to do now is order a new piston rings and clips. Then trim the skirt to match my intake port and grind a relief in the piston for the exahst and side ports.

But I do not know the part # of the piston I need

I jave the grubee gt5 my piston has only an arrow on top and when the piston is on a flat surface the top of the wrist pin hole measures 1 1/8 up from the surface . The closest piston I found said it was a type b and the hole measured 1 1/16 up ? Thats a 1/6 off and will alter port timimg ! The other said 15/16 up. Type a I think there are more but they are marked differant than mine on top . I want the correct dome and port timing here so I need to be shure I am getting the roght piston .

Can you guys help .

 

[Purple Haze]

The main difference is the compression height. (distance fron pin centerline to piston top) The Super Rat had a 40mm stroke, while most all others have a 38mm stroke. Not a big problem if you know how to shim the cylinder to get "0" deck height. Also, there is a piston with a domed top which I don't recommend, as it impedes flame travel, stick with a flat-top piston. It's also a little lighter, which helps balance and quicker revs. By the way, I don't think they make the Super Rat anymore, but still sell parts for them. Hope this info helps.

 

[Deleted member 12676]

If you're worried about port timing you have to measure to piston top edge, not the center top of the piston.

 

[KCvale]

gasbike is the importer of Skyhawks and has parts.

http://www.gasbike.net/scart/public.../www.gasbike.net/scart/public/scart/scart.php

Does yours have the old 2-parts crank or the new 1 piece?

 

[danlandberg]

I'm now having trouble finding the correct piston pin for my GT5 Pro racing. I ordered one from Kings and it is to short, 32.6 mm in length.
The pin I have is 36.9 mm in length. Dia is correct, 10 mm.
The needle bearing length is exactly the same as the rod width witch seems to short of a cage. 12.2 mm wide.
The gap between the piston pin bosses is 17.2 mm. this will allow the needle bearing to move left and right 2.5 mm. This doesn't seem right.
Where is a good place to get the right parts for this Vintage engine? LoL

 

[crassius]

many places on ebay sell wristpins in both short & long versions (they list length in ad) - some sellers of piston+rings+wristpins+clips as a set seem to use whichever length is handy and I've not seen a problem using the short pins

there was discussion years ago about using spacers on short bearings, but most bearings seem longer now - you might find lengths in some ads, but I'm not sure

 

[danlandberg]

I have been contacting vendors with measurement questions but have not heard back yet. I'm putting it back together now, it ran fine when I took the engine off to use it as a bike while I was waiting for a fuel tank. While it was off I decided to modify the skirt on the intake side. Thats when I noticed an area on the pin I don't like. So if it goes another week I'll be OK. I'm going to order a complete top end kit for the long rod engine.(High piston pin).