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Where To Buy. 1978 gs400 big bore kit

  • Thread starter Thread starter nate4d
  • Start date Start date
N

nate4d

Guest
looking for a big bore kit for my 1978 gs400. i am not sure where to find it i tried to ol google and got nothing, i figured if anyone knew itd be you peeps. thanx, link appreciated.
 
Good luck on that one. I bet you'll have to try and find stock pistons from a larger bike and try and determine if they will work on your crank and if your cylinders can stand that big a bore. I'd take the $1000 boring that engine would cost and buy a bigger bike.
 
An entire GS 500 twin top end might bolt right on. Get the base gaskets from both & see how much difference there is in the 2. We used to road race a GS 500 I built in Hawaii & it was a GREAT race bike. I did a LOT to that motor but it never gave us a single problem. You could also just bolt an entire 500 motor into your bike. That would be much easier. Ray.
 
I deal with Weisco . I send my rep a piston and they match the dimensions to spec or larger (custom valve pockets if necessary). XC styles are the least expensive and turn around is less than a month. they matched a set of 3 cylinder 2 stroke s-1 pistons for us just this spring. $200 a piece. clips pin rings complete.

you will have to have a proper account with them. but I can save you from retail prices.
 
trippivot said:
I deal with Weisco . I send my rep a piston and they match the dimensions to spec or larger (custom valve pockets if necessary). XC styles are the least expensive and turn around is less than a month. they matched a set of 3 cylinder 2 stroke s-1 pistons for us just this spring. $200 a piece. clips pin rings complete.

you will have to have a proper account with them. but I can save you from retail prices.
Click to expand...


My god do you mean Wiseco will do a one off set of psitons for a measly 200 bucks? that is amazing...I want tojuice up to a 650
 
trippivot said:
yep . where do you normally buy pistons from?
Click to expand...


if you mean where do I buy psitons from I do not...I do recall Wiseco made a big bore kit for the 572 cc engine in my bike back in the day but these have all doisappeared

it is interesting to know that you can get something done like this
I mean 200 is at par with the mass produced big bore kits is it not?
its cheaper than an OEM piston mor eor less....
 
The GS400 uses the same piston as the 77-79 GS750. 65mm diameter with a 16mm wrist pin. Therefore any big bore kits for the GS750 will give you 4 pistons for your project. GS425 pistons are 67mm, they too will work. Best of all the GS850 is 69mm and there are a bunch of used pistons for those floating around. Using GS850 pistons with the stock 60mm stroke will only give you about 450cc, but you have to find a head gasket that big. The Suzuki GS450 shares more parts with the GS1000, including the 18mm wrist pins, which won't fit your GS400 crank. Hope this helps. Dar
 
just swap the whole gs500 in, there is no way you can get anywhere near 500cc for cheaper (assuming you can find a donor cheaply enough)

I think they DO make a big bore kit for the 500...
 
GS 500 motor swap

GS 500 motor swap

The problem with swapping in a GS 500 engine is the exhaust pipes exit from the 500 head straight forward, whereas on the GS 400/425/450 head the exhaust pipes are angled outwards. Because of this, the 500 exhaust would hit the frame of the 400/425/450. You could try to modify the 500 exhaust so that it would angle outwards around the frame or try to mod the frame.

A big bore kit was offered but has not been in production since 1992. I have read of people using 78mm Weisco GPZ 1100 pistons to increase displacement to 541cc.

More info over on gstwins.com in these two threads:

http://gstwins.com/gsboard/index.php?topic=32958.0

http://gstwins.com/gsboard/index.php?topic=14401.0

If you do go through with either of these options, I'd be interested in your results. Good luck.

Edit:

Ther was also some talk on the GSR of transplanting a Suzuki Tempter 650 engine in a GS 400 since the Tempter exhaust ports are similar. However this is from 2006 and the thread just dies.

http://www.thegsresources.com/_forum/showthread.php?t=101798&highlight=450+motor
 
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