CYLINDER HEAD SWAPS

[pressalire]

DO OTHER HEADS FIT THE GZ250 WITH LITTLE OR NO MODIFICATIONS? LIKE THE QUADRUNNER OR THE 1980'S SP250 DIRTBIKES?

[Water Warrior 2]

DO OTHER HEADS FIT THE GZ250 WITH LITTLE OR NO MODIFICATIONS? LIKE THE QUADRUNNER OR THE 1980'S SP250 DIRTBIKES?
Not much you can do with the GZ to improve it. It is what it is. No big bore kits or real performance goodies available.

Oh yeah. All CAPITAL LETTERS IS LIKE YELLING ON THE FORUM.

[jonathan180iq]

No.

If you have an unlimited supply of money, knock yourself out and go for it.
But everyone who has ever come in claiming that it's possible, or that they already "had their mechanic working on it" have since recanted or just never came back to the forum due to embarrassment.

[Cooteboy]

Hey there guys, back after a long winter break. Now comes the local 5th season MUD! :D

The mid 80's quad heads DO FIT the GZ250!! You just have to make sure they are the 4 valve heads. LT250 (not the LT250R) and the GN250 both work very well.

The ONLY 2 differences are the slight modification in porting - which I didn't change on my bike at all and it runs great - and the fact that you will have to figure out a way to plug the pressure relief lever shaft where it goes through the valve cover - can be done with o-rings and some clever grinding/cutting of the original lever.

I've stated this in the past and it works great! Seriously if you guys want me to, I will get some pictures once the barn dries out so you can see what I did.

Sorry, just saw the date of the posting. I hope this still helps

[Cooteboy]

I just recalled there was a 3rd difference in the design - but like the porting doesn't require any modification to run. In fact the 3rd difference in my opinion should help the head to last longer. The Camshaft is longer on the older designs. It doesn't stop at the chain gear and hang in mid air like the newer engines. It extends to have one more contact point on the head to help stabilize the leverage/tension from the timing chain. I am personally glad I have the LT250 head on my bike - I'm fairly certain it will outlast the same repair had I used the GZ250 parts.

Also, I wanted to quickly explain what the "relief lever" was/is. The quadrunners were a pull start - and to relieve the pressure in the engine so that you could "easily" pull start it they had a lever that would press down on the exhaust valves just enough to keep them from seating firmly - therefore reducing compression and allowing for an easier pull start.

There is a small 5/16" hole on the valve cover located toward the front of the engine where the relief lever passes through cover itself. The way I sealed mine was by cutting/grinding the lever into a small shaft. I then cut a groove around the shaft on one end so that I could place an o-ring into the groove so that it would seal and not leak oil out onto the head.

I will try and post pictures once the weather is a little nicer. It's been raining cats and dogs adding to the MUD!

[alantf]

Also, I wanted to quickly explain what the "relief lever" was/is. The quadrunners were a pull start - and to relieve the pressure in the engine so that you could "easily" pull start it they had a lever that would press down on the exhaust valves just enough to keep them from seating firmly - therefore reducing compression and allowing for an easier pull start.



I recall something similar on my dad's 1940s Norton 500cc. There was an "exhaust valve lifter" lever on the handlebars of this big, single cylinder, engine, so that you didn't break your leg from the kickback on the kick starter. :)

[Water Warrior 2]

This is still a common practice on some modern bikes. They won't have to have a massive starter and battery to fire up those large cylinders. Larger Suzuki V-twins have this feature.