Will this work? Has anyone ever tried this. I have a ton of experience on the 300 4x4 but none with the EX. Have a oportunity to get a wrecked EX that has a busted case but a good cylinder, I have a 300 4x4 with a bad cylinder and head are they interchangable? I don't want to buy the wreck and then not be able to use it.

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Kevin Gowdy aka Kagey 1999 Polaris Magnum 500

 

I believe this would work. They look similar. I have a 300EX and my friend has a 300 4x4 and the cylinders look the same. They both have 4 valves, same bore, maybe different can though.

 

If it did work, you wouldnt gain a bit of performance. Maybe one hp. The ex motor is a slug. The main thing is the cam, stud pattern, and stroke and bore match up. I really dont think it will be worth the effort.

 

The 300 4x4 have 2 valves not 4.

 

Not really looking for performance out of this its more of a money saving deal for the owner of this 300. He works for the Insurance Company that has this wrecked Quad and can buy it very cheap. The 2 heads are diffrent as Boner said 2valve in the 4x4 verses 4 valve in the EX so the Engine should at least breath better.

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Kevin Gowdy aka Kagey 1999 Polaris Magnum 500

 

I'm not sure, you'd have to have both cylinders, heads, valves, etc and measure everything. Are they the same height, bore, same heads, VALVE'S AND CLEARANCE, cams, piston height, diameter, and WRIST PIN LOCATION ON THE PISTON, etc... Their is much more to it than just cylinder looks. My guess is they won't interchange, because the machines are built for different things. One my have different stroke than the other, thus making the bores different. Also a 300EX is actually just a stroked 250X (same bore as a 250X) and its displacement is actually 284cc, is the 300 4x4 the same?

Personally it sounds like you will possibly get yourself into too much trouble than it's worth. Instead of wasting time and possibly A LOT of money, just buy a new cylinder. If you don't want to get a new one just call a used parts yard like Cal ATV and see if they have used cylinders for your particular bike at half the price for a new stock one. And if nothing else, if you can get the 300EX cheap and you know somebody looking for a play quad, cases really are not that expensive, and it sounds as if you've tore into thumper engines before and could change a case on your own, then buy it and sell it or keep it yourself.

Good Luck,

Sickman

 

The switch has been done. It's not easy. Here's the basic problems encountered:

1. Stud placement. Weld up the ute cylinder to accept the different stud placement. Drill the head to match the oil passage coming up through the cylinder. Oh, and before you ask, the EX cylinder doesn't bolt on to the ute cases.

2. Build a reverse rotation camshaft. The cam in the ute travels in the opposite direction from the EX.

3. Fix often. The engine which we did this to still has cam & rocker arm wear problems. Probably from less oil getting to the head than it had with the stock setup.

 

Pam, thanks as always for the wealth of information and experience you share!

Based upon your input, to me, the short answer to the question, "Will it fit?", is, "No."

Tree Farmer