So I have noticed that there are two cylinder and piston designs available for the 400 motor. One with an intake flange that is perpendicular with the base, and one with an angled intake flange. I believe one uses a piston with round ports, and the other uses a piston with bigger oblong ports.

I have an oportunity to buy one for pretty reasonable all rebuilt and ready to go, however it is not the same as the one I have that needs rebuilt. I was wondering if these two sets of cylinders and pistons were interchangable? Is the deck height the same? are the upper motor mounts located in the same orientation? And will they use the same reed setup and intake? Connecting rod upper? Cooling system ports? Base and head bolt patterns???? I appreciate any info you guys may have on the subject.
Thanks

 

I thought the only difference was the intake boot between the two engine designs. I think everything else should be able to be swapped. Wait for other answers to double check though. Otherwise call Rick Ritter as that man knows probably more about those 400 motors than anyone else on Earth lol.

P.S. Great year, great machine. Taking mine out next Saturday.

 

Dropped intake manifold was for the Scrambler 400,straight intake manifold was for the 400L, Explorer, Express and Sportsman 400.Only difference between the two cylinders. Intake manifolds can exchange.

 

Thanks guys. Hopefully I will have this beast up and running soon!

 

If I went to a round port piston from the oblong one I have, would I have to change carb jetting as well?

 

Every engine is different. Don't change anything until it's up and running,then you'll be able to tell if jetting needs to be changed.

 

350L motors had intake boost ports going directly into the crankcase. but it had the intake flange even with the upper motor mount surface. I believe these cyls had pistons with small in the intake skirt.
In the 94 the motor had an increase in bore from 81mm to 83mm, making displacement 378cc. these cyls had no intake boost ports. The piston with these cyls had the large holes in it from the factory. This cyl was also used for 95 as well. With the stock cast piston they were most prone to skirt breakage. This cyl will likely starve a little with a small hole piston.

In 96 the cyl design changed again, the intake boost ports reappeared. these ports are often referred to as boyesen ports. they are a little bigger and aimed different than the 350 ones. It got the reangled intake flange needing the different carb boot, For the 96 it used the piston with the large holes still.

97-03 cyl is the same as 96 but polaris went back to the small hole piston.

With a stock pipe and porting the 94-95 cyls is fine, but it's power potential is less.

All wiseco pistons have the large slots.

 

So the motor is all buttoned up, and fired up 2nd pull. Went with a cast piston with the large intake ports. Was running a little lean, but seems better after some tinkering. Thanks for the help guys.

As for the break in period, I was wondering what you guys thought? I started off with some 32:1 mixed gas feed from a boat gas can, just to get the oiler all primed up and working. Now that it is working, it fouls plugs pretty quickly. I assume that I need extra oil, beyond what the oil injection provides during the break in. I would like to keep the oil injection and am wondering how, or if I should mix the gas in the tank too.

 

40-1 is plenty if you're premixing only. 50-1 is recommended on the first tank of fuel if you're keeping the oil pump. If the oil pump is working properly,you have the pump alignment marks adjusted right,it's set up from the factory to at least a 50-1 ratio or more at all speeds.You can add a couple ounces to the tank if you don't trust the pump or just simply defeat it and premix 40-1 as a lot of people do. Any richer and you just rob octane and foul plugs.