750 to 800?

"Dear Ralph" September 28, 1998 0
Dear Ralph, I plan to re-ring my ’93 750 Storm. I’m thinking about boring it to 800cc. The question is: does the ’93 750...

Dear Ralph,
I plan to re-ring my ’93 750 Storm. I’m thinking about boring it to 800cc. The question is: does the ’93 750 have the same case and cylinder as the ’94 800 Storm? If it is the same, can I resleeve to an 800 or is there an easier way to do this, via boring 0.010, 0.020, 0.030, 0.040, and putting 800 pistons in it?

Kyle Ohnstad
Mounds View, MN

This seems to be a yearly question – what to do with all of the older Storm engines. There are plenty of used Storms that dealers would love to sell at bargain prices, and a savvy tuner could turn one into a rocket for a lot less than a new machine. First a little background – rumor has the original Storm engine as 800cc with Nicasil cylinders, but was considered too “ballistic” for the market at that time. So to de-tune it and make it less expensive it was delivered to the consumer as an iron bore cylinder 750cc – and that’s when the “heat problems” started. Durability was the key issue as getting pistons to last was difficult.
Can you bore your 750 cylinders to 800? Unless you install new sleeves, I think you are limited to about 780cc. Even then, the cylinder walls will be very thin, the ports will be small, and you’ll still be fighting a heat problem. To install new sleeves and go up to 800cc is an option, but the heat problem will still be there. Another option is to send off your cylinders (with a new set of pistons) to get Nicasiled. But if you use bigger pistons you’re again back to thin cylinder walls and small ports.
Perhaps the best option is to drop on some of the newer ’97 Storm cylinders that are Nicasil coated, along with heads and pistons. This would be the most expensive route, but would be the most efficient. You would have to do some case work to give the larger diameter skirts room to drop into the case, but that’s pretty easy. With this mod you should also want to install the pressurized cooling system to make it right. Since the pipes were originally designed around an 800, they should would work just fine. You could start with the ’97 Storm jetting specs and be pretty close too. The latest Storm engines have been pretty reliable.
Of coure, the least expensive route is to simply clean up the bore, and check the tolerances to see if you can just re-ring. But my suspicion is the pistons in your engine right now will show “knife edging” (a sharp melted edge on the top of an over heated piston [at the exhaust port] that causes the ring to stick so it loses compression). If that’s the case you’ll have to drop in new pistons anyway. Might as well plan on buying at least three new pistons – go with Wisecos if you can get them – they were hard to get last year because of the high demand. They’ll be a bit more durable than the plain cast OEM Polaris pistons. We played around with some Elko (Austrian pistons from the same maker as Rotax, and now what the domestic Polaris engines use), but you might as well stick with what is readily available. They made the power, but still knife edged at about 1000 miles. Bottom line on the Storm is that if you’re investing any large amount of money in it, go with some form of Nicasil cylinders, install the pressurized cooling system update, and get ready to do some clutching.

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