SBT 717 MAIN BEARINGS

[DAVID_HX_XP_RX-DI]

Bryan,

I would like to know specifically what type, material and engineering classification of the main Bearings used in your (MY) SBT remanufactured Sea-Doo 717 engine.

The reason /
I would like to build the engine to a higher output (Yes, I know the warrenty is flushed if I do)

I just want to be sure the Mains can handle the increased torque of a H.O. engine with the bearings SBT uses, otherwise I will rebuild the lower end as well.

I already *know* the Crank is able to handle the load since it was recommended by a few others in the racing circuit for its' trueing and weld.

Keep up the steam !

David

[CaptToyota]

David, in regards to your brg question, the "ball"
brgs used on crank should have no problem. Use a
quality oil. As far as brgs, having a sister that has been in the bearing bussiness for 19-20yr now, currently Timken, ball (along with other designs) are same specs/tolerances between manufacture's (SKF,KOYO,NTN,FAG,NACHI, and others-SBT says they use NACHI), NACHI supplies Toyota the brgs for the rear axle at the end of the housing and others on our vehicles. The part that will require the added "BEEF" is the welding of the main and rod pins to the crank weights to make the crank more "structurely rigid" (won't twist and alter timing between front and rear cylinders).

[Greg Pickren]

David,

The bearings used by SBT for our Sea Doo engines are made in Japan by Nachi. Nachi is one of the largest bearing companies in the world and an OEM supplier to many manufacturers.

In general, the bearing industry is extremely standardized worldwide and bearings tend to carry universal part numbers like 6202, 6207, or 5207. Using these numbers, standard bearings can be ordered from a host of suppliers around the world.

The primary OEM suppliers for PWC manufacturers are:

KOYO/Japan (Yamaha and Kawasaki)
NTN/Japan (Polaris/Fugi)
NSK/Japan (Kawasaki)
SKF, Italy (Sea Doo)
FAG, Germany (Sea Doo)

As for the cage material (which I know has been an issue on other forums), all PWC manufacturers with the exception of Sea Doo use steel. Sea Doo, on the contrary, uses a nylon polyamide 6,6 glass reinforced resin. The advantages of plastic cage bearings are they are inexpensive to manufacture, lighter, and less noisy. The disadvages include low operating temperatures (less than 250 degrees F) and the tendency of the nylon to absorb water and expand. After interviewing numerous tuners, mechanics, and race teams as to the pros and cons of steal vs. plastic, we chose to use steel cage bearings in all of our PWC engines.

As for the quality, there are two basic grades for the types of bearings in PWC's -- normal and electric motor grade. Electric motor grade is the higher quality and the type used by SBT. To achieve electric motor grade, a bearing has to meet a certain harmonic profile under load at various RPM's. Bearings that have dimensional problems will fail this test. For example, many chinese bearings cannot reach the higher grade because or problems with "out of round" balls.

Bearing failures are just not something that we experience often with our trued and welded remanufactured crankshafts. Our failure rate on bearings is extremely low and we know of many racers that are using our cranks. Bill O'Neal put one of our cranks in a race boat two years ago as a controlled test and the crank is still in service.

Good luck with your mods and we are confident your SBT crankshaft will perform just fine.

Greg
SBT

[ October 15, 2001: Message edited by: Greg Pickren ]</p>

[97GP1200]

Mr. Pickren, very informative post. You might think about putting that information up on your site permantently.

IMO, the nylon ball separators that are used in Rotax skis are a carry over from their early sled days. My first experience with them was regarding a 1978 340 cc fan cooled twin ski-doo called the Olympic. In those days a real ripper, haha, but a relatively low spinning motor. I would estimate the rpm to be about 5500.

Well the cam in the points srewed up and the timing went out and the motor back fired and blew the crank seal out on the mag side and when I removed the mag I found the nylon ball separator had actually separated in two pieces. The bearings were all huddled together in one half of the remaining separator but it was still in place and the crank was firm. So with a little grease I spaced them back and snapped the other half of the nylon cage back on. That ski lasted another two years.

The point being that nylon separator was probably not too bad for relatively low reving motors in freezing temps, but I'd rather not have them in my 951 that turns an honest 7000 rpm. But that's owning a Sea-Doo for you. You get the great and the worst all in one package.

BTW, very professional and well managed website.

[DAVID_HX_XP_RX-DI]

Thank You Greg for the informative overview.

I wont have the finshed engine in the water till next early Spring but I will let you know how it holds up after a Level II package is installed.

I will allow the SBT Crank and Lower end to stand on its' own merits.

Thanks again,

David
"On the Tennessee River"