# Thread: Interesting Math on jetskis

1. ## Interesting Math on jetskis

Interesting Math on jet skis.

if you were going 5000 rpms going somewhere and was cruising for a an hour .In that time, the crank has turned 5000 times a min for 60 mins. thats 300,000 revolutions per hour.
Now add a 100 hours of ride time over a few years and you end up with 30,000,000.00 (yes thats million) revolutions of the crank shaft!. If someone knew how much gas that would take, it would be interesting to see how much gas that would scenario would go thru and the cost at 2.75'gallon.
Some skis have 200 hours on them or more>>>>60,000,000.00 revolutions on the crakshaft. thats a great set of bearings in there. Shows ya how important bearings and a straight perfect balanced crank will get ya!

Hope it had a triple fuel pump in it! lol

2. .

3. I can't imagine how much gas that would have used over its lifetime.

4. Might need to consider that all those hours are not at max RPM...a few are at acceleration and idle.

Still, that is a hell of a lot of revolutions!

5. I wished I had a dollar for every revolution.

6. now imagine a 4 stroke spinning 8000+ rpm with NO bearings!!!!

now imagine a 4 stroke spinning 8000+ rpm with NO bearings!!!!
Of course 4-stroke engines have bearings, they just happen to be filled with oil under pressure instead of small rollers.

Going back to the 2-stroke bearings; Each bearing has small rollers inside. Each little roller rotates multiple times for each revolution of the crank shaft.

So you can take that huge number of crankshaft revolutions, and multiple it many fold for each roller inside each bearing

8. Time for new bearings.lol Are there any super high tech, super expensive ones---ceramic or something else high tech for bearings for sale for a polaris besides the regular ol bearing? LIke a titanium ball bearing?
Cool.i just found a link that makes awesome ceramic bearings.

http://www.worldwidebearings.com/ they will make them.

I like the idea of lighter rotating mass and higher r's.

9. Originally Posted by bowsniper
Time for new bearings.lol Are there any super high tech, super expensive ones---ceramic or something else high tech for bearings for sale for a polaris besides the regular ol bearing? LIke a titanium ball bearing?
They make 6207 bearings in full ceramics, about \$225-\$250 each!!! But I am not sure how they would work in there. With the crank using 6 of those and a 6307NR, it would be one expensive rebuild!!! I thought I was going to blow the budget at \$20 per bearing, but then I found a half dozen 6207's for \$4 each. Good British made bearings too, not Chinese ones.

10. Originally Posted by bowsniper
Interesting Math on jet skis.

if you were going 5000 rpms going somewhere and was cruising for a an hour .In that time, the crank has turned 5000 times a min for 60 mins. thats 300,000 rpm.s per hour.
Now add a 100 hours of ride time over a few years and you end up with 30,000,000.00 (yes thats million) revolutions of the crank shaft!. If someone knew how much gas that would take, it would be interesting to see how much gas that would scenario would go thru and the cost at 2.75'gallon.
Some skis have 200 hours on them or more>>>>60,000,000.00 revolutions on the crakshaft. thats a great set of bearings in there. Shows ya how important bearings and a straight perfect balanced crank will get ya!

Hope it had a triple fuel pump in it! lol
assumptions:
gas consumption - 2 gal/hr
hours - 100
AVG RPM - 5000

Total Fuel = 200 gallons
Fuel consumption per RPM = Fuel consumption / (hours*RPM)
=200gal/((5000Rev/min)*100hr*(60min/hr))=.0000066666 gallons/rev

=.005 tablespoons per revolution