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  1. #1
    Skoog's Avatar
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    Is a 20T press adequate?

    Anyone do crank disassemble and what is you press rating? Have plenty of steel (gas drilling) and stick/MIG to stick it together.

    What is the largest crank cheek diameter and length since likely I have some new buds. Seem like seized cranks are common with PWC's so I figure $50 labor and they buy quality parts no OEM crap. Craigslist is loaded with seized PWC's must be planned failure after all who's going to buy a new one if satisfied with one they got. Even Honda is subbing part to China (Lifan) it won't be long until till they start selling their own.

    Did some train driving and decided I going to go with loose needle bearing in lieu of cage to decrease bearing loading, besides when you're retired it's easy to tell OEM's to take their over-priced/MSR PWC cranks and stick them in their anus.


  2. #2
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    Have you ever actually built a crank before? There is more involved than just pressing one together.

  3. #3
    Click avatar for tech links/info, donation request K447's Avatar
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    Quote Originally Posted by Skoog View Post
    ... Seem like seized cranks are common with PWC's so I figure $50 labor and they buy quality parts no OEM crap. Craigslist is loaded with seized PWC's must be planned failure ...

    ... decided I going to go with loose needle bearing in lieu of cage to decrease bearing loading

    .... OEM's ... over-priced/MSR PWC cranks...
    Watercraft crankshafts often fail due to exposure to water/moisture. Proper operation and preventative maintenance does of course help a lot, but many owners do not do so. Once rust shows up in the bearings, the end is inevitable.

    2-stroke PWC cranks need to be well built to handle the 6000+ RPM that these engines turn. A really well made crank will have runout of 1 thou or so. This requires special jigs and some experience.

    For Polaris, the OEM crank bearings and seals are actually quite good, and high quality.

    Well maintained Polaris 2-stroke engines and cranks can run for several hundred hours. It is not uncommon to freshen the top end with new piston rings, or perhaps a cylinder bore and new pistons+rings and continue to run the crank until the next rebuild.

  4. #4
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    Polaris uses Koyo bearings I believe

  5. #5
    Skoog's Avatar
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    Got crank rebuilding to a science

    Quote Originally Posted by BryanP View Post
    Have you ever actually built a crank before? There is more involved than just pressing one together.
    Thanks Bryan, the answer is no I haven't pressed a PWC crankshaft. How about motorcycles cranks, you know those 12K RPM crotch rockets ones where the tolerances are essentially +- 0.00001. Those have to be rotated on a mandril while using a strobe light and digital $3 accelerometer to measure vibration output triggers strobe to show heavy point. Other than precise phasing what you are working for is minimum vibration with connecting rods in place while running at 125% of max RPM with NO LOAD. At this speed any crank misalignment/bearing play will be apparent. The rods, bearings, and pistons must have <1 gram difference. I do feel confident though since I have worked on computers, radar, microwave, telecom, and test equipment which had close tolerances (NIST) and was an electronics instructor for 20 years.

    Remember Bryan I've been in electronics for almost 50 years. I built my own CDI in 1964 while cars still had points. No matter how fast a object rotates even a small turbo at 200K RPM (3333 rev/sec) in electronics that is almost standing still and yes I have rebuilt a turbo & engine for a 280Z! Remember I"m not going to rebuilt a PWC, this engine is going to swing a 5' prop 2.4:1 at 2400 RPM, PWC quits paddle, MC quits walk, Airplane quits without a place to land or parachute you die.

    I noticed no one has mentioned using witness marks made before dissemble then used in reassembly. This sure helps getting assemblies together in reasonably the right alignment.

    Test equipment: 2- 60MHz dual trace oscilloscopes 1-35MHz dual trace.
    600MHz frequency Counter, 5MHz function generator/counter, curve tracer, 3 DVOM w/frequency counters, 2 laser thermometers, laser tach, CO detector, Clamp on timing light, stroboscope, 4 vacuum gauges for carb sync, and 50HP Kubota w/front end loaded aka engine hoist a lot more junk as my wife calls it.

  6. #6
    Skoog's Avatar
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    Well I'm going to rebuild the Tigershark 640 Suzuki, and except for rain while flying it should never see the water again. As for rust a squirt of flogging oil normally does away with it. It seems flogging oil has got a bad reputation because some over fog making restart difficult. I was guilty of if one shot of grease is good 3 or more got to be better. Till a Tech Sargent had me clean out an ampudyne (3 phase motor driven DC generator) with 1/2 pound of got to better grease slung about.

    I use ATF + chainsaw bar oil it really sticks on my two stroke gear. WD40 is vegetable oil mixed with acetone or other strong solvent (you cannot patent a formula) so they keep adjusting solvent and mixing.

    One of the worst things to do to a 2 stroke is rapping the throttle, bikers do it all the time, but there 4 strokes with plenty of pure oil. You'll never see an aircraft doing this because of oil sucked around the rings fouling plugs and those props are big flywheels. Ideally a leak-down test needs to be done and recorded every 50 hours. If rings are failing you'll spot it faster than a compression test most light aircraft have leak down recorded on valve covers.

    I wonder how many PWC cylinders are running without chamfered ports?

    In my airplane design I plan on being able to convert to a 4 cycle or Orbit/Ficth 2 cycle to get better fuel economy. Some builders are getting 50+ mpg, and a motor glider flew from Orlando FL to NYC on 28 gallons. I just wish Smart Car Diesel hi-torque engines were available in the U.S. At least I can still get 100LL at the airport which is cheaper than 100 octane racing fuel.

  7. #7
    Click avatar for tech links/info, donation request K447's Avatar
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    Quote Originally Posted by Skoog View Post
    ... Remember I"m not going to rebuilt a PWC, this engine is going to swing a 5' prop 2.4:1 at 2400 RPM ... Airplane quits without a place to land or parachute you die.

    ...
    When did you first mention that you were building an aircraft using a watercraft engine?

    Why a watercraft engine? Do you somehow need the entire exhaust system and engine to be water jacketed? Seems like a lot of extra weight in a naturally air cooled machine.

  8. #8
    Click avatar for tech links/info, donation request K447's Avatar
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    Quote Originally Posted by Skoog View Post
    Well I'm going to rebuild the Tigershark 640 Suzuki, and except for rain while flying it should never see the water again.
    ...
    In my airplane design I plan on being able to convert to a 4 cycle or Orbit/Ficth 2 cycle to get better fuel economy.

    ... At least I can still get 100LL at the airport ...
    If you are looking for a light weight, compact but fuel efficient engine, look at the ETEC engines that BRP is putting into some of their current snowmobiles.

    The snowmobile guys also value light weight, especially the mountain climbing and stunt riders.

  9. #9
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    Koyo now owns Torrington bearings, maybe they can learn how to make better bearings especially those pricey needle bearings on the cranks. I just read virtually every bearing OEM buys bearing steel from Timken since it is of such high quality.

  10. #10
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    Other than a motorcycle engines which most have integrated gearboxes using same oil supply, where would you find a light weight 60+ HP engine for a few $100's? Besides aircraft engines have a great cooling fan which helps even more. They operate at fairly constant speed which is a function of a reduction drive acting like a shock absorber/speed damper between the big flywheel prop and hi-revving engine. You might wrap-up RPM's a PWC fast not so with a >5lb 60" prop so speed changes are gradual.

    Water cooled engines tend to be more reliable since the thermostat keeps all the cylinders at a constant temperature especially those not in path of direct airflow. Besides losing an engine in flight usually causes pilots to start sweating since a rotating propeller seems keeps them cool. You might curse at a stalled car or PWC yet, you're still normally safe at 1000'+ it's a long way down with out having angel wings or $3500 parachute.

    Now PWC usually have no water pump since the impeller can do the job so how to keep moving water? Well you have seen most engine radiator fans replaced with electric ones so to will engine water pumps. Since they are more efficient especially when a hot engine is turned-off keeping hot coolant moving through the electric fan radiator their are other benefits too especially for turbos.

    In Texas finding a snowmobile is a tough go and friends in Detroit and Chicago have mentioned winter snow isn't like it was 50 years ago. I'm no expert on snowmobiles since weren't even developed when I lived in those cities. From what I have seen on the web there are many water cooled snowmobiles for the same reason a PWC's stable cooling which allows engines to preform at hi-rpm's for extended periods with close tolerances. As for air cooled engines it appears at roughly the 50HP point they are replaced with water cooled ones. The only large air cooled engines are early designed aircraft piston engines like P&W R4360 which is it's CID and carried >100 gallons of lube oil and needed refilling before every flight, even Continental and Lycoming are working on liquid cooled power plants since precise cooling means tighter tolerances and greater efficiencies. When your refueling two 70 gallon wing tanks fuel prices do matter especially for 100LL aviation fuel.

    My son's boat is an example of the two best days in a boater's life; when he buys and when he sells it. 3 x 350 Yamaha 4 strokes + 40 foot boat = 0.7 mpg with 270 gallon of fuel at 27 knots. He's in electronic too, I taught him the basics and he aced the electronics portion of the Marines aptitude test, it must have worked.
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    If you ever discussed airplane power plant horsepower, really torque, most pilots would agree more is way better than just enough. As you know the days of large radial engines are long past. Even Rotax's latest 914 engines use oil to cool the head while using airflow for cylinders even so the piston tolerances are greater than a similar water cooled engine. As for engine RPM's any racer will tell you high RPM's is 'where it's at' and torque can be accomplished with gearing reduction. Ideally any of the new PWC 4 strokes would make great aircraft power plants, like Suburu, Chevy LS, Honda civic, and Smart Car Diesel which all give great mileage compared with typical air cooled boxers.

    One common example is in motorcycles which were once all air cooled even die hard Harley's are now water cooled with EFI. As much as I like the simplicity of air cooling, point ignitions, and carburetors those days are museum artfacts to an end just like Dodge 440 w/6 pack, Hemi-cuda's, and pony cars were in my 20-30's, when gas was 20 cents a gallon and the skies were clear. Remember change = constant and with computer the rate will go up logarithmically. Older than water Ed

    Depending on your age it is very likely you'll see the re-emergence of turbo-prop aircraft which most ducted fan jets are considering >50% of the inlet airflow is diverted around the compressor stages. USAF 1964-68 Older than Water ED

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