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  1. #1

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    Rebuilt Polaris MSX140 shake-down

    There are other posts on this Forum regarding aspects of an MSX140 rebuild which I’ve undertaken during the past Australian winter.

    Having completed the rebuild – and given that our family’s usual ski location is about a 90 minute drive (each way) from home – I sought a more convenient location to conduct some basic ‘in the water’ ski testing.

    We have a fairly large (40ft x 16ft), rarely used, salt water chlorinated swimming pool, so I thought why not use it to check the ski for leaks and basic running? I also wanted to get some idea about the water flow through the ski’s normal water intake.

    To avoid running pool water through the motor, some temporary re-plumbing was undertaken: an open discharge hose was installed at the water intake point just inside the hull (near the through-hull bearing); the rearmost end of the factory water inlet hose was connected to the mains (city) supply; an open discharge hose was connected to the thermostat outlet and an open discharge hose was connected to the discharge port on the EMM. This configuration ensured that mains water ran through the motor and it also enabled some basic monitoring.

    What did I find during two test sessions? On the first occasion, I performed tests for about 15 minutes at idle speed (about 1100 rpm) with the ski tethered (stationary), although I made some anecdotal notes on outputs at about 2500 rpm. I found that flow from the jet pump at idle was 1.8 US gpm; however, this seemed to increase substantially at higher revs and it would possibly increase further with the ski in motion. I set the inflow of mains water at about the same rate (1.8 US gpm), at which the discharge from the EMM was 0.6 US gpm. I didn’t measure the EMM discharge water temperature, but it was ‘cool’: not much warmer than the mains inlet temperature. During the test period, flow from the thermostat outlet was minimal and the temperature was 145°F.

    My second test (on another day) also lasted about 15 minutes and for this test I adjusted the throttle cable to hold a steady 2000 rpm. Flow (open) from the jet pump increased to 4 US gpm and flow from the thermostat housing also increased. I measured it at 0.8 US gpm, near the end of the 15 minute test and again the water temperature was 145°F. I increased the mains water flow slightly for this test – to about 2 US gpm – and bearing in mind that this flow rate didn’t increase with engine speed, I wasn’t surprised to note that as the motor warmed up and flow through the thermostat housing increased, flow through the stator/EMM reduced.

    There is nothing ground-breaking about any of this, however, I though the above information might be of some interest to MSX140 owners/operators. Although my readings were only taken at low rpm, I was amazed at the water flow from the jet pump – admittedly without restriction, other than the plastic restrictor in the intake tube – and the flow through the stator-EMM circuit. Noting K447’s video of water flow from the pisser attached to the EMM outlet on his MSX140, I would be interested in any similar observations (on water flows) by others – and I wonder whether anyone has a chart showing pressure as well as flow from the jet pump (plotted against rpm).

    For interest, I also attach some photos of the cradle and timber frame I constructed to move the ski. I fitted 6” diameter solid rubber wheels (not shown) to the steel cradle for use as a working platform and moving platform. At the pool, the roller assemblies and winch have been temporarily removed from my ski trailer. I used the timber frame as a ramp to move the ski on the cradle from my working area to the pool area – down a 5ft (drop) set of narrow concrete steps. The timber frame and a couple of old tractor tubes are used to raise and lower the timber frame (and any contents) at the pool edge. It all works well – and no damage (to date) – however, above 2500rpm the ski jet pump certainly creates some water turbulence: beware!

    These activities might seem a bit anti-social, but I should emphasise that my swimming pool testing is a short term arrangement – and in the interests of good relations with the neighbours, I try to run the ski when they are absent.
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  2. #2
    Click avatar for tech links/info K447's Avatar
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    Interesting reading

    Unlike the automotive world, PWC generally have terrific engine cooling capacity. The jet pump can supply a prodigious quantity and pressure of cooling water at speed. Overcooling is easily invoked when modifying the factory cooling system *

    To restate, the thermostat is there to maintain a minimum operating temperature when the engine is not working hard. I do not have specific/measured pressure numbers but fuzzy memory says that at speed the cooling system feed pressure can be at or above 30 PSI.

    The MSX 140 has an additional flow restrictor (white plastic disc, not present in carburetor models) in the water feed tube from the jet pump, in addition to the thermostat.

    And I think the pressure bypass valve in the MSX 140 thermostat housing also has a plastic spacer (perhaps only for the 2004 model year? ) to add tension to the long spring, which had the effect of raising the required water pressure (which would correlate to a higher engine RPM) at which the thermostat bypass valve will open. IIRC that spacer does not have a known part number?

    Clearly Polaris was focused on avoiding over cooling of the MSX 140 engine. Part of this may have been driven by the desire to maintain a California Low Emissions rating.

    My own MSX 140 never gave me a moments concern regarding engine cooling capacity. I added the side water exists (pissers) for EMM and magneto stator in part from curiosity. And to monitor water flow during and after encountering weeds while riding, which is not uncommon in my waters.


    * Polaris did omit the thermostat from a few years production (2000ish?) of some versions of the red carburetor engines, in at least some models. Unclear (to me) precisely why.

    Work done by TxPro showed some unevenness in cylinder cooling balance for the red carb engines. He also posted methods for improving the situation.

  3. #3
    martincom's Avatar
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    Sounds like you're well on your way to becoming the unofficial MSX140 repair depot down under.

  4. #4

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    Thank you for your responses, K447 and martincom.

    My interest in the MSX140 - and motivation to rebuild our family's ski, whose engine was damaged as a result of a severely pinched thermostat discharge hose, following through-hull bearing replacement by a local repair shop - has been greatly enhanced by the information provided by this Forum; not least by both of you.

    The rebuilt engine has the restrictor (white plastic disc) in the water feed tube and a new (and tested) thermostat, but the plastic spacer under the coolant pop-off valve spring was melted when I dismantled the engine and I haven't been able to source a replacement. From the remnants, it appeared similar to a short section of uPVC pipe about 1/2" in diameter and 1/2" long. I would appreciate it if anyone could provide the dimensions. I assume there's only one coolant pop-off valve for the MSX140; i.e. only one spring tension.

    On the broader issue of information sharing, I omitted posting my solution to the engine/jet pump alignment process. I was aware of the US-sourced alignment tool, described elsewhere on this Forum and being somewhat concerned that such a long (albeit, fairly 'meaty') rod might be bent in transit (to Australia), I had one made by our local machine shop. Not having one of the (Virage?) couplers on hand, the engineer made a substitute whose 'pocket' (the end which receives the alignment rod) was machined to match the 0.7874 +0/-0.001" OD rod, which has no 'step' at the crankshaft end.

    The engineer was on leave when the fabrication was done. One of his staff members made the coupler and apparently he tapped the female thread which fits onto the crankshaft. When I aligned the engine to the jet pump, I discovered that the rotational position of the coupler was inconsistent, so I took it back to the engineer and he remanufactured the coupler, this time machining the female thread. After the usual trial and error shim placement, I found that - as it should be - the alignment was consistent, irrespective of the rotational position of the coupler.

    This proved to be quite an expensive exercise, but I am satisfied that my alignment tool (which also includes the bush to align the through-hull bearing assembly) is now fit for purpose.

    No aspirations (nor the capability!) to become an 'unofficial MXS140 repair depot', martincom - but I find these machines fascinating and an interesting diversion from my classic Citroens. Speaking of overheating issues...!!!

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