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Gen 4 JDM Motor Flywheel Difference?

Discussion in 'Gen 3 Prius Main Forum' started by jimolson, Feb 24, 2023.

  1. jimolson

    jimolson Member

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    I'm helping my brother retrofit a Gen 4 motor into a Gen 3 Prius. We're at the stage where we're moving the Gen 3's flywheel input damper assembly to the Gen 4 motor.

    This retrofit is complicated because the Dallas-area JDM distributor sent us a Gen 4 motor that is (we think) from a Japanese Prius. The JDM motor looks new and not steam cleaned. The motor came to us with oil in it and its main wire harness whacked at the flywheel end of the block.

    The motor's pristine condition makes us wonder if it was taken from a Toyota test stand rather than a vehicle that had spent time on the road.

    These two attached pictures were taken of the Gen 4's flywheel assembly. It looks nothing like our Gen 3's flywheel input damper assembly.

    Anyone know what these Japanese Gen 4 pictures represent? What is the toothed ring and smooth plate?

    Japanese Prius 1.jpg Japanese Prius 2.jpg
     
  2. Tombukt2

    Tombukt2 Senior Member

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    There are pieces missing I believe You're showing the back bolts of the flywheel or where the flywheel would go You're a gen 3 equipment should bolt right up to that just like you took it off your again three engine both of these engines are the same as far as the series goes. Everything should bolt up there's no need to try to use the Gen 4 torque plate unless you have the Gen 4 transmission and that stuff there's no problems with the torque plates really
     
  3. Tombukt2

    Tombukt2 Senior Member

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    Mine was clean like that too.
     
  4. ChapmanF

    ChapmanF Senior Member

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    Is that what the sprag clutch of a Prime looks like?
     
  5. jimolson

    jimolson Member

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    Yes, indeed it is the Prime's sprag clutch. What I thought was a non-US market engine is a Prime one.

    I drove down to Bardstown, KY yesterday to the scene of the crime. My brother is doing this engine swap project in his pole barn. My role is arm chair quarterbacking from Indianapolis.

    Toyota has cleverly added the Prime's sprag clutch to the back side of the Gen 4 flywheel by thinning it somewhat. With the flywheel still on the engine it's easy to miss the sprag. The clue that something is different is a black stamped metal plate on the end of the block that "grounds" (an EE term) the reverse torque

    I initially questioned the durability of the sprag because its paws engage teeth that aren't hardened and its lubrication method is simple: grease smeared onto the paws. But the sprag's application is not demanding. The torque impulse at engagement is low and the freewheeling mode is rendered frictionless at high RPM as centrifugal force drives the paws open.

    During yesterday's Bardstown visit I observed the oft-noted enlargement of Gen 4's EGR system. You could drive a Tundra through the heat exchanger's gas passages.

    My EE training makes me envision a simple, custom-designed electronic module inserted in the electronic connection to the Gen 4 EGR valve. The module would spoof the ECU's read of the valve position and provoke narrower valve opening angles, offsetting the the EGR system's greater flow rates in Gen 3 retrofits.

    This hypothetical electronic interposer widget might also also generate the the missing signal needed to drive the new "flow shutting valve" that appears in Gen 4's coolant loop.

    More to the point, an entrepreneurial company would do well to create a kit to assist Gen 4-to-Gen 3 retrofitters in using more of Gen 4's improvements.
     
  6. ChapmanF

    ChapmanF Senior Member

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    The flow-shutting valve isn't in all Gen 4s, just the ones made for EU and JP markets (as far as I know). If you look up the water outlet fitting on the (US) parts.toyota.com, you get the part number for the one with no flow shutting valve.

    The ECU doesn't have any 'read' of the EGR valve position. The actuator is just a stepper motor, and the ECU only drives it. When it wants the valve closed, it just sends a whole lot of drive pulses in the 'close' direction and assumes the valve eventually got there and went no further. Then when it wants the valve opened n steps, assuming it's closed to start with, it just sends n steps in the opening direction. There isn't any actual position feedback to confirm that it worked. (There is a manifold absolute pressure sensor able to detect that something happened; it's used in the test for P0401.)

    So you'd be making some kind of stepper-motor interposer that would pass through some proportion of steps and drop some. I guess building that wouldn't be the hard part, but figuring out the right map might be. I'm not enough of a fluid dynamics wiz to even know if the right correction should just be a linear proportion or something else.
     
  7. Tombukt2

    Tombukt2 Senior Member

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    So my question is are you using the sprag clutch torque plate or are you putting on the normal Gen 3 setup that's on your original engine?
     
  8. jimolson

    jimolson Member

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    ChapmanF, thanks for that feedback. I thought I recalled seeing a position feedback potentiometer in the Gen 3 EGR valve as I cleaned it, but my memories of that unrewarding day have faded.

    But I double down on my comment about the need for a retrofitters kit. Engine recyclers are missing a business opportunity on this.

    I also lurk in the non-technical Gen 3 Prius Group on Facebook. Most of the postings there are from Gen 3 owners announcing their newly blown head gaskets. It's a Covid-like pandemic for cars that their owners planned to drive another 5 years.

    Tom, I suppose that we could have left the sprag in place without harmful consequences, but little brother (growing a bit weary of this project) prefers to use the Gen 3 flywheel as the safest option.

    As others have written, the splined hole in Gen 4's flywheel input clutch is smaller than the one in Gen 3. As a minimum, the Gen 3 clutch assembly must be moved to the new Prime-version Gen 4 motor to spline-match the MG.

    But the the Gen 3 and Prime version Gen 4 flywheels' clutch-facing footprints are carbon copies of each other.
     
  9. ChapmanF

    ChapmanF Senior Member

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    It seems to me that the area of greatest need, from the retrofit threads I've read at least, is for somebody to buckle down and determine the actual reason these Gen 4 into Gen 3 retrofits seem invariably to overheat. If I'm not mistaken, it's not all down to the flow shutting valve, and has also plagued people who have used the US-spec water outlet without it (or who have drilled through the flow shutting valve).

    I've got a nagging suspicion it's something very fundamental down to the way people are adapting the Gen 4 to Gen 3 plumbing. There seem to be at least a couple different diagrams floating around (this one and this one, one of which clearly has most of the flow indicated backwards and one of which at least looks more plausible) and most overheating threads don't say whether they followed the first one or the second one or did something else.

    Sometimes the threads seem to start off promising, but always end up exasperatedly hoping that fifteen more rounds of air burping or cutting the jiggle pin will fix it. Which, from a distance, looks way too much like throwing random actions at a non-understood problem.

    It'd be a super-valuable contribution for somebody to get to the actual bottom of that.
     
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  10. jimolson

    jimolson Member

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    Good point, ChapmanF! I hope my brother isn't one who experiences overheating because he'd drive up I-65, gun loaded, looking for me.

    It's clear that Toyota engineering was told that Gen 4 must correct the head gasket failures of Gen 3. Changes in Gen 4 seem focused on reducing temperature excursions in the upper part of the engine. Examples are the EXPAD water jacket spacers adjacent to the cylinders. It's possible that the Gen 4 temperature-leveling strategies raised heat dump into the coolant.

    Extra heat dump into the coolant would be offset by a radiator with greater cooling capacity, possibly assisted by additional (=faster) water flow through the block. It should be easy to examine a Gen 4 radiator for increases to its area, fin density, or flow tubes. It would be harder for garage mechanics to determine if Gen 4 coolant flow rate was increased. Increased flow rate could be accomplished electrically in the ECU by increasing the water pump's drive voltage and/or frequency.

    But retrofitted Gen 3s wouldn't be endowed with radiator improvements or faster water pump flow, possibly explaining post-retrofit overheating.

    Yesterday in Bardstown I noted that there's a new external 10mm coolant bypass tube running from the water pump's output, behind the motor, and over to the EGR heat exchanger. (The coolant bypass loop is shown in the Marklines color map of the Gen 4 cooling system you posted a while back. I printed it and stuck it to my office bookcase.)

    Does this coolant bypass line exist on all Gen 4s or just the JP/EU versions? If it's on Gen 4s universally I can imagine that it competes with the main coolant flow through the block. How a retrofitter terminates this bypass loop in the vicinity of the EGR cooler could reduce water flow through the motor itself. If Toyota intentionally restricted coolant flow in Gen 4's bypass loop, the restriction disappears when retrofitters do last-minute mods to coolant lines near the EGR.
    upload_2023-2-26_15-22-5.png
     

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    #10 jimolson, Feb 26, 2023
    Last edited: Feb 26, 2023
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  11. ChapmanF

    ChapmanF Senior Member

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    That line is present in the same regions that get the flow shutting (or, in that diagram, "selector") valve.

    As you can see, when the selector valve is shut (and the main thermostat hasn't opened yet), Gen 4 coolant from the block and head goes nowhere. (Except in a small amount, because I believe the selector valve has a small orifice open, even before a person takes a drill to it. ;)) Instead, the water pump is just pumping coolant right around the engine, through the bypass loop (where it mostly picks up heat from the EHRS and the EGR cooler, while delivering some to the heater and throttle body). This surely hastens warm-up.

    The small orifice in the selector valve should allow enough coolant from the engine to be flowing past to ensure the ECT sensor gets a good reading. And when the ECM decides accelerated warmup is no longer needed, or more engine heat is needed for the cabin heater, it can open the selector valve, and then the coolant from the engine gets to participate in the bypass loop (still in competition with the flow coming around the back).

    And when the bypass loop is hot enough to open the main thermostat, then the radiator comes into the picture.

    That appears to be how the Gen 4 (with selector valve) is meant to work (though I don't know all the ECM's rules for when it opens and closes the selector valve).

    I think most people doing the swap are just capping off the extra line at the timing cover, and (I hope) buying the US water outlet without the selector valve. (Drilling the selector valve seems so uncivilized.) That much seems sensible to me.

    The post-swap reports all seem to describe such awful cooling behavior, though, that I'm suspecting the answer is going to turn out to be something less subtle than we may be thinking.
     
  12. jimolson

    jimolson Member

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    Thanks for the feedback, ChapmanF.

    Yes, brother ordered the US version of the coolant output housing that omits the flow selector valve. However, the demand for them (presumably from retrofitters with JP/EU motors) is so great that Toyota has them on back order.

    "Drilling the selector valve seems so uncivilized..." I chuckled at that but what's really uncivilized is driving a hybrid vehicle to save the planet but shoving a quart of acetone, toluene, and/or TCE through a EGR cooler trying to unplug it.

    I still have black stains on my driveway after these potent solvents dissolved the container I used to catch them. The EGR cooler was still plugged but this exercise in futility seems to have banished all insects in my zip code for an eternity. :)

    A liberal like me isn't supposed to laugh off unwoke behavior like this.
     
  13. chaddarack

    chaddarack New Member

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    Maybe I can post a picture, but after the flow shutting valve, there seems to be a Y splitter. The Y has an electrical connector on it, that I suspect is just some sort of sensor. I wonder if you could delete the valve with the US water outlet flange but still include the coolant bypass tube that comes around the back of the motor along with the Y. I'll get a picture later and show you. But then there's no shutoff so I'm not sure how that would, possibly negatively, affect engine temperature.

    And if blocking the bypass tube, does it matter where to block it? At the outlet from the timing cover, or at the end of the tube over by the EGR/Coolant outlet?
     
  14. chaddarack

    chaddarack New Member

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    Maybe I can post a picture, but after the flow shutting valve, there seems to be a Y splitter. The Y has an electrical connector on it, that I suspect is just some sort of sensor. I wonder if you could delete the valve with the US water outlet flange but still include the coolant bypass tube that comes around the back of the motor along with the Y. I'll get a picture later and show you. But then there's no shutoff so I'm not sure how that would, possibly negatively, affect engine temperature.

    And if blocking the bypass tube, does it matter where to block it? At the outlet from the timing cover, or at the end of the tube over by the EGR/Coolant outlet?
     
  15. chaddarack

    chaddarack New Member

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    Maybe I can post a picture, but after the flow shutting valve, there seems to be a Y splitter. The Y has an electrical connector on it, that I suspect is just some sort of sensor. I wonder if you could delete the valve with the US water outlet flange but still include the coolant bypass tube that comes around the back of the motor along with the Y. I'll get a picture later and show you. But then there's no shutoff so I'm not sure how that would, possibly negatively, affect engine temperature.

    And if blocking the bypass tube, does it matter where to block it? At the outlet
     
  16. black_jmyntrn

    black_jmyntrn Senior Member

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    wait... you took the sprague clutch off Do you still have it?

    Do you need or want a lightened flywheel for the Gen 3?

    I need that Sprague clutch so that with the Gen 5 swap to Gen 3 Plugin, I can attempt to achieve the higher EV mph like the Prime in my Plugin! With the work I've done to make this swap possible, it has enabled lightened flywheels for the Prius to have been developed.
     
  17. black_jmyntrn

    black_jmyntrn Senior Member

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    This is correct, heh, lets just say I have many flywheels for the various engines all in the name of attempting to get some performance gains that others haven't attempted to venture into.
     
  18. Tombukt2

    Tombukt2 Senior Member

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    That's what I was wondering so the plug-in hybrid car has some kind of a sprauge clutch involved . My Italian big bore scooters have this item located in essentially the same area although this is on a motorbike not a motor car but the same principle I was wondering if the Prius plug in used something like this Not sure what this is going to have to do with the Gen 3 but certainly you're going to try to Evie the car like the plug-in hybrid then you're going to need all the bitch and pieces.
     
  19. black_jmyntrn

    black_jmyntrn Senior Member

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    Differences between V and non V CVT? | PriusChat

    I think this is the thread, I thought it was another specific to the Prime and that clutch where the folks here helped me determine in order to get into Prime MPH of 80+ in EV mode, I would need that clutch. I've been holding off on finishing the 2.0L swap with the hopes I can obtain a used one to install and worry about the ECU stuff later just... don't know if I can wait any longer.
     
  20. Tombukt2

    Tombukt2 Senior Member

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    2litre what engine is that ?
     
  21. black_jmyntrn

    black_jmyntrn Senior Member

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    the new Gen 5 Prius motor, only I got mine out of a UX250h before it was announced the new Gen 5 would have the same motor.
     
  22. black_jmyntrn

    black_jmyntrn Senior Member

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    when you press play i made the video start right before the 2.0L stuff