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Thread: A work of pure genius! - Brilliant "Revetec" Engine

  1. #151
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    Pattakon Engine

    Interesting animations. I supose I can comment on the rollers that control side thrust by saying that roller bearings don't like stop start reverse operation but I supose they should or probably are using a slide type of arrangement when building one. I wouldn't mind seeing what torque lever length they have at what degrees of rotation. If I have time to graph it I will but is there anyone out there that has the time to do it and post it?

    I would also probably comment that their cam design would probably not be as flexible in design options as ours. I then looked at the animation of the multi bearing/lobed engine an can see the outer cams cutting through the opposite shaft. Hmmm...

    The multi cylinder engine has cutouts in the shafts to allow the opposite cam to pass through which looks to be a weak link.



    The bearings also look very small on the outer cams. There are other issues but like our company they may not be disclosing updates and newer designs. I would be interested to see if they have successfully tested any of the shown designs or others other than their valve train designs.

    BTW. in 2-3 days our website will be updated. All previous information which was correct at the time of posting but is out of date now due to design and configuration changes will be removed. So no 3:1 gearing comments to confuse figures posted with current engine layouts and operation. The 3:1 gearing was an older special use engine and hasn't been used for 3 years.

    I think that when we release details of our new design when our website is updated you all would be a bit interested in the compactness of our latest design.

    Manolis: Alastor and yourself were correct about the 100mm conrod. I went back to my calculation sheet and realised that I had played with it and resaved it by mistake. Ouch! I should have spent more time to make sure that it was correct and not assume it was correct. I suppose my only defence is that I'm very busy designing our new engine and didn't have the time to go through the speadsheet and make sure it was correct. I will be more careful in the future because I can tell you all are very passionate about engines and have a high degree of knowledge so I'll only post here if I triple check everything.... :-)

    Cheers
    Last edited by revetec; 10-18-2006 at 10:13 PM.

  2. #152
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    Brad

    Great to hear your response regarding updating the web site in addition to clarifying the issue regarding the 3:1 gearing issue.

    We await the updated web site details and I for one look forward to the engine stats for this new engine.

    I am curioous, given the fuel effeciency characteristics of your engine I would expect that if you were to inetgrate your technology into a petrol/electric application similar to Honda & Toyota that the fuel economy figures would be quite outstanding. Especially given you coment regarding the compactness of your new engine (it will obviously weigh less) so it would also have a power 2 weight advanatge in addition to packaging effeciency.

    Are there any plans for a pterol/electric concept perhaps in the future?

  3. #153
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    Quote Originally Posted by pneumatic
    It's like a 4 cylinder 2-stroke with reed valves, and where 2 cylinders are supercharging the other 2. The not so pretty part is connecting the two cranks together to keep them in synch.
    Pneumatic,

    If the diameter of the low pressure side of the pistons is greater than the diameter of the ‘combustion’ side of the pistons, like:

    the engine is supercharged.

    The synchronization of the two crankshafts is a problem.
    But think that in case the load is directly attached to both crankshafts,
    as happens in the Portable Flyer or in an ‘absolutely vibration free’ power plan –think of two identical electric generators driven directly by the two crankshaft – or in an outboard engine having one propeller on each crankshaft etc,
    the synchronization is very easy and light, as it transfers no loads: the torque goes directly to the load.

    In motorcycles the rule is the “primary transmission’, so the following PRE arrangement



    for a motorcycles adds nothing – compared to conventional - as it uses the ‘primary transmission to a main shaft (having the clutch on it) as the synchronization.
    Note here that the synchronization of the two crankshafts of the PRE engine is not critical and needs not special accuracy, i.e. the PRE will still operate even if you change the phase of the two crankshafts for a few degrees.
    And here comes another characteristic / advantage of the PRE : if you deliberately change the phase difference of the two crankshaft more and more, then you have the way to change the compression ratio of the PRE without other complications. If there is interest, I will make some animation to explain the case.

    Thanks
    Manolis Pattakos

  4. #154
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    Quote Originally Posted by revetec
    Interesting animations. I supose I can comment on the rollers that control side thrust by saying that roller bearings don't like stop start reverse operation but I supose they should or probably are using a slide type of arrangement when building one. I wouldn't mind seeing what torque lever length they have at what degrees of rotation. If I have time to graph it I will but is there anyone out there that has the time to do it and post it?

    I would also probably comment that their cam design would probably not be as flexible in design options as ours. I then looked at the animation of the multi bearing/lobed engine an can see the outer cams cutting through the opposite shaft. Hmmm...


    . . . . . .

    Manolis: Alastor and yourself were correct about the 100mm conrod. I went back to my calculation sheet and realised that I had played with it and resaved it by mistake. Ouch! I should have spent more time to make sure that it was correct and not assume it was correct. I suppose my only defence is that I'm very busy designing our new engine and didn't have the time to go through the speadsheet and make sure it was correct. I will be more careful in the future because I can tell you all are very passionate about engines and have a high degree of knowledge so I'll only post here if I triple check everything.... :-)

    Cheers
    Brad,

    Pattakon’s GRECO cam design is as flexible as the trilobe cam design, i.e. it can realize any reciprocating motion that the trilobe can. In other words, if you give me your desirable reciprocating motion profile (realized by a trilobe cam), I can design the relevant single cam lobe profile.

    When the outer cam ‘cuts’ the inner cam in twin cam GRECO design, there are no twisting moments on the piston and this is important. Like:


    On the other hand, there is always the solution of single shaft which is lighter, simpler, need not synchronizing gears etc

    The thrust roller bearings are not so different compared to the main rollers of Revetec’s and Pattakon’s design. If the thrust bearings do not like the start stop reverse operation, the main bearings do not like the high speed – low speed repeated operation either. Here is the reason:
    We start with a revetec/trilobe cam having 100 mm minimum eccentricity and 200 mm maximum eccentricity (i.e. 100 mm piston stroke). At 1600 rpm (of the trilobe cam) the periphery of the main rollers has a maximum velocity of (1600rpm/(60sec/min))*(2*pi*0.2m) =33.5 m/sec, and a minimum velocity of (1600rpm/(60sec/min))*(2*pi*0.1m)= 16.75 m/sec. The maximum velocity happens once per piston reciprocation.

    1600 rpm with trilobe cam means 4800 complete piston reciprocations.

    Now suppose you take the side loads with thrust rollers identical to the main rollers.

    The thrust rollers periphery has a maximum velocity – at the same revs – of 25.13 m/sec (i.e. 2*pi*0.05m*4800rpm/(60sec/min) ) and a minimum velocity zero. The maximum velocity of the thrust rollers happens twice per piston reciprocation.

    So the energy to and fro in case of the main rollers is 33.5^2-16.75^2=841.7 energy units, while the energy to and fro in case of the thrust rollers is 25.1^2=630 energy units.
    The power to and fro is 841.7 power units in case of the main rollers and 1260 power units (i.e. 2*630) in case of the thrust rollers, i.e. 50% more.

    But the thrust loads are far weaker than the main loads, so the thrust rollers can be times lighter than the main rollers.

    So, if Revetec achieved to keep the main rollers rolling (and never sliding) on the trilobe cam, the problem of the thrust rollers of GRECO design is already solved.

    Thanks
    Manolis Pattakos

  5. #155
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    Greco Engine

    Dear santostripoli,

    We are involved in an electric hybrid project. This project is in an early stage and I supose that we will release details regarding this relationship in the near future. Thanks for your comments. Our new engine design is very compact which has evolved from our new aviation project. Details of this will be posted on our website early next week.

    -----------------------------------------------------------------------------------------

    Interesting response Manolis.

    This is not an attack. Can I pose some questions and comments for discussion as I'm interested in peoples comments regarding the GRECO engine? You did the same regarding our engine and have been agressive in doing so. Please don't be one sided as you are being very protective of engines you believe in and scathing of others.

    The axial twist of the drive shafts in the location I showed previously shows a problem? Shafts must be strong in controlling any axial twisting. Any comments?

    The bearings on the guides may be able to handle the load. This is not what I was saying. I said the stop start operation, which will cause wear at the ends of travel. This is where you need the greatest of acuracy on the side load direction change. Too much wear at this point will cause an audible knock. Any comments?

    The cam design we are using is of a size that reduces the change of bearing speed over the cam face to a point that is reliable. Do you think that the GRECO engine doesn't require the same type of operation given the application and loading is the same?

    When a GRECO single cam engine's main bearings contact the drive cam to induce rotation they must contact at an angle to provide rotation. The side thrust generated from this loading is transfered to the guide bearings which need to handle the load, sometimes it is equal when a 45 degree angle is experienced from the piston bearing load contact. As a rule.... over 30 degrees of deviation from the piston(on a single cam engine) causes too much side thrust and is not desirable due to guiding load handling requirements. Given that 30 degrees is the desireable limit for reliability, the result is a low torque lever similar to a swash plate type of arrangement (great as a driven pump but not a drive motor due to high loading of components). This is why I prefer counter rotation of two or three cams. Any comments in this area anyone?


    Manolis: The design you just showed has the piston bearing boss inbedded into the shaft and it is not at BDC yet. The bearings are too small to handle the type of loads from a piston/capacity of that size. The final design will not be as compact as shown and I'm looking forward to seeing how they address this in final designs as it may relate to some components in our engine.



    The minimum rolling diameter of the cam is far less than our design due to the fact that the roller travels closer to the shaft centre. I have designed our cams with a minimum rolling diameter to achieve reliability of the bearings. and reduce slippage which causes wear. I could do a CAD model which has a smaller cam to make our engine look more compact . If the stroke is the same and the bearing separation is the same distance then the dimensions wouldn't be much different (Slightly larger due to multiple lobes) given the same piston design. But would it be reliable in actual engine testing? I tried this in my first engine ten years ago but wasn't succesful.

    Looking into the future of how this engine may be configured for production I performed some basic bearing calculations and refered back to data from our own product plus consulted information from our SKF bearing database.

    To make the bearings reliable for consumer products the bearings require to handle full loads at the required top RPM for around 5,000+ hours I searched our database. The only bearings that I found in the marketplace at a reasonable cost for manufacture that I have found are cylindrical roller bearings or oil pressure fed rollers (Maybe a bit hard to do but not impossible).

    The bearings must be encapsulated in a case due to the fact that the bearing outer wall is too hard and brittle for this type of application, and have a case wall thickness of approximately 2.5mm. I have tried bearings straight on a cam and they fail due to impact shock causing the outer cases to crack. On calculating the operation application and the encapsulation of the bearings, a bearing selection would lead me to selecting a bearing for roughly the capacity shown of a diameter of no less than two and a 1/2 times the size shown in the models. Does anone know of alternative bearings that can be used as I'm very interested in this area?

    The bearings being a lot larger changes the configuration to a point that a production model would not be as compact as the one in the concept design. Any comments?

    Please Note: I'm not criticizing the design concept. Just looking at compactness of a production model for my reference.

    I do realise that they are just models and they may not be displaying their latest designs.
    The basic theory looks OK at this point but I cant see a production model being as compact as shown. I maybe wrong.

    A final running engine design will have to be made and tested for reliability, at which point we can compare sizes :-)

    We have had 4 complete engine versions running and are designing our 5th series of engines now. Wait till you all see how compact our new engine is! It will be on our website next week!

    I'm not going to comment any further on other issues as I've spent 10 years researching roller based piston engines and I don't want to disclose any more information gained from our development program that has come as a great expense to our company.

    It's hard to compare a concept engine to an engine that has been developed over 10 years, built an tested. What do other people think of the GRECO engine in design? Is there any other comments out there from anyone on their design/prolems/benefits as it may relate to some components in our project?

    Cheers
    Last edited by revetec; 10-19-2006 at 07:36 PM.

  6. #156
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    Pattakon-PRE engine

    Re:Pattakon-PRE

    I have seen this type of configuration before. It is better if the combustion process is performed in the middle of the engine to reduce thermal losses. Not a bad design and I have heard there are still a number of these type of configuration engines still on the road such as the Common Knocker.


    (Common Knocker)

    This can be in the Pattakon configuration and use gears to transfer power and time the engine, such as suggested by Manolis.





    So how do you assemble the Pattakon engine? How do you get the crank/counterweights through the piston? Is the shaft in multiple pieces or is the piston split in two parts and which way? If the piston was in two pieces it wouldn't be good to split it through the piston crowns so how is it done? Is the conrod one piece as it would be a bugger to bolt the big end cap together?

    The ports are configured like a two stroke engine in the centre so I assume that the combustion is in the centre and it's a two stroke like a common knocker? Is there more detailed pictures out there that explains these questions as I am interested in the construction of this engine?

    Cheers
    Last edited by revetec; 10-19-2006 at 06:48 PM.

  7. #157
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    I measured the graphic roughly and worked out it was using a 1.375:1 reverse conrod ratio. Is this graph roughly right? If not right please someone else do it and I'll remove mine.

    Comments in regards to breathing and power stroke differences this would cause? A torque lever graph would be useful too...Can anyone do one and post it?
    Last edited by revetec; 10-19-2006 at 08:41 PM.

  8. #158
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    Quote Originally Posted by revetec
    The bearings must be encapsulated in a case due to the fact that the bearing outer wall is too hard and brittle for this type of application, and have a case wall thickness of approximately 2.5mm. I have tried bearings straight on a cam and they fail due to impact shock causing the outer cases to crack.
    I and others had picked up running a bearing directly on the lobes would never work and would just result in cracked bearing cases. From the photo's and animations on your website it looked like you were just trying to run deep groove ball bearings (or needle rollers?) directly on the lobes.

    The problem is the races are brittle and hard like you say. Due to these properties, the races cannot handle any bending moments / loads. These essentially must be encapsulated so the capsule takes all the bending and contact stress type loads, and the race only ever see compressive loads between the roller and the capsule. This is where you will run into problems. For example, even if you have a rolling element bearing that is a loose fit on the shaft, the inner race will flex enough on that shaft to crack from the resulting fatigue load.

    You may want to calculate the contact stresses. This will give an idea if the capsule is thick enough. From the peak contact stress you can also calculate the surface hardness required to prevent pitting of the trilobe / capsule surface.
    Attached Images Attached Images
    Last edited by pneumatic; 10-19-2006 at 10:13 PM.

  9. #159
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    Quote Originally Posted by manolis
    Note here that the synchronization of the two crankshafts of the PRE engine is not critical and needs not special accuracy, i.e. the PRE will still operate even if you change the phase of the two crankshafts for a few degrees.
    And here comes another characteristic / advantage of the PRE : if you deliberately change the phase difference of the two crankshaft more and more, then you have the way to change the compression ratio of the PRE without other complications. If there is interest, I will make some animation to explain the case.
    By changing the phase you also change the relationship between the intake and exhaust port timing. But the problem with having them out of phase is vibration.

    And added a few gears on looks fine in a concept 3D model, but once you added bearings and other items to support it all then the concept starts to look not so simple.

  10. #160
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    Pneumatic:
    Your right in your comments. Our animation is just a representation. On our first engine in 1996 we found deep groove bearings to not be suitable. We use cylindrical bearings or solid bushed rollers in our prototypes. Ever since the first prototype we have encased bearings. The material and surface hardening has been the same since. Even though I'm not stating what material we use, the surface hardness or the hardening process, I can tell you that it has not been a problem since. Our software has a calculation base for contact stresses and material selection as well as bearing selection giving us data of bearing life to approximately 1/100 of an hour (Ha ha...well that's what it says although I can't imagine it to be that acurate). The graph was good one for everyone to look at for reference... :-)
    Last edited by revetec; 10-19-2006 at 11:36 PM.

  11. #161
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    Yeah, take some programs with a grain of salt. I use ANSYS for my finite element analysis models, and they are very accurate, but only as accurate as the data that goes in. It calculates contact stresses but I still like to check with a hand calculation just to be sure the FEA is behaving properly.

  12. #162
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    We use Solid Edge which is proably the best CAD software for what we do. The Engineers Reference Guide has calculations of just about every mechanical component and SE now has Femap Express which is good FEA for basic checking of components. Other detailed analysis we outsource. We also consult with companies such as SKF if needed.

    Cheers
    Brad
    Last edited by revetec; 10-20-2006 at 12:10 AM.

  13. #163
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    We have quite a lot of different brands and types of software, but in general I use Solid Edge for the parametric 3D modelling, and export the geometry to ANSYS for analysis. We also use CFX for computational fluid dynamics.

  14. #164
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    GRECO engine

    Brad,

    You write:
    The axial twist of the drive shafts in the location I showed previously shows a problem? Shafts must be strong in controlling any axial twisting. Any comments?
    The U-6 Pattakon GRECO engine you quoted is:
    The most compact design I know
    It is absolutely balanced (not just as I-6 or V-8 but absolutely as the Wankel rotary engine)
    It can use a unique cylinder head, if desirable (like VR-6 of VW)
    It can be reduced to a U-4 full balanced - even firing arrangement (removing a pair of cylinders and rotating the cams)
    It can turn to a 12 cylinder by just adding six pistons and a cylinder head at the bottom.

    If the only problem is the twisting of the drive shafts, all you need to do is to increase the distance of the two drive shafts and the size of the two synchronizing gears. This way you can increase the minimum section of the drive shafts as much as you like.


    You write:
    The bearings on the guides may be able to handle the load. This is not what I was saying. I said the stop start operation, which will cause wear at the ends of travel. This is where you need the greatest of acuracy on the side load direction change. Too much wear at this point will cause an audible knock. Any comments?
    The side rollers begin to decelerate right after the middle of the stroke. I.e. they have plenty of time to completely stop at TDC and then – progressively – to start accelerating at the opposite direction. Then again, after the middle stroke the process repeats. Another way to reduce inertia of the roller is to have the pin on the wall or the cam and the ring on the piston. Such use is shown in the animation http://www.pattakon.com/greco/GrecoS...leShaftPin.exe.

    You write:
    The cam design we are using is of a size that reduces the change of bearing speed over the cam face to a point that is reliable. Do you think that the GRECO engine doesn't require the same type of operation given the application and loading is the same?
    The only way to reduce the change of bearing speed is by shortening the piston stroke, either in Revetec design or in any other design. In my previous reply I calculate the maximum and minimum speed of the rollers rolling on the cam. Unless I get your writing wrong.

    You write:
    When a GRECO single cam engine's main bearings contact the drive cam to induce rotation they must contact at an angle to provide rotation. The side thrust generated from this loading is transfered to the guide bearings which need to handle the load, sometimes it is equal when a 45 degree angle is experienced from the piston bearing load contact. As a rule.... over 30 degrees of deviation from the piston(on a single cam engine) causes too much side thrust and is not desirable due to guiding load handling requirements. Given that 30 degrees is the desireable limit for reliability, the result is a low torque lever similar to a swash plate type of arrangement (great as a driven pump but not a drive motor due to high loading of components). This is why I prefer counter rotation of two or three cams. Any comments in this area anyone?
    The single lobe cam can be increased in diameter as desirable. In the following plot the three cams are for the same piston stroke.
    Increasing the size of the single lobe cam, you can get as small thrust loads as you want. It is, as always, a matter of compromise.

    You write : Manolis: The design you just showed has the piston bearing boss inbedded into the shaft and it is not at BDC yet. The bearings are too small to handle the type of loads from a piston/capacity of that size. The final design will not be as compact as shown and I'm looking forward to seeing how they address this in final designs as it may relate to some components in our engine
    .

    The rollers are small in diameter but you can use more than three rollers per piston, in parallel (i.e. you can use, as the stroke is too short, three cam lobes in parallel on the one drive shaft and two on the other drive shaft, that is five small rollers in parallel per piston, which distributes the loads on the wide piston directly to the cam lobes making the piston light and nevertheless strong). This way the compactness can remain as shown.

    You write:
    Looking into the future of how this engine may be configured for production I performed some basic bearing calculations and refered back to data from our own product plus consulted information from our SKF bearing database.

    To make the bearings reliable for consumer products the bearings require to handle full loads at the required top RPM for around 5,000+ hours I searched our database. The only bearings that I found in the marketplace at a reasonable cost for manufacture that I have found are cylindrical roller bearings or oil pressure fed rollers (Maybe a bit hard to do but not impossible).
    The bearings must be encapsulated in a case due to the fact that the bearing outer wall is too hard and brittle for this type of application, and have a case wall thickness of approximately 2.5mm. I have tried bearings straight on a cam and they fail due to impact shock causing the outer cases to crack. On calculating the operation application and the encapsulation of the bearings, a bearing selection would lead me to selecting a bearing for roughly the capacity shown of a diameter of no less than two and a 1/2 times the size shown in the models. Does anone know of alternative bearings that can be used as I'm very interested in this area?

    The bearings being a lot larger changes the configuration to a point that a production model would not be as compact as the one in the concept design. Any comments?


    Please Note: I'm not criticizing the design concept. Just looking at compactness of a production model for my reference.

    I do realise that they are just models and they may not be displaying their latest designs.
    The basic theory looks OK at this point but I cant see a production model being as compact as shown. I maybe wrong.

    A final running engine design will have to be made and tested for reliability, at which point we can compare sizes :-)

    We have had 4 complete engine versions running and are designing our 5th series of engines now. Wait till you all see how compact our new engine is! It will be on our website next week!

    I'm not going to comment any further on other issues as I've spent 10 years researching roller based piston engines and I don't want to disclose any more information gained from our development program that has come as a great expense to our company.

    It's hard to compare a concept engine to an engine that has been developed over 10 years, built an tested. What do other people think of the GRECO engine in design? Is there any other comments out there from anyone on their design/prolems/benefits as it may relate to some components in our project?
    You know the problems. One of them is the roller bearings reliability. The present state of the art cannot yet guarantee such roller bearings. Maybe tomorrow, and hopefully at an affordable price.
    So, it is a matter of new technology.
    On the other hand, the PRE engine is based only on yesterday, conventional, tested technology.

    Thanks
    Manolis Pattakos

  15. #165
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    Re:Pattakon-PRE

    Brad,
    You write:
    I have seen this type of configuration before. It is better if the combustion process is performed in the middle of the engine to reduce thermal losses. Not a bad design and I have heard there are still a number of these type of configuration engines still on the road such as the Common Knocker.

    (Common Knocker)

    This can be in the Pattakon configuration and use gears to transfer power and time the engine, such as suggested by Manolis.
    In Junkers-PRE, the combustion happens in the middle. Here is the famous, during 2nd world war, Junkers airplane engine:



    top power concentration and top thermal efficiency (due to the absence of cylinder heads, the through scavenging, the compact combustion chamber etc). The worst is the long distance of the two crankshafts: the required gearing is heavy, expensive and not fault free. Another problem is that it the needs additional scavenging pump.

    Pattakon Junkers-PRE is actually a Junkers with short crankshafts’ distance and built in scavenging pumps. More importantly it provides a lot of additional time around TDC, increasing the constant volume portion of combustion thus resulting in improved thermal efficiency and improved power concentration.


    You write:
    So how do you assemble the Pattakon engine? How do you get the crank/counterweights through the piston? Is the shaft in multiple pieces or is the piston split in two parts and which way? If the piston was in two pieces it wouldn't be good to split it through the piston crowns so how is it done? Is the conrod one piece as it would be a bugger to bolt the big end cap together?
    Which one of the PRE arrangements?
    Here is a straight four PRE for car engines.


    Here is a Junkers-PRE
    See also the file www.pattakon.com/pre/blueprint.pdf

    In this arrangement, the piston is a single piece.
    The crankshaft is single piece too, having a balance web at one side. At crankshaft’s other side the synchronizing gear is cut as the second counter web. The connecting rod is necessarily split as in conventional engines. The block seems reasonable to be in three pieces, a central one comprising the combustion chamber, the intake and exhaust ports and the half of the main crankshaft bearings, while the other two parts comprise the other half of the main crankshaft bearings and the reed valves.
    By the way, take a look at one application of the PRE-Junkers engine at www.pattakon.com/fly/Flyer4.exe.



    Crazy it seems, but who knows.


    You write:
    The ports are configured like a two stroke engine in the centre so I assume that the combustion is in the centre and it's a two stroke like a common knocker? Is there more detailed pictures out there that explains these questions as I am interested in the construction of this engine?
    I see no special difficulties whatsoever in manufacturing or assembling the PRE engine. Take a look at the drawings and the animations in www.pattakon.com/pre/index.html and I will be happy to answer to any specific question.

    Thanks
    Manolis Pattakos

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