Topic: cb500 2 stroke engine

[rb550four]

  Recently, I had an idea about making one of my 500 engines that need rebuild  and make it no longer a 4 stroke but make it a 2 stroke. I don't know if it's been tried or if it should be tried but I really want to do it this year. I've been going through it in my head for the past few days and posting my thoughts , and possible plan of attack of how I would want to do it . There have been some stumbling blocks that I think have been systematically finding answers that I think could be both sensible and possible.  Which took me from a block of aluminum with tons of machine work to reinventing the use , placement and altering of stock parts to keep it as stock as possible that will operate differently, This is not to say that there won't be a mess of items that won't be stock but I would rather be able to get replacement parts from a warehouse then to have every piece custom machined each time something breaks.
  I wrote these ideas on the 500/550/650s that followed me home thread that I will try to transfer to this thread because I'm looking to share opinions,collective knowledge and bounce around some ideas on this subject to make it a viable reality, no matter how frightening it may be.
   Transfer of thread coming up...as soon as I figure out how.

[rb550four]

 Okay, so I'm back on the superpube tube,repair surgery this coming Tuesday and hopefully back in the swing of things in a month or so,then I can take care of my wife. So during this idle time of doctor's office visits,surgery and bedrest, I've been thinking of what project I should do next and came up with a somewhat different idea than I've had at any time before.
   Ready? Warning to those with weak stomachs. Drum roll please. Change a four stroke 500four engine to a 2 stroke!
Ta Daaaa.
  Twice as much fire than the four strokes! More POWER! How much fun would that be on an 1/8 or quarter mile? Now this plan is just starting to come together in my head, and let me remind you that the hospital has pretty strong drugs and I've had some time on my hands
 I would like to start with removing the head, toss the camchain,cam, valves,and everything above the head gasket.  Machine exhaust ports just above the piston at the bottom of the stroke . What kind of piston is to be determined at a later date, but would like a high compression dome style and machine a large hemi head from one block of aluminum or some kind of alloy with room for a spark plug and compression release. I want the intake ports high in the head, but not too high so it'll fit in a 500 frame.May need to get stronger head bolts. I'm thinking that the cooling fins should look excessive since there will be more heat with more fire. The header system will also have to be custom made. and I would like to cap the old oil passages going up the the jugs and reroute oil pressure to the crank , wrist pins and cylinder walls from the bottom up to keep the bottom end cool and lubricated. This is all off the cuff right now but , I think I'm on a roll. I'm thinking that timing should be about the same on the stock setup  only have to make them fire twice as often ....Smaller points cam maybe or 4 sets of points or 2 sets of electronic ignition on the same plate or separate plates...again off the cuff. As for carbs, I'm liking the idea of 2 big snowmobile carbs, or 4 that I have on the shelf or stay with ...doesn't matter yet it's all in idea stage now.
   What do you all think? Has it been done yet? Should it be done? I want to do this . I would like the groups input about all aspects of this idea. I haven't talked about this with Mike and I know he's the man to talk to about machining stuff like this, so I'm looking to put together a plan that could make this a viable reality instead of something that explodes on the first kick ...and would like some of the unforseen bugs that haven't entered my mind to possibly be exposed by anyone who is interested so this could turn out to be a decent, worthwhile project...even if it sounds stupid
So what do you all think?






I have a 550 frame, 5 500 engines that need rebuild. Maybe the 500 trans isn't the best trans to work with but I don't have any beat 650 engines on the rack, that would be a better setup. Still in idea stage.
 Yes a cr500 would be great in a perfect world but it's not a 4, and I don't have a cr.  And I just can't help but wonder what a 2 stroke 4 would be like. Perhaps I should be on the lookout for a beat 650 engine and use that as a base. Hmmm.

[rb550four]

 I was reading a thread a while back involving a supercharger on a 550 and got to thinking wouldn't that pressure be nice to have on a lower intake side port to blow the exhaust gases out of the top of the  cylinder through the exhaust valve instead of waiting for another revolution for the piston to push it out. Intake valves could be removed and another cam could be ground to open the exhaust just long enough for the gases to escape with the the help of pressurized air from that supercharger and close that exhaust valve on the piston's way back up making ready for another compression stroke with fresh air. Of course this probably means some sort of fuel injection system that delivers fuel directly through the intake port at a moment when the hot gasses have left the cylinder just as the exhaust valve has closed. Wouldn't want to be blowing in an air/fuel mix while flushing the cylinder. This way the head,cam ,and exhaust valve can be used cutting down on a mess of machine work, may not even have to change the exhaust system to an expansion type ,not sure but wouldn't it be great to use some stock parts.
 I went with the supercharger idea not for extra power but for it's pressure and fresh air. Most 2 strokes get and store the pressure created from the piston on the down stroke, momentarily storing pressure in the crankcase until the piston is in position just before bottom dead center when the intake port is no longer being blocked by the piston, then allowing the crankcase pressure to escape through the intake port. I don't think I need anymore pressure in the bottom end as these engines aren't built or sealed for this,and even if it could be compartmentalized there is a pan of oil to deal with and pressure could not be contained .
   The ignition would have to fire twice as often, I'm thinking about an electronic ignition with 2 extra magnets in the cap over the spark advance. Haven't worked it out yet but it seems doable in my head.
   The fuel injection parts and it's timing is something that I don't know much about now but I'm hoping to learn something about how Honda has been doing it in recent years and figure out a retrofit for the 500... it may have been done here before but I haven't searched it yet. This is sounding more possible to me all the time.

[rb550four]

I've been looking for a solution to this fuel injection thing all afternoon. Although there are threads regarding possible  type of  kawasaki  efi, so far I haven't found a completed project . Not that it would work on my configuration because of a possible/probable pre ignition issue that would exist while introducing the fuel air mix as the burned air is escaping through the cylinder via the exhaust valve. I had a plan on abandoning the intake valve ,so I'm thinking that an injector could replace that valve in it's position in the head. spark plug stays in the spark plug hole and the exhaust valve stays where it is only timed twice as often by the reground lobe for the exhaust valve.The intake lobe could be cut back to make clearance for the injector who's size is unknown at this point. The intake tappet will be removed so there should be room ,I  think at this point. Thus solving the probable pre ignition issue.
   New sealing method will have to be used around the tappet covers that should have a hole drilled through it to accept  injector and fuel line.
   Also been looking at the AMR500  and the AMR300, guess I can wait and see how the Big Bang chopper handles the 500 before making the choice between the 500 or the 300.
   The next problem to tackle will be the electric fuel pump ,fuel rail , timing for an injector pump of some sort,this and proper air/fuel mix is an issue for me tonight but it'll give me something to think about tomorrow.
    At this point I could throw in some 16 to 1 pistons and make a 2 stroke diesel out of it all. But  this isn't about torque,it's about hp and if I find enough information on the subject ,with a few spare engines,  I guess it could end up being about both I suppose.Anyone know anything about an outboard injector pump that might do the trick?

[rb550four]

 So, no takers on the outboard fuel injector pump question...I'm going to research some of these systems used on smaller diesel excavators (mini hoes) , bobcats and larger lawn tractors to see if anything can be made to be useful for a fuel delivery system  then start looking at 4 cylinder cars to see if anything could be made to work from that angle. Let the games begin.
   Also, I have had a few 550s come into my possession over the years with oil coolers. I never have put one back on an engine so I still have them on the shelf. I wonder if anyone has had any reviews about them? And  wondered if they are even worth putting on this engine to cool it down a little bit. It always seemed to me , and I may be wrong , that adding more oil line with that small radiator would cause extra strain on the oil pump and cause premature wear in to the oil pump or starve other areas that take a little more effort to lubricate ,like up in the valve train and cam ? Like I said, I could be wrong. I haven't seen many builds with an oil cooler on it and wondered if there is some sort of problem with them that would cause failure or premature wear to internal parts. Has anyone had any experience  with them?

[rb550four]

So that's where I'm with the plan so far,I know I'm not a genius so I ask for help when unsure or just don't know.
 Did I miss anything on the basic engine?
 Do you think a double lobe on the cam might be too much and just float the exhaust valve at speed?
  Do you think the extra magnets might be a good short cut to get fire twice as often in time?or will I have to double the pick ups? or deepen the cover just double up on points and condensers if there's room on the backing plate.
 Is there some other type of injector pump that is known to man that would actually work on this application?
 would a mechanical pump be better that an electric pump?
 And  any ideas on what system would regulate and control the air/fuel mix electronically?
 I think , if these questions have an answer we would be well on our way to a 500 2 stroke.
 What do you think ? Could it float?
 

[Terry in Australia]

To turn a 500 4 stroke 4 cylinder engine into a two stroke, you'll need to remove the head and machine a new one, with just 4 combustion chambers. You'll need to build 4 new cylinders with intake and exhaust ports built in, using reed valves for each intake port. you'll need to change the crankcase so that the fuel/air mix is directed into the sump, and drawn back into the combustion chambers by way of internal cylinder porting.

You'll need to block the crankcase off from the crankshaft, so that you're not drawing gearbox oil into the engine, unless you're trying to build a fog machine. You'll need to disassemble the crank so that you can put a crank seal between each cylinder, so probably construct a built up crank, rather than a cast crank like you have now, but with roller bearings, not shells like you have now. You'll need to build 4 separate expansion chambers for exhausts (you can build a 4 into 1, but there's a lot of science involved)

So you've now replaced the head, cylinder block, crankshaft, crankcases and exhaust. You'll need to retime the engine, (port timing) install and plumb an oil pump and a tank for the engine oil, and replace the pistons with 2 ring types. (no oil ring required) The CB500 carbs aren't really suited to a 2 stroke, so 4 VM series Mikuni's and air filters would be a good option.

I've probably forgotten a few things, but that'll give you a basic idea of what you'll need to get your project started. Or maybe just try to find a 2 stroke engine that someone else has designed and built, like maybe a snowmobile or jetski engine? It will still be a problem shoehorning another engine designed for something completely different into your frame, but hey, if you wanna be different, why not?        

[Stev-o]

Or maybe just try to find a 2 stroke engine that someone else has designed and built...
 

+1  like the mighty Kawasaki H1 triple...your bike will really fly!

https://www.ebay.com/itm/72-Kawasaki-H1-B-H-1-500-Triple-engine-motor/402124954612?hash=item5da083dbf4:g:WMkAAOSwEXZeWB4u

[bill440cars]

To turn a 500 4 stroke 4 cylinder engine into a two stroke, you'll need to remove the head and machine a new one, with just 4 combustion chambers. You'll need to build 4 new cylinders with intake and exhaust ports built in, using reed valves for each intake port. you'll need to change the crankcase so that the fuel/air mix is directed into the sump, and drawn back into the combustion chambers by way of internal cylinder porting.

You'll need to block the crankcase off from the crankshaft, so that you're not drawing gearbox oil into the engine, unless you're trying to build a fog machine. You'll need to disassemble the crank so that you can put a crank seal between each cylinder, so probably construct a built up crank, rather than a cast crank like you have now, but with roller bearings, not shells like you have now. You'll need to build 4 separate expansion chambers for exhausts (you can build a 4 into 1, but there's a lot of science involved)

So you've now replaced the head, cylinder block, crankshaft, crankcases and exhaust. You'll need to retime the engine, (port timing) install and plumb an oil pump and a tank for the engine oil, and replace the pistons with 2 ring types. (no oil ring required) The CB500 carbs aren't really suited to a 2 stroke, so 4 VM series Mikuni's and air filters would be a good option.

I've probably forgotten a few things, but that'll give you a basic idea of what you'll need to get your project started. Or maybe just try to find a 2 stroke engine that someone else has designed and built, like maybe a snowmobile or jetski engine? It will still be a problem shoehorning another engine designed for something completely different into your frame, but hey, if you wanna be different, why not?        

    Whoa, this could very easily, run into a long process. Terry was right on, with all he said and I would like to add & stress the fact that the crankcase has to be totally setup, with no chance of drawing air, from any source except through the induction system. IF, after it is gotten to run, it were draw air anywhere besides where it is supposed to, you could easily have a runaway motor. Another point, I saw times, back in the 1960's, where a 2 stroke suddenly started accelerating like crazy and the only way to shut it down, was to put the front wheel against something solid and pop the clutch, with it in gear. Otherwise it could detonate. What caused that situation, back then, was a small piece of carbon got lodged in the sparkplug, causing it to be like a glow plug and turning the switch off and turning the gas off, won't help, right then. Back then, they cut off part of  the part of the spark plug, that you bend, to adjust the gap. Sorry, I would call it a "tang", maybe? Anyway, they would cut that piece, to where it came up to the lower side of the center electrode. That seemed to help keep any small piece of carbon from getting lodged in there. My apologies, for my clumsy way of relating what I was trying to say. Good Luck, with your project by the way.

            

[BenelliSEI]

Or an engine swap? Here’s a two stroke 550 I had a while back. A rocket ship!

[rb550four]

 Thanks for answering Terry. I understand what you are saying about a typical 2 stroke engine and have addressed some of these issues, I think. This thread has been a think as I go,  so problem solving techniques may have been overshadowed by the  vast difference between  these two types of engines .
  In other words , since the idea has been evolving , I have been trying to write down a cure fore each issue like in reply #2 and #3 and of course one issue can lead to another that would also need a solution. Since thoughts are a little scattered about throughout the entire tread I can see where it would be difficult to keep up with. My fault. So I would like to take this opportunity to start with what I have in mind in order so it makes some sense. the evolved idea at this point ,using as many stock parts as possible. So her's the condensed version.
   Address the crankcase pressure issue by eliminating the usual 2 stroke port where air fuel mix enters the crankcase from the carbs by the creation of vacuum caused by the piston in the upward stoke. I don't want to have the fuel /air mix or pressure in the 4 stroke's crankcase at all. My way around that is to relocate the intake port for each cylinder below the the original positions of the stock intake locations into the jug, at the top of the piston at bottom dead center and cap off the original intake openings after removing the stock intake  manifolds. This would bypass the bottom end issue of fuel or pressure in the crankcase, leaving the bottom end to operate as it would if it were stock.
  But it presents a new issue. What would force air into the chamber without the conventional source of vacuum  through the crankcase then? My answer is a blower would push compressed air into a holding chamber/with 4 manifolds in the new port positions as described above. Can I use a carburetor ,no, because the fuel mix would detonate as it entered a hot cylinder.
So if that's the case, I think an fuel injector in the intake valve position in the head would be a safe option.
  Exhaust... I want the least cycles possible to releave the cylinder of spent fuel/air and I want to stay as stock as possible... I'm thinking to use the stock exhaust valve setup with a different cam grind  (a double lobe peak)that will open the exhaust valve twice as often then stock. And with the help of compressed air from the blower, as the piston comes down on the power stroke the exhaust valve opens midway, Once the piston hits bdc the pressurized intake blows the spent air/fuel mix out the top of the cylinder through the exhaust valve until it closes. The  piston goes up compressing clean air along the way, fuel is then injected through the injectors that now occupy the space of the original intake valve and starts the power stroke again.   and that's where I'm at in my head.
    The next things to address are injector pumps...electric or mechanical...we already know that we don't have enough electric to run pumps, computers for air/fuel mix and lighting at lower rpms so I'm hoping that someone may have idea on a mechanical pump that could work. Or a combined set up that could work. Or back to the drawing board  a stock system form a newer Honda that would require an electric upgrade too. I'd entertain any idea about this.
    I hope this condensed summary clarifies this project idea in a way that is understandable and would make it interesting enough to chime in with some ideas about whatever. I think it's doable, if enough thought has gone into it I don't see a reason why any of these issues couldn't  be overcome.

[rb550four]

  Okay, I was out on the road to meet a customer when it hit me . The blower idea that was to bypass the crankcase by bypassing through a lower intake port won't work , yeah, it can feed the cylinder air while the piston is at bottom  and blow out the exhaust   but when the piston travels upward past the port ,the blower pressure would still be blowing into the port right into the crankcase. Another uh oh, embarrassing  moment, thought I covered the bases, didn't. Guess if it was that easy to do everyone would have done a 2 stroke already. I think I'm going to reconsider my options for these 500 engines. unless there is a stroke of genius that happens that would enable the intake to be sealed until it needs to be open. Hmmm, nevermind. Sorry guys, thought I was onto something.
Bennelli, That bike is beautiful. did you make it yourself? Maybe I should just find a donor engine . SteveO said the same thing! So did Seanbarney and Terry.  Must be something to this idea . And Terry, my apologies , I thought that you misunderstood the idea of the thread, when in fact it , I misunderstood just how difficult pulling something like this off could be. Think I'll go find a rock to crawl under for a while.

[Terry in Australia]

No worries mate, go find yourself a nice old two stroke road bike like a Suzuki T500 Cobra, and while you're at it, find one for me too, they're rare on the ground here, but were so much fun back in the day, and would scare the sh1t out of a CB750 rider. Probably don't weigh as much as a CB500 either.

[Stev-o]

No worries mate, go find yourself a nice old two stroke road bike like a Suzuki T500 Cobra

Like this!

https://portland.craigslist.org/wsc/mcy/d/portland-1972-suzuki-t500-titan-2/7079785000.html

[Terry in Australia]

No worries mate, go find yourself a nice old two stroke road bike like a Suzuki T500 Cobra

Like this!

https://portland.craigslist.org/wsc/mcy/d/portland-1972-suzuki-t500-titan-2/7079785000.html

Oh wow, I'm drooling over those pics Steve! I'm hoping to retire soon, an d when I do, I'm coming over with a rented truck and a U Haul trailer!

[Tracksnblades1]

I was reading a thread a while back involving a supercharger on a 550 and got to thinking wouldn't that pressure be nice to have on a lower intake side port to blow the exhaust gases out of the top of the  cylinder through the exhaust valve instead of waiting for another revolution for the piston to push it out. Intake valves could be removed and another cam could be ground to open the exhaust just long enough for the gases to escape with the the help of pressurized air from that supercharger and close that exhaust valve on the piston's way back up making ready for another compression stroke with fresh air. Of course this probably means some sort of fuel injection system that delivers fuel directly through the intake port at a moment when the hot gasses have left the cylinder just as the exhaust valve has closed. Wouldn't want to be blowing in an air/fuel mix while flushing the cylinder. This way the head,cam ,and exhaust valve can be used cutting down on a mess of machine work, may not even have to change the exhaust system to an expansion type ,not sure but wouldn't it be great to use some stock parts.
 I went with the supercharger idea not for extra power but for it's pressure and fresh air. Most 2 strokes get and store the pressure created from the piston on the down stroke, momentarily storing pressure in the crankcase until the piston is in position just before bottom dead center when the intake port is no longer being blocked by the piston, then allowing the crankcase pressure to escape through the intake port. I don't think I need anymore pressure in the bottom end as these engines aren't built or sealed for this,and even if it could be compartmentalized there is a pan of oil to deal with and pressure could not be contained .
   The ignition would have to fire twice as often, I'm thinking about an electronic ignition with 2 extra magnets in the cap over the spark advance. Haven't worked it out yet but it seems doable in my head.
   The fuel injection parts and it's timing is something that I don't know much about now but I'm hoping to learn something about how Honda has been doing it in recent years and figure out a retrofit for the 500... it may have been done here before but I haven't searched it yet. This is sounding more possible to me all the time.

Is this 1938 Detroit Diesel  "Deja vu" ?

[strynboen]

you vill need a bearing crank..think that is a show stopper

[Tracksnblades1]

you vill need a bearing crank..think that is a show stopper

Detroit Diesel did it with plain bearings in 1938 with a supercharger replacing the crankcase compression cycle. Maybe over your way in the lend lease program too.

[strynboen]

ship engines use fuel injektion and pressure air loading for long time too..so not any new here..but a 5000 + rpm engine is somthing different

[Tracksnblades1]

I expect you've never been around a Detroit when the infamous governor spring broke....

[Bodi]

Although it may be possible I have never heard of a blower induction 2 stroke spark ignition engine.
The old Detroit Diesel blower induction 2-stroke diesels have very long pistons - and sleeves - to avoid pressurizing the crankcase. The heavy long pistons, plus other reasons, limit the redline RPM. The entire 71/91 engine series are rated for power at 2100 RPM, I don't know the max RPM but it probably isn't too much higher.
The DD 71 and 91 series engines have a large airbox surrounding the sleeves, sleeves have a lot of intake ports around them. That gives a lot of opening to let the intake air flow in, the limiting factor in scavenging efficiency is the exhaust valve area. There are 2 and 4 valve head variants, the 4 valve head increases power output considerably. All the valves, of course, are exhaust valves.
I don't think a Honda four can accommodate extended sleeves and pistons to use this approach if you could fabricate an airbox.
So with a blower, where does the intake go in? You could blow through the intake valve, but with no cylinder vacuum you need fairly high pressure behind it to scavenge the cylinder. The horsepower needed to make high pressure becomes a serious percentage of engine power output... drag racing V8 engines drive the supercharger through a 3" wide toothed belt for a reason: several hundred horsepower is needed. It also gets scary if you're using a carburetor or fuel injection before the blower: the explosion hazard is extreme.
Direct injection will be better but also much more complex.

And yes, the DD governor can fail. There is always an emergency intake air cutoff flapper, but in normal use it isn't used often (if ever) and tends to jam open from lack of maintenance. If the governor fails with the injector rack in full fuel and you can't close the flapper... things gets very loud, very smoky due to incomplete combustion at high RPM, and usually the engine breaks apart in dramatic fashion after a minute or two - the internals just can't tolerate the high RPM reached in a runaway.

Best to find an old T500 engine and try to shoehorn it in, maybe an RG500... if you feel very adventurous a TZ750 engine would be interesting! There are also quite a few possibilities from snowmobiles but adapting them to use a clutch and gearbox is very challenging. And the snowmobile torque converter drive seems, well, just wrong on a motorcycle.