2 cycle out of a 4cycle? - PeachParts Mercedes-Benz Forum

Cervan · #1 02-12-2008, 12:52 AM

How would one convert a 4 cycle mercedes 240d into a 2 cycle engine? Sounds like fun to me.. strap a supercharger on it and change the cams, what do you guys think?

pawoSD · #2 02-12-2008, 01:02 AM

You would need to re-work the camshaft to open the exhaust valves while the piston of each cylinder is near bottoming out on the power stroke, and close them when it bottoms out, then open the intake valves when the piston is bottomed out, then close them right away so it can raise the piston and complete a compression/power stroke again. You would need to re-work the injection pump to introduce a fuel pop 2x as often.

So, new camshaft, and re-worked injection pump.

And, you'd be left with an engine that would run at probably 1/5 the speed but would have a ton of torque/hp at that speed. That is, if it actually worked. 2 stroke diesels are generally direct injection, who knows if it'd even function as an IDI.

Good luck with all that.

Cervan · #3 02-12-2008, 01:29 AM

Quote:

Originally Posted by pawoSD

You would need to re-work the camshaft to open the exhaust valves while the piston of each cylinder is near bottoming out on the power stroke, and close them when it bottoms out, then open the intake valves when the piston is bottomed out, then close them right away so it can raise the piston and complete a compression/power stroke again. You would need to re-work the injection pump to introduce a fuel pop 2x as often.

So, new camshaft, and re-worked injection pump.

And, you'd be left with an engine that would run at probably 1/5 the speed but would have a ton of torque/hp at that speed. That is, if it actually worked. 2 stroke diesels are generally direct injection, who knows if it'd even function as an IDI.

Good luck with all that.

Why couldnt i raise the RPMS with making it two stroke?

pawoSD · #4 02-12-2008, 01:31 AM

I'm not scientifically sure on that......but I do know that most large engines that run 2-stroke have a "full speed" operating rpm of like 950, and idle at like 250-300ish. There's got to be a reason....unless its just because they're so big....perhaps a small engine like a 240 could run faster. No idea. Anyone?

Cervan · #5 02-12-2008, 01:39 AM

Quote:

Originally Posted by pawoSD

I'm not scientifically sure on that......but I do know that most large engines that run 2-stroke have a "full speed" operating rpm of like 950, and idle at like 250-300ish. There's got to be a reason....unless its just because they're so big....perhaps a small engine like a 240 could run faster. No idea. Anyone?

Im simply thinking of it at this point, it may be because of the internal stresses two strokes put on the parts. An extra explosion every stroke really stresses everything. I have an extra engine that i just may give this a try.. The internal cam in the injectionpump will have to be changed, the cams in the head will have to be changed as well.. then a supercharger will have to be modified and put on there. (I think a hybrid, turbo/supercharger would be a good idea, Putting a supercharger that only creates enough psi of boost for the engine to idle, and then a turbo for the rest of the running boost. that way it would be easier to tweak instead of changing pullys)

pawoSD · #6 02-12-2008, 01:47 AM

Quote:

Originally Posted by Cervan

Im simply thinking of it at this point, it may be because of the internal stresses two strokes put on the parts. An extra explosion every stroke really stresses everything. I have an extra engine that i just may give this a try.. The internal cam in the injectionpump will have to be changed, the cams in the head will have to be changed as well.. then a supercharger will have to be modified and put on there. (I think a hybrid, turbo/supercharger would be a good idea, Putting a supercharger that only creates enough psi of boost for the engine to idle, and then a turbo for the rest of the running boost. that way it would be easier to tweak instead of changing pullys)

Go for it! That'd be awesome to come up with a working 2-stroke 616.

sixto · #7 02-12-2008, 02:24 AM

Quote:

Originally Posted by Cervan

Why couldnt i raise the RPMS with making it two stroke?

The IP is goverened to something like 2800rpm which limits a 4-stroke engine to 5600rpm. If you need a fuel squirt with every revolution...

You'll probably hit the dynamic limit of the preignition set-up before 5600 IP rpm unless you radically advance IP timing.

I think you'll burn the valves in short order if they're meant to transfer heat to the seats 75% of the time rather than only 50% of the time.

I wonder if it's easier to fit a crank sprocket on the cam or grind a cam with diametrically opposed lobes. Then fit a crank sprocket modified to take an IP timer on the IP and you're good for at least 2800rpm

Sixto
87 300D

Cervan · #8 02-12-2008, 02:37 AM

I could machine a peice to adjust the cam like a cam adjuster they have for honda engines out there. I could just machine the crank gear to accept the IP that would be easiest. I would probibally have to adjust the interals too because i may convert to DI So i might need to raise pop pressure or just use existing setup ( i think the compression will be lost in the extra cubes within the precomb chamber) I will be building the engine, im not sure if i should start with a 617 wich has oil pistion coolers, or to just use this free 4cyilnder that i have sitting. i am sure that ill be building the engine, new valves 6 angle valve grind hogged out oil and coolant passages, then oringed head and prepped for copper gasket. ill go .5 over on all the cylinders to get them perfect then get the same size pistons and get them matched to each cylinder, then get the entire rotating assembly balanced and the crank microbuffed. Maybie ill get the rods shotpeend and cryofrozen. I may have to get special pistions made because of it being two stroke. Ill just try to use the existing pistions for now.

sixto · #9 02-12-2008, 02:41 AM

DIs run 2-3x the pressure of IDI so I don't think it's as simple as "tweaking" the IP. You might tweak 10-20% more pressure. You're not going to get 20,000 psi out of it.

Sixto
87 300D

Cervan · #10 02-12-2008, 02:56 AM

Quote:

Originally Posted by sixto

DIs run 2-3x the pressure of IDI so I don't think it's as simple as "tweaking" the IP. You might tweak 10-20% more pressure. You're not going to get 20,000 psi out of it.

Sixto
87 300D

The DI im thinking of is waay under that. the DI engines i used to rebuild, 2100 psi is what they used to run at..

junqueyardjim · #11 02-12-2008, 11:31 AM

There is no way you or anyone else is going to change a 4 cycle into a two cycle. First of all, the 2 cycle has valves in head, either two or four, but they are all exhaust. It doesn't have intake valves. The way it gets it's intake is through an air system built in the block and a set of ports around the lower part of the cylinder bore. Then when the piston is at the down part of the stroke, the pressureized air from the blower is ready to surge in on top of the piston. Then the piston goes up and closes off the air flow, the air is compressed, fuel is squirted in, and "kazaam" you have your power. Now figure out how you will do that on a 617. And no PawoSD, truck two strokes are not limited to 1200 rpm. The pair I had, ran 750 at idle, 2850 for full power and 3100 or 3200 redline.

rrgrassi · #12 02-12-2008, 12:06 PM

IIRC, EMD diesels in locomotives are two stroke.

I think you would have to build an engine from the ground up, but you could design in MB parts like the crank and pistons.

#13 02-12-2008, 02:02 PM

I think it might be cheaper to make that common rail system.

pawoSD · #14 02-12-2008, 04:00 PM

I always wondered why those Detroit engines sounded so different. 2-stroke engines.....interesting. Ok, now I know they can run higher than 1000rpm.

Somehow I don't think its ever going to happen/work.

patbob · #15 02-12-2008, 07:56 PM

Changing to DI has been discussed.. you need a new head of your own design. So, $$$ If you do this, then you have a lot of options, and the below doesn't apply unless you want it to.

You''ll need a new cam that opens both intake and exhaust valves simultaneously. You'll need a supercharger so you can raise the intake air pressure to blow the exhaust out for the next cycle. You'll need the IP to pump twice as often.. I think it might work if you can run it at 2X RPM, but I doubt you could substitute a smaller sprocket to accomplish that. You'll use 2X fuel at all RPMs and you'll have to have a manual transmission as I doubt the torque converter & ATF could withstand converting all that extra torque to heat when stopped.

I like your idea of using a supercharger and turbocharger, but the supercharger will be partly pumping the turbocharger, which sounds difficult to control to me. Mightbe easier to let the supercharger change intake air pressure with engine RPM.

If you do this, certainly write back.. success or fail, I'm sure lots of people would be interested

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