640cc Engine Swap...

[1975 Argo 8x8 2-Stroker]

Hey guys!!

I have my old 1979 Argo 8, it is powered by it's origional 440cc Chaparal... which dosen't really have that much power (even though it is running a VM-40mm Mikuni it origionally had a 42mm Tillitson!). I have an old ski-doo Alpine with a Rotax 640cc Twin 2-stroke engine... so I got to thinking...

I took my digital vernier measuring scale (basically a very accurate device with two jaws that open up to give a accurate reading in inches or mm) and first measured up the 440 Chararal mounts... then the 640, they were pretty different, but I measured my Argos frame mount, and both engines were within the measurments so... my question would be, could my transmition take the torque that the 640 can throw at it? Can the frame take it? I am sure I am not the fist guy to put a bigger 2-stroker in an Argo (and hopefully won't be the last ) just wondering if the old girl will take it?!

Thanks in advance!

P.S. See photos of tranny...

007 (2).jpg

[hydromike]

The 640 Rotax engines are rated at about 35hp at the tippy-top end of their rpm range. I don't know the torque numbers they put out, but I'd guess that they're around 30 ft-lbs or so. Perhaps 10-20% more or less, but that's a good figure for that displacement. The G44B you're currently running likely has more horsepower when properly tuned/carbureted (read: yank the tilly), so the engine swap may actually be a step in the opposite direction.

The bottom line is that your frame and transmission should be able to handle either of these engines with ease.

[1975 Argo 8x8 2-Stroker]

Oh, really?

The G44B is definately a strong engine, but I had no idea it has more hp than a 640, and yeah, that is right, the 640cc is 35hp. I could not find the post you were talking about... where is it?

Thanks!

[hydromike]

There are a lot of different numbers out there for the G44B, but I think 40-44hp is a safe estimate for the engine. If you make it breathe a little better by swapping the carb and throwing a better exhaust on it, it might be closer to 48-50hp, who knows? What's the compression on your engine? It might simply need a refreshing with some rings and a hone job.

Are you looking for a post *I* posted before about the G44B? I think you and I were talking a while ago about it... I'll have a look for it..

[mike bar]

I want that tranny. It would probably look better in my machine LOL

[1975 Argo 8x8 2-Stroker]

I want that tranny. It would probably look better in my machine LOL

Hey, hey! Watch it there! I have a fine looking Argo with a fine looking transmition... it looks good in MY machine and ONLY my machine!!

And "HydroMike", really!!!??? 40-50hp??!! Why so much hp, out of such a small displacement engine?

And I was talking about when you said read the "yank the tilly" post.

Thanks guys!

[hydromike]

And "HydroMike", really!!!??? 40-50hp??!! Why so much hp, out of such a small displacement engine?

*Why?*, or *How?* ? I think they just breathe THAT much better. For an axial fan-cooled engine, that's a pretty reasonable number. Guys in the ultralight crowd can get upwards of 60hp out of 500cc Rotax engines, still running the fan. It's like comparing a 472 Cadillac engine with a 455 Stage I Buick engine. The Buick is smaller, but just makes better use of its cubes.

And I was talking about when you said read the "yank the tilly" post.

Oh, it wasn't an actual post. I was just saying pull the Tillotson off and replace it with a VM34 (or so) Mikuni. There might be a couple more hp lurking in there.
If you DO get a chance at checking the compression on each cylinder, I'd be interested in seeing what it is.

[1975 Argo 8x8 2-Stroker]

Ohhhhhh... okay, I see. Well, my G44B was originally using a vertically mounted 42mm HD Tillitson... I put a VM-34 Mikuni on it and it cut the power in half... so I bought a VM-40 Mikuni (Huge carb, don't know if it will hit the tranny or not!) that I will be putting on, I actually haven't tried the VM-40 Mikuni yet, so I am hoping that will solve it's problem.
And, as for the compression, I will test it this weekend.

Thanks

[1975 Argo 8x8 2-Stroker]

[QUOTE=1975 Argo 8x8 2-Stroker;91068] I actually haven't tried the VM-40 Mikuni yet, so I am hoping that will solve it's problem.QUOTE]

I am hoping to build an air breather of sorts() on the Mikuni so it will get the required air with little restriction... hard with that G44B in there, space is VERY limited...

The Pics are when it still had the Tillitson on it... Look at the space in there between the engine intake port and the tranny, try putting a huge VM-40 Mikuni in there...
002.jpgArgo Engine.jpg

[hydromike]

When you swapped out the Tillotson for the VM34, did you try to rejet the carburetor at all? It's unlikely that the Mikuni was jetted correctly for your engine. What did it come off of? A simple jet change out might have been required. Did the engine idle well, but just not produce top-end power? Your main jet might have been way to small, or way too large. It really is easy to do.

Oh heck, you're even running a CDI on that engine. It's probably a G44BSS, then. While your space is limited, you might have to just unbolt the elbow on the carb and put a thin phenolic spacer on it to get the Mikuni's carb body past the upper engine shroud. There are a few different ones out there, and I'm sure you can make it work even in those tight quarters. By the "breathing better" comparison between engines, I'm refering to the intake/exhaust ports in the engine, and how airflow *within* the engine takes place. It's like the difference between older JLO engines and the upgraded Cuyuna/ 2Si engines. Refined intake ports and head design really make a big difference.

That engine looks nice in there....