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Big Block Talk! Everything about swapping a big block engine into your cart!



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Old 05-04-2023, 08:28 AM   #1
saamember4880
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Default Cuyuna 440cc in Yamaha G9

Hey guys, thought I'd show off my latest project. This is my first post in this forum! I have an '85 G2 that I'm installing a 2-stroke Cuyuna 440cc engine in. I'm in the "mock-up" stage right now. I intend to bolt a pulley onto the end of the primary pulley so I can have electric start as well as help charge the battery and short of a 4" lift so I can fit 23" tires on it, I want to keep it looking as stock as possible. I had a lucky day rummaging through a scrap pile and found a tree climber stand. I'm going to cut the center of the bag well and the section above it in order to gain access for maintenance (carb, belt, exhaust, diff, etc.) and with some very light modification, this tree stand will be perfect to cover it up - with the added benefit of getting more airflow to the engine compartment!

Anyway, since this engine is rated for 40hp, I KNOW I don't want to keep the 12:1 gear ration in the dif. At the same time, I don't want to crack the diff open, AND the only upgrade available is an 8:1 ($400!), which is still too high for me. I'm not trying to make a "torque monster" here. I want a high-speed cruiser with some light off-roading capabilities (think open trails). I'm thinking about using the driven pulley's shaft from the snowmobile's chain case on a fabricated mount, and adding a sprocket to it that can connect to the diff's input shaft paired with the CVT clutch. This way, I have an easy way to mess with different ratios until I'm happy with one (I'm thinking 3:1) Has anybody started manufacturing a **** sprocket/adapter for this yet?!

Another hiccup I've ran into is that the engine is too long by about 1" to fit without removing either the gas tank or the pull start. I don't want to relocate/replace the gas tank (keeping the stock look externally) and the drive pulley already has a pull ring (not sure what it's called but you can wrap a rope around it and pull it to turn the engine over), so I'm not really concerned about keeping it anyway. I DO want to make some kind of cover for the magneto flywheel though. It has a belt-ran cooling fan above it so it'll never be waterproof but if I can keep direct splashes and debris from hitting the flywheel, I'll be happy enough. I'll be sure to keep a gap at the bottom so if any water does get in there, it'll be able to immediately drain out. It'll be pretty close to the gas tank anyway and that should help protect it too.

The exhaust will need the intake pipe cut off, rotated, and angle adjusted a bit, all while hopefully not affecting the performance. Somebody in the past welded a piece of threaded pipe to the output and I intend to use that to my advantage by adding a union to the end of it and adding some sort of muffler to it. I want the sound to be comparable to the original engine's level (or the wife won't like it lol). By using a union, I can run it sideways, under the cowl, and easily disconnect it if I need to work on things behind it. I don't know how common it is to use unions in exhaust but I've had luck with them in the past sooo... why not? Due to how close the exhaust will be to the head and belt, I'm going to heat wrap the entire thing starting just short of the manifold to just short of the tip. Hopefully this will also keep our backs cooler while riding - especially since I'm adding the expanded metal access panel.

That's all I have for now. It's a bit longer than I planned on but now you're up-to-date on this build.

Please let me know if you have any suggestions (especially about the input sprocket) as well as what you think!
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Old 05-04-2023, 09:12 AM   #2
Cartmaster
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Default Re: Cuyuna 440cc in Yamaha G2

My suggestion is that you should at least install disk brakes to the front of the cart before considering this.
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Old 05-04-2023, 09:41 AM   #3
saamember4880
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Default Re: Cuyuna 440cc in Yamaha G2

It's definitely in the plans ! I don't want to do all this work just wrap it around a tree! First things first though, and that's to make sure all the parts are gonna "play nice" with each other and I have a usable drivetrain. There's no point in dropping a bunch of money into stopping if I can't even get moving!
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Old 05-04-2023, 10:31 AM   #4
raydhd
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Default Re: Cuyuna 440cc in Yamaha G2

You might want to look at my 440 cc F/C Suzuki swap into a 82 HD cart. In the sled section of big block swaps. The easy way to use the Sled's primary with a suitable belt to the cart's secondary.Also used the sled's stock starter and alternator with a Kohler rectifier/regulator. Even with 2 stroke gearing of the HD cart the cart could easily do 30's. With the 4 stroke gearing of the G2 I would think the 40's should be easy to obtain. With larger diameter tires even more. And despite some naysayers dire predictions about using a stock HD cart muffler on the sled engine all that was needed was one step leaner on the VM's 34 needle. Just some food for thought.
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Old 05-04-2023, 12:35 PM   #5
saamember4880
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Default Re: Cuyuna 440cc in Yamaha G2

Thanks for the input! I've been devoting way too much of my time thinking about this today, considering I'm at work *shhh*.

The problem I'm seeing is that the cart's secondary is only rated for 5,000 RPM. Even with 25" tires, my max speed calculated at 5,000 RPM is about 31 MPH. I know that's only 66% of the engine's capabilities but I don't want to blow the secondary clutch up! - Not to mention overspin the starter generator (S/G). I don't have electric start on this 440 so I want to retain the S/G for both starting as well as additional battery charging. The 440's stator is capable of only producing up to 150 watts (at 12v, that's 12.5 amps). I've actually thought about creating a rev limiter after some careful consideration is put into the pulley ratio I want for the S/G - which is rated for up 8,000 RPM continuous (that's the S/G RPM, not the engine).

Also, the snowmobile's secondary clutch won't fit because the aside from the different bore diameters, the input shaft is too close to the axle to even fit the snowmobile's larger diameter clutch. Heck, the stock secondary is so close that it's difficult to even get the belt on! I actually CAN'T get the snowmobile belt on because it's about 1/8" thicker.

My current idea is to build a jack shaft mount that 1: attaches using the axle bolts (getting longer bolts to accomodate, of course), 2: extends past the input shaft (with a bearing in it that'll actually stabilize the mount by riding on the shaft), and 3: hold a jackshaft above it for the secondary clutch. The secondary clutch will then have a sprocket that'll be connected to a sprocket on the input shaft (basically spaced just far enough apart to avoid the sprockets hitting each other).

If I can do this the way I'm picturing in my head, I should be able to change my gear ratios to whatever I like (provided I save at least a little space between the sprockets), create more room for the snowmobile's secondary clutch so I don't have to worry about the 5,000 RPM max, and MAYBE even be able to slide the engine over far enough that I won't have to eliminate the pull start!

As far as reusing the 4-stroke muffler goes, I looked at the pics on your post. Your muffler is way different than mine. I don't think mine could handle the extra airflow that'll come from this engine. The muffler pics I attached are from an eBay sale item but it's the same as mine. The pipe looks so small!
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Old 05-04-2023, 04:15 PM   #6
raydhd
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Default Re: Cuyuna 440cc in Yamaha G2

I am not sure where that secondary rpm max came from. My other cart is a yamaha G14 with a heavily modded VC460 on it. I have turned 5600 rpms on it's secondary. I just installed my Omega VC based engine designed to rev with a 6500 rpm red line. I never heard perhaps wrongly that there was a Red line on the yamaha G series secondary. I have heard the S/G being limited but since 2012 I have been spinning way over the 5000 rpms with an engine speed of 5600 rpms which spins it a whole lot faster. It is a genuine Hitachi. I also had the original HD cart 2 stroke running @ 6500 rpms also with a Hitachi S/G. It was the HD's engine fan that couldn't take the revs and blew apart big time.P.S. Maybe some Yamaha expert will weigh in on IF there is a red line on the secondary clutch. I know I am not the only one running near engine speeds of near 6K thru the yamaha secondary.
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Old 05-04-2023, 06:58 PM   #7
saamember4880
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Default Re: Cuyuna 440cc in Yamaha G2

I'm sure there's a good chance you're right. I'm not an expert on these things. I got that number based on it being stamped right on the replacement clutches though. I'm also sure they likely cut the rating down for liability reasons. Lots of products are like that.

Regardless, I know I said I'm looking for high-speed cruising but I don't mean 100! Through some more calculating, I found that with a 5:1 ratio, I can hit nearly 55 MPH at 4,000 RPM, while running a 2:1 ratio on the starter generator which will put that at its 8,000 RPM max as well as keep it above 1,000 RPM when the engine is idling. Obviously, I won't likely be hitting 55 MPH all the time so the S/G shouldnt have any problems. Also, the engine won't be screaming nearly as much at 4,000 RPM - which will make the wife happy, and I'll be using less gas - which will make my wallet happy

And while I know how to count well enough to know 4,000 RPM is less than 5,000 RPM (by exactly 1,000 "ooh, look at the big brain over here!" ), if I use the snowmobile's driven clutch, I know I'll have made the smarter choice as far as strength goes. Also, in order to get my gear ratio where I want it, I'll have to use the only shaft the cart's secondary can fit on and I already have the right size shaft for the snowmobile's.

It may not be the choice everybody would make, and I respect that, but I'm being realistic of my likely uses here. I feel like 55 is plenty fast enough for a golf cart and this is the fuel-friendly ($) approach. Also, in case I ever get the suicidal urge to test my luck, I know the S/G is rated for 12,000 RPM for up to 3 minutes. The calculator says that's good for a nerve-wracking 82 MPH!
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Old 05-04-2023, 07:01 PM   #8
saamember4880
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Default Re: Cuyuna 440cc in Yamaha G2

Look, I cut a hole!... then I immediately covered it This is going to make a world of difference when it comes to this build and any future maintenance! It'll also give people a peek at what's "lurking" underneath!
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Old 05-04-2023, 07:14 PM   #9
raydhd
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Default Re: Cuyuna 440cc in Yamaha G2

With the speeds you are talking I hope you are planning some SERIOUS suspension mods
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Old 05-04-2023, 09:12 PM   #10
saamember4880
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Default Re: Cuyuna 440cc in Yamaha G2

Welp, the external gearbox idea is nixed. There's no room for it because of the exhaust routing. There's nowhere else to run the exhaust without some kind of "smokestack" setup which A) I'm not sure how that'd affect the performance although I'm positive it will and B) I'm not sure the wife would appreciate the "smokestack" look AND she wants a back seat, meaning it'd have to go up alongside the backrest, which isn't a terrible thing, except I'd have to be real careful when going through the woods. Pretty disappointing but I'm NOT about to pay for a custom made tuned exhaust!

The only choice I'm left with is to use the cart's driven clutch,hoping I don't tear it apart, and eventually buy the $400 8:1 gearset for the diff. I'll still be able to go 43 MPH @ 5,000 RPM. With the current 12:1 ratio, speed is 28.5 MPH. With the 18" tires I currently have on it, I'm looking at only 22.3 MPH. Obviously I can still exceed 5,000 RPM but then I think it'll really start screaming like a snowmobile.

Frustrated but not defeated! I'm gonna talk to the wife and see how she feels about a redneck smokestack and anticipate changing needles in the carb...
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exhaust, gear ratio, input shaft, sprocket, starter generator
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