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

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Old 04-02-2024, 01:37 PM   #71
Not Yet Wild
Join Date: Nov 2022
Location: MI
Posts: 52
Default Re: Cuyuna 440cc in Yamaha G9

Update: it's been so long that I bet people assumed I abandoned this thread. In truth, I "back-burnered" the entire project. After honing my cylinders, I reassembled the engine - still only about 70PSI compression. This irritated me so much that I didn't even bother finishing the wiring! In fact, I haven't touched the project since - swearing I'd still get it done in time for spring. Well, it's officially springtime, despite snow being in the forecast - and I haven't touched it.

I DID buy a different engine. A Rockwell 400 w/electric start. 120PSI compression in both cylinders. The problem is, once I got it home, I started realizing all the "little" modifications I'd have to make in order to install it.

Problem/modification 1: a)the starter may interfere with the starter/generator (unconfirmed). Since I eventually want lights and a sound system (not to mention a useable 12v outlets for other accessories), I don't really want to remove the S/G. With the way it turned the engine at 70PSI though, I now have doubts that it's strong enough to turn one at 120. It's still my preferred method for charging the battery - although I may entertain the idea of an alternator, if my engine has electric start. B) The electric starter on the Rockwell turns a "flywheel" on the pulley. IF I use this engine and want to maintain the electric starter, I'd either have to abandon the S/G altogether, due to lack of a secondary pulley, or figure out a way to add a secondary pulley to the drive pulley with the "flywheel" - probably not impossible (modifying a 1/2" x 8" pulley to attach to the backside of the flywheel and hope the starter doesn't hit the belt - but that means more parts and more fabrication...

Problem/modification 2: the Rockwell engine is set up for dual carbs. This would mean that a) I'd have to install a pulse pump (the Cuyuna's single carb has one built in). Not a big deal, I have a couple of them lying around and even if I didn't, they're cheap; b) install a larger diameter gas line, and a splitter for both carbs to have their own feed. Alternatively, I can buy a pulse pump, or maybe better yet, an electric one, with dual outputs and feed each carb on their own lines from it.

Neither of these are major issues but wait, there's more!

Problem/modification 3: The exhaust, rather than the collector cutting to a 45 degree angle upon exiting the heads like the Cuyuna's, they go straight back. This means I'd have to modify my exhaust... again - and I risk affecting the flow, potentially throwing my exhaust too far out of tune to easily correct -- not to mention that I don't even know if the Cuyuna exhaust is tuned the same as a Rockwell's (there IS a 40cc difference even though the hp is roughly identical).

None of the Rockwell and Cuyuna parts appear to be interchangeable. I'll likely just hold onto the Rockwell for a future build.

Ok, yesterday, I finally purchased two replacement cylinders and a head with a centered spark plug hole. The seller said he'll ship them on Friday. That means that due to the remote work I do, I have to wait AT LEAST a week just to even look at them. Note: in case you haven't noticed, the heads currently on my engine are mismatched - one with a centered spark plug hole and one with an off-center, slanted spark plug hole. The slanted hole is technically the correct one for my year engine and supposedly offers higher performance - but the centered holes run cooler and they're interchangeable. Since I'll be running it in the summer, I decided to go with centered holes, replacing the slanted one.

And finally, my ignorance caused yet another issue. When I honed the cylinders and reassembled the engine, finding I still had low compression, I read somewhere that rings will seat after the engine has ran for some time. In my misguided, under-informed, and hasty attempt to get the engine started despite the low compression, I used some starting fluid (with upper cylinder lubricant - I'm not completely ignorant lol). Well, that turned out to be a terrible idea. I wound up blowing out the crankcase seal! Apparently the crankcase doesn't use a gasket - just some high-tack sealant (says so right in the manual, for those that doubt me - see pics), and can't handle the extra pressure starting fluid can create. In my defense, starting fluid with upper cylinder lubricant worked perfectly on my old 90hp outboard so I didn't even question it... So, I'll be resealing the Cuyuna's crankcase as well. Live and learn, I suppose! (Say you don't know all the differences between 2-strokes and 4-strokes without saying you don't know all the differences between 2-strokes and 4-strokes )

Anyway, barring any unforseen issues, I plan to get back into this build in short time. Maybe, with springtime fighting to show it's face, I can even bring the cart back down to where I'm staying. If I can, I'll have more room to work and more days/week to work on it without compromising "wife time."

Topside progress: I printed my new backlit overhead double gauge pods. They turned out great! Unfortunately, as nothing positive ever seems to be able to happen in my life without a catch, my resin printer is down and I can't print the letters until I figure out what's up with it. I want to print the face "beauty" rings (sandwiches between the gauges and the pods to hide the top and bottom slots that the gauge mounting hardware slides through when installing) with it too, since they'll be backlit and while I have translucent green filament for my FDM printer (same printer I used for the pods), the rings won't be "crystal" like the resin printer can make.

I attached a couple pics of the assembled double gauge pod (printed in two pieces) - as far as assembly can go anyway without my resin printer working. The backlighting will be achieved with the electrouminescent (EL) wire you can see already embedded in the mount under where the letters will go, and dressed into the pod faces. This EL wire is like the wire used for decorative addtions to costumes, etc. (pic attached for clarity), WITH one hopefully noticeably resulting difference. The wire I bought is only available through a store in the UK (via eBay), costs roughly 4 times as much (still only about $45 so not a huge investment), and it uses twice the power - BUT they claim it's twice as bright. We'll see if I wasted my money once I finally get it assembled and tested...
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