yanmar repower

[RichCarter]

Doug,
Glad to hear that you’re using my notes. It was a lot of work to create. I assume that you’ve seen my cost breakdown. The engine is only about half the cost of a full repower, excluding labor. Are you replacing everything including v-drive and prop? Will you do the work yourself or hire it out?

I’m not sure the RV-20 V-drive would take the torque from this engine with a 2.7 gear reduction. That’s about 400 ft-lbs. If you plan to reuse your V-drive, consult Walter.

The newer Yanmar 75hp is a slower turning engine. You won’t need as high a gear reduction as me. 2.7 seems perfect. I have 2.0 through the V-drive.

If I were to do it again, I wouldn’t change anything except the pitch on my prop. I should have gone for a bit more bite. I love the engine. It just purrs along at about 2600 RPM with the boat doing over 7kts. It would be nice to have a bit higher gear reduction but its not necessary. A higher gear reduction would probably allow a bit more efficient prop. If you go with the yanmar transmission, the shaft comes out at a lower angle so you’ll have to raise forward end of the engine and lower the rear. You might find that the engine pan hits the bilge or the engine cover doesn’t fit over the engine exhaust riser. (Yanmar now shows a ZF30M parallel transmission option. This might fit) I went with a the high riser exhaust option. The stock riser might be OK. Take careful measurements before making your purchase. There is really nothing wrong with the BW velvet-drive. If you reuse your BW, you’ll need two spacers. Yanmar overcharges for them. they are just standard SAE spacers. You could probably find them cheaper elsewhere. Mounting an external heat-exchanger was a pain. All things considered, a new transmission might be the best choice if it fits. Double-check the direction of rotation with the new transmission. It might be opposite the BW rotation.

If you put an accessory mount on for an second alternator, beef it up more than as shown on my notes. I cracked one side mount of the accessory rail. No big deal. Just a bit of extra steel and welding.

The ‘C’ type instrument panel looks different. It might fit. I had to fabricate my own panel. Still no fuel gauge, but you could relocate the key switch and free-up enough space for a fuel gauge.

I’ve cc’d the 424 mailing list. Others might be interested or have helpful comments.

Feel free to ask questions.

Rich

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