Need engine mock up advice

Dsmith1279

So I'm hip deep into a BB conversion. I've got an unusual cart, a Yamaha G17a, which only a handful made it over the pond. I'll take a pic of the wiring harness but to sum it up I've seen smaller harnesses in cars.

So far I've stripped it down to bare chassis. I've had to stretch the rear cradle and now have room for the 18hp horizontally opposed Briggs. I've purchased the Comet 780 and ordered the 47 1/2" Columbia belt. This will give me the room I need from the transmission/rear end.

So the guidance I need is how to calculate the center to center distance of the driver to driven clutch. I took the sticky belt calculator and reverse calculated it to 14.7" but didn't know if there was another magical way to come up with this calc.

I'll post pics soon.

BGW

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smokindawg

I found it easiest to pull all the original wiring from my cart when I installed my big block. I rewired it all and made it a key switch start. It made it easier to wire by adding a fuse block and I wired in a relay for the lights so I didn't have to run as many hot wires from the battery. I just put the fuse block up on the dash and run all my lights and accessories from there.

Easy-Peasy!

slonomo

For the belt, the best way is to set all your components in, line them up with the belt, then mark your holes. If you rely on the calculator only you'll be frustrated when the belt is too short or long. The calculator will get you close, but I always mock it up to mark the holes. Once you have the belt super tight, you can then measure the center to center for reference.

If you aren't using an aftermarket engine mount, I'd recommend making your mount adjustable by slotting out the mounting holes for about 3" of adjustment front and back. If you can, make the mount adjustable side to side the same way. This will make your life much easier when installing/removing the belt and engine in the future. Trust me, been there.

sho305

The other way is mock it up and use a rope/etc to measure around the outside of the secondary and down in center of primary, then add 1" to that and round up to next belt size available usually 1 or 1/2 increments. You should have room to tighten the belt, should have 1-2" slack when you press on the top of the belt at rest, iirc 1.5" in the manual. When I did clones I wanted to use stock belt so I duplicated the stock center measure, the engine ended up slightly higher at the crank and it uses stock belt size....but yeah with an opposed you need more room for sure. 1 3/16 or 1 1/4 if you have worn clutches are available in many sizes.

Dsmith1279

Thanks guys for the guidance. I actually found another thread that had an example of what Slonomo had talked about.

So far I've stretched the rear cradle. Mocked up the plate and engine. Took it all back out to paint. Now all I have to do is drop it in and I'm done with engine.

My rearend, pictured, actually had a electro magnetic brake attached to it that would disengage upon the engine catching and beginning to move forward. Once you stopped the electro magnent would disengage and lock the transmission back up. I couldn't figure out how to make that work, **** computer, so I've figured out a hand brake mechanism from a 07 GM sedan that should do the trick.

As far as exhaust I think I'm going to try and made it out of 1" tubing.

Let me know if you have any suggestions or guidance. I don't know what I don't know.

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scottyb

Sweet looking motor - it fits?

sho305

Robertsontorquetubes or many gokart places sell 1" tube and bends for exhausts. Robertson went up lately but the pieces to make your own were quite cheap.

Dsmith1279

Yup, but only because I stretched the rear cradle. Definitely a wide engine. I had it on my sons go cart for the past three years and it runs like a champ!

scottyb

Less vibration from the opposed cylinders too.

lockman1

Great start to a great build!

Maybe I'm looking too deep into this, but I have a concern about the connection from the front of the cradle to the frame...
I'm wondering if... when the cradle twists, (one tire higher then the other) wont that connection stress and break?