RaT build, nearly ready

**JohnsonM50** · 06-24-2010

The boat its for..

Above's a shortened 31.8ci OMC with a 102 gearcase. It was limited to 3" because of the tilt pin location, the water pump & limited mostly by the lower mount. To get around this I decided to extend a plate that joins the upper & lower parts of the 'sectioned' tower to replace the lower soft mount with a hard one.

The gearcase is 1:1, the motor will be about 16 1/2" from clamp to prop shaft center & it will weigh about 70 lbs. Most any if not all 31.8 power heads would bolt on, up to 35hp. Its 5 1/2 " shorter at the tower, the gear case & sub foot is shorter than stock so it should fit the hydro at its transom without blocking it up saving yet more weight.
Still hindsight kicked in & Id like to shorten one even more. If I had made a new extended upper steer pin plate & extended the gear case mount plate I could've used a full length steer pin. That would set the motor back about 2" more & when it turned, the side travel of the foot would be more per less turn radious. [good or bad?]. I made an assembly kit to hold it all centered & straight for welding, a steel rod from an old longshaft that fits, A ring to hold center where the drive shaft meets the motor 2 sleeves to hold centers along the middle that can be saved for next time. This motor will put like a fish-er & go like a racer.

A long way from my 1st RaT gearcase.

**Mark75H** · 06-25-2010

U R sick

**JohnsonM50** · 06-25-2010

[QUOTE=Mark75H;93519]U R sick

Thanks Sam, It aint easy but is fun.

**bandit** · 06-25-2010

With makin a mid like the racers do from pipe, since you aren't going to shift any way?

**JohnsonM50** · 06-26-2010

[QUOTE=bandit;93537]With makin a mid like the racers do from pipe, since you aren't going to shift any way?

My thinking is to make a mid that exhausts at the bottom [not too loud], drop the C of G, weight & run the stock water pump for the motor. The low pickup gear case sends water straight to the pump internally.
Id like to go with a stack but it isnt something being made for sale that I know of. I have seen pics of one made with the 22ci type Beyer stack & a home made filler block. Ive also read the 31.8s dont do well with force fed cooling & can cook before getting on plane. I guess you could build a stick tower with a pump otherwise.

**genea01** · 06-26-2010

[QUOTE=JohnsonM50;93540]

Originally Posted by bandit

With makin a mid like the racers do from pipe, since you aren't going to shift any way?

My thinking is to make a mid that exhausts at the bottom [not too loud], drop the C of G, weight & run the stock water pump for the motor. The low pickup gear case sends water straight to the pump internally.
Id like to go with a stack but it isnt something being made for sale that I know of. I have seen pics of one made with the 22ci type Beyer stack & a home made filler block. Ive also read the 31.8s dont do well with force fed cooling & can cook before getting on plane. I guess you could build a stick tower with a pump otherwise.

the guy that made hustler stacks had a mold for the omc 31.8

**JohnsonM50** · 06-26-2010

[QUOTE=genea01;93559][QUOTE=JohnsonM50;93540]

the guy that made hustler stacks had a mold for the omc 31.8
Thanks, 31.8's are legal C-mod power heads & would probably need that to compete.

**JohnsonM50** · 07-01-2010

I got the welding done today, Bob did a great job at a great price. I carefully prepped & jigged it, locked it together with threaded rod & held center with a driveshaft. I turned the driveshaft end to be a tight fit into a socket that fit tight where the the coupler rides & locked it all together on center. The expected distortion was minimal so it should be easy to fine align. Now to get a drive shaft squared & some bushings made up for the steering pin..That & a few odd$ & end$ should finish it.

**JohnsonM50** · 07-02-2010

[QUOTE=JohnsonM50;93770]I got the welding done today, Bob did a great job at a great price. I carefully prepped & jigged it, locked it together with threaded rod & held center with a driveshaft. I turned the driveshaft end to be a tight fit into a socket that fit tight where the the coupler rides & locked it all together on center. The expected distortion was minimal so it should be easy to fine align. Now to get a drive shaft squared & some bushings made up for the steering pin..That & a few odd$ & end$ should finish it.

A couple pics..

One of the objectives being light, 35 hp at 70lb's? Maybe, It stands at 66.

**BRIAN HENDRICK** · 07-02-2010

Originally Posted by Mark75H

U R sick

Yes, and he got that way hanging out with Glock

I know you know, but to avoid confusion that is not a Y102, but a Yamato horizontal split Hatchet.
Ist I thought it was a Konig 'split-case' with a nose job.

You could have used a Konig 'LINKS' with the exhaust snout incorporated , and bolted it on higher, w/o the water pump.
Most of the issues with force feed on start up can be alleviated by arranging the plumbing so that the block is full of water.
I always did this on my '497', after cooking the #1.

Attached is a pic of a B-Z similar to yours. recently refinished,
and from the same area. Also, one of a 'LINKS' adapted to a M20. Neat job, and quiet.