Will Yamaha 70/90 fit 40/50 mid?

[chipg]

Will either the Yamaha 70 or 90 powerhead bolt onto a 15" 40/50 midsection?

[Fast Fred]

no.

[Fast Fred]

70 and 90 have thare own mids, thare are 15" mids for each

[cdixon4950]

I know this thread is old but what about a custom machined powerhead adapter?

[Fastjeff57]

You'd also need a drive shaft adapter, for the splines are most likely different as well.

It's still do-able if you're as dedicated to such things as I am. Note the Merc 850 power head on a Mark 55 tower. It required both a custom adapter for the power ead and a drive shaft adapter. Motor is 40 pounds lighter than a stock Merc 850 and has a slimer LU.

Jeff

[cdixon4950]

My thoughts exactly. I'm working on lighting up a 90 Yamaha as we speak in the same manner.

[88workcar]

Yes you can put a 70 powerhead on a 40 mid, you have to build an adapter plate. It is some work and takes a little longer to pull the powerhead if needed but it is actually common.

[Fastjeff57]

The splines are the same?

Jeff

[88workcar]

no, you have to build a adapter

[David Mason]

Couple It. Meaning split your driveshaft, have someone make a coupler (square holes in a round shaft) and you don't have to worry about the splines. I am sure you thought of this already, but remember to check gearcase fitting on the tower as well. I don't know, but someone does I am sure, if you can use that gearcase on a bigger CI powerhead. On the stock(fishing) engines, it is likely a different gear ratio ?