Change tranny ?

[BLACKBIRD2]

The motor in our boat is a reduction gear,,the motor i have (not in the boat)
looks like a direct drive?.how much trouble will a swap be? new shaft? and im sure a host of other things, swap meaning one motor out and the other in.. OR..?

[Ken Rockwell]

It depends on a lot but, great post. Send some more pictures. And the boat specs. Accessibility and cost seem to be big factors. I'm a little confused about what you're trying to do.

[ndutton]

I've done this once, like 45 years ago and although I don't remember the details I do recall it wasn't that big of a deal. To the best of my memory the biggest part was the reduction gear required a different tailshaft than the direct drive.

[thatch]

Blackbird, The official factory A4 diagrams show the reduction model to be about 4" longer than the direct drive model. More importantly, the output flange on the reduction unit is slightly more than 1" lower than the D.D. model. Since the mounting points on both models are the same, lowering the transplant engine and lengthening the propshaft will be the biggest challenges. The exhaust will most likely have to be modified a little. When doing engine transplants in cars, we usually just placed the new powerplant in place to get a "visual" on clearances, etc. This might be the best approach here.
Tom

[edwardc]

A simpler solution would be to transplant the reduction gear, and the reversing gear assembly, from the old engine to the new engine.

Swapping the whole reversing gear assembly is much easier than trying to press out the tailshaft.

This way you'll have an identical drop-in replacement.

Having a 2:1 reduction enables you to rev much higher at normal operation, allowing the A4 to get up higher in its potential horsepower range.

[thatch]

Ed brings up a good point. Since your boat appears to be on the larger end of the A4 powered group, staying with a reduction unit would make sense. If, on the other-hand you were planning on switching to a smaller, higher speed prop like an Indigo, then the 1to1 ratio would tend to maximize the prop's potential.
Tom

[romantic comedy]

If the output shaft is 1 inch lower, you would have to raise the engine 1 inch, Right?

[joe_db]

Do NOT convert from a reduction gear to direct drive. I wish I could go the other way, my boat is really too big for a direct drive engine.
It will be far less work to put the reduction gear on the new engine than to re-engineer the whole installation and switch props.

[BLACKBIRD2]

tranny

Ken,,and every one..the saga continues,im trying to remove the head too replace the head gasket,,and will need to replace a value spring ,The head removal has got me ,,stopped in my tracks, so i thought it might be easier to drop in the other motor,but now the tranny will be a bigger issue,so i will go back to pecking on the head,once again thanks too all for your advice and support, what a great group ..