How long should my motor be?

[JoeCrow]

I think after several post and a lot of replaced parts, I can assume there's nothing wrong with the cooling system on my motor
It's a 1986 Force 125, on a 19' Bayliner Capri cuddy
New impeller, pump housing, thermostat, thermostat spring, countless flushing from every direction, even changed the prop to lower rpm's, but at WOT it still overheats, pumps lots of water, but overheats ONLY at WOT
I measured the transom it's 25"
I measured the motor from anti cavitation plate to motor base, is 25"
But the anti-cav plate is still about 6" above the keel and the "torpedo"
where the water intake is, is about 3" below the keel
Is this the right size motor?
Or is it too short?
Should I be running a 30" motor, is there such a thing?
I've attached pix that show the set-up
Any ideas are welcomed,
There isn't really enough room to lower the transom
Thanks,
Joe

 

[JB]

Re: How long should my motor be?

Don't know exactly how you came up with 25" for the both the shaft and the transom, but your transom is clearly a good 5-6" deeper than the AV plate.

You need a longer shaft outboard. At speed the water intakes are getting too much air and not enough water.

I am really surprised you are not seriously ventilating the prop as well.

 

[tashasdaddy]

Re: How long should my motor be?

your motor should be no higher than 1 1/2-2 inches above the red line. also the AV plate should be horizonal with the line, you are tilted to far in. this is fine for take off, but not when crusing. it is pushing the bow down, causing it to plow. click on pic to enlarge.

 

[JoeCrow]

Re: How long should my motor be?

Thanks guys
Now I can stop banging my head on the wall
I was measuring the shaft length from the base of the motor to the av plate, not from the mount, big difference
So I have a great running Force motor and a great lower unit
Do I just need a mid section?
Or does everything have to be changed from the powerhead down?
As I said, cutting the transom isn't an option
the most I could get would be 2 inches and I'd still be afraid of backwash swamping the boat when slowing
Thanks again for all the help,
Joe

 

[tmcalavy]

Re: How long should my motor be?

I don't know about motors as new as yours or the Force brand, but some brands can be lengthened by bolting in an extension, and adding a longer driveshaft and shift rod/connector. I've done both to two late 50's OMCs. Maybe someone here will know whether such a creature/option exists for your Force outboard. Only other option is to do surgery on the transom or use a jack plate that will lower it. After looking at your pix, just lowering it 3 inches would make a difference.

 

[JoeCrow]

Re: How long should my motor be?

How about the addition of a jackplate?
Could I steal a few inches that way?

 

[tashasdaddy]

Re: How long should my motor be?

using a jack plate to lower the motor, may interfere with the tilt clearance. also you could swamp the motor when slowing, or a quick stop. you need an extention kit. or a long shaft lower unit.

 

[Nandy]

Re: How long should my motor be?

My Babcock/Mercruiser combo has the same problem. The previous owner solved it with a jack plate. However, like TD says, It interferes with the tilt clearance of the motor. However, for me that have not been a problem. You will have to check your clearance while towing. I have never have the motor swamped or any other problem. Good luck.

 

[JoeCrow]

Re: How long should my motor be?

Fixed it,
Sort of.....
It took a 2002 Merc 125, a new controller, all new wiring,
a few 2x4's and some real fancy language, but the prop reaches the water now

 

[JB]

Re: How long should my motor be?

Looks good, Joe.