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F90 Engine for 1979 Montauk
Marinero	#1  Posted on 05/25/15 - 1:48 PM
Member Posts: 2 Comments: 0 Joined: 05/14/15	Hi All. I just picked up 2004 Yamaha F90 for my classic 1979 Montauk. I still have to purchase the controls and gages. The F90 is a four stroke motor, FI with a 25" shaft, power tilt & trim. I will mainly use the boat for cruising the bay with two to six people, maybe a day of fishing near the coast. Question: What problems should I expect with the 25" shaft since a 20 " shaft is what's called for? The motor weight in at 379 lbs without the prop. Any special precautions I should take when mounting the motor? What prop should I get? Any suggestion on prop, controls,or gages? I'll appreciate any suggestion or recommendations. Thanks.
Phil T	#2  Posted on 05/25/15 - 2:47 PM
Administrator Personal Page Personal Album Project Albums Posts: 6985 Comments: 6 Joined: 03/26/05	They make "jackplates" that add height and distance off the transom. You will need a 5" (vertical) jackplate to raise the motor. This has been done by members on various models with motors too long. It is important to understand that you want the absolute minimum setback. Adding setback can adversely affect the ride. Respected brands include CMC, Detwiller and Bob's Machine Shop. As for rigging, I think the two basic 2" multifunction gauges will suit you. Command Link gauges are not fully supported in that model year and are very pricey. Tach/Trim/Hr meter: http://www.simyamaha.com/Yamaha_Tach_...-00sim.htm Speed, Fuel, Trip: http://www.simyamaha.com/Yamaha_Speed...-s6-00.htm For a prop, a painted stainless steel Yamaha K Series 13.25x17 or 13-1/8" x 17" Stiletto Advantage Q 4.25. I had this setup for my 2003 Yamaha F115 (see personal page) A good source for parts and assistance is Andy @ SIM YAMAHA.
Marinero	#3  Posted on 05/25/15 - 3:23 PM
Member Posts: 2 Comments: 0 Joined: 05/14/15	Phil-T, thank you. That all sounds like great advice. I'll look into those suggestion. Thanks again.
Finnegan	#4  Posted on 05/25/15 - 11:55 PM
Member Posts: 1926 Comments: 16 Joined: 05/02/08	As an owner of a 1979 Montauk, I think installing a 25" engine on the boat is a big mistake, Although raising it up 6" on a jackplate will work, it will not look good and will be awkward in rigging, etc. If I were you, I would have a Yamaha shop remove the 5" extender on the lower unit, and convert it back to a 20" engine. You may find the drive shaft, shift shaft and water tube are even sleeved 5" for the 25" length, so shortening up the engine should not be any more expensive than the jackplate purchase and extra rigging labor. A 25" 90HP engine is an oddball situation, which is why you probably got it cheap. Changing it back to a 20 will be advantageous all the way around, and for the time when YOU want to sell it.