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Are 1969 and 1973 18 HP Fastwin main components interchangeable?

A

alaskanick

New member
Hi all, to be more specific, can a 1973 18 horse Fastwin powerhead bolt onto a 1969 body, and mate with the 1969 lower unit?

Also, if one Fastwin kicks out of gear and lower unit/driveshaft is NOT the issue (does it with a known good lower unit just the same, and both are in good condition and mechanic inspected), does it hold water that it's probably the lower crankshaft bearing? There seems to be some looseness though the motor runs well.
 
Yes the 73 will bolt on.-----Doubt it is a lower crankshaft bearing issue !!-----Shift linkages and adjustment would be my guess.----Easy fix on my workbench.
 
racerone said:
Yes the 73 will bolt on.-----Doubt it is a lower crankshaft bearing issue !!-----Shift linkages and adjustment would be my guess.----Easy fix on my workbench.

[/Nick:]
Well, I've adjusted shift linkage till cows come home, and totally know how to cheat it as far as it can go. So is there another adjustment? 2 different lower units, both in excellent shape, one rebuilt, do the exact same thing. Starts and idles fine, will run in a tub, but jumps out of gear immediately when under load, both forward and reverse. Has defied diagnosis by two very solid mechanics; and I ran my first 18 in the late 70s in arctic Alaska and kept it going somehow for a few hundred miles of abuse on the Kobuk and tributaries when I was young and broke. That said, I really am scratching my head. Last mechanic (all these guys working at it for a living) said definitively too much play in lower bearing of crankshaft. But that don't mean he's right!

Very much appreciate your response and assistance.
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If the lower bearing is " suspected " then take it apart !----These 2 mechanics have said that it is the problem.-----Or maybe the spline is worn out ?
 
Is it really kicking out of gear (shifter handle moving or jerking)? If it is, that is a sure sign of a worn out clutch dog and / or forward gear. Certainly not a crankshaft bearing, which is a major problem (junk).
 
bobbyc said:
Clutch Dog? Kicks out and goes back in or stays out?
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-Nick It kicks out and stays out, forward and reverse both, no matter how linkage is adjusted. Sometimes stays in gear a bit longer sometimes than other, but always before you get on step. On a light small aluminum skiff. Does it with two different lower units exactly the same. One lower was entirely rebuilt by a certified mechanic and other looks great, identical.
 
Nick: Well, I sure appreciate all the responses by so many. You'd sure think it was the clutch dog; that's what I thought, and two different pro mechanics, and all of us were apparently wrong. I agree sounds unlikely the lower bearing is the issue, even if a full time pro tells me so, dead certain it's the issue. Problem for clutch dog theory is, I have two complete lower units that both seem in great shape, one completely rebuilt by one of those pros, and both act the same. And it ain't the shift linkage. No matter how you cheat it up or down, jumps out of both forward and reverse soon as it gets under any load (throttling up to get on step). And yes, the shift lever jumps out. You can't even hold it in place. If you run it in a barrel, it'll run without popping out at least some of the time.

This thing has made all of us scratch our heads. I'm not a great mechanic but have nonetheless been successful more often than not over 40 years of 2 stroke tinkering and repairs.
 
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