Outboard choice conundrum 76' Evinrude 9.9/15 vs 2008 Merc 15hp 4 stroke

kalebg

Seaman Apprentice
Joined
Jul 22, 2019
Messages
40
Okay so so far ive collected 3 free longshaft Evinrudes: one 74' 9.9hp 76' 9.9hp and 78' 15hp. None of them ran but all 3 were completely free. Out of those the first sucked a headgasket and has seized and corroded. The second was bored .030" over and has a gouged cylinder low compression and has some weird what looks like sharp metal slivers and gouges where it looks like something was hammering into the crank girdle on the piston side? The pistons looked to be in good shape so I was a little confused there as to what caused it of course maybe thats why it got rebuilt. Im assuming the gouge was one of those slivers coming free and getting caught in the wrist pin hole of the piston and stuck in the very bottom lip of the piston. The third was a good rebuild able core with 40psi ie low compression with minimal cylinder scoring that is still stock bore ready to be bored out. So in total i have 3 good longshaft lower units, the full electric start kit with the beside flywheel starter, multiple rope starts two 9.9 carbs and a 15hp carb and parts for a full motor and them MUCH more for repairs. Have the updated pee hole cowling and water jacket cover. The only not great part is the head where the only good one without preignition pitting is the older style 9.9 head. Now it it worth the $40 to get the newer head? My other concern in the electric start/charge flywheel, it looks like the upper crank bearing was loose or the steel laminates were not adjusted so theres a bit of wear to the inside of the flywheel. No magnets are damaged but there is a lot of wear to the metal lip to the side that holds the magnet. Is that a concern? Should i have it re balanced?

Okay so heres the dilemma...Rebuild kit is 300 plus coil packs etc and whatever it needs and i have a running 2 stroke motor with 0 hours and plenty of parts and people swear by its reliability. That considered I was was just given a 2008 Mercury 15hp 4 stroke completely free from a family friend its an F15M. He siad it ran even after the lower unit died but has been broke for a while and has no forward gear, oil filter is dated 2010. Compression is 110 115 and thats on a Harbor freight compression tester so accuracy is idk? When I did the compression test i noticed it spraying oil out the bottom plug hole and did see some oil pooled below the outboard (lower unit off) after 10-20 total pulls betqween both cylinders. Is that normal? Rings stuck? Just from sitting for years?. Has the bracket for electric start so im sure down the road i could do a conversion. As a kicker/trolling motor i could use a drop down bracket but i'm not sure if it would be better vs a long shaft. Ive seen a $250 extension kit avail but not sure if its good? The issue on that one is the lower unit though.... forwards gear is missing like 5 teeth, reverse has a few damaged teeth and large prop shaft bearing is siezed whether or not it was before or after its been drained and open for a while is unknown. From some staining on the stainless shaft im guessing some water intruded. It would need 2 new gears bearing and a new seal set etc. Im not sure if its cheaper to rebuild a lower unit or replace with used. This motor also needs a prop and a cover.

Which one should i go with? Maybe one now one later?
 
Last edited:

kalebg

Seaman Apprentice
Joined
Jul 22, 2019
Messages
40
I'd just find a running motor...scrap that stuff ...

Id consider that if a used 1960's 9.5hp didnt go for $400 with average condition running 1970's 9.9's and 15s in the $600 range and almost all motors here being saltwater motors....I was thinking for the same price i could use the parts I have and the same $600 max and end up with a .030" over motor with perfect compression rebuilt carb, rebuilt water pump, etc and not have to worry about a second hand motor with decent compression i know nothing about....know what I mean?
 
Last edited:

kalebg

Seaman Apprentice
Joined
Jul 22, 2019
Messages
40
I'm also not mechanically challenged in the least bit so id be doing the work myself besides machining the bores.
 

flyingscott

Fleet Admiral
Joined
Apr 8, 2014
Messages
8,177
Rebuild the 78 15 hp and be done with it. If the 74/76 model is electric start it may not work on the 78 model. The flywheels might be different. But I just had a 74 here and the flywheel looked identical to my 79 model.
 

thatone123

Banned
Joined
Mar 7, 2009
Messages
707
The OMC will have much more acceleration and lightweight. I've had 15 4 strokes and never again. Light, Simple, reliable, foolproof is the hallmark of the 15 OMC. Nothing else like it. Yamaha 2 stroke 15 is heavy, Merc has complex fragile, choke primer. etc. I've got a NOS one of these OMC from late 80's, used once or twice. Expect it to be running 50 years from now.
 

kalebg

Seaman Apprentice
Joined
Jul 22, 2019
Messages
40
Yeah that 4 stroke is a heavy motherf*** lol. I kinda figured the main merit to a 4 stroke is with a more effective oiling system with proper maintenance a 4 stroke would outlast 2 strokes any day. Of course you also introduce multiple more points of failure. On that note though what life span do these motors expect post rebuild? Additionally what sort of break-in procedure is there as far as oil mix or operation on first start? Anything like dirt bikes with the rev to 1/3 throttle let reach operating temp, shut off, let cool, and cyle a few times, then warm up before full revving throttle?
 

thatone123

Banned
Joined
Mar 7, 2009
Messages
707
Actually from what I know and hear the old 2 strokes will outlast 4 strokes. There are a lot of internal stress factors with a valve engine. They also need in general higher compression that causes stress in a small engine. I may be wrong so I'll let the experts here chine in if they want, but my experience, rebuilds on 2 strokes especially do not seem to have the longgevity of the original engine. But what do I know? The cooling off I have never seen described for an outboard. Many times it is idle for a while, then gradually increase speed over a period of hours. 1/4 back off, 1/3 back off, 1/2 back off and don't do full throttle except for short bursts until you go thru the sequence, then extend the full throttle for a bit but back off quite a bit til you go thru the sequence a number of times. Jut use common sense and just like you should not stress your body when you first work out, but work up to it. At least that is what folks do that don't like to injure themselves.
 
Top