Info needed on 40 hp mercury please.

[hardwater fisherman]

I am going to look at this motor and it looks around 1980-1982.. Is there anything I should be careful of with it... I have seen new old stock ignition parts still in the box with crumbling wires...Supposedly has had a tune up and a fresh impeller.. thanks..

 

[jimmbo]

A Tiller model

Compression Test
Spark that can jump 3/8" gap
Check Gear oil for signs of Water, Chunks of Metal
Myself, I would drop the gearcase and inspect the Impeller.

33.3 cubic inches
WOT range 5000 - 5500
Gear Ratio 2:1

That cowl Decal was used 1980 thru 1983.

 

[hardwater fisherman]

Thanks.. He told me he has proof of some work done and impeller change done by local shop.. I was wondering if the wiring was still a problem by this time? I have seen some 70s models that had bad wiring.. Do you know if this motor is prop rated?

 

[Chinewalker]

Easy enough to look - it'll be apparent if the wiring is an issue.

 

[hardwater fisherman]

Yes I was just asking more to know if wiring could be suspect.. I am thinking someone probably would not spend money for work/impeller change if the motor had major problems.. Thanks again.

 

[Sylva-Ranger]

This motor is not prop rated, the 35 mid '80 is exactly the same engine whit same carburetor/jets.

I haved one 40 hp like this for 25 years until this summer and very love it.

 

[jimmbo]

This motor is not prop rated, the 35 mid '80 is exactly the same engine whit same carburetor/jets.

Not quite the same, in 1984, when it became the prop rated 35, the WOT range changed to 5400 - 6000 rpm, so there may have been some internal differences.

 

[The Force power]

IF...am correct these motors were called Rocket and built by Yamaha for Mercury & a lot of these the gasket on the water-jacket leak (not a big deal to change, when the bolts don't break)

 

[jimmbo]

IF...am correct these motors were called Rocket and built by Yamaha for Mercury & a lot of these the gasket on the water-jacket leak (not a big deal to change, when the bolts don't break)

You need to learn a bit more about Mercury

Mercury did have a block/engine they referred to as Rocket, in the 1940s and/or 50s, 7 1/2 hp

The 40 mentioned above, is a True Mercury Motor.

Some early 40hp Mariners were made by Yamaha, but they were never labeled Mercury

 

[Sylva-Ranger]

Not quite the same, in 1984, when it became the prop rated 35, the WOT range changed to 5400 - 6000 rpm, so there may have been some internal differences.

May be porting or some bloc difference ? I have the p/n 90-42794 Merc's service manual that cover 35 & 40 and it the same ci displacement, same ratio, same main jet , same max timing advance and same primary pick-up ...But youre right, not exactly the same max rpm , they specify 5200-5500 for the 40 and 5400-6000 for the 35

 

[jimmbo]

One would have to go thru the Factory Parts Fiche lists to see what part #s were different between 83 and 84. A piston with a bevel on the crown where the ports are, would effectively change the Port Timing, no differences to the Block. Maybe differences to the Reeds. Maybe there were no changes and Mercury just wanted to reduce lugging the engine, by adding a few rpms to the spec, which would require lower pitch props. I have never seen any Service Bulletins stating to reprop the the pre 84 engines for 5400 - 6000. I guess some probably retired, Mercury Engineers are the few that know the Differences.

 

[hardwater fisherman]

So I bought it today. It has 150psi top and bottom. it was tuff to get the gauge in the bottom hole though. Strong spark of 7/16 plus on both. Not super clean but that does not bother me.. When I hear someone say hardly used or just like new I wonder why. The only thing is the top spark plug looks fouled and the bottom looks okay. That 3 piece cowl is something new for me being an OMC guy...

 

[The Force power]

You need to learn a bit more about Mercury

Mercury did have a block/engine they referred to as Rocket, in the 1940s and/or 50s, 7 1/2 hp

The 40 mentioned above, is a True Mercury Motor.

Some early 40hp Mariners were made by Yamaha, but they were never labeled Mercury

I actually had a 1978 40 HP/ 2 Cyl. mercury that clearly had in small letters "Rocket" stamped in it. from what info I gathered back then; it was built by Yamaha.

I'm not about to spend time looking up "proof" to confirm as I could not care less if it was true or not!!

I clearly said: IF...I'm correct these motors were called Rocket and built by Yamaha for Mercury

 

[The Force power]

So I bought it today. It has 150psi top and bottom. it was tuff to get the gauge in the bottom hole though. Strong spark of 7/16 plus on both. Not super clean but that does not bother me.. When I hear someone say hardly used or just like new I wonder why. The only thing is the top spark plug looks fouled and the bottom looks okay. That 3 piece cowl is something new for me being an OMC guy...

you did good, those are good motors

 

[flyingscott]

I actually had a 1978 40 HP/ 2 Cyl. mercury that clearly had in small letters "Rocket" stamped in it. from what info I gathered back then; it was built by Yamaha.

I'm not about to spend time looking up "proof" to confirm as I could not care less if it was true or not!!

I clearly said: IF...I'm correct these motors were called Rocket and built by Yamaha for Mercury[/QUO

May you shouldn't be so thin skinned because someone knows more than you.

 

[The Force power]

[/QUOTE] May you shouldn't be so thin skinned because someone knows more than you.[/QUOTE]

Fair enough & Yes you will defiantly have more knowledge about outboards as I do

 

[Sylva-Ranger]

My 1979 Merc 40 hp also have the "Rocket" letter stamped on the engine block, but for me it a true Merc production, whit the reed valves around the crankshaft, and all the bolts are hiches size, instead of metric like normaly all japanese product including Yamaha have.