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Capt.Woody here been a long time........ any way I got the power head rebuilt for my merc 55L they were unable to find 2 new pistons and a set of rings for my 35A. I put the power head on the 55 power head on the 35A short shaft. Test ran in the barrel to check. OK Me and my son both over 200+ lbs. took it to the river for a test run. I have the small brass prop from the 35 on it. The thing jumped out of the hole like bull shoot in the butt with rock salt. Ran it up to 36.4 mph with trottle left at 5800 rpms. I have a larger prop from the 55A. Wanting to know if I should change it out or leave things as they are? Any thoughts or comments?

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A very good friend once told me it's not what you don't know that will get you....it's what you do know that ain't so

Woody you need to know more about the Heat of the engine and exhaust temp before you can say if swapping props will help your speed or maybe kill that engine.
If finding pistons is a problem. Burning another one is the Death Knell of that engine.

I'd try it and see what RPM you get.....won't cost you anything....you already have the prop.

If the RPM is in the recommended range,you'll be fine.

I've never seen anyone measure exhaust temp or even engine temp on an outboard in 56 years!!!

_________________
Boat building can best be defined as an endless series of
tragedies obscured by the occasional miracle, followed by a good bottle of beer.

Don't Dream Your Life, Live Your Dream

Ol' pirate made me re-read my post.
If your engine heat and exhaust temp were OK with the small prop, mark that, and then try the big prop for a time and check that Heat.

As Pirate says, if you can reach the noted Rpm, and the Heat etc is still OK, it'll probably work.

I'm unsure what rpm this motor should run. The 35A is the one that had burnt pistons in it the 55 just need to be honed and ringed we put new bearings in it also. Went through the carbs but I have not set the high limit on the linkage. Any help on setting this up would be helpful. Thanks Capt.Woody

_________________
A very good friend once told me it's not what you don't know that will get you....it's what you do know that ain't so

Woody,
What's a 35A and a 55L ?
It'd help if we all knew what we were discussing.
You have some photos for us?

I re-thought about my post and remembered that my Mercury Optimax has a temp sensor & light,but no gauge,as probably do most of the other new fuel injected,computer controlled outboards.

That said,I've not seen any provision for a temp gauge on the older outboards.

When I've burnt pistons in my motors,(twice on one inline six), it was due to running the motor after sitting for a long spell(two years or more) without cleaning the carbs.

you've done that,so that shouldn't be a problem.

My old time Merc mechanic also sets up the ignition timing different for the old motors due to the current types of gas

Try to find a source for non-ethanol fuel, and an online source for old motor specs....maybe http://store.eastcoastmarineservice.com/Default.asp

galamb on the forum here might be of help too....try PM'ing him

_________________
Boat building can best be defined as an endless series of
tragedies obscured by the occasional miracle, followed by a good bottle of beer.

Don't Dream Your Life, Live Your Dream

The motor in question is the 55L I used the 35A short shaft lower end the get the height I needed for the short shaft transom I built on my Zip. The 55L is the super thunderbolt with the big carbs. I think it is a 50 hp. If I'm correct. It is a 1959 year. I'm running the stock prop from the 35A.

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A very good friend once told me it's not what you don't know that will get you....it's what you do know that ain't so

Capt. ,

If your motor in question is a 55L that is a little odd for 59'. But who's to say it isn't. For the 1959 mark 55's they were 40 h.p. motors the serial numbers should be between 1221731-1279684. Does the motor have an alternator? The motor should be cloud white with blue lettering.

Travis

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It's like anything you Build. You have to be Patient.

Measure Twice, cut Once.

Hi Captain - my understanding for prop selection is that the most critical thing is WOT - as long as you are running at or near the recommended Wide Open Throttle rpm your prop is fine - and from what you state I think 5,800 is right in the ballpark. That being said shouldn't be much harm in trying the other prop and seeing what your WOT rpm is.

Should you want to - the photos below show how I connected both a water temperature and water pressure gauge to my Mark 35A, a 1959 since the 'A' indicates that it is a 20th anniversary mode.

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This is my first, last and only boat build.

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