85 4 cyl 50 Merc

[HGipson]

Got an old 50 4 cylinder Merc short shaft wanting to know some upgrades for it get some higher rpm and more hp. I've seen a few of these motors tuned up running good speeds just want to do a complete rebuild and upgrade everything I can with available parts

[Yellowjacket]

The classic 50 is the motor that has been a staple in APBA kneel down racing for over 50 years. Here is a link to a thread on building this motor for ABPA stock racing. The dimensions for porting the motor can be found on the APBA site in the rules sections if you want to mildly port the motor.

The biggest thing you will have to do to that motor to turn it higher than 6,000 rpm is that you need to send the rods out to increase the clearance. Mercury made a change in the 60's to reduce the clearance in the rods and if you spin the motor to higher speeds without doing that you will scorch the rod bearings in very short order. You need to send the rods to machine shop that has a proper hone for this, it can't be done with a hand hone, even though not much metal is being removed.

Here is a link to the step by step building of a 44 cubic inch Mercury follow these and put in a set of Boysen reeds and you'll have a strong stock motor.

http://www.boatracingfacts.com/forums/showthread.php?3322-44XS-Secrets

A motor built to these specs will make over 55 hp and will run to as much rpm as you like.

[HGipson]

Thanks man. I'm going to be putting this motor back on a duck boat after I get done with it. Maybe a 14'36" flat bottom. I want to get the maximum hp and rpm out of it that I can. Boat weight including battery and gas would be about 275 lbs. I've had this motor for 15 yrs. All three motors run just wanting to do every upgrade possible and have got the machinery to do it. Just haven't tried before ! Thanks for any replies

[zul8tr]

The build instructions in the link above by Jerry Weinandt are what is needed for a race engine and may be somewhat excessive for your use? Before pulling apart do a compression check with throttle wide open and all plugs out, rotate crank till max reading on gage. Look for variation in compression between cylinders, best for them to be close (less than 5 psi difference). Pressure numbers less than 100 psi show wear present. Then squirt some outboard oil in the cylinderes rotate engine some revs to distribuute oil and do another compression test. Compare results, the readings will be higher than first test and gives an idea of how much ring seal is gone.

After that the most important item you need to do is pull the pistons out and micro mic the cylinderes to determine the wear pattern and see if there are any deep scratches or signs of piston scuffing. No doubt there will be out of round and taper from top to bottom in the cylinderes. For the Hp to develop you need to have true bores as a base for a strong engine. At that point you will know if the cylinderes are in good shape or a bore over size with new pistons is needed. Parts are available but not cheap. You might find NOS stuff or have to resort to after market new parts. Here are some links for parts, there are others.

http://www.aeroliner-boats.com/index.html

http://stores.intuitwebsites.com/OutboardParadise/StoreFront.bok

Also Jerry Weinandt has parts since he is selling his supply.

Note for your intended use you want reliability as well and max Hp might compromise that?

Report back on your compression readings.

[David Mason]

I hunt ducks, ditch that engine and put a Mud Buddy on it. It will get you more places than that old Merc ever dreamed of. That style of Merc is best left for racing, and the mud motors are best left to skinny water duck huning. The Black Death engines get the job done in no time. And there is a TON of mods you can do if you are equipped with a machine shop and have the skills. Expensive to buy those mods, but if you can do it yourself, you can get yourself running faster with the mud motor than that merc would on that boat.

[zul8tr]

He never said he hunts ducks so maybe the duck boat will not be used for duck hunting just the boat he has and wants to go fast? Looks like the cost is around 5000 for an engine Vanguard 23 for the size boat he has. These engines in the 5000 to 10000 range, that's not cheap.

http://www.mudbuddy.com/HyperSport.htm

[HGipson]

Naw I don't hunt ducks... I kill em ! But on a serious note I'm making a runner boat just for speed and hunting. I like to combine the two makes hunting a lot more interesting running through the swamp at 40 mph! I just knew that these motors could be turned into monsters with the right amount of TLC. Mud motors are fun but I hate Briggs motors their about as reliable as an ex wife. I can do most of the work myself if I have a schematic of what materials need I be removed and tolerances. Appreciate y'all's help man anymore input would be appreciated!

[David Mason]

Naw I don't hunt ducks... I kill em ! But on a serious note I'm making a runner boat just for speed and hunting. I like to combine the two makes hunting a lot more interesting running through the swamp at 40 mph! I just knew that these motors could be turned into monsters with the right amount of TLC. Mud motors are fun but I hate Briggs motors their about as reliable as an ex wife. I can do most of the work myself if I have a schematic of what materials need I be removed and tolerances. Appreciate y'all's help man anymore input would be appreciated!

Get the 10K plus engine, Black Death. You can't ever have enough motor when it comes to duck hunting. They sound as cool as a real mod engine, and they can definately get you over the 40MPH mark. ROn Hill (owner of this site) makes props for these engines. At our race in Quincy IL last year in Sept it happened right during early teal season. I got to watch several of these rigs in person. Impressive to say the least. I hunt in some skinny water and with the short tail version, I can scoot in my 1750 Beavertail. Put the 25 Eveinrude on it and it slows down. Mine is not black death engine, just a normal 30HP short tail.

Besides, 10K for a monster is still cheaper than a ex wife !

If you really want some reliable tips for your merc, don't mod it like it is a mod engine. Porting is for open exhaust megaphone style. A lot of times that porting does not work with a closed exhaust in terms of a noticable gain. Not sure if your engine has the same set up as a 44XS on the tower, and exhaust, but it might work if you get a 44XS tower and tuner. Maybe there is a way to adapt your gearbox to it. Another mod that might benefit you is line boring, and reeds. Not sure how far you want to go with the project, but you could make one bad *** Duck Killing Machine !