2 Stroke vs 4 Stroke Outboard motor mounts

[finefurn]

Why the difference between 2 stroke and 4 Stroke Outboard motor mounts. I understand the weight difference between a give hp rating of a 2 vs 4 stroke. But why would this make a difference in the design of the mount if the mount exceeds the hp and weight rating of the motor being used. In short can a Mount that's listed for a 2 stroke be used for a 4 stroke IF the mount exceeds the weight and hp rating of the mount being used.

[Reefmagnet]

Small 4 strokes can vibrate and shake much more than two strokes when running.

Sent from my SM-G900I using Cruisers Sailing Forum mobile app

[FSMike]

Originally Posted by finefurn

-----In short can a Mount that's listed for a 2 stroke be used for a 4 stroke IF the mount exceeds the weight and hp rating of the mount being used.

I think you mean "- weight and hp of the MOTOR being used." Emphasis added.
I see no reason why you couldn't use the mount for either engine, with the caveat that some 4 strokes produce more torque at lower rpms than 2 strokes.
Are we talking dinghy kickers here, or monsters with hundreds of horsepower?

[Siberianhusky]

Don't know if there is much difference, I know mine is rated for both, can't remember the numbers but it was something like a 15 4 stroke or a 25 2 stroke. I do know mine is a "mid sized" one. Pretty beefy unit with strong springs, with a 9.9 Yamaha 4t on the back only takes a couple fingers to lift.

[thomm225]

Originally Posted by finefurn

Why the difference between 2 stroke and 4 Stroke Outboard motor mounts. I understand the weight difference between a give hp rating of a 2 vs 4 stroke. But why would this make a difference in the design of the mount if the mount exceeds the hp and weight rating of the motor being used. In short can a Mount that's listed for a 2 stroke be used for a 4 stroke IF the mount exceeds the weight and hp rating of the mount being used.

I have a 58 lb 4 stroke 5 Hp Engine mounted on a two stroke bracket which was spec'd for a 20 hp 2 stroke with engine weight 115 lbs or less.

No problems for 5 years. It's a Panther Bracket

It's this one:

SKU: 550020A (see below)

Outboard Motor Brackets | Fixed-Mount 4-Stroke & Lightweight

This one gives a bit though. If I had it to do over, I'd probably go with one of the black 4 stroke heavy duty brackets at the top of the page above so I could just leave the engine down until I was ready to pull it up

[a64pilot]

Although it's been pretty much accepted that four stroke are heavier, that is changing, there are relatively light weight four strokes coming out now.
Four strokes do usually vibrate more that is often true.
Believe it or not while on average a four stroke has more torque than a two stroke, that is not always true for outboards, Mercury had to Supercharge their four stroke Verado to give it the "hole shot" of a two stroke.

More and more it's getting so that differences between the two engines are beginning to merge.

Weight and HP would be the relevant limitations of a mount I believe, I doubt if being a two or four stroke would matter

[rendern]

Originally Posted by FSMike

I think you mean "- weight and hp of the MOTOR being used." Emphasis added.
I see no reason why you couldn't use the mount for either engine, with the caveat that some 4 strokes produce more torque at lower rpms than 2 strokes.
Are we talking dinghy kickers here, or monsters with hundreds of horsepower?

I would respectfully disagree with the statement that 4 strokes produce more torque at lower RPMs than 2 strokes. The opposite is generally true due to fact that 2 strokes make power on every cycle, 4 strokes make power on every other cycle. Evinrude has a video of their 2 stroke motors pulling other vendors 4 strokes backwards in an on the water "tractor pull".

[valhalla360]

Originally Posted by rendern

I would respectfully disagree with the statement that 4 strokes produce more torque at lower RPMs than 2 strokes. The opposite is generally true due to fact that 2 strokes make power on every cycle, 4 strokes make power on every other cycle. Evinrude has a video of their 2 stroke motors pulling other vendors 4 strokes backwards in an on the water "tractor pull".

That's always been my understanding and why manufacturers resisted 4 strokes for so long. They simply couldn't generate the low end torque of a 2 stroke in the same HP engine without making a much larger engine.

4strokes are coming closer but they are still heavier.

Of course, if it's to power a sailboat, just go easy, there is rarely any benefit to firewalling he throttle from a standstill.

[a64pilot]

The "average" four stroke motor is torquier than the "average" two stroke, average being things like lawnmowers, chainsaws and the like.
The reason four stroke out boards are down in torque is in order to get high power per cu in and lb, they are pretty much high performance motors, think like a 600cc sportbike, makes gobs of power, but only once up in the higher RPM band.

It's unusual to have both high torque and high horsepower in a motor, exception being to some extent a forced induction motor, supercharger being the best to boost torque as you can get high boost at lower RPM than the typical turbo, reason Mercury Supercharged the Verado line, not so much to increase HP, but to increase "hole shot" or torque

[hamburking]

I had an 8hp honda 4 stroke on my C&C25, with a mount intended for a 2 stroke up to 10hp. The weight of my 8 was the max of the mount.

One of the aluminum angle braces on the mount cracked. I noticed before it turned into a disaster. I took the whole mount apart and replaced the cracked piece with piece of 2x2 aluminum L angle given to me free from the garbage pile at metalcraft marine, here in Kingston (great guys).

Soon after, the locking mechanism (after lifting) became unreliable, and the outboard would SLAM down unexpectedly after some big wave. So I stopped raising the outboard, and just left it down, dragging.

I would suggest you use a mount which is rated bigger than your outboard, especially if you are using a 4 stroke.

[coastalexplorer]

I Became involved in this question myself because of a donation of a Garelick Manufacturing Co. Outboard bracket of a vintage that is apparently so old that no one at the company recalls them being made with aluminium sand castings.

(It is just possible that a historic outboard motor collector might love to have it in their collection? if so PM me)

The advise from Darrell Weier of Garelick Manufacturing Co (651-788-4138) is that the product Number on the casting designates it for 2 stroke outboards only and has asked me not to mount the 9.9 Hp 4 stroke Honda. on it. The reason given is the 4 stroke outboards produce more torque and the bracket has to be made substantially stronger. Previous to receiving this advise it was temporarily attached to a 35 foot motor launch and used to move it approximately one Kilometre before flexing of the bars was noticed.

While there are now several manufactures of outboard motor brackets, Garelick started with their EEz-In boarding ladder in 1950 and has been in this business for over sixty years. So I will trust the advise given; which is to use their offshore model #71091.

For reference...ALUMINUM AUXILIARY MOTOR BRACKET FOR 4-STROKE MOTORS - Garelick EEz-In

It is a simple thing for the many differing opinions of boat owners to come into play on any question, there is no doubt it is possible to 'get away' with anything for a while even IF it is against the 'experts advise' So I am constantly trying to decide exactly who the experts are. When or IF their opinions conflict that is when I decide after thoughtful deliberation what my best guess and comfort level is and thus which course to take.

[ebsail]

I used a new aluminum motor mount on my O'Day 25 which was rated for 2 cycles up to 15 HP. I had an electric start 9.9 Mercury on it. After one season ON A MOORING, with the engine up 95% of the time, the aluminum ears began to bend outward, and this allowed the engine to flop back and forth (port to starboard) on every wave. It was obvious that this was going to get worse daily. The springs were too weak to allow easy lifting of the motor. We then replaced the mount with a much heavier duty steel one from Gaerlich rated for a 4 cycle up to 25 HP. We also changed down to a 6 HP 4 cycle Tohatsu weighing only 65 lbs. Engine now easy to lift and needs a slight push to go down (maybe 15 lbs) . Everything is solid as a rock. The moral is buy a bigger, stronger mount than you think you need.
Especially if you're on a mooring.

[coastalexplorer]

Ebsail, Thank-you for your reference to Garelick, It seems like a recommendation?

Do you have the 71091 offshore model with a 15 1/2 " lift ?

Since I have a 25 degree raked transom I will have to make a wedge shaped transition to mount one, I have been considering making a foundry pattern and casting one in Aluminum.

[hsi88]

I ended up with the MarineTech 55-0416 which has a lift of 16 inches and was designed for 4 strokes up to 35 HP and 263 LBS. The bracket weighs over 30 pounds. About the weight of a 2.5 HP outboard. It is "VERY" heavy duty. Although I have an inboard diesel, I use the bracket as a backup power source and to store the dinghy outboard. When its time to mount the outboard on the tender, it can be lowered down for easier reach.

[valhalla360]

Originally Posted by a64pilot

The "average" four stroke motor is torquier than the "average" two stroke, average being things like lawnmowers, chainsaws and the like.
The reason four stroke out boards are down in torque is in order to get high power per cu in and lb, they are pretty much high performance motors, think like a 600cc sportbike, makes gobs of power, but only once up in the higher RPM band.

It's unusual to have both high torque and high horsepower in a motor, exception being to some extent a forced induction motor, supercharger being the best to boost torque as you can get high boost at lower RPM than the typical turbo, reason Mercury Supercharged the Verado line, not so much to increase HP, but to increase "hole shot" or torque

Assuming the same hp engine:

2 stroke has more torque particularly at low RPM where every other stroke being a power stroke makes a big difference. On engines with few cylinders it's also better at building up RPM, as you are getting that extra fuel converted to extra power quicker.

Once up to speed, assuming similar gear ratio and prop, torque will be similar as HP=torque*RPM

Agreed, turbo or super charged engines are whole different animals.