How to tell dock buster prop rotation?

[etc]

Hi all -

I have some old dock busters, stashed for a few years along w/a couple later unknown 6-cyl block/crank/pistons sets and a bunch of shrouds, that I'm finally trying to sort out.

I've determined from the sn's that I have a '58 MK 75A, a '59 MK 78AE, a '60 800EL and a '61 700EL.
None are currently completely assembled, tho' 1 (don't know which yet) was said to need only the starter reinstalled to be good to go.
I know some, if not all, were available w/counter-rotation.
Is there a quick check to determine this?

Thanks,

regards,

 

[Texasmark]

Re: How to tell dock buster prop rotation?

Yes. Pull the starter through with the engine and see which way the drive shaft turns. Normal prop rotation is Right handed meaning that the propshaft applies pressure when it is driven in the CW direction by the drive shaft. When testing by rotating the prop, CCW should be firm and CW ratcheting. Remember when testing via the prop you are using the normally "receiving" shaft as the "driving shaft" so the pressures will be exactly opposite.

Mark

 

[1946Zephyr]

Re: How to tell dock buster prop rotation?

Dock Busters run both ways, actually. The engine and lower unit run in reverserse, when you have the motor start in reverse. Then it runs clockwise when you're in forward. It goes according to which way you turn that starter to determine which way you want the motor to run. LOL The "Dockbuster" was a totally direct drive motor. I was told that they were banned from a lot of boat ramps, because of their claim to fame. Pretty awesome looking engines though. Your 800 and 700 are both shifter motors though.

 

[etc]

Re: How to tell dock buster prop rotation?

Thanks guys, but prob is, since they run either direction, rotation of the propshaft depends on whether the engine is "set" for forward or reverse operation, unless they default to forward when shut off.
I know some stuff moved around when shifting - distributor and/or other stuff maybe?
Seems the position of the variable components would tell me which, if I knew what to check.

The '60-'61 700s & 800s were available DR or FGS, with different blocks of sn's for each - mine are all DR, according to the sn list I found.

 

[Laddies]

Re: How to tell dock buster prop rotation?

The props were LH

 

[etc]

Re: How to tell dock buster prop rotation?

The props were LH

Tnx, but no props on 'em.

 

[Laddies]

Re: How to tell dock buster prop rotation?

In forward the crankshaft turns RH, if it has one

 

[etc]

Re: How to tell dock buster prop rotation?

In forward the crankshaft turns RH, if it has one

That's the problem Laddies - with these engines (no gearshift levers) I don't know how to tell if they're in fwd or rev.

 

[emckelvy]

Re: How to tell dock buster prop rotation?

A Direct Reversing motor always turns Clockwise as viewed from the top of the flywheel, for forward gear (just like a "normal" Full Gear Shift motor). And conversely rotates CCW for reverse.

The standard rotation for forward direction for a D.R. lower unit is CCW (Left-Hand) as viewed from the Aft end of the propshaft.

So, if you were to rotate your Mystery Motor Clockwise at the flywheel you can see which way the propshaft turns.

If you have a lower unit by itself, just rotate the driveshaft Clockwise and watch the propshaft.

BTW the D.R. lower unit doesn't 'ratchet'. Just grab a prop (with the motor off of course!) and turn it back and forth, you'll notice the direct coupling to the crankshaft, with only the free play between the pinion and drive gears.

HTH.....ed

 

[etc]

Re: How to tell dock buster prop rotation?

A Direct Reversing motor always turns Clockwise as viewed from the top of the flywheel, for forward gear (just like a "normal" Full Gear Shift motor). And conversely rotates CCW for reverse.

The standard rotation for forward direction for a D.R. lower unit is CCW (Left-Hand) as viewed from the Aft end of the propshaft.

So, if you were to rotate your Mystery Motor Clockwise at the flywheel you can see which way the propshaft turns.

If you have a lower unit by itself, just rotate the driveshaft Clockwise and watch the propshaft.

BTW the D.R. lower unit doesn't 'ratchet'. Just grab a prop (with the motor off of course!) and turn it back and forth, you'll notice the direct coupling to the crankshaft, with only the free play between the pinion and drive gears.

HTH.....ed

So then they're always in forward "gear" unless electromechanically reversed?

 

[1946Zephyr]

Re: How to tell dock buster prop rotation?

Well, as I stated earlier, The mark 75 and mark 78 is a direct drive motor, but has reverse capability. To run it forward, choose the forward selection on the starter switch. To run it in reverse, choose the reverse selection. These motors are set up to run both directions. There really is no "electromechanically reversing" it's just the motor runs in the CCW direction in reverse and CW direction in forward. In order to change directions on these motors, you shut it down and re-start it in the direction you want to go. Pretty wild huh? On your Merc 700 and 800 you will have a shifter.

 

[etc]

Re: How to tell dock buster prop rotation?

I understand what you're saying , Captain, but to rephrase the issue about which I'm still in doubt:
If the engine is shut off while running in reverse, and the engine is then taken off the boat, with no controls connected, does it stay set to run in reverse, or do the internal parts that determine whether it's fwd or rev automatically "reset" to forward start position?

 

[Faztbullet]

Re: How to tell dock buster prop rotation?

A DR motor is always in forward no matter what. Its only in reverse when you restart off the control box in reverse position. The motor actually starts and runs in opposite rotation(CCW).

 

[etc]

Re: How to tell dock buster prop rotation?

Ok, got it - once again I've been overthinking this - no matter what, if I turn the crankshaft CW (viewed from top) the propshaft will turn CCW on a standard rotation engine, or CW on a counter rotation engine, as emckelvy said.

A big thanks to all who contributed and a bigger one for putting up with me!

regards,

 

[gus-gus]

Re: How to tell dock buster prop rotation?

I am sorry I missed the entire discussion.

I bought a 1999 Skidoo Skandic 500 fan cooled snowmobile, with the Rotax electronic reverse. (RER) It always started in forward, but you didn't have to shut it off to reverse the engines direction. Pushing a button would change the timing and the engine would just switch direction. It was so fast and smooth it was wild. I ran the heck out of the machine and it was flawless, is this the same technology discussed here?

 

[1946Zephyr]

Re: How to tell dock buster prop rotation?

I understand what you're saying , Captain, but to rephrase the issue about which I'm still in doubt:
If the engine is shut off while running in reverse, and the engine is then taken off the boat, with no controls connected, does it stay set to run in reverse, or do the internal parts that determine whether it's fwd or rev automatically "reset" to forward start position?

The gear it's in, all depends on which way you make the starter spin the next time you start it. It's a direct drive motor, just like any of your pre-war antiques.

 

[CharlieB]

Re: How to tell dock buster prop rotation?

A unique feature of all two strokes is, they don't care which direction the crank turns, they are just as happy running CW as they are running CCW.

Advancing or retarding timing improves the efficiency of how the motor runs and will gain power when timing is set for the direction of rotation.

But..........the old Merc did NOT have any shifting in the gearcase, it was ALWAYS 'IN' gear.

Shifting was accomplished by reversing the starter motor, push the 'R' button and the starter turned in reverse and started the motor in the opposite direction.

Early dirt-bike hill climbs often would 'spit' a rider over the handlebars if he 'lugged' and stalled his motor on the hill, as one turn backwards, the motor would start. Usually the rider had the throttle held WOT. Surprise!

 

[gus-gus]

Re: How to tell dock buster prop rotation?

A unique feature of all two strokes is, they don't care which direction the crank turns, they are just as happy running CW as they are running CCW.

Advancing or retarding timing improves the efficiency of how the motor runs and will gain power when timing is set for the direction of rotation.

But..........the old Merc did NOT have any shifting in the gearcase, it was ALWAYS 'IN' gear.

Shifting was accomplished by reversing the starter motor, push the 'R' button and the starter turned in reverse and started the motor in the opposite direction.

Early dirt-bike hill climbs often would 'spit' a rider over the handlebars if he 'lugged' and stalled his motor on the hill, as one turn backwards, the motor would start. Usually the rider had the throttle held WOT. Surprise!

Let me get this straight, the mercury motors had to be shut down to reverse direction? The reason I ask is the snowmobile I described earlier didn't. I could be running at 70 mph and push the reverse button and nothing would happen as long as I kept the RPM's above idle, but as soon as it drops to idle it would switch directions almost so fast you couldn't tell it had happened, except the reverse alarm beeper. It only had a pull cord start and only started in the normal direction (forward).

 

[gwukena]

Re: How to tell dock buster prop rotation?

That electronic reverse, the engine is basically almost coming to a stand still for a fraction of a second, the timing is changed and gets it to fire way advanced and starts spinning backwards. You can't even detect the changeover.

 

[gus-gus]

Re: How to tell dock buster prop rotation?

That electronic reverse, the engine is basically almost coming to a stand still for a fraction of a second, the timing is changed and gets it to fire way advanced and starts spinning backwards. You can't even detect the changeover.

Exactly. You are saying Mercury is the same? Or?