Gear Ratios for Speedmaster #3's

[Jon Fuller]

Originally Posted by Matt

So what am I missing? I assume (and I appreciate assume makes an Ass out of U & Me) the drives are counter rotating and that the counter rotation is handled by the gearboxes bolted to the motors? So 1 lower is designed to handle clockwise, the other counter clockwise?
Yours, ignorantly...M

No, the drives are handed. I believe (not a SSM expert) the drive rotation is decided by where the final driven gears sit on the propeller shaft, ie, if they sit fwd of the front shaft and aft of the rear shaft you get one rotation, and if they sit in between the shafts, you get the opposite.

In the day, Daytona crash boxes would sit between motor & drive, they're just 1:1 lock up dog clutches, no option on rotation.

As I said, some did build handed motors (some still do, Richard Carrs 'HoneyParty' has handed blower Chiefs, crash box's & surface drives)

[Jim Brooker]

Martin if you are going to buy drives buy MK4 and spacer kits, MK4 are stronger than MK3 in all respects.
As for the MK3 when fitted to the Sabres and running them backwards, I would fit the right hand rotation drive on the left hand side and the left hand rotation drive on the right hand side, so that makes the drives run backwards,
the lower unit has two shafts one driving shaft and one driven, both shaft have backlash on the gear sets, the top set of gear on the lower unit connect the two shafts, they have backlash and must be set in direction of rotation so that the lower gears keep there backlash, so if you run the drive on your petrol engines the driven gear will have on backlash.
If the drives have been run a lot, you can't then run them in the normal direction the gears will not like being run onthe back of the teeth.
I hope this makes it a little clearer, I am beginning to think I should't have started this.

[Pash 1]

Glad you did Jimmy

[Matt]

Just thinking outside the box - new reverse rotation cam & starter motors for the engines.
Still doesn't solve the gear ratio, I know, but......

[Jon Fuller]

I've just been trawling the net trying to find an expoloded view, or cutaway drawing to explain the dual lower downshaft thing, but couldn't find anything.

The revised 3A is supposed to have the same bearings, gears etc as the #4 & #5, stronger casings and is rated the same as those, but still has the 6" longer (lower propshaft) lower unit.

One would have to set the drive back a fair way to make up for that 6" higher propshaft height I would think, and setting the gimble 6" lower in the transom probably isn't possible.

3A is the answer I guess.

Originally Posted by Jim Brooker

Martin if you are going to buy drives buy MK4 and spacer kits, MK4 are stronger than MK3 in all respects.
As for the MK3 when fitted to the Sabres and running them backwards, I would fit the right hand rotation drive on the left hand side and the left hand rotation drive on the right hand side, so that makes the drives run backwards,
the lower unit has two shafts one driving shaft and one driven, both shaft have backlash on the gear sets, the top set of gear on the lower unit connect the two shafts, they have backlash and must be set in direction of rotation so that the lower gears keep there backlash, so if you run the drive on your petrol engines the driven gear will have on backlash.
If the drives have been run a lot, you can't then run them in the normal direction the gears will not like being run onthe back of the teeth.
I hope this makes it a little clearer, I am beginning to think I should't have started this.

[Tony Davis]

111a

[Jon Fuller]

Well looking at that, the rotation must be decided in the upper. not as I thought.

[Jim Brooker]

No the LH & RH rotation is in the lower unit, as for the MK4 the transom plates must be put at 18 ins apart and the adjust the hight with spacers.

[Jim Brooker]

In the right hand lower unit there are 3 gears and in the left hand lower unit there are 4 gears.

[Jon Fuller]

oh, ok. with the #3 / #4 thing, I was refering to the difference in centres between CSL and propshaft, the 3/3A is I think 6" longer than the #4/#5, so runs deeper. a #4 would effectively raise the propshaft, and thus the thrustline by 6", and may not give the bow lift needed to carry the bows, and make it 'go'.

[Jon Fuller]

Originally Posted by Jim Brooker

In the right hand lower unit there are 3 gears and in the left hand lower unit there are 4 gears.

so in the right hander, is the 3rd gear a back to back 'double gear' running between the 2 shafts?

And....how is the varying backlash tween shafts done? is there differing numbers of splines top & bottom of each shaft? (vernier)

Sorry to ask so many 'Q's

[Jim Brooker]

Yes but as the transom plates would have to be moved you could adjust the hight with the transom plates and spacers in the drive to get a much better performance and you could make a stand off box for the transom, better still.

[Matt]

Unless they're helical gears & shims?

Originally Posted by Jon Fuller

so in the right hander, is the 3rd gear a back to back 'double gear' running between the 2 shafts?

And....how is the varying backlash tween shafts done? is there differing numbers of splines top & bottom of each shaft? (vernier)

Sorry to ask so many 'Q's

[Matt]

Sorry, that was stupid. I'll go away now.

[Jim Brooker]

Hi Jon, no the two shaft are shim up and down and the prop shaft gear is adjusted with spacers and shims backwards and forwards, there are 8 different shiming set ups in the lower unit on the MK3 & 4 and 7 on the MK5

[Jim Brooker]

Matt There was helical gears up to 1977 but now are straight cut.

[Matt]

I was just thinking that with helical gears, you could shim the gears to get the right backlash - whereas I couldn't visualise a mechanism to adjsut the backlash on straight cut gears.

I had my second birthday in 1977, don't think I progressed to lego technic until about 1979/80.

[BluFin]

One damm good thread

[Jono]

Originally Posted by Matt

....
I had my second birthday in 1977, don't think I progressed to lego technic until about 1979/80.

...that's why your ideas are so piss-poor..... should have been "Fischer" technic....which was for boys...as opposed to "lego" technic...which was obviously for girls......so stop "thinking" outside the box...and get back in it......

[Matt]

Jeez! Is my name rupert now?