Super Speedmaster meets Dr. Frankenstien

[Mark75H]

In 1968 Mercury introduced a very complicated racing lower unit for their 1250 BP and 1000 BP racing motors we saw in other threads on some offshore boats.

These lower units featured narrow profile bullets, mutliple driveshafts and full gearshifting. Here is an alternate design patented by Carl himself. The units sold to racers were different.

[Mark75H]

The BP lower units sold as customer racers used this arrangement for reduction and shifting.

This arrangement allows fairly quick change of drive ratio and places the water pump lower where it is more likely to work well.

Note that this type Speedmaster uses three thinned driveshafts and a total of 11 gear surfaces (15 if you count the dogs on the shifter mechinism).

Apologies to dialup users, I just couldn't reduce the image anymore without sacrificing quality


Can anyone explain how the shift mechinism works (besides you start up the motor, slam it in reverse and the whole thing explodes! that happened often enough a kit came out to limit the speed the motor could run when you shifted into reverse)


The base image here is from the US Patent application for the BP, but I claim ownership of this enhanced, corrected and colored version. Feel free to save it on your personal computer and print for yourself, but PLEASE DO NOT repost this to another bulletin board, put on a website (yours or someone else's) or print in a magazine or book without my written permission.

[crazy horse]

That's alot of hardware turning at 6 to 7 grand. The shift setup looks like the purple dog moves up and down to ingage the case. The driveshaft stops at the shift dog and foward gear would be with the shift dog up. driving the back two shafts, The reverse gear ratio would be what ever the case is and foward gear you could change the ratio with the red and green gears. Am I right? One thing I noticed is the routing of the water passage though the gearcase you think they could have ran it strait though like the SSM'S. Sam, Was there something in the way that's not shown on the drawing or did they move it back to keep the leading edge narrower on the case ?

[Mark75H]

The patent diagram is not an engineering/set up diagram.....somethings maybe placed just for convenience or better visability I don't know the answer to the water passage question.

Your description is basically correct, but all three lower shafts turn together all the time; the blue gear is constantly engaged to the gear behind it and that one to the gear in the back.

So, as Crazy Horse has described for forward the purple shifter dog (which is splined on the upper driveshaft) is raised and it engages the the green gear. The driveshaft does not turn the green gear directly.....as far as the driveshaft is concerned the green gear is just a hollow disk it runs thru. The green gear turns the red gear. The red gear is on the same shaft as the back gear of the 3 gear train. This turns all three driveshafts and the three pinion sets (orange on my diagram) that turn the propshaft.

If the red and green gears are not the same size (with the same number of teeth) there is a change in speed between the motor and the lower driveshafts. The production BP's had these reduction ratios listed 1:1, 1.25:1, 1.5:1, 1.75:1 and 2:1, but the gears were not interchangeable front to back; the bearing support surfaces were not the same, the back gear is splined and the front gear is just hollow.

For reverse, the purple shift dog drops down and drives the blue gear at the front of the 3 gear train; causing the train to run in the opposite direction from the way it turns when driven by the green and red gears. (While you are in reverse the green and red gears turn because they are solidly connected to the back shaft of the train, but there is no connection to the upper driveshaft.)

This image shows the 3 gear train. Notice the tall shaft on the right, this is the back shaft. The red gear fits on those splines. On the front gear (colored blue on the colored diagram) you can see 2 of the 3 pie shaped dogs (ears) that engage with the shift dog that does the shifting (the third one is behind the fork). You can also see the fork that raises and lowers the shifter dog on the splines of the driveshaft .

[crazy horse]

Sam, Was the gearcase ratio 1 to 1 on all the BP cases ?

[Mark75H]

The foot ratio is 15:16 (almost 1:1), but the green and red gears were the reduction ratios or 1:1 as I mentioned above.

Here is an image showing the green and red gears and the purple shifter just barely visable. Note that the gear on the right (red on the colored diagram) is larger than the gear on the left (green). This is a reduction set. For 1:1 they would be the same size.

For later reference note the six studs screwed into the case that stick down when the motor is upright.

[crazy horse]

Did the top gears run submerged in oil ?

[Mark75H]

No, see the brass fittings and plastic tube in the picture with the train gears? That is part of the lubrication system. I think oil came up from the bottom at 1/2 psi or so from a passage near one set of the pinions. The top stuff just ran in a mist of oil splashing around.


Like their more sane cousins the BP's came in right and left. All the images we have seen so far are of a right hand rotation BP. For left hand the double sided gear would be between the middle and back lower driveshaft gears and the single gear would be at the front instead of the back. (These are the little orange bits on the colored diagram.)

[crazy horse]

I thought that might of been somebodies after thought. That's interesting that would save them some power not trying to drag those large gears though oil.

[Dave S]

OH NO! I forgot if I put the shim in the back of the case. I guess that will be OK if I don't tell ol' Carl. Really, I don't think the oil pump on this masterpiece was a afterthought.

[Mark75H]

Or more accurately, where I left off and didn't finish.

Looking at the mid sections ..... here is a 1968 BP mid. The sides of the mid housing are smooth and the lower fasteners are studs anchored in the mid section facing down to go into the transmission box


The nuts will go on the bottom.

[Mark75H]

Here is a '69 and later Super BP mid.

(sorry it is upside down:rolleyes: )


Notice each side has 2 big scallops.........

The studs are now in the transmission housing and facing up.

The nuts are on the top.

[Mark75H]

Here is a '69 and later Super BP transmission and lower unit.......studs facing up ready to go up thru the holes in the Super BP mid

[Mark75H]

The same type mid section, but with an adapter to let you use a regular non-shift Super Speedmaster under the SuperBP mid


This evolved into the Twister 2 mid section with a few changes

[Mark75H]

From some 1969 Merc sales literature:

[Mark75H]

But what most people think of when you say BP Merc:

The tuned stack kit:

This one belongs to a guy in Australia who is looking for a more correct prop.

[T2x]

Hummanah...hummana.... Boy do I want that motor...and its twin brother

Gimme...gimme....gimme. and to think I used to take them for granted...... Probably explains why I've been so dreadful at being married too.;) ;)

T2x

[Raceman]

I've seen several BP props on E Bay in the last several years. As a matter of fact I bought one of em brand new for 60. Merc's even got some late style cleaver on the one they display from time to time. Looks like that motor could use some other detailing also. I sho' could make it purdy with a couple of day's work.

[Mark75H]

:D :D :D And I bought the other BP props:D :D :D

[Mark75H]

Yeah there are a bunch of details wrong on that BP, just like the one Merc displays, duh.


A 1969 should have the white model designation decals on the top for one. What else? Are the stripes 68 stripes or 70 stripes, they sort of don't look like the ones on the blue picture. If the cowls are 1970 we can forgive the 69 decal missing. If the stripes are 68 stripes..........well, oof, that isn't the right lower unit, is it?


Even in the picture the paint looks like enamel to me.......sort of icky wet and thick. Mercs look best with the baked on lacquer, thin, hard and sharp! Like a polished black diamond, not wet tar.

We could probably find clamp handles on the junk pile somewhere between here and Sydney for him, too.

speedmasterkey

[Mark75H]

Here is a diagram showing the route the power takes
getting thru a BP lower unit for forward:

Start at the top and go down the yellow shaft to the purple shifter dog, then up to the hollow green gear, to the red gear, across all three of the upper 3 gear train and equally down each shaft.

[Mark75H]

Here is the path in when in reverse:

[Mark75H]

In reverse the hollow green gear and red gear are cut
out of the job of power transmission; they are just along
for the ride.

When running in reverse the drive shaft drives the purple
shifter dog which is now directly meshed with the front (left)
dark blue gear of the three gear train. Both dark blue gears
and their shafts now rotate in the same direction as the
yellow drive shaft.

Here is what some people have found confusing:
the red gear remains rigidly attached to the shaft
with the back (right) dark blue gear of the three gear
train. It also continues to be engaged with the green gear.
But since the green gear is hollow, the green gear has
no effect on the drive shaft - freaky thing is the drive shaft
and green gear are now turning the opposite directions relative
to each other.

[Raceman]

Both of mine are that way too Jim, but I've never seen one with the rubber coupler. Mine have what amounts to a driveshaft extension, although it's fatter in the spline area than the old Bay Machine type that convered short inlines to long.

While we're on the subject, I sho' do need a first design BP lower (down studs type) to complete a 1250 BP (non Super)

[Raceman]

Now Jim............... you know all those nice AOMCI guys that won't allow pricin' on thier website wouldn't have anything overpriced don't you??????:D :D :D

[Mark75H]

Change at AOMC .... pricing in ads will begin very soon.

It passed a referendum and was approved by the executive council .... directive to allow pricing in ads was passed to the editors just this week.

[Raceman]

Y'all ain't April Foolin' again with the AOMCI pricin' thing are you? When I was a member, they were so adamantly opposed to it, and the very mention on the inner sanctum brought a vigorous response. I'm very surprised it got changed if it does.

[Mark75H]

No foolin on the pricing

[Dave S]

You all call?:D Happy FOOLS DAY .... from the KING.:p

[Mark75H]

Here's another image with the upper and lower sections lined up.

[Raceman]

Sam, I sure do need that unit.

[Mark75H]

Here is DaveS's cutaway BP foot he made from one with a cracked case (in case you thought he was just cracked enough to make something like this from a good case)

[raymar]

The Mercury part number for the Reverse Limit kit is A-49248A1 in case any one has one of these old kits occupying space in their parts bins. As Mercury says: THIS KIT MUST BE INSTALLED IN A SINGLE-LEVER MERCONTROL OR SERIOUS DAMAGE TO THE LOWER UNIT WILL OCCUR !!
I will say many lower units were damaged by not using this kit to limit control travel in reverse. :mad: :(

[seeroy]

Sam - I noticed that you have not talked about the BP exhaust. As I remember, it exhausted above the horizontal plate/water and sounded very throaty. Sounded awesome when 4 of them were cooking along behind me at speed. Even more awesome when they came out of the water and "barked". Sounded like a thousand pound dog, as opposed to a stacker which sounded like a thousand pound hornet. I think we ran 2 left and 2 right hand rotation...long shafts on the inner engines and short shafts on the outers. Also, regarding the shifting issue...as I remember, in the Offshore boats, we shut the engines down to shift and then restarted in gear. Damn, those days were fun.
-Steve Sirois

[Mark75H]

Good point Steve.

The immediate successor to the BP style Speedmaster was the right hand Super Speedmaster with an adapter to put it under the later BP mid.

I'll make another new thread with the next unit used in racing

[GENE LANHAM]

To the top for first time in 9 or 10 years!!

[GENE LANHAM]

To the top for first time in 9 or 10 years!!

Thanks Sam--