Reverse rotation
 

I have twin 350 Chevy inboards with the port standard rotation and the
starboard reverse rotation. The port has a standard timing chain while the
starboard has timing gears which means that the cranks turn opposite but the
cams turn in the same direction. Both engines use the same part number
Mallory distributor. On the starboard, the firing order is reversed by
reversing the sequence of the wires in the distributor cap. It all seems to
make sense so far.

In looking in the Mallory catalog, I note that they list a reverse rotation
distributor for this engine as well as the standard rotation model. The
helix on the reverse model is opposite hand. This would mean that it would
have to mesh with a camshaft gear which was also opposite hand helix.
Reversing the hand of the helix on the gears switches the direction of
thrust so that it would remain upward against the distributor housing thrust
washer with the distributor shaft turning backward. This would seem to
indicate that there must be some engines that reverse the cam as well as the
crank for opposite rotation. However, since the distributor shaft drives
the oil pump, the pump would also turn backwards and this isn't possible.

Can anyone clear this up for me? Thanks.

I thought the reverse rotation was created by the outdrive?

"Jim" wrote in message
. ..
I have twin 350 Chevy inboards with the port standard rotation and the
starboard reverse rotation. The port has a standard timing chain while
the
starboard has timing gears which means that the cranks turn opposite but
the
cams turn in the same direction. Both engines use the same part number
Mallory distributor. On the starboard, the firing order is reversed by
reversing the sequence of the wires in the distributor cap. It all seems
to
make sense so far.

In looking in the Mallory catalog, I note that they list a reverse
rotation
distributor for this engine as well as the standard rotation model. The
helix on the reverse model is opposite hand. This would mean that it
would
have to mesh with a camshaft gear which was also opposite hand helix.
Reversing the hand of the helix on the gears switches the direction of
thrust so that it would remain upward against the distributor housing
thrust
washer with the distributor shaft turning backward. This would seem to
indicate that there must be some engines that reverse the cam as well as
the
crank for opposite rotation. However, since the distributor shaft drives
the oil pump, the pump would also turn backwards and this isn't possible.

Can anyone clear this up for me? Thanks.

These are straight inboards. They have direct drive Velvet Drives. No
outdrive present.

Reverse rotation inboards are becoming a thing of the past since the newer
transmissions, unlike the older 71 and 72 series Velvet Drives, are capable
of running full power in reverse or forward. On these installations,
counter rotation is accomplished with the transmission linkage.
"JGK" wrote in message
...
I thought the reverse rotation was created by the outdrive?

"Jim" wrote in message
. ..
I have twin 350 Chevy inboards with the port standard rotation and the
starboard reverse rotation. The port has a standard timing chain while
the
starboard has timing gears which means that the cranks turn opposite but
the
cams turn in the same direction. Both engines use the same part number
Mallory distributor. On the starboard, the firing order is reversed by
reversing the sequence of the wires in the distributor cap. It all
seems
to
make sense so far.

In looking in the Mallory catalog, I note that they list a reverse
rotation
distributor for this engine as well as the standard rotation model. The
helix on the reverse model is opposite hand. This would mean that it
would
have to mesh with a camshaft gear which was also opposite hand helix.
Reversing the hand of the helix on the gears switches the direction of
thrust so that it would remain upward against the distributor housing
thrust
washer with the distributor shaft turning backward. This would seem to
indicate that there must be some engines that reverse the cam as well as
the
crank for opposite rotation. However, since the distributor shaft
drives
the oil pump, the pump would also turn backwards and this isn't
possible.

Can anyone clear this up for me? Thanks.

In article ,
says...

I have twin 350 Chevy inboards with the port standard rotation and the
starboard reverse rotation. The port has a standard timing chain while the


If the crank and cam turn backwards, the reverse cut helix causes the
distributor and oil pump to turn in the 'normal' direction. Two reverses
equal a forward, much as 3 lefts equal a right.

Any pair of gears, helical, spur, miter etc. will rotate in opposite
directions. You cannot change the direction of rotation by changing the
hand of the helix. Additionally, on intersecting shaft applications only
helical gears of the same hand will mesh. The only consideration when
selecting the hand of the pair is the direction of the resultant thrust
which, in this case, must be toward the distributor housing.

If you check a power transmission catalog, such as Browning, they will show
diagrams to explain this.
"Gudmundur" wrote in message
...
In article ,
says...

I have twin 350 Chevy inboards with the port standard rotation and the
starboard reverse rotation. The port has a standard timing chain while
the


If the crank and cam turn backwards, the reverse cut helix causes the
distributor and oil pump to turn in the 'normal' direction. Two reverses
equal a forward, much as 3 lefts equal a right.

In article ,
says...

Any pair of gears, helical, spur, miter etc. will rotate in opposite
directions. You cannot change the direction of rotation by changing the
hand of the helix. Additionally, on intersecting shaft applications only
helical gears of the same hand will mesh. The only consideration when
selecting the hand of the pair is the direction of the resultant thrust
which, in this case, must be toward the distributor housing.

If you check a power transmission catalog, such as Browning, they will show
diagrams to explain this.

Crap, you are correct, I just drew some fake gears on two 1 inch dowels
laying here on the bench. And no matter which way I drew them, the shafts
went the same direction. Wow, I'd have bet you a paycheck the outcome
would have been differant!

It can get a little confusing. As a side note, helical gears are also used
on parallel shaft applications. When used this way, only a left hand and
right hand will mesh.

I looked up the Crusader Marine web site and they have an on line parts
manual for their counter rotating engines. They do not indicate that the
right hand engine has timing gears so the assumption is that it has a
conventional timing chain like the left hand. This is supported by the fact
that they call out opposite rotation distributors for the left hand and
right hand engines. However, they do not call out different oil pumps.
"Gudmundur" wrote in message
...
In article ,
says...

Any pair of gears, helical, spur, miter etc. will rotate in opposite
directions. You cannot change the direction of rotation by changing the
hand of the helix. Additionally, on intersecting shaft applications only
helical gears of the same hand will mesh. The only consideration when
selecting the hand of the pair is the direction of the resultant thrust
which, in this case, must be toward the distributor housing.

If you check a power transmission catalog, such as Browning, they will
show
diagrams to explain this.

Crap, you are correct, I just drew some fake gears on two 1 inch dowels
laying here on the bench. And no matter which way I drew them, the shafts
went the same direction. Wow, I'd have bet you a paycheck the outcome
would have been differant!