Reverse rotation

[mr 88]

Have twin inboard 305s. Starboard engine distributor turns counter clockwise and has two sets of plug numbers on cap ,larger sized numbers for normal rotation and smaller for counter.The engine itself turns clockwise when running , I think , as I just discovered this when a no start issue came up. I put a " normal "starter motor in it and n
ow it wont start. I did have a hydro lock issue ,blew out cylinders ,fixed riser gaskets and new plugs put in.,compression is 150 across the board and I am.getting spark at plugs.What is the purpose of the counter R if the engine itself is not. (Firing order is correct for counter R . )

 

[Scott Danforth]

if the firing order is correct for a RH rotation motor, then its a RH rotation motor

putting a LH rotation starter on a RH rotation motor would suck water and air up the exhaust and try to blow everything out the carb

most inboards of old had one LH (standard) motor and one RH rotation so your props rotate against each other as the gear drives had differing ratios FWD and REV.

later motors area all LH rotation and the gears are different.

 

[Rick Stephens]

Can't imagine the expense of the limited number of counter rotation parts for the motor. Cam shaft, starter, oil pump, I suppose the crank is the same. Water pump? I guess funky things could be done with belts to keep accessories the same, or not.

 

[mr 88]

They are 1987 engines . Closed cooling and I would think the raw water pump that is belt driven would move water regardless of rotation. I do wonder if the alternator works no matter what direction it turns as its mounted on the same side as the port engine ,port side.. I was seeing small splashes of fuel being pushed up out of the carb after I cranked it for a bit. That did not make sense to me. Did not see any water being pushed out but that's a long way from the transom, through the mufflers and up the risers. NOW ,I pulled the boat yesterday and noticed the transom exhaust flapper was wedged into the "pipe " Wondered to my self what that was about. So what Scott replied would make perfect sense for that . Taking original starter to rebuild shop tomorrow to verify and probably have them go through it if is indeed a LH unit. Thanks Scott D ,old dogs learn new tricks, every once in awhile !

 

[Bt Doctur]

What direction are you facing when you report the engine rotation? Most GM dist turn only clockwise no matter what engine rotation. Just the firing order is reversed 1.8.4.3.6.5.7.2 Std 1,2,7,5,6,3,4,8 Rev

 

[Scott Danforth]

What direction are you facing when you report the engine rotation? Most GM dist turn only clockwise no matter what engine rotation. Just the firing order is reversed 1.8.4.3.6.5.7.2 Std 1,2,7,5,6,3,4,8 Rev

BT, is correct on the distributor as they change the direction of the cam with a gear set vs a chain set.

a RH engine has the reverse knurling in the crank for the RMS, it also has a different cam, a slightly different cooling pump, and will have a gear set vs a chain set driving the cam, so the dizzy will turn the same But the will turn RH vs LH.

 

[mr 88]

Standing at the stern looking towards the bow . Distributor is at the back of the engine and rotor spun the opposite of port engine. Your fiing numbers are correct as labeled on cap.

 

[mr 88]

So does it use a " standard " turning starter or reverse rotation starter ?

 

[mr 88]

When the rotor rotation was checked I had a different starter motor in it than what was originally used ,so that rotation , original , has to be verified . New starter motor is normal rotation.

 

[Bt Doctur]

The easiest way is to locate #1 plug wire at the cap and go clockwise 1,8,4,3,6,5,7,2 this is a standard rotation . Now heres where is get confusing .You have inboard engines usually with aft entry starters on the rear bell housing instead if engine mounted starters.So a standard rotation motor,(left hand) uses a reverse rotation starter. A reverse rotation (right hand)engine uses a standard starter But no matter what the dist turn clockwise

 

[mr 88]

Yes ,the confusing part to me is , "no matter what the dist turns clockwise " . How does that happen if you turn it over LH then RH , would the dist not turn in the opposite direction. Definitely reverse firing order on it.

 

[Bondo]

Yes ,the confusing part to me is , "no matter what the dist turns clockwise " . How does that happen if you turn it over LH then RH , would the dist not turn in the opposite direction. Definitely reverse firing order on it.

Ayuh,...... By changin' the timing chain, to timin' Gears,......

 

[Scott Danforth]

Yes ,the confusing part to me is , "no matter what the dist turns clockwise " . How does that happen if you turn it over LH then RH , would the dist not turn in the opposite direction. Definitely reverse firing order on it.

see post #6 and the last line of post #2 in addition to Bondo's response in 12 and BT's post in #5.

a standard rotation engine uses a standard timing chain setup that turns the cam the same direction as the crank. a RH or reverse rotation engine uses a gear set to turn the cam opposite of the crank. in both cases, the cam and the distributor will turn the same

because you put in a standard rotation starter vs a reverse rotation, you turned your motor into a water pump sucking water from the exhaust filling your motor with water.

 

[muc]

MerCruiser inboard engines can have conventional mount starters or rear entry high mount starters. If you post a serial number we can look and see what you have.

Sounds like you put the wrong starter in.

 

[mr 88]

I have the high mount starter that bolts into the bell housing about 1/2 way up. Will get back with serial numbers tonight. Original starter motor is being rebuilt and I will not have it back until late next week , he is waiting for a part to show up.

 

[Bt Doctur]

Look at the plug wire at the cap . locate #1 plug wire and trace it to the cap Going clockwise where does the next wire connect to. 8 would be a standard motor rotation 2 would be a reverse rotation motor

 

[mr 88]

Definitely a reverse rotation as the cap has the firing order on it with a big number on each wire mount for standard rotation and small number under the big number for reverse rotation. That's the way it was set up and ran like a top untill riser gasket let go.

 

[achris]

Can't imagine the expense of the limited number of counter rotation parts for the motor. Cam shaft, starter, oil pump, I suppose the crank is the same. Water pump? I guess funky things could be done with belts to keep accessories the same, or not.

It's not as much stuff as you think (Just in the process of pulling 2 engines out of a friend's boat, one LH the other RH, and 383ing them)...

The cam is the same, the crank is the same, the starter is ALMOST the same. The starter has the brushes in the end cap wired slightly different, and that makes it run the other way. The cam is gear driven, not chain, allowing it to turn the same way as a LH engine, so the oil pump is the same too. The alternator is the same (alternators don't care which way you turn them as all they are doing is cutting magnetic flux lines), the raw water pump just has its hoses swapped. The engine circ pump is the same, it's just a centrifugal pump, and centripetal forces doesn't care which way the impeller spins. The only other significant difference is the seals for the crank. The oil 'return' lines on them have to run the other way... That's it...

Chris.........

 

[km1125]

The Bendix drive on the starter also has to be different or it would never engage the flywheel.

One way to check the rotation on older engines is to look at the timing marks near the damper. You can tell which way is BTDC and which way the timing mark on the damper would approach the timing mark affixed to the block.