Once and for all, you engine won't fall apart if you turn it counter clockwise.. - Page 2 - PeachParts Mercedes-Benz Forum

estod · #16 11-08-2007, 11:08 PM

Off Topic ....

Just as a matter of interest, some marine Diesels have a drive shaft with no gear box, and are stopped, then re-started in reverse to provide prop reversal (as in, to stop before hitting the dock).

I operated a tugboat set up that way.

Brian Carlton · #17 11-08-2007, 11:12 PM

Quote:

Originally Posted by Justfacts

sigghhhhhhhh now i know why..............................

...........well..........enlighten us...........!

DZL_Damon · #18 11-08-2007, 11:18 PM

Quote:

Originally Posted by estod

Off Topic ....

Just as a matter of interest, some marine Diesels have a drive shaft with no gear box, and are stopped, then re-started in reverse to provide prop reversal (as in, to stop before hitting the dock).

I operated a tugboat set up that way.

Yup, I work on them all the time! Usually large 2 strokes but sometimes you'll find a direct reversing 4 stroke. I've never worked on one though. Anyway, they either adjust the lobes on the cam itself, or the cam has 2 sets of lobes and the camshaft will shift for the ahead and astern set of lobes.

Dad has a 454 gasser in his lobsterboat (don't get me started on why a diesel isn't in there!!). When we got it it originally ran backwards. We just swapped the cam and the starter and away she went CW!

Matt L · #19 11-08-2007, 11:20 PM

Don't marine engines typically run "backwards?"

Hatterasguy · #20 11-08-2007, 11:21 PM

Quote:

Originally Posted by DZL_Damon

Yup, I work on them all the time!

Dad has a 454 gasser in his lobsterboat (don't get me started on why a diesel isn't in there!!). When we got it it originally ran backwards. We just swapped the cam and the starter and away she went CW!

Thats how they used to counter rotate them. One engine would spin left, and the other right, now they do it in the gears. That must be an old engine, they havn't built them like that in all of 20 years.

The large marine engines still reverse.

DZL_Damon · #21 11-08-2007, 11:24 PM

Usually most things run CW when looking at the end that they drive. I guess that would be backwards for our cars because from the driveshaft, the engine is running CCW, but from the accessory end it's CW.

Yes, most boats use a right handed propeller and thus turn CW looking at the engine from the shaft, but CCW on the accessory drives. However on a twin or quad engine set up, the starboard engines will have left hand props, and the port engines will have right hand props... I believe there are cavitation issues if they flip flop them. Anyway, the counter torque reduces roll in smaller boats, and eliminates prop walk.

Dad got his engine off the starboard side of a twin engine boat where the port engine blew and they owner repowered the whole vessel.

DZL_Damon · #22 11-08-2007, 11:27 PM

Quote:

Originally Posted by Hatterasguy

Thats how they used to counter rotate them. One engine would spin left, and the other right, now they do it in the gears. That must be an old engine, they havn't built them like that in all of 20 years.

The large marine engines still reverse.

Ya, dads engine is an older girl, but only 200 hours when he got it!

I've been told they still do it on some applications to eliminate torque from lifting one side of the boat on large HP applications in little boats. However, just getting a counter rotating reverse gear is done more often.

vstech · #23 11-08-2007, 11:29 PM

apples to potatoes... gear drive timing on those boat motors. no slack on the timing in a 454, the 616 and up (maybe even lower... no idea) OM's have a chain that is longer than needed to reach all the gears, and a tensioner keeps the slack, if you back it up, can't the tensioner get over tight, and cause excessive wear on the chains? wouldn't the timing get thrown off by the tensioner movement? I don't think any skipped tooth scenario's could happen, but down the road problems? sure. that tensioner has a ratchet mechanism, it will not loosen up if it extends too far.

Matt L · #24 11-08-2007, 11:33 PM

I don't think the tensioner will loosen unless it breaks. But you really don't want to break it.

Brian Carlton · #25 11-08-2007, 11:34 PM

Quote:

Originally Posted by DZL_Damon

However on a twin or quad engine set up, the starboard engines will have left hand props, and the port engines will have right hand props... I believe there are cavitation issues if they flip flop them.

On twins, the starboard engines have right hand propellers and the port engines have left hand propellers. There are no cavitation issues if you reverse them...........but the boat won't handle very well when attempting to rotate within it's length.

DZL_Damon · #26 11-08-2007, 11:43 PM

AH! I always get stuff like that backwards it seems! All I knew was there was some issue about reversing the normal way. I may have heard it goes faster one way and handles right the other?? IDK. My gig is making sure the oil is where it needs to be, it's purified properly, the generators are getting their maintenance, and the lights stay on!! The mains are usually the 2nd's or 1st engineers job!

Brian Carlton · #27 11-08-2007, 11:53 PM

Quote:

Originally Posted by DZL_Damon

AH! I always get stuff like that backwards it seems! All I knew was there was some issue about reversing the normal way. I may have heard it goes faster one way and handles right the other?? IDK. My gig is making sure the oil is where it needs to be, it's purified properly, the generators are getting their maintenance, and the lights stay on!! The mains are usually the 2nd's or 1st engineers job!

Due to the shaft angles, a right hand propeller will tend to push the boat to port due to greater thrust from the "falling" blade. Therefore, it's preferable to have this propeller on the starboard engine. The converse is true for a left hand propeller. If you reverse them, the propeller thrust fights the turning moment generated by the offset shafts.