Once and for all, you engine won't fall apart if you turn it counter clockwise..
 

I was at the Dealership the other day talking to a customer at the Parts Dept. A Mercedes mechanic overheard me tell a customer how to set up to change out his fuel pump . I said if you turn it a few degrees past TDC you can back it up" On that sentence and the mechanic came excitedly running over and said "See, don't listen to just anybody. He's not a Mercedes employee" The customer fled and the mechanic walked away.

I saw him later as I left. I smiled and I intoduced myself and told him I am an engineer by profession and I asked him politely, "Why can't you turn an engine counterclockwise.What's the real reason" He mulled it for a minute...I asked him, "ever see an engine backfire?" He was young--some of these modern gassers never backfire...
We went through the whole scenario about the tensioning device being on the soft side of the belt-and might have to work harder, but otherwise, there is no difference except the oil pump isn't going to put out pressure.
I wouldn't run the engine ccw. But you can turn it ccw.
At least he was man enought to apologize.

You should NEVER turn the engine CCW for any reason. It can introduce slack into the chain and cause it to skip a tooth. One tooth on the OM6xx diesels is 18*, close enough to possibly cause piston-valve impact.

Even suggesting that it might be okay to turn it CCW is very bad advice.

I agree.

Turning it CCW for small increments is not going to harm anything if the chain is under tension.

You mist beware with that kind of wording. A small increment to you might be 1/4 of a rotation to somebody else.

1/4 rotation is a small increment. No harm will be done to the engine.

Beside's that
 

Diesels that are properly assembled and timed to run, do not back fire. Backfire on a gas engine usually comes from a flooded or over fueled cylinder that that fires just as you let off the starter.

Due to backlash, final positioning most definitely should be in the normal direction of rotation.

Not a good idea on a MB V8 with their really long timing chains!:eek:

You can turn them backwards a bit, as said above about 1/4 of an inch or so.

Factory service manual for 615,616,617.91 engines page 05.4-210/3

Subject- Valve adjustment

"Do not turn crankshaft backward"

sigghhhhhhhh now i know why
 

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

this one i really loved
 

this one i really loved

Really now, just how often does a modern diesel engine run in reverse?

Never seen one do it. OTH a 2 stroke engine, yes.

I know that it was possible with the old engines. I don't know if that still applies.

They used to reverse the old Packards in the PT boats. They didn't have a reverse gear, the engines would have to be stopped and started again. That was pretty commen back then.

Reversin engines
 

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.

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

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!

Don't marine engines typically run "backwards?"

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.

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.

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.

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.

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

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.

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.

Just put the shift lever on R
 

I run my MB ccw all the time. Just put the shift lever in R. :)

funny funny... I'm PRETTY sure only the driveshaft, diffy and wheels go backwards then! My engine seems to run without a beat when I go into rewind.

took a nap....
 

as long as everyone is stimulated challeneged and chiming in thats the ultimate object--

Here it is in the section on Valve adjustment.

This has never been about the engine possibly running in reverse. I am sure you can never crank a 616 or 617 in either direction fast enough with a ratchet handle to start it.

This is about the timing chain and engine timing. The first issue is the accurate setup of the timing - you can only accomplish that in the forward direction. If you reverse, there is a certain amount of chain slack that will need to be taken up (not much) and the timing will not be the same as in the normal CW direction.

The second issue is potential chain slip on a sprocket. Especially on a 616 engine, because the 616 does not use a ratcheting tensioner. The 616 tensioner only applies significant tension to the timing chain when oil pressure comes up. That's why you can get the chain "rattle of death" on a 240D when it starts up. You hear that and its time for a new chain to go in. There is some tension available from the 616 tensioner due to the spring, but over time that spring weakens somewhat.

The 617 has a ratcheting tensioner, and is less likely to slip a sprocket tooth if turned in reverse. But if you have reached the end of the tensioner ratchet due to an elongated chain, then you are probably more likely to slip a tooth on reverse.

So why take such a risk? Only turn the engine clockwise.

Ken300D

You could pop the clutch on a manual, into reverse gear with the car going forward. I thought I might have heard something about someone doing that in a 240?

I'd like a bit of data.

Has anyone slipped a tooth on the camshaft while rotating a 616 or a 617 in reverse???

Due to the tooth engagement, the chain would need a lot of slack for this to occur......but, maybe it's possible on a 616. I don't see any possibility on a 617.

Let's see what we get.............

I think the issue is where the slack "piles up" on the chain path when you turn the engine over at the crankshaft with the wrench in each direction. If the chain is pulling through the injection pump drive sprocket, and up over the cams, the slack if the chain tensioner isn't really tensioning a lot, is on the chain tensioning rail side of the crank sprocket. The relative positions of the sprockets is always "locked" by the chain because you do not introduce the opportunity for the slack to accumulate between the sprockets. Turn it the other way and the opposite happens, and it is possible the chain and sprockets won't all line up the same when you change directions again. If the chain is pretty used up, the slack can affect timing of the pump. Check how far you can turn the crank in either direction before the camshaft sprocket turns and you will get an idea of what I am talking about. You will get more than a single link of rotation, meaning slack, in the backwards direction on our older engines with worn tensioning rails and stretched chains. Which means you can loose your timing and that is never good. Jim

I would have hoped that a professional engineer could have done better than that.

Answer
 

Yes, I have experienced tooth skip on the 616/617, generally due to a bad/broken chain tensioner and/or guide rail.
The warning is there for good reason.

'1/4 rotation is a small increment. No harm will be done to the engine. '

What freaks me out is no unit designation. 1/4 rotation could be interpreted as '1/4 of a degree' or '90 degree rotation of the crank'. Big difference there. I did rotate mine back maybe a degree. I had a new chain and new guides and tensioners. I was setting it up to put the injection pump back on. The compression kept bumping the crank forward a bit from 24 degree setting.
Tom

Engines turn backwards a small amount quite frequently. An aborted start attempt, a piston is most of the way up the compression stroke when the starter disengages... what do you think happens? The compression pushes the engine backwards more than a few degrees. Older carburetted gasoline engines FREQUENTLY would run on after they were shut off due to the deteriorating fuel quality at the time. Frequently this "run on" would be with the engine going backwards, resulting in smoke and foul smells coming out of the air cleaner.

Park a manual transmission car on a hill with the tranny in 2nd gear. Steep enough hill... backwards rotation. I bet it has happened to 90% of the manual transmission cars ever made.

I would say that any MB engine without worn out timing chain, tensioner, and rails, can be safely rotated backwards by hand about as much as you'd ever want. Yes, setting timing, etc should only be done with rotation in the correct direction. But if you miss and want to go back 1/4 turn before going forward again, no problem. I always like to rotate an engine several revolutions in the right direction when checking/replacing a timing chain or belt to check my work before calling it "good."

Kent Bergsma of ********** has warned a bunched timing chain as a consequence of CCW rotation. Got it in one or more of my recipe books from him.

I would not do it but as JonL says, it happens in manual transmission cars all the time. I try to always put my trans in the proper gear for the slope its on.

We did have a 240D almost running backwards. It was trying.

We were towing the car forward, not knowing that the car was in reverse.

Detroit Diesel 8V71 two-stroke bus engines which are all gear driven, can and did run backwards and blow up.

Of the MB diesels and gassers, the only ones that can be turned slightly CCW are the W 136 and OM 636, because they have a gear arrangement only and no timing chain.

I have been told the OM 352 can also, but I have no personal knowledge.

I have an OM 621 190D of 1959 vintage that is so loose that the timing can be slightly turned ccw, but that's due to wear on a engine with 520,000 km or so that is on its last legs.

For the most part, don't do it.

Always check the manual to be sure.

Thats what parking brakes are for . . . us it, or fix it if it does not work, then use it!:D

Of course, but in the "real world," this happens ALL THE TIME to standard transmission cars. Unless it's about ready to break anyway there will be no harm. Also, you know that those ATE brake systems with the little vestigal parking brake shoes inside the rear disc hub aren't worth ****. They barely work when they're perfect, which they seldom are.

i had a 87 280G run bakwards for a few minutes and the engine still runs very good

Most of the diesels likely "wobble" on shut down backwards a bit. I can feel the rocking of the engine moving back a bit when shutting it off....but I bet any significant amount of reversing the engine would = bad things.

turning most engines backwards is just plain retarded and asking for trouble.

I am not sure why Camshaft was specified on the tooth slip...
when I look at the route the chain takes I think the main problem is the probability of the injection timing tooth /chain relationship getting off..... than the cam tooth.