Turning the Engine Backwards?

[belrix]

OK I'll admit it! During my valve check I turned my engine clockwise while trying to line up the marks. Now I've read that during the engine backwards can break the cam chain tensioner spring.

I am still waiting on new cylinder head bolts (another story), but should I remove the cam chain tensioner and inspect it? If I do, do I really need to replace the cam chain tensioner bolt?

Thanks!

belrix

 

[MZ5]

I can't answer you as to what you should do. I can tell you that I've turned mine backwards just a very little ways while doing that same job. The tensioner on mine remains fully operational. <shrug>

 

[3rdgeargrndrr]

i went slight clockwise on mine, no big deal, if its easily accessible, go ahead and check it, but if something snapped, you definitely would have felt it turning the bolt.
next time, put the gear in reverse when you turn it clockwise

 

[Deleted member 1183]

I think a tensioner should be able to cope with the crank turning backwards. Sometimes a motor will not fire properly initially on start up, and will "kick back". Such a kick back is much more violent than one of us gently turning the crank back with a socket. It is not great for the starter motor clutch and gears as I found out with one of my KTM's, but I have not heard of a cam chain tensioner breaking because of it. I could be wrong but.......

 

[belrix]

Pulling out the tensioner doesn't look too hard and I have the service manual.

Do you think it would be OK to reuse the tensioner bolts if I used lock-tite?

Sent from my XT1030 using Tapatalk

 

[DirtFlier]

[...but I have not heard of a cam chain tensioner breaking because of it. I could be wrong but...]

I agree completely. I have from time-to-time turned the engine backwards just a hair when the timing marks went past too quickly, and it never caused any problems with tensioner or other parts. Removing the spark plugs can make it easier to turn the engine without it speeding past TDC.

Belrix - the bolts you broke are probably for the Cylinder Head Cover and NOT the cylinder head. The cover bolts are usually 6 mm thread while the head bolts are 8 mm and much more difficult to break. Cover bolts usually have an shoulder that acts as a positive stop and going much beyond that contact point can result in breaking off the threaded portion.

The torque is so low for 6 mm that I usually use two fingers on a short wrench.

 

[JoeTx]

Over the years, it seems the only people who've had problems had turned their engines backwards. Being to new to all this I've pay close attention to what others have done, when I miss the mark I just crank it one more time.

 

[DCTFAN]

DCT engine, which can leave 1st gear engaged and with engine off, the clutches
are disengaged.

I have a driveway that slopes at 15 deg. and since I park the DCT head first into my garage
need to coast backwards out of the garage since there is no room to turn.

Done is many times, and in this maneuver the engine is not turned backwards a little,
it goes through several backwards revolutions.

Ask me how my cam tensioner is doing.

 

[Beemerphile]

Ask me how my cam tensioner is doing.

Apparently your cam chain tensioner is doing fine.. However, among other things, running the engine backwards runs the oil pump backwards. This sucks oil out of the oil galleries and backwards through the oil filter. It is a positive displacement pump that will pump in either direction. After running the engine backwards, at engine startup there is a period of time without oil on the bearings until the pump gets primed and the oil galleries are refilled. The engine will not likely go "bang" and blow up, but you could be robbing it of significant service life.

Moving an engine backwards a little bit to line up TDC is one thing. Running the engine through a significant number of revolutions backwards is, I think, a very bad idea. As far as moving the engine backwards to line up TDC, even that is unnecessary as the cam has a pretty broad base circle and a little bit off on TDC will not significantly affect valve lash.

Whether you have gotten away with it or not, moving an engine backwards is a practice that should be avoided.

 

[lootzyan]

Engine recoil or kickback did happen because of premature mixture ignition mostly because of wrong timing or self-ignition.
Who remember manual engine cranking and crank recoil? It's the thing of past and happened mostly with carbureted engines.
Even if this would happen, crankshaft would turn backward no more than a half turn and stop.

As of oil sucking out by pump turning backwards... This is open, one direction lubrication system, with many open holes. So turning backwards not much oil can be suck out.
Oil pressure is build between pump and filter. Every time filter is changed there is no initial oil pressure. Practically, by design, at engine start up after filter change, for short time engine runs without adequate oil pressure. So no worries here.

To adjust valves, service manual suggests turning crankshaft counterclockwise because this is correct sequence of engine strokes. But nowhere says that turning clockwise can damage anything. If yes, it could be considered as bad design.

To be efficient with servicing multi-cylinder engine, experienced mechanic is turning crankshaft in both direction depending from initial pistons positions. Besides, if T.D.C. mark is passed, usually there is no need to turn back more then 1/4 (90deg.) of turn. If you not sure, continue turning counterclockwise. No harm done.

 

[Beemerphile]

Oil pressure is build between pump and filter. Every time filter is changed there is no initial oil pressure. Practically, by design, at engine start up after filter change, for short time engine runs without adequate oil pressure. So no worries here.

An oil filter change happens maybe 20 times in the life of an engine. Smoking twenty cigarettes in your life will not hurt you either. This is different from sucking the oil out of the galleries and filter every time you start it. If this posed no problem, then oil filters for horizontal mounting would not need anti-drainback valves. What is the purpose and need of an anti-drainback valve if it is no problem for the filter to start empty every time? This does not even address running collected contaminants back through the oil pump.

To be efficient with servicing multi-cylinder engine, experienced mechanic is turning crankshaft in both direction depending from initial pistons positions.

I don't know how many experienced mechanics you have polled, or whether you consider yourself to be one, but I doubt this conclusion. Among the mechanics I have worked with, it is considered a standard or best practice to only turn the engine in the intended direction. Not much thought is given to what could happen, it is simply avoided.

 

[oldhack]

I have never heard of any damage coming from turning the engine backwards either, and turning a little bit to line up TDC is common practice even for experience mechanics. Unless you're making several full revolutions, don't worry about it.

 

[Beemerphile]

I have never heard of any damage coming from turning the engine backwards either, and turning a little bit to line up TDC is common practice even for experience mechanics. Unless you're making several full revolutions, don't worry about it.

It may be common practice, but unless the cam chain tensioner is of the ratcheting type (or non-automatic), moving the crank backwards doesn't even begin to move the cam until all of the cam chain slack has been moved to the other side. In other words, moving it backwards a little bit does not always move the cam - just the crank. You may feel better, but you have changed nothing. As I said before, a small miss on the TDC mark is of little impact to valve setting. However, if you are fastidious about it, your choices are to either turn it forward 720 degrees and try again, or, if you insist on being Professor Backwards, turn it backwards enough to again approach the TDC with the crank moving in the correct direction with all slack on the proper side. Only then are you assured that the relationship between the crank and the cam are correctly timed. On some engines, moving the crank backwards creates no issues. There seems to be some amount of folk wisdom that this is the case with the NC. On some the amount of slack chain where it isn't supposed to be can bind or cause the chain to skip a tooth on the sprocket. On some engines you risk loosening the harmonic dampener, flywheel, or alternator rotor. It can be said with certainty that turning it in the intended direction always works. The same can not be said on all engines for turning it backwards.

Every mention of turning the crankshaft in the service manual under valve adjustment instructs to turn it counterclockwise. What is the aversion to simply performing the service correctly?

 

[lootzyan]

An oil filter change happens maybe 20 times in the life of an engine. Smoking twenty cigarettes in your life will not hurt you either. This is different from sucking the oil out of the galleries and filter every time you start it. If this posed no problem, then oil filters for horizontal mounting would not need anti-drainback valves....

So, how many times in engine’s lifetime there would be a need to turn crankshaft backwards? Let's say the same number of times as a filter change. 20 x 2 turns with relative speed 2 RPM. (?!)
It's good you mention anti-drainback valve in the filter, which, according to FRAM: "...prevents oil from draining out of the filter (and not opposite, from channels). This anti-drainback valve is actually a rubber flap that covers the inside of the inlet holes of the filter...". So, galleries are protected, right? (Even if there would be a chance, mostly what would be sucked, 99% of it be air). How much oil you can suck out from filter to be worried? After couple of days of engine not running "...some oil may have drained from the filter in spite of the special valves...".(FRAM).
How many there did preventive measure before starting engine after 5 months of winter storage? Is there any instruction in owner manual?

...This is different from sucking the oil out of the galleries and filter every time you start it...

It's impossible to start engine backwards.

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...I don't know how many experienced mechanics you have polled, or whether you consider yourself to be one, but I doubt this conclusion. Among the mechanics I have worked with, it is considered a standard or best practice to only turn the engine in the intended direction. Not much thought is given to what could happen, it is simply avoided.

You like to patronize and judge people.
As for my experience and skills? After servicing over thousand of vehicles, couple of thousands of valve adjustments (8 per engine in average), even if this was almost 30 years ago, with little effort, one could find my satisfied customers. As for my knowledge - yes, I was mechanical engineer (and industrial electronics technician) who got his hands dirty in own tune-ups and diagnostics shop. You want to challenge me in this field? No, I have better things to do in my retirement time than disprove pseudo technical tales.
I trained couple of my guys myself, but never told them to avoid thinking.

 

[drstimpy]

Looking at the cam chain tensioner, it is hard to imagine how the chain going one way or the other could do any damage at all. The slide that contacts the chain is convex so there is nothing to hang up on.


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