Can rotating an engine backwards by hand damage the timing?
Discussion
Whilst replacing a clutch and dual mass flywheel on my daughters BMW 118D (N47 engine) I inadvertently turned the prop at least a single rotation when the car was still in gear - this will have turned the engine backwards.
After finishing the job, the engine is very rough and it drives as if it’s got a bad misfire.
I checked all the normal stuff and even went as far as disconnecting each injector to try and isolate the issue, to no avail.
How likely is it that by turning the engine backwards, I have caused the timing to skip a tooth or two?
After finishing the job, the engine is very rough and it drives as if it’s got a bad misfire.
I checked all the normal stuff and even went as far as disconnecting each injector to try and isolate the issue, to no avail.
How likely is it that by turning the engine backwards, I have caused the timing to skip a tooth or two?
The 2.2 litre TDCi engine as used by Jaguar in the Ford era cars can be damaged by trying to start in gear by accident whilst the clutch pedal was up. If I recall, it had a long and a short run in the timing chain and with no hydraulic pressure to actuate the tensioners there was sufficient slack in the longer run that when the starter stalled against the mass of the car trying to lurch forwards, it whipped backwards and popped the chain over a tooth or two. Don't quote me with regard to all engines, but on this one engines were not unknown to be wrecked.
Yes its possible. Renault trafics have s
t handbrakes so lots of people leave them in gear.
Unfortunately they also have st timing chains, so if they get parked on a hill then the timing can slip. Mechanic friend looks clairvoyant when he gets one in for slipped timing and says let me guess, the handbrake doesn't work either?
t handbrakes so lots of people leave them in gear.Unfortunately they also have s
t timing chains, so if they get parked on a hill then the timing can slip. Mechanic friend looks clairvoyant when he gets one in for slipped timing and says let me guess, the handbrake doesn't work either?Well good news and a surprising result. Thought I'd post it in case it helps someone.
Whilst doing the clutch, I noticed the gearbox bushes were broken. It was a Sunday and nowhere to get them. I had some nylon lying around and made them into 2 new bushes with a steel insert. I made sure the steel insert was *much* shorter than the bush so there was no metal contact.
It turned out that these caused the whole issue. They literally made the car feel like it was going to explode and the engine sound and feel like is was missing.
Facing the prospect of having to remove the DMF and clutch again or even worse, remove the engine and redo the timing, I thought I would remove the bushes and try with the old broken ones. Sure enough the car was back to normal.
Totally shocked at how bad the vibrations were with more solid bushes.
Old broken ones on the right - homemade ones on the left
New bushes in situ.
Whilst doing the clutch, I noticed the gearbox bushes were broken. It was a Sunday and nowhere to get them. I had some nylon lying around and made them into 2 new bushes with a steel insert. I made sure the steel insert was *much* shorter than the bush so there was no metal contact.
It turned out that these caused the whole issue. They literally made the car feel like it was going to explode and the engine sound and feel like is was missing.
Facing the prospect of having to remove the DMF and clutch again or even worse, remove the engine and redo the timing, I thought I would remove the bushes and try with the old broken ones. Sure enough the car was back to normal.
Totally shocked at how bad the vibrations were with more solid bushes.
Old broken ones on the right - homemade ones on the left
New bushes in situ.
tux850 said:
Thanks for posting back but, jeez, you thought it worth mentioning the crank being turned backwards but not the homemade bushes?!
I know it sounds stupid, but it was so bad, we scratched our heads for ages thinking it must be flywheel fitted incorrectly or bad timing. The car shook, violently, even at idle on the ramp. Didn't even think that those gearbox bushes could cause that.GreenV8S said:
cashmax said:
Didn't even think that those gearbox bushes could cause that.
Presumably you haven't thought about what the purpose of the bushings is, then.cashmax said:
<snip>
The car shook, violently, even at idle on the ramp. Didn't even think that those gearbox bushes could cause that.
You might have got away with it with the silky smooth 6 cylinder, but surely not the 4 cyliner diesel which I guess vibrates like a small earth tremor...The car shook, violently, even at idle on the ramp. Didn't even think that those gearbox bushes could cause that.
Useful post OP, I wouldn’t worry about the wealth of posters who would obviously have looked at that first 
You may have saved someone a lot of expense in time when they google this.
Incidentally, and to address another post about the 4 cyl / 6 cyl suggestion, I have a pretty extensively modified 6 cylinder petrol BMW, over the years it’s undergone all kinds and has polybush engine mounts, spherical suspension arm bushings, pretty harsh track focussed spherical top mount bearings however none of that was as much of a marked difference as changing those 2 very similar gearbox bushings to polybush items from PowerFlex. An astounding amount of NVH.
Glad you worked it out.
You may have saved someone a lot of expense in time when they google this.
Incidentally, and to address another post about the 4 cyl / 6 cyl suggestion, I have a pretty extensively modified 6 cylinder petrol BMW, over the years it’s undergone all kinds and has polybush engine mounts, spherical suspension arm bushings, pretty harsh track focussed spherical top mount bearings however none of that was as much of a marked difference as changing those 2 very similar gearbox bushings to polybush items from PowerFlex. An astounding amount of NVH.
Glad you worked it out.
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