I learned today that it's possibly a bad idea to rotate an engine backwards

[Nayov]

I replaced the accessory belts (all 3, old style not serp) on a 93 Sentra with 352,000 miles. I cheated a bit by walking the belts on, but yes, after loosening the adjusters. what I mean is I turned the crank pulley back and forth to force the belts on so at some point it (engine) went backwards for a bit. I started it up after all was said and done only to be greeted by a disconcerting start up rattle which lasted a few seconds. also, under the valve cover it sounded like loose marbles banging around which lasted about a minute. All noises went away and it drives fine...not too worried about potential damage.

So I guess some hydraulic thing having something to do with the timing chain possibly drained oil and lost tension until op built up. Not sure if that makes sense but it's all I have. All original TC components.

 

[Leo99]

As long as the noises went away... and they don't come back. Good luck. Hate for your PM to be what killed it with that many miles on it.

 

[Astro14]

That’s exactly what happened…

The timing chain tensioner is usually on the return (non tension) side of the chain between cam(s) and crank, and when you rotated the engine backwards, you put tension on that side, enough to collapse the tensioner, and leave the chain slack.

A few minutes of running, and it re-tensioned the chain.

 

[slacktide_bitog]

WOW a 93 Sentra still used old belts? and you have three belts?

 

[D60]

Turn something like a Ford 3V or 3.5 backwards more than a few degrees and you risk jumping time, but a little bit certainly does create some nice slack at the correct times to get everything reassembled with ease

 

[Tomioka]

WOW a 93 Sentra still used old belts? and you have three belts?

This guy has the fancy pants air conditioning option. When I had a 92 Sentra I didn’t have A/C or an automatic with overdrive.

 

[Carburetor1]

Turn something like a Ford 3V or 3.5 backwards more than a few degrees and you risk jumping time, but a little bit certainly does create some nice slack at the correct times to get everything reassembled with ease

How would it jump time

 

[Number_35]

WOW a 93 Sentra still used old belts? and you have three belts?

Same with our late great '97 Mazda MPV - as I recall, AC and PS each had separate belts, and alternator and WP shared a belt.

There was also the timing belt under a plastic cover.

 

[mfewtrail]

WOW a 93 Sentra still used old belts? and you have three belts?

Nissan was using multiple belts at least until 2008(or maybe later on some models).

 

[Astro14]

How would it jump time

Slack in the chain, created by rotating the crank the wrong way (see above, puts more pressure on the tensioner, collapses it). Resistance from the cams holding the cam sprockets in place, and you rotating the crank, I could see jumping a tooth...

 

[Cdn17Sport6MT]

Alfa 164's had it so bad that if you parked in gear, uphill, slack in the timing belt would occur and a disaster ensued. Those folks that fit lighter flywheels quickly learned that engine shut-off and compression kickback would do the same. The heavier stock flywheel would have just enough angular momentum to avert this.

 

[paulo57509]

The timing belt installation procedure for the Lexus states:

18. CHECK VALVE TIMING
(a) Temporarily install crankshaft bolt.
(b) Slowly turn crankshaft pulley 2 revolutions from TCC to TDC.
"NOTICE: Always turn the crankshaft pulley clockwise."
(c) Check that each pulley aligns with the timing marks as shown in the illustration.

I don't know why it would matter; the belt is equidistant around the pulleys and the tensioner pulley takes up slack CC or CCW. The only thing I can think of is the VVTi cam sprockets rotated CCW can mis-time the intake valves causing piston interference.

I just don't manually rotate the engine CCW.

 

[Jetronic]

The timing belt installation procedure for the Lexus states:

18. CHECK VALVE TIMING
(a) Temporarily install crankshaft bolt.
(b) Slowly turn crankshaft pulley 2 revolutions from TCC to TDC.
"NOTICE: Always turn the crankshaft pulley clockwise."
(c) Check that each pulley aligns with the timing marks as shown in the illustration.

I don't know why it would matter; the belt is equidistant around the pulleys and the tensioner pulley takes up slack CC or CCW. The only thing I can think of is the VVTi cam sprockets rotated CCW can mis-time the intake valves causing piston interference.

View attachment 108448

I just don't manually rotate the engine CCW.

You can also remove all oil from the oil pump if you turn an engine backwards long enough. Maybe it primes again, maybe not. Wiggling a few degrees to get some slack is fine, but wouldn't do more than that.

 

[paulo57509]

Back in the day, I was told to never leave a Mopar crankcase empty for longer than it takes to drain and refill it. The claim was the pumps could drain and loose prime.

 

[clinebarger]

Back in the day, I was told to never leave a Mopar crankcase empty for longer than it takes to drain and refill it. The claim was the pumps could drain and loose prime.

How does that explain all the times I've taken off oil pump pickup tubes without issue.....If the oil pump doesn't have the ability to suck oil out of the sump, Something is wrong with the pump.

Ran Buick 455's for years & know all about "Loosing prime" which is slang for the oil pump is worn out, I would disassemble the pump & pack it full of Lubriplate to get me to work.

 

[Bailes1992]

How does that explain all the times I've taken off oil pump pickup tubes without issue.....If the oil pump doesn't have the ability to suck oil out of the sump, Something is wrong with the pump.

Ran Buick 455's for years & know all about "Loosing prime" which is slang for the oil pump is worn out, I would disassemble the pump & pack it full of Lubriplate to get me to work.

I have no idea about the engines you're talking about but I know this is an issue with the 3.2 litre 5 cylinder Ford diesel engine, so much so they released a TSB about it saying that the engine must be drained and refilled within 10 minutes or you may have a pump that cannot prime itself.

 

[2EHA]

I have no idea about the engines you're talking about

you may be familiar with the buick oil pump from the rover v8

 

[Asterix]

It completely depends on the engine. My 1988 Toyota 7M can be turned backwards just fine. In fact, the service manual says to do just that before removing the distributor. This engine has a timing belt.

 

[Carburetor1]

If you hold the gas pedal down when you turn the key it will prime the oil pressure up then let your foot off pedal and it will start. For Ford's anyway. My question is will it change the timing if the 5.4 3v is turned backwards while changing crankshaft pulley? Or will it only change timing if the chain jumps?

 

[clinebarger]

Assuming you're using an Impact to loosen the Balancer Bolt......There's no reason to turn the engine backward (Counterclockwise) while changing the Balancer/Crank Pulley.