How bad is this for your car?
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- First Gear
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How bad is this for your car?
I've read several times that spinning your crankshaft backwards is a big no-no. For example if someone is doing a timing belt job and they are trying to align the crankshaft marks and accidentally turn the crank counter-clockwise for a few revolutions instead of clockwise. Is this really bad? What symptoms might come of this, or how would it effect the engine? To me personally, it doesn't seem that it would be a horrible thing, but I don't know. Any input is appreciated.
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- Fifth Gear
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I've always wondered this as well. See when I have done timing belt jobs I've often accidently moved it a bit past the mark and then just moved it counterclockwise a little bit to get it lined up instead of moving it two more rotations clockwise.
Exactly why is it bad to turn it backwards?
Exactly why is it bad to turn it backwards?
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It's supposedly bad to turn the crank backwards because it put's the slack in the timing belt opposite the tensioner, increasing the chance of a skipped tooth.
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'94 FWD and '95 AWD Laguna Blue SVXs.
2017 Pure Red BRZ Limited w/Performance pack
It only applies after the belt is on. If you make sure the belt doesn't skip, then there is no harm in rotating the crank backwards.
The cam lobes provide quite a bit of resistance when you turn them. This is what will place a lot of tension on the belt. Because of the way the belt works the tensioner is almost always placed right before the belt 'returns' to the crank sprocket. This is the point that slack naturally accumulates, so is the best place for the take-up to occur.
If you rotate the engine backwards, the 'natural slack' now developes on the other side of the crank sprocket. In fact, the tension caused by pulling the cams will want to compress the tensioner more then normal causing even more slack to develop on the 'wrong' side. If enough slack occurs, the belt can jump.
The cam lobes provide quite a bit of resistance when you turn them. This is what will place a lot of tension on the belt. Because of the way the belt works the tensioner is almost always placed right before the belt 'returns' to the crank sprocket. This is the point that slack naturally accumulates, so is the best place for the take-up to occur.
If you rotate the engine backwards, the 'natural slack' now developes on the other side of the crank sprocket. In fact, the tension caused by pulling the cams will want to compress the tensioner more then normal causing even more slack to develop on the 'wrong' side. If enough slack occurs, the belt can jump.
'93 Winestone SS Auto, '91 Pearl White SS.
'93 Pure White SS EJ20G slanty intercooled, SIDESWIPED! In stasis.
'94 FWD and '95 AWD Laguna Blue SVXs.
2017 Pure Red BRZ Limited w/Performance pack
'93 Pure White SS EJ20G slanty intercooled, SIDESWIPED! In stasis.
'94 FWD and '95 AWD Laguna Blue SVXs.
2017 Pure Red BRZ Limited w/Performance pack
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- Third Gear
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AFAIK, there's no reason at all you can't turn the crank counter-clockwise. The rings and bearings don't care, especially if you're turning the engine by hand at 10 RPMs or so. I guess there may be a chance the t-belt could skip a tooth if you went too fast, but even that wouldn't hurt anything...you just gotta re-set the belt.
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- First Gear
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OK yeah, I thaught so. It only applies if the belt is ON the vehicle. If the belt is off the vehicle you can rotate whatever you want in whatever direction you want without causing any harm, I believe (as long as everything is lined back up properly when installing the belt).
Last edited by codfizzle on Sun Dec 07, 2008 5:08 pm, edited 1 time in total.
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- Fifth Gear
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This is assuming you are working on a non intereference motor, correct? I have an EJ20H DOHC motor and I thought that if you turned the crank independently from the cams it will bend your valves.codfizzle wrote:OK yeah, I thaught so. It only applies if the belt is ON the vehicle. If the belt is off the vehicle you can rotate whatever you want in whatever direction you want without causing any harm, I believe.
98 Metro Hatch Daily Driver :)
91 SS EJ20G Engine/Tranny/Diff Swap Build Thread Here
"Your testes are close to your bottom but you still play with them all the time." Jeremy Clarkson
91 SS EJ20G Engine/Tranny/Diff Swap Build Thread Here
"Your testes are close to your bottom but you still play with them all the time." Jeremy Clarkson
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- Fifth Gear
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And the newer '97+ EJ22/'99+ EJ25 SOHC are interference, too.
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(Yes, I know this is an old-school forum.)
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