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While trying to remove the main pulley from my timing belt, I place a screwdriver in the flywheel.

I failed to realize that the screwdriver had 'popped' out of place and proceed to crank the engine backwards ( counter clock wise ) 3- 4 revolutions.

This happened on a 2003 Subaru Outback ( Interference Engine ).

Is it possible I have done damage to my engine? How do I check?

  • 1
    Was this prior to removing the timing belt, or had the belt been removed? – Zaid Nov 22 '15 at 14:14
  • The old timing belt was still on when I did this. – Calvin Nov 22 '15 at 14:45
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As long as your timing belt was still attached you should be okay. When turning an engine in reverse, the only things it can damage are the oil pump and possibly the water pump. You'd have to do it QUITE a bit though, four revolutions shouldn't hurt it. The reason it CAN damage the engine is because you're forcing the internal mechanisms to run in the opposite direction they were engineered to turn. Like I said above though, you'd need to do it quite a bit. Many vehicles require you to actually rotate the engine backwards to install transmissions and valve-train components; Honda, Toyota, and Hyundai are perfect examples. I've worked on quite a few Subarus and I've had my timing and crank shaft slip backwards. I never had an issue.

The term "Interference" just means that when your camshaft and crankshaft timing are not cohesive, the piston will hit valves once it reaches it's TDC. As long as you had your timing belt on BEFORE you did this, you should should be fine. If not, rotate the engine VERY slowly with a breaker bar or long handled ratchet and wait to see if it catches anywhere. I worked on a Hyundai Tiburon and the person before me was off by a couple of teeth on the timing belt. It started, but sounded like a tin can full of marbles (The valves slapping the pistons!). I hope this helps you!

  • 2
    Just out of interest, how can the oil and water pump be damaged? – HandyHowie Nov 22 '15 at 15:11
  • Depending on how exactly the water pump works is what can determine if it can be damaged by counter rotation, but the oil pump's bearings and seals are not engineered to turn in reverse. Basically you're "Sucking" where you should be pumping and when something is engineered to do one thing when you make it do the opposite, you have negative consequences. The water pump system would most likely be damaged because of the bearing being rotated in a direction it isn't supposed to be. You could "Possibly" damage the system if reverse flow of coolant disrupts the laminar flow within the engine. – cloudnyn3 Nov 22 '15 at 15:19
  • Sorry if the above comment was vague, I'm limited to how much I can post =( – cloudnyn3 Nov 22 '15 at 15:22
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    Centrifugal pumps permit reverse-flow. Unless the water pump is a positive-displacement-type, I don't see how reverse flow would hurt it, especially at hand-cranking speeds. At such low RPM, I'd say that even the oil pump is unaffected. – Zaid Nov 22 '15 at 15:22
  • Yes -Zaid. Hence why I said he should be perfectly fine unless he counter rotated engine with the starter for 10 minutes haha That wasn't intended to sound snarky either, i was agreeing with you. – cloudnyn3 Nov 22 '15 at 15:24
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DO NOT TURN ENGINE BACKWARD! SHIT HAPPENS!

Just to share about my personal experience today.....I did an overhaul to a Honda K24A2 engine on a Acura TSX, replacing the timing chain tensioner and clutch. I and my friend were struggling to get the crank pulley off: my friend use a prybar to lock the flywheel side, while I try to loosen the crank bolt. My friend slipped a few times, inadvertently rotating the engine counter-clockwise, just a few times.

We finish up and put everything back together, and start the car. The car ran like shit, and threw an engine code of the VTC sensor (P1009). We thought it must be impossible that we messed up the timing, but we checked anyway, and the timing was off by like a few tooth. We believe when we turned the engine backward while undoing the crank bolt, the chain lost tension and skipped a teeth or two, and that was while the chain tensioner was on!

My take on this is, yes, the engine is engineered to be turning clockwise, that there is a tensioner for the timing belt/chain for it to turn clockwise. If it turn backward, for whatever reason, there is no tensioner for the timing belt/chain, and shit can happen.

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