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Discussion and questions related to the course How to Degree a Cam
Question but with the stop in place you are rotating the engine both directions to find where it impacts the stop. I was always told to only rotate the engine in it's direction or rotation. Is this true or is in generally safe to rotate the engine in its counter direction from whichever way it normally rotates under normal operating conditions?
In my experience you can turn it both ways, but when you are taking measurements on the valvetrain you should turn it only in the direction of rotation as you will have some slack in the timing belt / chain / tensionner and that will mess your data.
Some engine DO NOT respond well to being rotated backwards, mostly due to tensioners screwing up and the belt/chain skipping teeth when the tension on the belt on the driven side is removed, so while most should be fine it's worth checking first.
If you do rotate it backwards (I have done it on on engines with manually locked tensioners, but still checked first), make sure you go a bit too far and rotate the engine in normal direction to come up to the BTDC point - as Francis pointed out, there can otherwise be problems with the chain/belt tension loading things the wrong way.
If in ANY doubt, just keep rotating it the correct way - it also makes sure everything is as it should be and if there is any sudden resistance, STOP! There will be a variation in the torque required to turn the engine, but it should increase and decrease relatively gradually - a sudden stop means 99.99% of the time that something is wrong, usually incorrect cam'(s) timing, but sometimes if one hasn't checked V2P clearances properly, or even just assumed because one was told that there was no problems one didn't even do that, there could be a problem there.
Don't forget, when you think it's right and you've locked it down, to give the engine several turns by hand and to recheck it.