Time to refresh and upgrade the M20. Looking for feedback on both.

[digger]

Rotate the engine without plugs it's much easier when you aren't fighting compression and hard spots will be legitimate uh oh

[r-mm]

Ive done a bunch but they’re all different. Porsche flat six timing set with dial indicator. MFI Alfa timing of injection pump needs coordinated with block and head events. Porsche flat four timing is done when case halves joined. Always something new to learn.

[zaq123]

It takes a good amount of force to bend the valves when turning an engine by hand, actually, one would almost need a breaker bar or long handle ratchet.

and yet so many posts about bent valves on reassemblies.....people think they are fighting valve spring pressure .....while they are bending valves.

My advice is if one is not 100% sure what one is doing, do not spin the crank and cam independently. BMW should have done it fool proof with a possibility to lock cam and crank in place for TB job...like vw did on their diesels.

[ForcedFirebird]

You are doing this for a living, not sure how many of this OP did...my guess is none judging by his question. Just would hate to see another “did I bent my valves” post


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Actually learnt the trick on my 78 Datsun truck 4cyl back when I started wrenching as a hobby in the early 90's, but it works on any inline config.


It takes a good amount of force to bend the valves when turning an engine by hand, actually, one would almost need a breaker bar or long handle ratchet.

[zaq123]

I do that all the time :P


If you rotate the crank 20° past TDC, then all the pistons are down far enough that none can possibly hit the pistons. When doing a cam seal while doing a timing belt job, I always rotate the crank to avoid any possible problems.

You are doing this for a living, not sure how many of this OP did...my guess is none judging by his question. Just would hate to see another “did I bent my valves” post


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[ForcedFirebird]

Make sure you are setting this before the head is installed. Don’t rotate cam/crank independently


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I do that all the time :P


If you rotate the crank 20° past TDC, then all the pistons are down far enough that none can possibly hit the pistons. When doing a cam seal while doing a timing belt job, I always rotate the crank to avoid any possible problems.

[zaq123]

No, set the head to tdc and the crank to tdc and install belt. Rotate 1 crank rev and the head is 180 "out" rotate another crank rev and it's back inline at the head.

Make sure you are setting this before the head is installed. Don’t rotate cam/crank independently


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[digger]

Yes the lines match up every second rev

[r-mm]

Time to refresh and upgrade the M20. Looking for feedback on both.

I believe we are saying the same thing two ways. The crank shows TDC twice at the vibration damper for every one time the cam shows TDC. I am confirming that there is not a single correct crank to cam TDC relationship and that either pair works the same provided the marks line up.

[digger]

No, set the head to tdc and the crank to tdc and install belt. Rotate 1 crank rev and the head is 180 "out" rotate another crank rev and it's back inline at the head.

[r-mm]

Thanks I found that I needed to loosen the slack on the water pump in order to get the tensioner fully slacked I also found that I needed to advance the cam gear slightly in order to get the belt to seat but then once tension was applied the marks lined up perfectly through several revolutions.

Does it matter which TDC you time the motor to?

In other words - The cam sprocket completes one revolution (and points to its marker) for every two revolutions of the crank. Does it matter which revolution of the crank you use?


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[digger]

Does anyone have a description of how hard it should be to slip the timing belt over the tensioner (which i understand is the final thing its slipped over)? Like, all the strength in your arms and it barely makes it? Or walk in the park?

Other thing im struggling with is how much slack is there bt intermed sprocket and cam sprocket? Muscle the hell out of it to go one tooth further and get it hella taut or take her easy, decent amt of slack.


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lock the tensioner in place fully retracted, the the last thing is to slide over the cam gear so start at crank then pull tension on it over the tensioner then start on the RHS of the cam gear. to get it over the cam gear just get it started but only on a few mm of the edge. once you have a few mm of the entire cam gear then sliding it back fully is easy. then release the tensioner so the spring tensions the belt

[digger]

no those oil holes are nolonger important when the shaft is installed as they are isolated

[r-mm]

Does anyone have a description of how hard it should be to slip the timing belt over the tensioner (which i understand is the final thing its slipped over)? Like, all the strength in your arms and it barely makes it? Or walk in the park?

Other thing im struggling with is how much slack is there bt intermed sprocket and cam sprocket? Muscle the hell out of it to go one tooth further and get it hella taut or take her easy, decent amt of slack.


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[r-mm]

Is there an intended relationship between the head bolts washers and what I presume are oiling holes? To a limited degree there is some ability to bias the washers one way or the other