DIY How To: M20 Valve Adjustment

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DIY How To: M20 Valve Adjustment

Postby Dontrusthise30 » Tue Aug 27, 2013 4:38 pm

Ok folks, a while back I said I would do this so now I am. Everything here is being done on a cold 1989 m20b25. Adjusting the valve clearance is a simple task that is well within the capability of any person familiar with turning a wrench. So lets begin! First off, for purposes of those who know how to do it already, and perhaps just need clearance and torque specs- here they are:

Order of adjustment: 1-5-3-6-2-4
Clearance with coolant above 176*F: 0.30mm (0.012in)
Clearance with coolant below 95*F: 0.25mm (0.010in)
Adjustment nut torque: 10NM or about 7 ftlbs

OKay, now for anyone else!

Tools needed:
10mm deep socket and ratchet
10mm closed end wrench
allen wrench
feeler gauge meeting the requirements of clearance (just buy a full set)
Flathead screwdriver

*Reminder- you may need to replace the valve cover gasket depending on how old it is. Best to just do it anyways*

1. Remove the valve cover. Remove the eight nuts (10mm) from around the valve cover as well as the four bolts that connect the cover to the intake manifold. Disconnect the valve cover vent hose (one hose clamp). Remove the valve cover.

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2. Take your 1/2" ratchet with 22mm socket and slip it onto the crank bolt. Rotate the engine clockwise until the No.1 cylinder's camshaft lobes are pointed downward. If desired, or being changed at the same time, taking the spark plugs out make rotating the engine much easier. When the lobes on cylinder No.1 are pointed down, the valves will be fully closed and can now be adjusted.

3. Take your feeler gauge and slide it between the rocker eccentric and the top of the valve. there should be slight tension on the feeler gauge. If you are unable to slide it between them or it has no tension, you will need to adjust.

Image

4. Using your closed end 10mm wrench and your allen wrench, loosen the nut on the rocker until you are able to rotate the eccentric. With the feeler gauge in place, rotate the eccentric until is has proper tension on the gauge. Set the screw and repeat for the other valve on cylinder No.1.

Image

5. Using the order of Cylinders: 1-5-3-6-2-4, watch cylinder No.5 next and rotate the crankshaft roughly 1/3 turn clockwise or until the cam lobes on No.5 are pointed roughly down. Repeat steps 3 and 4 until all cylinders have been adjusted.

*Don't forget to remove the ratchet from the crankshaft bolt!!*

6. Install your valve cover gasket, valve cover, and bracket to intake manifold. Drive!
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Re: DIY How To: M20 Valve Adjustment

Postby M20_fever » Wed Aug 28, 2013 3:34 am

Another great addition to our sticky collection, well done!
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Re: DIY How To: M20 Valve Adjustment

Postby 87e30 » Thu Aug 29, 2013 8:33 pm

I'm doing mine next weekend. This is almost word for word the same as the DIY I printed out a few weeks ago, don't remember where I got it though, and it's not in front of me. lol, good post.
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Re: DIY How To: M20 Valve Adjustment

Postby Dontrusthise30 » Thu Aug 29, 2013 9:30 pm

I used the Bentley manual as my source for the specs and steps. It's basically an abbreviated version. Looking back I wish I took a few more photos.
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Re: DIY How To: M20 Valve Adjustment

Postby 87e30 » Thu Aug 29, 2013 10:25 pm

Whoever posted the other DIY prolly did the same as you. Good to see it here so I can check back if I need help doing mine. I got a unrelated question for you... How the hell did you get the engine looking so clean? You could eat out of there! When I pull off my oil cap it looks like Hershey syrup sludge inside.
Schwarz 5-speed 87 325is (newest project)
Arktisblau 5-speed 86 325e (current DD)
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Re: DIY How To: M20 Valve Adjustment

Postby Dontrusthise30 » Thu Aug 29, 2013 11:42 pm

Haha, it's brand new. I just installed that engine 2 days ago and got it running. That head hadn't had oil through it yet.
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Re: DIY How To: M20 Valve Adjustment

Postby 87e30 » Fri Aug 30, 2013 12:14 pm

That makes me sad for 2 reasons. 1, I thought you were gonna give me a HA-UGE engine cleaning tip, and 2, I want a new engine too! lol
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Re: DIY How To: M20 Valve Adjustment

Postby e21jps » Sun Sep 08, 2013 2:12 am

Here is a really usefull tip!
if the head is not new the method described can often still result in the wrong clearance, this is because the eccentric usually wears a little hollow in the tip of the valve stem, the feeler gauge bridges this hollow and holds the eccentric above it so you end up with a much bigger clearance that you think and the engine still ticks :cry:

So a better way is to put the feeler gauge between the cam and the follower BUT!!!! you must then account for the rocker ratio and the setting should be only 007" or 0.16mm

This will work every time no matter how worn the eccentrics are and you should have a nice quiet engine again 8)
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Re: DIY How To: M20 Valve Adjustment

Postby Yoshi » Sun Sep 08, 2013 11:36 am

That explains why I got such better results when I went a smidge tighter on all of my valve adjustments.
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Re: DIY How To: M20 Valve Adjustment

Postby Dontrusthise30 » Sun Sep 08, 2013 12:07 pm

Very good input there!
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Re: DIY How To: M20 Valve Adjustment

Postby Ryki » Sun Sep 08, 2013 2:19 pm

Two posts and I already appreciate this guy! I like the write up! This will do me well as I'm helping someone pull their M20 and trans to replace the trans and clutch and redo the lifters in exchange for a M42 chip, M20 chip and some help with my trans swap :P Thanks for putting this together!
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Re: DIY How To: M20 Valve Adjustment

Postby ponycarman » Sun Sep 08, 2013 2:57 pm

That is very interesting and helpful. I'll have to remember that next time I adjust mine. How often does the clearance need adjusting?
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Re: DIY How To: M20 Valve Adjustment

Postby M20_fever » Mon Sep 09, 2013 3:23 am

One of the reasons I replace the eccentrics every couple years. On my original m20 in my current e30 the eccentrics were so worn they simply wouldn't adjust to spec.
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Re: DIY How To: M20 Valve Adjustment

Postby Aussie 325i » Thu Sep 12, 2013 6:27 am

Has anyone seen or have a write-up for eccentric replacement? To my mind it should be simple, and i have one definitely to do so was considering replacing them all
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Re: DIY How To: M20 Valve Adjustment

Postby Dontrusthise30 » Thu Sep 12, 2013 9:50 am

Rather than just loosening the nut, remove it. Slide the bolt out and replace it. It's as simple as you think it is.

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