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Thread: M20 Head swap questions

  1. #1
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    M20 Head swap questions

    Hey Guys,


    So I picked up a new(ish) M20 head, rebuilt and machined, for a stupid cheap price with new gaskets and bolts. I was just curious what all I need to do the swap and what I should look out for, I am planning to do it this Saturday and Sunday.

    Would it be good to just follow a head gasket replacement write up? Seems to be the same for the most part.

    Here are the parts I have:

    1x refreshed head
    1x head gasket set(head gasket, valve cover gasket, intake mani gasket, exhaust gasket, random o-rings, etc)
    1x head bolt set
    1x water pump gasket(I just did my timing belt and tensioner and fucked up the gasket, so going to be re-doing it.)
    1x thermostat
    1x thermostat bleeder valve bolt(mine is stripped to hell for some reason)

    I should have all the correct tools, I plan to buy a new torx bit for the head bolts because I just dont trust mine, would rather not strip it.

    Any advice is greatly appreciated, can't afford to have a shop do it so I'm gonna tackle this myself.

    Just a note,
    I've already replaced a ton of stuff, timing belt, tensioner, cap, rotor, fuel regulator, icv, spark plug wires, spark plugs, a bunch of other stuff I'm forgetting)

    Thanks in advance!
    Last edited by GamersCreations; 10-11-2017 at 12:51 AM.

  2. #2
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    same procedure as a head gasket. assuming it's for the 87 325i , make sure the head is for an m20b25 - 885 casting. i always replace the timing belt when doing a head swap / gasket as a precaution no matter when it was last done. good to have a bentley around to follow when doing this, and there are piles of forum write-ups that are excellent. decent wikizone article on it : http://www.e30zone.net/e30zonewiki/i..._Gasket_Change

    do you have a reason for replacing the head ?

  3. #3
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    Quote Originally Posted by 82eye View Post
    same procedure as a head gasket. assuming it's for the 87 325i , make sure the head is for an m20b25 - 885 casting. i always replace the timing belt when doing a head swap / gasket as a precaution no matter when it was last done. good to have a bentley around to follow when doing this, and there are piles of forum write-ups that are excellent. decent wikizone article on it : http://www.e30zone.net/e30zonewiki/i..._Gasket_Change

    do you have a reason for replacing the head ?
    I will double check it's the correct head thanks for that!

    I replaced the timing belt/tensioner literally like a week and a half ago with all brand new parts, do you really think it's necessary to replace it again?

    The real reason why I'm replacing it is a really nasty lifter tick, I've tried adjusting the valves and new oil, with no resolve(I got this head+the bolts+the gaskets for $70 bucks, rebuilt and machined by a shop, no sense in leaving it to rot), it also gives me a good excuse to replace all the gaskets in between and clean up the parts. I am also replacing the injector o-rings and cleaning them up as well while I've got the intake mani off. I do have a bentley repair manual that I will be following, I just wasn't sure if it was a good idea to follow the head gasket replacement write ups, or if there was an actual head swap write up somewhere, I have only been able to find them for different heads(m30 onto something else, etc)

    Thanks a ton for the reply.
    Last edited by GamersCreations; 10-11-2017 at 01:51 PM.

  4. #4
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    its super easy. just follow head gasket steps. you can do it on Saturday and be driving sunday, easily
    Still in the game

  5. #5
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    Quote Originally Posted by superj View Post
    its super easy. just follow head gasket steps. you can do it on Saturday and be driving sunday, easily
    Thanks! I needed someone to give me a bit more confidence, big project. XD XD

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    Quote Originally Posted by GamersCreations View Post
    I replaced the timing belt/tensioner literally like a week and a half ago with all brand new parts, do you really think it's necessary to replace it again?
    depends a lot on brand and belt quality. if a head is newly machined i replace it no matter what. belts conform a bit to the components they are installed with. it's cheap insurance. i've switched up to gates blue belts recently as quality has fallen on conti and other brands recently imo.

    Quote Originally Posted by GamersCreations View Post
    The real reason why I'm replacing it is a really nasty lifter tick, I've tried adjusting the valves and new oil, with no resolve
    m20's normally sound like a sewing machine even when in spec. just be aware of that. once the head is off clean up the piston tops and check for valves touching the piston head. inspect and deburr any edges where contact may have occurred to reduce hot spots that can weaken the piston.

    a compression check and leakdown prior to pulling the head could identify any weak or bent valves before starting on the swap.

    finally - save your old head. original casting bmw m20 heads are becoming rare and are far superior to the terrible aftermarket castings that have infiltrated the market recently.
    Last edited by 82eye; 10-12-2017 at 10:25 AM.

  7. #7
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    Quote Originally Posted by 82eye View Post
    depends a lot on brand and belt quality. if a head is newly machined i replace it no matter what. belts conform a bit to the components they are installed with. it's cheap insurance. i've switched up to gates blue belts recently as quality has fallen on conti and other brands recently imo.



    m20's normally sound like a sewing machine even when in spec. just be aware of that. once the head is off clean up the piston tops and check for valves touching the piston head. inspect and deburr any edges where contact may have occurred to reduce hot spots that can weaken the piston.

    a compression check and leakdown prior to pulling the head could identify any weak or bent valves before starting on the swap.

    finally - save your old head. original casting bmw m20 heads are becoming rare and are far superior to the terrible aftermarket castings that have infiltrated the market recently.
    Thanks for all the advise I really appreciate it! I have verified it is the correct head using a post I found on here to find all the random numbers on the intake/exhaust side to be sure XD, I will order a new timing belt, like you said I suppose it is worth the assurance. When cleaning the top of the block, you're not supposed to touch the cyl walls right? put the piston up to the top of the chamber then clean it? Sorry if that is a silly question I just do not want to do something stupid.

    I had the engine compression/leakdown tested when I first got it and at the time it was fine, that was only about three months ago so I'm sure it will be fine.

    I will be keeping my old head as I would like to get more into building engines, and this head wasn't in awful shape to begin with so I am going to start there and maybe find a cheap block somewhere like I did with this head.

    Trust me, I know swapping the head is a lot of work for probably no gain aside from clean parts, but its a good project for me to learn and stuff. I do appreciate all the advise so far.

  8. #8
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    get someone to help you lift the head onto the block its heavy when you stretch your arms out. spray the shit out of exhaust manifold nuts with some shit to help them break free.

    you know you are supposed to replace the timing belt again right? also check the vee belts out they might be shagged if they haven't been checked
    Last edited by digger; 10-13-2017 at 04:21 AM.

  9. #9
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    Definitely replace the timing belt again. Tensioner can be reused.
    Make sure the intake manifold gaskets are the correct ones. The 'e' and 'i' ones are not interchangeable. Just compare them with the ports on the new head to make sure the port sizes match.
    Intake manifold to cylinder head nuts torque values are 16-18 lb-ft/22-24 Nm. At least my edition of the Bentley manual has that value wrong.
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    Quote Originally Posted by digger View Post
    get someone to help you lift the head onto the block its heavy when you stretch your arms out. spray the shit out of exhaust manifold nuts with some shit to help them break free.

    you know you are supposed to replace the timing belt again right? also check the vee belts out they might be shagged if they haven't been checked

    I will have someone there to help, no plans of attempting to lift that thing out of the bay myself . I do plan to replace the timing belt, again, even though this one went on 2 weeks ago and hasn't been driven on really ;P. The only Vee belt I have, is the alternator, and it was also just replaced. No ps or ac.

    - - - Updated - - -

    Quote Originally Posted by richardodn View Post
    Definitely replace the timing belt again. Tensioner can be reused.
    Make sure the intake manifold gaskets are the correct ones. The 'e' and 'i' ones are not interchangeable. Just compare them with the ports on the new head to make sure the port sizes match.
    Intake manifold to cylinder head nuts torque values are 16-18 lb-ft/22-24 Nm. At least my edition of the Bentley manual has that value wrong.
    Thanks for the info!

  11. #11
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    Quote Originally Posted by richardodn View Post
    Make sure the intake manifold gaskets are the correct ones. The 'e' and 'i' ones are not interchangeable. Just compare them with the ports on the new head to make sure the port sizes match.
    Just going to add that m20b23 (731 head) and m20b25 (885 head) intake gaskets aren't supposed to be interchangeable either.

    You also might want new exhaust manifold studs and nuts as well as gaskets and hardware for the downpipe-to-exhaust-manifold connections (and possibly penetrating oil and/or a blowtorch and/or an impact driver and/or a lot of curse words).
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  12. #12
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    Quote Originally Posted by hotdish View Post
    Just going to add that m20b23 (731 head) and m20b25 (885 head) intake gaskets aren't supposed to be interchangeable either.

    You also might want new exhaust manifold studs and nuts as well as gaskets and hardware for the downpipe-to-exhaust-manifold connections (and possibly penetrating oil and/or a blowtorch and/or an impact driver and/or a lot of curse words).
    It was the correct head(m20b25 on my 325i, or 885 head like you said.) All the gaskets were correct and the head had 100% replaced studs(It was completely rebuilt all around)


    HOWEVER, some issues came up with my car needing a catalytic converter, I wasn't expecting to need to pass smog as I had a car that was the same year be exempt, unfortunately this one is not? Lol oh well. Long story short I sold the head, had my exhaust worked on and added a cat. Maybe refresh the head some other time XD

    Either way thanks for the advice everyone!

  13. #13
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    dude, that sucks about having to pass smog and selling the head
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