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Thread: DIY valve lapping/valve seat grinding? has anyone done it themselves?

  1. #1
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    DIY valve lapping/valve seat grinding? has anyone done it themselves?

    I am in the process of building a fresh s52 for an e30 swap. I have the head from an M52 I have lying around (I will install s52 springs seats and cams)

    I will have it decked, checked for flatness, checked for cracks and vac/pressure tested and I am wondering if its crazy to think I can do the valve seat grinding and lapping myself + install new valve stem seals.

    2 reasons - I want to save on shop work and I really enjoy doing as much of it myself as I can... it's my first engine build


    It seems easy enough... take everything apart, label the valves, get a kit that has a suction cup drill bit attachment, put some valve grinding compound on the valve and seat, spin drill forwards and backwards a couple times until valve seat and valve are clean metal, clean everything, done

    Am I missing something?


    '96 328iC, '96 328i, '89 s52 swapped 325i
    Shadetree30

  2. #2
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    Grinding the valve seat and valve will put everything back to the correct angles, and seat location. Lapping compound will only remove a tiny amount of material and will not correct for any wear on the valve seat or valve.

  3. #3
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    Quote Originally Posted by mgthompson View Post
    Grinding the valve seat and valve will put everything back to the correct angles, and seat location. Lapping compound will only remove a tiny amount of material and will not correct for any wear on the valve seat or valve.
    Ok, I figured I was mixing them up. So grinding would basically have to be done at a shop.

    Is there any benefit to doing valve lapping myself with the compound?


    '96 328iC, '96 328i, '89 s52 swapped 325i
    Shadetree30

  4. #4
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    If the shop does the valve grind properly, there's no need for lapping.

  5. #5
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    Quote Originally Posted by jakermac View Post
    If the shop does the valve grind properly, there's no need for lapping.
    Yea I would assume so. The idea was to try to avoid extra shop fees by doing the valve lapping and maybe then the valve grinding wouldn't be necessary.

    I think I'll just take the head to a shop have it checked for flatness, cracks, decked if needed (probably), cleaned, pressure/vacuum tested and if valves are leaking have them attended to.


    '96 328iC, '96 328i, '89 s52 swapped 325i
    Shadetree30

  6. #6
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    I was going to say it shouldn't cost much from any decent head shop, then I saw California


    I recently had an S54 head built, polished out the ports, +1 valves ground in, then the typical blah blah blah....$400 said and done.

  7. #7
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    Quote Originally Posted by SneauxM3 View Post
    I was going to say it shouldn't cost much from any decent head shop, then I saw California


    I recently had an S54 head built, polished out the ports, +1 valves ground in, then the typical blah blah blah....$400 said and done.
    That's a good deal.


    '96 328iC, '96 328i, '89 s52 swapped 325i
    Shadetree30

  8. #8
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    Lapping the valves can tell you alot about how they sit on the valve seat. Lap them and inspect the surface with around the valve seat that is newly finished

  9. #9
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    Quote Originally Posted by jakermac View Post
    If the shop does the valve grind properly, there's no need for lapping.
    Grinding the head properly will also make make the seat width and location correct. We used to grind the valve seat and valve angles off by about a degree. That gave great sealing on the first start without lapping, and after a few minutes of run time the valve an seat angles were matched.

  10. #10
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    I used to lap valves with a cordless drill and compound but be very carefull not to let it get on the stem or your guides will be shot. It has been years since I did any ofthat type of work.Back then it was mostly air cooled engines and we did everything in house. The seats were done with a grinder and the valves were usually new so the lapping was a "finishing touch." If the valves are right you can pull them out about an inch and smack them with your finger they will bounce back off the seat and make a nice "ping" sound. If its dull they need more lapping or the guides are too tight. Even though I am a do it yourself guy I let the machine shop take care of all that now as long as they are reputable.

  11. #11
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    Thanks for the info guys, I appreciate it


    '96 328iC, '96 328i, '89 s52 swapped 325i
    Shadetree30

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