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Lapping valves

Discussion in 'XJ Technical Chat' started by olinrj, Jul 24, 2008.

  1. olinrj

    olinrj Member

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    Just reviewing a few things on my list of to-do's and although I have moderate experience with a wrench and a willingness to tackle just about any project, I'm completely in the dark on how to properly lap valves. is there a short video or a pic-by-pic demonstration of this process? If there is maybe it could be posted for viewing, if not, is there someone who may be doing this in the near future that would be willing to snap a few pics and post them for those of us who might try to takle it in the future?

    Thanks.
    Bob
     
  2. schmuckaholic

    schmuckaholic Well-Known Member

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    Yeah, what he said.
     
  3. SyracuseXJ

    SyracuseXJ Member

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    I just lapped my valves in and I must say, unless you are experiencing low compression due to valve leakage or something of the sort, it's not something I would reccomend. All the steps are easy if you look at them individually, but when you pack them together there's alot to do
    remove valve cover
    remove cam sprockets
    Tie cam chain to something like a long piece of wire
    remove cams
    Unbolt exhaust headers and move them away from the head (a broom handle between the frame and the headers works well for this (go gently)
    [​IMG]
    Remove head
    remove shim buckets and start a per-cylinder organized parts collection
    (if you don't take them out now, when you flip the head they will fall out and go all over... learned by experience)
    Compress valve springs with a specialized tool
    (looks like an oversized lever actuated c-clamp)
    If the springs don't pop into a compressed position with relative ease rap on the valve end (not the end inside the combustion chamber) lightly with a small hammer and try again.
    Once the springs compress you can remove the collets (two tictac sized curved pieces of metal) and then release the spring. A retrieval magnet works nicely for this step.
    Place both collets, both springs, the valve and the retaining plate in the cup with the corresponding shim bucket.

    [​IMG]

    Repeat, repeat repeat

    Decarbon the valves by soaking with (i used) Seafoam DeepCreep (a day or two, apply 2x daily), Scraping gently with a painters multi tool (glorified putty knife) and polish with wire brush or die grinder with a pad (not a stone) be very careful around the part of the valve where it actually touches the head (I did this part with a brass brush by hand)

    [​IMG]

    Decarbon the combustion chambers, and intake and exhaust passages
    [​IMG]

    Spread a little valve lapping/grinding compound on the valve perimeter and re-insert into the proper port.
    Place the suction cup w/ dowel on the cylinder side of the valve and rotate/spin it between your palms (like your trying to start a fire) remember to lift the valve off the head ever so slightly on occasion to allow more compound to get between the valve and the head. (you will feel the renewed cutting action of the new abrasive) do this for about one minute. When you remove the valve and wipe it off you should see a light grey line all the way around the perimeter of the valve and the area it touches on the intake or exhaust port.
    repeat for each intake and exhaust valve in its own port

    remove the valve seals (they should be replaced if you are this far)needle nose vice grips worked best for me.

    clean everything within an inch of its life. you just used liquid sandpaper you don't want it making it's way around your engine.

    Clean gasket surfaces

    Put everything back together

    I will try and post some pictures of the lapping process later

    I also assume no responsibility for the correctness of this process. I am only relating what worked for me.

    Any edits or other suggestions by others I'm sure would be appreciated.
     
  4. schmuckaholic

    schmuckaholic Well-Known Member

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    Saw someone do this a while back whilst they were rebuilding an engine for their older model Jeep:

    1) spread on the lapping compound
    2) put the valve in
    3) chuck the spring side of the valve in a drill

    Not sure how well that worked, but that's what I remember seeing.

    Your procedure, though... now you've got me wanting to do mine. ;)
     
  5. SyracuseXJ

    SyracuseXJ Member

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    The drill setup was suggested to me as well when I was getting set to undertake this. I was concerned about marring the valvestem (was told this would not be a concern though) and for the 60 seconds this takes by hand it actually seems as though the drill would be overkill. I've also seen someone slip a length of fuel line over the valvestem end and use that to spin the valve. The suction cup thing works best though. You don't have to keep flipping the head over and back and the cup sticks well enough to easily spin the valve and then pull it out when you're done.
     
  6. Gamuru

    Gamuru Guest

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    Great write-up! Valve lapping is a tedious process but necessary for any valve job to be considered complete.
     
  7. TIMEtoRIDE

    TIMEtoRIDE Active Member

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    NO ! do not lap using a drill !! The lapping must be done in arcs in a random fashion, after 20 to 30 of the "campfire" swishing motions, lift the valve and tool, and turn about 90* and do it again.

    A drill can be used to clean and polish the valves:
    wrap making tape around the stem before chucking the valve in a drill,
    put a glove on your left hand, 400 - 600 grit in your hand, fold around the valve, run the drill, slowly change the position and shape of your hand.
    Your valves will look perfect, then lap 'em in.
     
  8. olinrj

    olinrj Member

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    Thanks a ton for the information. I wasn't planning on doing this until possibly winter, depending on how the bike is doing, but it occurred to me that I've never seen this done. I think i'll pick up the suction cups and lapping compond and tear apart one of my extra lawn mowers and give it a go!
    Once again this site has been an amazing wealth of information, thanks to its members.
     
  9. Hillsy

    Hillsy Member

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    Nice write Syracuse - but just a few things I've learnt from working in a bike shop:

    You can use a wire wheel on a bench grinder to take the carbon off your valves (they are very hard - you will not damage them)

    Take the valve seals out before you start lapping (less resistance)

    The lapping area on each valve face should be around 1.5MM max (about 1/16 inch). Any more than this, or any significant variation between the cylinders and the valves / seats ideally need re-facing (best done by a shop).

    Like anything mechanical, it's not hard - it's just methodical.
     
  10. SyracuseXJ

    SyracuseXJ Member

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    Finally got the picture of the lapped valves off the camera.

    [​IMG]

    You can see the nice thin matte gray line running all the way around the valve and port.
     
  11. Gamuru

    Gamuru Guest

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    Man! That's almost like porn to a mechanic. Me likey! Very nicely done.
     
  12. jgb1503

    jgb1503 Member

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    Thanks for the write-up! I just busted 5 bolts on my manifold boots, so I gotta disassemble everything - figured i'd tackle this while its apart. This write up is a great help! The pics help a lot!

    Any other tips/tricks/pics for a engine virgin? ;-)
     
  13. spinalator

    spinalator Member

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    Great write up. I sense a stickie in the future, if we can get a few more pics up.
     
  14. jgb1503

    jgb1503 Member

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    A couple of ignorant questions if I could...?!

    So, I am looking to take everything off here in the next day or two - lap the valves and all that. Now the instructions here say that you take off the cams etc..etc..etc.. But everything I have read from Rick said don't mess up the auto tensioner.. I am kinda confused.. How do I disassemble everything, but not mess that up? Also; I want to get it as disassembled as possible if I am bringing it to a machine shop to drill out my manifold cap screws that broke.... I am trying to cover all my bases and get it straight in my head before I touch a screw.

    I'm already looking at parts from Chacal (Valve Stem seal, gaskets, shim tool - however I read that its not the right one for 750's?, new spring keepers, feeler gauges) and I figure once I get her open I can figure out the 'extra' parts I might need - new shims, springs, etc...

    another side question (I am full of them) are the bolts on this as bad as the manifold cap screws?? (i.e, should I also order replacement bolts?)

    I apologize for my beginner-ish questions. But I just learned about (and focused on) carbs so this is a very new area for me ;-) All of your help, advice, and write-ups have been awesome! and I will definitely say that I wouldn't have gotten 1/5 as far as I am without everyones help, advice, encouragement!!!!! The service manuals are nice; but this type of help is priceless!

    thanks again!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

    josh
     
  15. TTTT

    TTTT New Member

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    HI,
    I have recently bought a 82 midnight maxim xj 750 and i was wondering
    how hot my head should get the bike dont like loose any power but it kinda sounds nosie on top end and the bike only has 10,583 miles on it. When i ride it like 15 miles about it seems very hot and if i drip a drop of H2O on the head it sizzels to nothing dosent that seem to hot ? I kinda wonderd if the oil is breaking down im useing oil my local yamaha shop recomends i think it is yamaha 4 stroke oil with somthing in it for the clutch i think its 20w50 if any one has an answer or any questions please let me know sorry so long thank you
     
  16. chacal

    chacal Moderator Moderator Supporting Vendor Premium Member

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    HIGH-HEAT PAINT PRODUCTS: Engine Cases, Covers, Final Drive, and Brakes:


    How Hot is Hot?:

    The following information was measured on a stock, un-modified XJ650 YICS engine, with the air temperature between 60- to 70-F. Modified engines, engine tune conditions, different air temperatures and humidity levels, etc. will affect these readings up or down.

    Using our HCP9959 Digital Infrared Heat Thermometer, we verify that the cylinder heads are the hottest part of the engine, with the front of the head (exhaust port side) reaching 350-F during and immediately after spirited riding, while the intake side of the cylinder head was consistently 50-degrees cooler (300-F), about the same readings as obtained on both the front and rear of the cylinder jugs. Valvecovers were relatively frigid, as can be expected, just barely breaking the 270-F mark.

    Brake rotors were measured at 300-F or more after 10 consecutive maximum-force braking events from 50mph. Calipers were approximately 80-F cooler.
     

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