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When to Lap Valves?

Discussion in 'The Garage' started by abyssmaltailgate, Jul 12, 2016.

  1. abyssmaltailgate

    abyssmaltailgate Greenhorn Mechanic

    Another greenhorn question, but when should one lap the valves? There's a lot of great information on this site about HOW to lap, but I have yet to see WHEN to lap the valves.

    I'm installing new Kibbelwhite valves, and I assume since they're new, the valves need to be lapped. Other than that... should valves be lapped only when the valves are leaking?
     
  2. Jack

    Jack XS650 Junkie Top Contributor

    new valves,you re-cut the seats by doing a three angle valve job not relap. Do it right the first
    time around. Also just lightly cut the new valve faces.
     
    Last edited: Jul 12, 2016
  3. abyssmaltailgate

    abyssmaltailgate Greenhorn Mechanic

    oh... machine shops will do 3-angle jobs I guess?
     
  4. peanut

    peanut XS650 enthusiast & inveterate tinkerer Top Contributor

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    don't be too hasty in getting your valve seats recut .
    When rebuilding a head with new valves it is generally considered sound practice to replace the valve seats at the same time and recut to the new valves, which is all very well on a modern head thats only a few years old where replacements are easily and cheaply obtained.

    If a leak down or compression test doesn't reveal a compression leakage problem then unless you intend racing the bike all you should need to do when rebuilding is to decoke and lap your valves to the existing seats to achieve a perfectly satisfactory seal.
    You'll need to make this decision by carefull visual inspection and measurement of acceptable wear tolerances when you remove and clean the head and lap your valves

    If you choose the seat recut option there is a good chance on a 35+ year old head that removing and fitting new valve seats inserts could damage the aluminium head and you'd then be looking for a replacement head !
     
  5. Jack

    Jack XS650 Junkie Top Contributor

    Yes maybe 40 to 50$ investment
     
  6. Jack

    Jack XS650 Junkie Top Contributor

    There are no valve seat inserts on the XS and when you install a $200 plus valves you don't install then on a cheaply lapped seat job,your cheating yourself on performance.
     
  7. peanut

    peanut XS650 enthusiast & inveterate tinkerer Top Contributor

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    so the valve seats are made of aluminium are they Jack !?:laugh2::laugh2::lmao:

    I would question the commonsense in spending $200 on valves for a part rebuild on an old standard engine anyway


    Abyssmaltailgate have a read of this article on cylinder head refurbishment and valve lapping written by someone who knows what he is talking about.Dr Rod
    https://www.mikesxs.net/xs650engine/Part2.html
     
    Last edited: Jul 14, 2016
  8. grizld1

    grizld1 Grumpy old man Top Contributor

    No, bright guy, the seats aren't made of aluminum, and Jack is right, they're not replaceable with inserts. The seats are part of a one-piece iron combustion chamber cap which is not replaceable.
     
  9. peanut

    peanut XS650 enthusiast & inveterate tinkerer Top Contributor

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    QUOTE="grizld1, post: 466786, member: 285"]No, bright guy, the seats aren't made of aluminum, and Jack is right, they're not replaceable with inserts. The seats are part of a one-piece iron combustion chamber cap which is not replaceable.[/QUOTE]

    exactly how the valve seats are incororated into the aluminium head is not the issue .

    if the seats do need to be recut then the general consensus seems to be that it is advantageous to replace them with a higher grade harder steel than standard.This would involve milling the existing valve seat areas out and installing new steel inserts into the head and then recutting the necessary profiles.
    This image from the Lorenzo article in bikersworld shows that the valve seats are an integral part of the steel combustion chamber insert which incorporates the spark plug thread


    I do know its not necessary to recut the seats unless they are excessively worn. A simple 10 minute hand lapping is all that should be needed as you should very well know.
    07.jpg
     
    Last edited: Jul 14, 2016
  10. grizld1

    grizld1 Grumpy old man Top Contributor

    Yeah, you're real bright. Clearly the guys who developed the service procedures in Yamaha's factory manual could have learned from you. The recommendation to install inserts with harder material than the original had to do with early motors that were designed to run on fuel with tetraethyl lead added; harder seat material was needed to use lead free gasoline in those motors. That was not an issue in any Yamaha 4 stroke engine.

    BTW, because seat and valve face profiles can vary, it's usual to need to cut the seats when new valves are installed, and it's almost always necessary to cut the seats when new guides are installed to maintain correct alignment of valve face to seat. You won't get that done with a little lapping.
     
    Last edited: Jul 14, 2016
  11. Jack

    Jack XS650 Junkie Top Contributor

    exactly how the valve seats are incororated into the aluminium head is not the issue .

    if the seats do need to be recut then the general consensus seems to be that it is advantageous to replace them with a higher grade harder steel than standard.This would involve milling the existing valve seat areas out and installing new steel inserts into the head and then recutting the necessary profiles.
    This image from the Lorenzo article in bikersworld shows that the valve seats are an integral part of the steel combustion chamber insert which incorporates the spark plug thread

    WTF are you coming up with all this bull shit. Have you ever tried to install seats in an XS head? Ain't gonna happen cuz there isn't enough meat in the combustion cap to retain it,of course some one as smart as you already knew that.


    I do know its not necessary to recut the seats unless they are excessively worn. A simple 10 minute hand lapping is all that should be needed as you should very well know.
    View attachment 86535 [/QUOTE]
    IF I want a cheap 10 minute lap hand job I'd go to the titty bar,not on my XS head. I've been wrenching for some 38plus years and I don't know of one respectable machine shop that lap valves in a reconditioned head.
     
  12. Jack

    Jack XS650 Junkie Top Contributor

     
    Last edited: Jul 15, 2016
  13. peanut

    peanut XS650 enthusiast & inveterate tinkerer Top Contributor

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    the good thing about forums is that everybody has the right to voice their personal opinion .
    The bad thing about forums is that some asswipes can't bear anyone having a different opinion to them because it threatens their fragile egos.


    If the po ever returns to this thread I am sure that he will make his own mind up. His decision could well be restricted by how much money he has put into a cheap 35 year old bike . We don't all have the financial wherewithall that you two seem to have.!
     
    Last edited: Jul 16, 2016
  14. peanut

    peanut XS650 enthusiast & inveterate tinkerer Top Contributor

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    jack if you wern't so pig ignorant I'd tell you all about the XS650 heads that do have valve inserts and how it is quite possible to insert valve seats into capped heads if you have deep pockets but I can tell by your limited intellect that I'd be wasting my time .

    The point I made to the po ,that both you and grizzly are trying so hard to avoid, is that I would recommend he has the head inspected by an Engineer to see if it actually needs new valves and the seats recut and not just go ahead and spend a small fortune on such a tiny aspect of the engine unecessarily.
    Obviously this wouldn't apply to you because you've clearly got more money than sense!.
     
  15. peanut

    peanut XS650 enthusiast & inveterate tinkerer Top Contributor

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    jack if you wern't so opinionated I'd tell you all about the XS650 heads that do have valve inserts and how it is quite possible to insert valve seats into cappped heads if you have deep pockets but I can tell by your limited intellect that I'd be wasting my time .

    The point I made to the po ,that are both trying so hard to avoid, is that I would recommend he has the head inspected by an Engineer to see if it actually needs new valves and the seats recut and not just go ahead and spend a small fortune on such a tiny aspect of the engine maybe unecessarily .
    Obviously this wouldn't apply to you because you've clearly got more money than sense!. :lmao:
    :laugh2:
     
  16. weekendrider

    weekendrider Iron Horse cowboy Top Contributor

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    peanut regardless of what you've read. Regardless of who the authors are, you are well outta your league here.
    Those two members have forgotten more than you and I are likely to learn about the XS650.
    Attacking them with personal insults will just piss them off enough to not post.
    And that denies the rest of us access to their knowledge.
    Don't cut your nose off to spite your face may apply here.
     
    Signal likes this.
  17. 650Skull

    650Skull SSSSSSSSSlither Top Contributor

    This is a perfect example to show how a belligerent and ill informed member can cause major damage and cost to an intricate part of a rebuild.

    :popcorn:
     

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