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Thread: Important lash cap question

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    Default Important lash cap question

    Well important to me anyway......

    Lash caps were originally used so that the valve stem would not have to be head treated at the point of bucket/rocker contact.
    The lash cap was pressed on and the hardened cap acted as a bearing surface, OK?
    The cap stayed in place by interference fit on the softer valve stem material.

    Now, the big question I have is>
    Can an acceptable interference fit be obtained between the two if the lash cap is fitted to an already hardened valve stem originally designed with a hardened end surface.

    Or will the lash cap dislodge in time or crack, given that the two materials are of similar hardness?

    Im sure on the softer stem some galling/or compression occurs at time of fitting and this helps to aid fit.

    Can anybody give me a definite answer on this. I need to know should i remove temper and then fit, or if theres need.

    Thanks.
    Last edited by Brian.G; 24th September 2009 at 14:11.
    http://www.youtube.com/watch?v=vz1TJeuwQV0 < VW 2.0l 16v cutaway video
    http://www.youtube.com/watch?v=C7rXuaJMhOc < VW 1.8T cutaway video
    http://www.clubgti.com/forum/showthread.php?t=215166 < Agg 8v Cutaway Pictures.
    http://www.youtube.com/watch?v=KINvUOd6Zjs < Vr6 bore offset effects

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    Banned after significant club disruption Dec 5th 2014 Chris Eyre's Avatar
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    Quote Originally Posted by Brian.G
    The cap stayed in place by interference fit on the softer valve stem material.
    Do they definitely rely on interference fit? My thinking is if they were, you could never be 100% sure they were sat snug on the top of the valve.

    Since they have skirts which exceed the valve clearance in height, they won't dislodge for that reason, rather than requiring interference to keep them where they are.

    ?

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    Quote Originally Posted by Chris Eyre
    Quote Originally Posted by Brian.G
    The cap stayed in place by interference fit on the softer valve stem material.
    Do they definitely rely on interference fit? My thinking is if they were, you could never be 100% sure they were sat snug on the top of the valve.

    Since they have skirts which exceed the valve clearance in height, they won't dislodge for that reason, rather than requiring interference to keep them where they are.

    ?
    You see thats what im not sure of Chris, any drawings Ive seen of caps have a very shallow skirt, and have very tight tolerances with regards diameter, as in you can buy 10 different sizes between 7mm and 7.5mm so thats why i thought it was an interference thing?

    In your opinion > shim bucket, or lash cap?

    Thanks Chris.

    Im thinking lash cap as it would be lighter?

    Obviously a lash cap would lessen spring preload, but I can overcome that.
    Last edited by Brian.G; 24th September 2009 at 14:55.
    http://www.youtube.com/watch?v=vz1TJeuwQV0 < VW 2.0l 16v cutaway video
    http://www.youtube.com/watch?v=C7rXuaJMhOc < VW 1.8T cutaway video
    http://www.clubgti.com/forum/showthread.php?t=215166 < Agg 8v Cutaway Pictures.
    http://www.youtube.com/watch?v=KINvUOd6Zjs < Vr6 bore offset effects

    Strive for perfection in everything we do. Take the best that exists and make it better.
    When it does not exist, design it. Accept nothing nearly right or good enough.

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    Banned after significant club disruption Dec 5th 2014 Chris Eyre's Avatar
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    I've spent some recent time sorting lash caps on my motor, and have been over at a Vauxhall engine specialists (SBD, Chessington) who produce some proper motors and I believe are held in good esteem.

    I have simply bought 7mm lash caps, since that's what they're using on the Red Tops and subsequent motors.

    I also went to QEP in Sussex and the specs were again by the millimetre, rather than 0.1mm.

    I had a couple of snug/interference lash caps which I didn't think were sitting on the valves properly, so I opened them up until they were.

    Never a mention by SBD of 0.1mm interference and the rest.

    Skirt depths I decided myself - I just didn't want them anywhere near the collets, and cut them so they were well clear. 0.3mm off the collets was a quoted minimum skirt depth, but I just made sure they were well clear, 0.4mm or more.

    I was advised that if that wasn't possible, to turn them upside down and skirt them around the bucket, though I didn't need to.

    I've not seen bucket shimming - never had to touch this stuff before - but I believe lash caps are the proper solution.

    Needs a surface grinder or someone you can trust to grind them parallel to a precision.

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    lash caps over shims any day - not definately sure about your main question though
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    Right, all taken on board.
    I have seen lash caps sold in incremental sizes but that doesent seem to matter now given what you said above Chris.

    @ Rob, its for a head im doing, i need to make up some space/play in order to keep standard valve lengths.
    Perhaps I should drop my intake cam carrier journals the required amount, this would be the correct way, but I then loose symmetry and it makes journal machining harder as I then have to rejig when cutting the intake journals, as opposed to cutting exhaust and intake journals on the same plane.
    The bucket/carrier girdle then has to be stepped too.
    http://www.youtube.com/watch?v=vz1TJeuwQV0 < VW 2.0l 16v cutaway video
    http://www.youtube.com/watch?v=C7rXuaJMhOc < VW 1.8T cutaway video
    http://www.clubgti.com/forum/showthread.php?t=215166 < Agg 8v Cutaway Pictures.
    http://www.youtube.com/watch?v=KINvUOd6Zjs < Vr6 bore offset effects

    Strive for perfection in everything we do. Take the best that exists and make it better.
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    Banned after significant club disruption Dec 5th 2014 Chris Eyre's Avatar
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    So far I've seen lash caps up to 3.14mm.

    The problems arise when they're getting to short, ie there's not enough meat in them.

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    Quote Originally Posted by Chris Eyre
    So far I've seen lash caps up to 3.14mm.

    The problems arise when they're getting to short, ie there's not enough meat in them.
    Ok, well I need to make up 2.5mm, so is this an ok way to do it or is it a compromise given the fact I can do what I please?
    Should I drop journals or are you happy with lash caps Chris? Any horror stories?
    http://www.youtube.com/watch?v=vz1TJeuwQV0 < VW 2.0l 16v cutaway video
    http://www.youtube.com/watch?v=C7rXuaJMhOc < VW 1.8T cutaway video
    http://www.clubgti.com/forum/showthread.php?t=215166 < Agg 8v Cutaway Pictures.
    http://www.youtube.com/watch?v=KINvUOd6Zjs < Vr6 bore offset effects

    Strive for perfection in everything we do. Take the best that exists and make it better.
    When it does not exist, design it. Accept nothing nearly right or good enough.

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    Depending where you get your buckets from, its possible you can get them with different stem lengths I would think
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    my motor runs lash caps and regularly goes to 8.5K
    2013 Misano Red S4 Avant 3.0SC Black Edition
    2009 Telegrey/Black Radical SR8-RS 2.7RPX
    2008 Daytona Grey A6 Saloon 2.0TDI S-Line
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    Banned after significant club disruption Dec 5th 2014 Chris Eyre's Avatar
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    Quote Originally Posted by Brian.G
    Quote Originally Posted by Chris Eyre
    So far I've seen lash caps up to 3.14mm.

    The problems arise when they're getting to short, ie there's not enough meat in them.
    Ok, well I need to make up 2.5mm, so is this an ok way to do it or is it a compromise given the fact I can do what I please?
    Should I drop journals or are you happy with lash caps Chris? Any horror stories?
    As far as I can tell, this is the correct way. It is very time consuming, but the correct way for high revving 16V motors (> 7.5k rpm ballpark). They look like rubbish, but it seems this is what people use.

    I wouldn't attempt to suggest I'm experienced with this - I was just fixing overly wide clearances which should have been done by the originator, but as I say, it's time consuming and requires precision.

    Horror stories can arise from anything, installed heights, coilbound springs etc, and that could throw a lash cap out, but it's already self destructing by then.

    You can largely do what you please. Put in 1 valve which is 1mm shorter (edit: above the collet) if you wanted, and make it up on the lash cap. Makes no theoretical difference.

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    Last edited by RobT; 24th September 2009 at 15:31.
    2013 Misano Red S4 Avant 3.0SC Black Edition
    2009 Telegrey/Black Radical SR8-RS 2.7RPX
    2008 Daytona Grey A6 Saloon 2.0TDI S-Line
    2008 Anthracite Bentley Continental GT Speed 6.0T W12

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    Ok, a very big thanks to you both, Im going to think about this more later, at least now I have something to think about.
    What a brilliant forum the fact you can get answers immediately on something such as this.
    Thanks again, Brian.
    http://www.youtube.com/watch?v=vz1TJeuwQV0 < VW 2.0l 16v cutaway video
    http://www.youtube.com/watch?v=C7rXuaJMhOc < VW 1.8T cutaway video
    http://www.clubgti.com/forum/showthread.php?t=215166 < Agg 8v Cutaway Pictures.
    http://www.youtube.com/watch?v=KINvUOd6Zjs < Vr6 bore offset effects

    Strive for perfection in everything we do. Take the best that exists and make it better.
    When it does not exist, design it. Accept nothing nearly right or good enough.

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    Banned after significant club disruption Dec 5th 2014 Chris Eyre's Avatar
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    Thanks Brian. Saw the article in Golf+. Keep at it. Can't wait.

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    Interesting.. the lash caps in my KWL 8v head attach to the stem of the bucket.. not the valve..

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    Banned after significant club disruption Dec 5th 2014 Chris Eyre's Avatar
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    If the bucket 'pin' has a different diameter, it's specific to that.

    If it has the same diameter as the valve, it can go in either way, subject to lash cap skirt => collet clearance.

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    Quote Originally Posted by Chris Eyre
    Thanks Brian. Saw the article in Golf+. Keep at it. Can't wait.
    Oh I wil Chris, I just want to have all machining angles covered first before I start the thread, so as I dont run into a problem and have to go...um...ah...umm..
    http://www.youtube.com/watch?v=vz1TJeuwQV0 < VW 2.0l 16v cutaway video
    http://www.youtube.com/watch?v=C7rXuaJMhOc < VW 1.8T cutaway video
    http://www.clubgti.com/forum/showthread.php?t=215166 < Agg 8v Cutaway Pictures.
    http://www.youtube.com/watch?v=KINvUOd6Zjs < Vr6 bore offset effects

    Strive for perfection in everything we do. Take the best that exists and make it better.
    When it does not exist, design it. Accept nothing nearly right or good enough.

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    One more question, what happens the lash caps if the engine is over revved and the valves bounce?
    http://www.youtube.com/watch?v=vz1TJeuwQV0 < VW 2.0l 16v cutaway video
    http://www.youtube.com/watch?v=C7rXuaJMhOc < VW 1.8T cutaway video
    http://www.clubgti.com/forum/showthread.php?t=215166 < Agg 8v Cutaway Pictures.
    http://www.youtube.com/watch?v=KINvUOd6Zjs < Vr6 bore offset effects

    Strive for perfection in everything we do. Take the best that exists and make it better.
    When it does not exist, design it. Accept nothing nearly right or good enough.

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    Banned after significant club disruption Dec 5th 2014 Chris Eyre's Avatar
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    No certainty to that one (gravity and crossed fingers?), but if a piston has clipped a valve, separate problems are already developing and it's head off time anyway to start junking some valve springs and valves.

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    Quote Originally Posted by Chris Eyre
    No certainty to that one (gravity and crossed fingers?), but if a piston has clipped a valve, separate problems are already developing and it's head off time anyway to start junking some valve springs and valves.
    Ya I suppose so, maybe Im just getting paranoid...
    http://www.youtube.com/watch?v=vz1TJeuwQV0 < VW 2.0l 16v cutaway video
    http://www.youtube.com/watch?v=C7rXuaJMhOc < VW 1.8T cutaway video
    http://www.clubgti.com/forum/showthread.php?t=215166 < Agg 8v Cutaway Pictures.
    http://www.youtube.com/watch?v=KINvUOd6Zjs < Vr6 bore offset effects

    Strive for perfection in everything we do. Take the best that exists and make it better.
    When it does not exist, design it. Accept nothing nearly right or good enough.

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    Quote Originally Posted by Brian.G
    One more question, what happens the lash caps if the engine is over revved and the valves bounce?
    My last engine went to 10.5K 'accidentally' - the result was 2 broken springs, but the lash caps stayed put
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    Quote Originally Posted by RobT
    Quote Originally Posted by Brian.G
    One more question, what happens the lash caps if the engine is over revved and the valves bounce?
    My last engine went to 10.5K 'accidentally' - the result was 2 broken springs, but the lash caps stayed put
    NICE!
    http://www.youtube.com/watch?v=vz1TJeuwQV0 < VW 2.0l 16v cutaway video
    http://www.youtube.com/watch?v=C7rXuaJMhOc < VW 1.8T cutaway video
    http://www.clubgti.com/forum/showthread.php?t=215166 < Agg 8v Cutaway Pictures.
    http://www.youtube.com/watch?v=KINvUOd6Zjs < Vr6 bore offset effects

    Strive for perfection in everything we do. Take the best that exists and make it better.
    When it does not exist, design it. Accept nothing nearly right or good enough.

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    Banned after significant club disruption Dec 5th 2014 Chris Eyre's Avatar
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    Probably worth mentioning that the valve clearances I've seen specified from Cat Cams and Schrick are in a range of 0.2mm to 0.35mm, so this is the ballpark level of slack which should be in there.

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    An off topic question but whats the record rpm for hydros?
    http://www.youtube.com/watch?v=vz1TJeuwQV0 < VW 2.0l 16v cutaway video
    http://www.youtube.com/watch?v=C7rXuaJMhOc < VW 1.8T cutaway video
    http://www.clubgti.com/forum/showthread.php?t=215166 < Agg 8v Cutaway Pictures.
    http://www.youtube.com/watch?v=KINvUOd6Zjs < Vr6 bore offset effects

    Strive for perfection in everything we do. Take the best that exists and make it better.
    When it does not exist, design it. Accept nothing nearly right or good enough.

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    depends on cam profile - I was told 7800 for a 16V but Badger Bill has had his 20VT up to 8500 with hydros and std cams
    2013 Misano Red S4 Avant 3.0SC Black Edition
    2009 Telegrey/Black Radical SR8-RS 2.7RPX
    2008 Daytona Grey A6 Saloon 2.0TDI S-Line
    2008 Anthracite Bentley Continental GT Speed 6.0T W12

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