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  1. #1
    1000+ Posts jo proffi's Avatar
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    Default engine autopsy

    I just pulled the rocker cover of a bitsa motor from a fuego (bitsa this and bitsa that) and I found the cam has some machining marks where all the other cams on all my cars do not.
    Might this indicate it has been balanced at some point???

    Jo

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    Attached Thumbnails Attached Thumbnails engine autopsy-cam-1.jpg   engine autopsy-cam-2.jpg  

  2. #2
    1000+ Posts robmac's Avatar
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    I don't think they are balancing marks. Balancing is often done with a high speed grinder, that looks like it's been done with an abrasive disk?

    Possibly it's a factory marking to indicate tolerance range or even type of grind.

    Some of the Peugeot liners have 'notches" in the bottom rim to indicate the liner seal thickness.

    Balancing grinding, looks as per the image...
    Attached Thumbnails Attached Thumbnails engine autopsy-balance-07.jpg  

  3. #3
    Fellow Frogger!
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    I've seen these marks on lots of shafts including cams. I have always assumed they are merely where the casting marks have been ground off. When you cast an item some of the metal can leak into the joints where the 2 halves of the mould come together.

    Cheers

    Jim

  4. #4
    1000+ Posts Wildebeest's Avatar
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    Default

    Wot he said.

  5. #5
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    Default Hot Cam

    Probably a "Hot" cam and someone has ground the serial No. off!
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  6. #6
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    Default Pull it out and measure the lobe profile

    Jo

    only way you will solve any difference (potential difference) is to pull the cam out, mount the bearing surface on vee blocks or between lathe centres and check the cam profile with a dial indicator.

    If it is different it should show up as such when checked against others.

    I lean towards the standard, cam with manufacturing cast slub roughly ground off.

    Ken

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    Quote Originally Posted by Kenfuego View Post
    Jo

    only way you will solve any difference (potential difference) is to pull the cam out, mount the bearing surface on vee blocks or between lathe centres and check the cam profile with a dial indicator.

    If it is different it should show up as such when checked against others.

    I lean towards the standard, cam with manufacturing cast slub roughly ground off.

    Ken
    Thanks for the replies, guys.

    Ken, that is the logical thing to do, but bugger me if on top of all the other things I've got on my plate to sort out I'll measure them with a dial gauge.
    Suck it and see will be the chosen philosophy.

    I was just curious as none of the other cams I've ever seen on a fuego have casting joins or anything remotely like this.

  8. #8
    1000+ Posts jo proffi's Avatar
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    As it turns out this is a modified cam.

    It was not imeadiatly obvious to my untrained eye until I put an OE cam and this cam together and saw the massive difference in base circle diameter.

    So I can now guess that the cutting marks origionaly shown were to remove some meat just to allow the regrind to occur.

    Now that it is all bolted back together, I dont like what i see in regard to the offset angle the lifter impacts the valve stem. If I pushed my trumpet's valve down like that, It would stick and eventually wear out.
    Its like I need a tappet with a more acute angle between the cam pad and the ajuster screw or a screw post with a round/drum end.
    To compensate for the lower base circle diameter the screw now sits near the end of its travel.
    I wonder how much gain an agressive cam like this gives VS how quickly the valve train will self destuct.
    Jo



    Attached Thumbnails Attached Thumbnails engine autopsy-rocker-adjuster.jpg  

  9. #9
    1000+ Posts Wildebeest's Avatar
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    Default Autopsy...

    jo,
    The angle of the rocker and the contact area of the adj screw looks OK to me.
    I can see your argument, the trumpet valve simile is a good one.

    Looking at the rocker/valve position I would say the valve is closed with some rocker clearance.
    Because of the rocker design it moves in an arc when pushing on the valve, with the valve fully depressed and at its highest spring load the contact of the adj screw would be ideally in the centre of the valve stem.

    To overcome the not so perfect rocker to valve principle is possibly one of the reasons roller rockers are adapted ?

  10. #10
    1000+ Posts jo proffi's Avatar
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    Quote Originally Posted by Wildebeest View Post
    jo,

    Looking at the rocker/valve position I would say the valve is closed with some rocker clearance.
    Because of the rocker design it moves in an arc when pushing on the valve, with the valve fully depressed and at its highest spring load the contact of the adj screw would be ideally in the centre of the valve stem.
    I spent a few hours last night looking, turning the motor, sipping scotch, thinking more, and i came to the conclusion that on the OE valve/cam set up the rocker smacks the valve at almost the same angle of the stem, and at maximum lift the gap opens up. This would make sense to my uneducated/unexperienced way of visualising the movement, as i would imagine the most destructive moment in the whole travel is when the rocker rises up the cam lobe ramp and closes up the gap by smacking into the valve, and the least destructive moment would be as the valve approaches max lift, where the valve already has momentum.
    I have not measured lift but i would expect this cam gives more lift too, so I would guess that both ends of the arc of rocker relative to the valve stem are being enlarged, considering no other modifications to the valve train geometry appear to have been made.
    I guess by screwing the adjuster so far up and changing the attack angle of the rocker, I'd be moving the 'gap angle' in a linear fasion through its travel, which I guess would compensate favourably at full lift and unfavourably at no lift.
    This is going to be one hell noisy motor.



    Jo
    Last edited by jo proffi; 7th April 2011 at 02:27 PM.

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    I was perusing an old copy of unique cars on Monday (off work sick) and there was an article on this very thing.

    The technique was to use engineer's blue on the top of the valve with assembly valve springs and rotate the cam through a complete cycle. Using a variable length pushrod, the length of the pushrod was correct when the length of the witness mark on the valve top was as small as possible. There were some values mentioned as acceptable for the witness mark length but I can't remember them and the mags went out with the recycling this morning.

    You would then presumably order a pushrod in the size of the adjustable one.
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  12. #12
    mlb
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    I'd be looking at how the adjuster looks at half of maximum valve lift. If the adjuster is in line with the stem at that point, then between fully open and fully closed will be an even arc each side. Only possible solution I could think of would to machine the base of the rocker pedestals to bring it all down or to build up the following faces. Not being too familiar with the head arrangement on the engine though I'm not even sure if this is possible.

    Matt
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  13. #13
    1000+ Posts jo proffi's Avatar
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    Quote Originally Posted by Uffee View Post
    I was perusing an old copy of unique cars on Monday (off work sick) and there was an article on this very thing.
    I have done a fair bit of searching in regards to tappet/valve intersection angle, but I cant find too much on the net about it.
    I think I might have to buy a technical book made of paper to get the info I need.


    Jo

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  15. #15
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    I've got that one, Its a ripper.

    Jo

  16. #16
    1000+ Posts jo proffi's Avatar
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    Quote Originally Posted by mlb View Post
    I'd be looking at how the adjuster looks at half of maximum valve lift. If the adjuster is in line with the stem at that point, then between fully open and fully closed will be an even arc each side.......
    Matt
    As per Burgess/Gollan recomended book.

    Interestingly the pictured rockers they have have ball ends.
    Whats with ball ends and flat ends??
    The book saves any such detail (or I fully missed it).

    As per the photo, mine have what were originally flat or slightly convex heads, but are a bit worn out after so many Km's
    I can see the history of every tappet adjustment in the heads of the adjuster bolts so I could do better.
    If nothing else, I know I'm going to be making up a dummy rocker cover for regular adjustments of this head.
    I cant imagine I'm going to get deadly acurate settings as it is now.


    Another question.... Without any specs or details of the cam grind and suggested tappet clearance, how do I go about guestimating that one???


    Jo

  17. #17
    1000+ Posts Wildebeest's Avatar
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    Default Autopsy..

    jo,
    Your real or imagined description of the rocker "smacking" the valve shouldn't be a problem.
    With the valve closed the spring tension is minimal and providing the valve clearance is maintained to spec [very close if I recall as with most Douvrain engines], the contact of the rocker to valve at this stage should be "gentle".

    With any modifications to the cam the rocker angle of attack has been compromised. Even with a std cam the rocker design at contact with the valve can only be described as a mean angle ?
    Any increase in adjustment would incur some loss in valve opening and make for increased cam wear and a hellava lot of noise !

    A closer look at your pictures shows the adjustment screw to be a fair way in. In your case this would show that with a modified cam the adjustment screw has had to follow up the removal of metal.
    With an OE cam this would be a good indication of cam lobe and rocker wear. Not uncommon on earlier PRV engines.

  18. #18
    1000+ Posts jo proffi's Avatar
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    More detail has come to light.
    here are some specs.
    Cam one is fuego standard, cam 2 is the regrind.



    Attached Thumbnails Attached Thumbnails engine autopsy-cam1.jpg   engine autopsy-cam-2.jpg  

  19. #19
    1000+ Posts Wildebeest's Avatar
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    jo,
    Nothing to do with the cases in point but...One of the adjuster locknuts appears to be odd? The one with the deep flanged nut. Normally Douvrain rocker adj locknuts are plain.
    Did someone in the past lose one?

    I have no clever reply to your flat ended and round [radiused] adj screws. Although the radiused contact would be more suited to your engine.

  20. #20
    1000+ Posts jo proffi's Avatar
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    As far as I have experienced, this is what R21 looks like.
    Attached Thumbnails Attached Thumbnails engine autopsy-r21.jpg  

  21. #21
    1000+ Posts Wildebeest's Avatar
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    jo,
    Re the adjuster nuts. Consider me chastised. Place blushing smiley here x.

  22. #22
    1000+ Posts jo proffi's Avatar
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    Quote Originally Posted by Wildebeest View Post
    jo,
    Re the adjuster nuts. Consider me chastised. Place blushing smiley here x.
    No chaste for you, As I mixed up the pot by showing two different style rocker and nuts. If anything, well spotted.

    But I think (haakon/simon may correct me) The R21 is the only dourvin 4cyl renault to have alloy rockers and those type of nuts.

    The first image is of the steel rocker gear, with the shorter nuts found on fuego, r25 r20.

    Jo

  23. #23
    Demannu-facturing! Demannu's Avatar
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    Mid-1988 onwards, all Douvrin engines had alloy rockers.
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