rocker shaft rocker clearance
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  1. #1
    1000+ Posts jo proffi's Avatar
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    Default rocker shaft rocker clearance

    I'm trying to find out about douvrin rocker shaft to rocker clearance, but cant seem to find any details showing the range of sizes.
    Does this info exist anywhere?

    Jo

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  2. #2
    1000+ Posts schlitzaugen's Avatar
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    I have tried in the past to find the clearance for the 807 engines (12G/17G) but no info came forward. Hope you have more luck.
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  3. #3
    bob
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    G'day Jo,

    can't see anything obvious in the manuals and my ancient general stuff is a bit hard to get to at the moment.

    Reckon that rule of thumb could be reasonably applied. "Nice running fit" I think was the old fitters term, which probably relates to only a couple of thou. You've got a few shafts there, test a few clearances by rocking them on the shaft and get a feel for the movement - that's a lateral movement of course The end movement will be a magnified version of the clearance.

    If they feel "nice" they probably are.....

    cheers,
    Bob

  4. #4
    1000+ Posts jo proffi's Avatar
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    Quote Originally Posted by bob View Post
    G'day Jo,
    You've got a few shafts there.....
    cheers,
    Bob
    Thats a problem too....
    For starters I can not measure bore yet, but just running a micrometer around the shaft shows that the steel rocker gear off the r25 has a shaft that is fractionally bigger, and the steel rockers 'feel' more snug on the shaft compared to the alloy rockers on their shaft.

    Neither of the shafts are totally round. The r25 is 19.970- 19.985mm whereas the r21 is 19.960- 19.970mm, so smaller and more round.

    Jo

  5. #5
    bob
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    G'day Jo,

    the alloy ones, unless they are made of stuff that work hardens, will likely wear at a greater rate than the ferrous ones. They will also wear the shaft less.

    The little fellas also only run in a very restricted part of the shaft, can the shaft be turned 180 to use the "untouched" zone ? and maybe give the rockers marginally more bearing area... Oil path, both entry and exit, may preclude any shaft rotation though.

    You don't need to be able to measure the bore directly. If you want to really fussy you can mount them up so that you can measure, with a dial indicator, the amount that longer end of the rocker moves when you rock it from side to side. Compare them all on the same bit of shaft with the short end fixed in the same relative position each time to pick the least worn in the bore and best fit to the shaft. A bit of school-time-trig will tell you what the actual bore clearance is.

    Should keep you amused for hours.....

    cheers,
    Bob

  6. #6
    1000+ Posts schlitzaugen's Avatar
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    Bob is right but practically it is not that easy to weed out all the uncontrollable variables. Like the fact that the bloody rocker is going to wobble every each other way than that which would help you get an error free measurement.

    Jo, I would suggest you find yourself a good nut and bolt place. These places have something called a "jobber". These are a drill bit in really odd sizes, like 4.2mm or 6.75 and so on. These are precision ground, and in fact they are marked say 4.200 (that means it is guaranteed to be accurate to the third decimal place) or even 4.2000 (that is .0001mm precision!). Most I found are german made which is reassuring (say anything you want, but that's me). If you're lucky you will find a few helpful sizes on the shelf. Try these until you find the closest two that can bracket the inside diameter of the rocker hole (perhaps use a rocker arm that has no scoring inside, or the one you think it's least worn).

    If you had a precision lathe (or a nice machinist friend) you could ask them to make up what in my language is called (literal translation) a "caliber". This is a shaft with a lot of shoulders and sections of various diameters, each say about 2cm (or whatever width you might find helpful) wide used again to bracket the inner diameter of your rocker. Each "shoulder" is say about .01mm larger in diameter than the previous. Slide this shaft in until the rocker is a tight fit. Measure respective shoulder and you have the diameter (or a close approximation). If you want to be more accurate, you can go back to your machinist friend and now ask him to make you another "caliber" with even finer steps between the one that had your rocker arm stuck and the next smaller one by .01mm. You can have say .002 steps this time. Repeat procedure as above.

    I didn't have to do this. I had my rockers measured for wear by my machinist who had all the right tools. He then honed all of them to the same oversize internal diameter and then I had the shafts steel sprayed (loaded) and precision ground to give .02mm oiling clearance. My reasoning was that if .02 is fine for the crankshaft journals, it should be enough for the rockers where I expect pressures would be lower. My machinist was of the opinion this should be good enough a clearance for my 807 engine.
    Last edited by schlitzaugen; 12th June 2012 at 02:58 PM.
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  7. #7
    1000+ Posts PeterT's Avatar
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    Quote Originally Posted by schlitzaugen View Post
    Jo, I would suggest you find yourself a good nut and bolt place. These places have something called a "jobber". These are a drill bit in really odd sizes, like 4.2mm or 6.75 and so on. These are precision ground, and in fact they are marked say 4.200 (that means it is guaranteed to be accurate to the third decimal place) or even 4.2000 (that is .0001mm precision!). Most I found are german made which is reassuring (say anything you want, but that's me). If you're lucky you will find a few helpful sizes on the shelf. Try these until you find the closest two that can bracket the inside diameter of the rocker hole (perhaps use a rocker arm that has no scoring inside, or the one you think it's least worn).
    No. A "jobber" drill is just another name for a parallel shank drill, designed to be held in a jacobs chuck, rather than with a morse taper.

    4.2mm and 6.75mm (6.8 more common) are tapping size drills for M5x0.8 and M8x1.25 threads. Very common in fact.

    Perhaps you're thinking of "numbered" drills?

    Next myth. It's impossible to drill to a 1/100 of a mm, let alone a 1/1000 of a mm. Holes requiring that degree of accuracy are reamed/honed. Drills leave a poor surface finish, that would be +/- 0.05mm.

    Most good toolmakers/fitters can sharpen a drill to cut oversize, because inevitably they do.
    Last edited by PeterT; 12th June 2012 at 04:57 PM.

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  8. #8
    1000+ Posts schlitzaugen's Avatar
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    Quote Originally Posted by PeterT View Post
    No. A "jobber" drill is just another name for a parallel shank drill, designed to be held in a jacobs chuck, rather than with a morse taper.

    4.2mm and 6.75mm (6.8 more common) are tapping size drills for M5x0.8 and M8x1.25 threads. Very common in fact.

    Perhaps you're thinking of "numbered" drills?

    Next myth. It's impossible to drill to a 1/100 of a mm, let alone a 1/1000 of a mm. Holes requiring that degree of accuracy are reamed/honed. Drills leave a poor surface finish, that would be +/- 0.05mm.

    Most good toolmakers/fitters can sharpen a drill to cut oversize, because inevitably they do.
    No.

    They are sold as jobbers. I have never heard the term before and I don't claim to speak the jargon, so take it as you will.

    The sizes I listed are only examples. But in the 4mm size I have seen 4.2000, 4.4000, 4.6000 and so on up to 5.0000. This place has many more sizes that weren't of interest to me.

    Not sure what they're for, but they look to me like a drillbit. Measured with my micrometer, they are indeed the size they claim to be (to the second decimal - beyond that ....). I'll try to fish one out when I get home.
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  9. #9
    1000+ Posts PeterT's Avatar
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    Bunnings and my local $2 shop also sell jobber drills.

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  10. #10
    1000+ Posts driven's Avatar
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    Number and Letter drill bit sizes,
    Check out
    http://en.wikipedia.org/wiki/Drill_bit_sizes

  11. #11
    1000+ Posts schlitzaugen's Avatar
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    Here you'd be hard pressed to find anything but common drill sizes in Bunnings. Recently they dropped all taps and dies too.
    ACHTUNG ALLES LOOKENPEEPERS

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  12. #12
    1000+ Posts PeterT's Avatar
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    Bunnings also sell long series drills, in addition to jobber drills.

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