Rocker ratio airheads

Discussion in 'Airheads' started by chasbmw, Jan 9, 2013.

  1. chasbmw

    chasbmw Long timer

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    Well, there is a lot of discussion here, most of the stuff that I find understandable, seems to come out of the Antipodeses or Germany:deal

    I will sart to strip down my engine next week, there are a couple of jobs to be to the flywheel, that need outside work, but hopefully I will have the new cam in place and the cylinders and heads back on in a couple of weeks, so I will be able to take some measurements.

    Interested to get a walk through from someone who has actually done this, rather than endlessly discussed the theory.

    This site looks interesting and I think will help me even though much of the Mathis is may beyond my pay grade.

    http://www.tildentechnologies.com/Cams/Tip_DegreeCam.html
    #21
  2. BOETJE

    BOETJE Been here awhile

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    That is quite a good website you mention there.

    For the rest : stick to what TOFGASP , Max Headroom and MGREGOR told you and you will be fine.
    Not a pushrod airhead, but you get the idea.

    [​IMG]
    #22
  3. supershaft

    supershaft because I can

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    It says valve lift? But cam lift causes valve lift. We already know there are typos and errors in these bulletins. This might be one of them. I hope so so that we can better time our cams. That is my point. There are no standards in the cam industry but there are traditions for good reasons. Calling cam specs cam specs and valve specs valve specs is one of them. The 336 bulletin I have mentions cam lift and valve lift. The rest of it reads like cam specs to me and I hope they are!

    The pushrod side of the arm will have a fraction of the errors the valve side has for not having any lift ratio to deal with. It's that simple.

    Cams are always designed and timed with a specific lifter design in mind as far as the lifter design effecting cam timing. That should be a given. You are all over the map. Get back on a road . Any road. There are basics that HAVE to be. It seems like MH and others still haven't figured out what a lift check point is and now your telling lift depends on the lifter. Of course it does!
    #23
  4. supershaft

    supershaft because I can

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    I have timed a few cams but not a 336. That is a decent article but I suggest reading a lot more. IMO Smokey Yunick is a good source. It's nice to see someone besides me mention a cam card!

    Timing SOHC and DOHC engines are apples and oranges compared to OHV engines. For instance, on a lot of DOHC engines cam timing IS valve timing to the tee. It's the same as working from a lifter on our engines. The photo of the DOHC RS54 engine? Despite any rocker arm ratio and I suspect there is, there is probably no other way to time the cam. Not so with our engines.
    #24
  5. RGregor

    RGregor Been here awhile

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    Yet another fruitless "discussion".
    You hope something and that counts more than any argument.

    That's fine with me. Just say at the beginning: "I hope the world is a disk and better not contradict me".
    Or put it in your footer.

    I suggest the following: take your engine and time your cam wherever you like. Then we all will know what kind of specs these are. That would put you on a road. So you have all means to do it, just do it.
    #25
  6. BOETJE

    BOETJE Been here awhile

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    Timing SOHC and DOHC engines are apples and oranges compared to OHV engines
    
    No it's not...

    Off course OHC engines have a rocker ratio. And it varies a lot during the valve movement. That's why they have to
    grind the cam lobe asymtrical, to get a symetric valve lift curve.
    It's the job of the cam designer to shape the cam lobe to get a certain valve lift curve, taking all the geometry into
    consideration.....not an easy job I believe.
    Nobody cares what it does at the cam itself as long as the goods are delivered at the valve.

    I like Smokey Yunick's book, but I like other books even better....

    DAMN !!! I was adamant not get involved in this ! :cry
    #26
  7. supershaft

    supershaft because I can

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    More psycho analysis? You should be hoping too since you are like me in that you know as little as I do about our cam specs specifically. The difference between the two of us is that I do know about the basics of cam specs in general and I am using that as a basis for my discussion. You, on the other hand, were and still are very unaware of some very basic cam timing knowledge. At least you now seem to understand what and why specs need a lift check point unlike a good number of contributors that are trying to tell me about cam basics. I walked you through that and you are still giving me grief? It is a pretty sad state of affairs. You should let those of us that understand and do these things get on with our discussion.

    I have already described why I haven't timed my 336 as yet: It is running good and I have no way to adjust the timing if I wanted to. Time my cam where ever I like? In order to duplicate the specs which is the whole point of checking a cam's timing to start with I can't time it where ever I like. It will check out or come close to checking out at the cam or at the valve. I hope it's at the cam since that is where the smart money times their cams for all the variables the pushrods and rocker arms bring into the picture. You can call that a fruitless discussion all you want. It wouldn't be fruitless if you boned up on cam timing a bit.
    #27
  8. chasbmw

    chasbmw Long timer

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    boertje,

    Thanks for the advice, I will continue to ignore the verbiage that comes from people that don't appear to have timed a cam, just read about it. That's a very special engine you have there.

    motoren Israel supplied me with a very well made timing wheel and the dial gauge arrived today:clap

    Charles
    #28
  9. BOETJE

    BOETJE Been here awhile

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    Well done Charles ,

    The RS54 is not mine , but an oversea's collector. I was asked to take it appart to see if there was no funny bussiness going on in there.

    Don't take too much notice of some posters arrogant boorish behaviour,MGREGOR.
    I'm sure I'm not the only one who apreciates your comments.
    #29
  10. supershaft

    supershaft because I can

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    You guys are cracking me up! Only here on the idiotnet can someone who actually knows a little cam basics and has actually timed a few cams in the past and goes to the trouble to explain to some of you the most basic elements of timing cams get accused of being arrogant and boorish by people that obviously know almost nothing about it. From what I can tell, myself, pj, and that guy on the other cam thread that timed one of the other cams in question are the only people that write as if they know what they are talking about. Moorespeed says he has timed tons of them but won't give up a single detail while at the same time making generalized comments about the 336 that are the polar opposite of what myself and other inmates here have experienced. Then some came to his defense saying that it was proprietary. What!?! Checking a cam's specs is not proprietary! It's part of installing a cam! In the mean time inmates are mocking me discussing check points like I made the subject up. Hilarious! I am real green when it comes to cams but at least I know where to start. I am still here to learn. Some of us do this stuff ourselves and want to figure out what is going on while you two and others bitch and whine about the rest of us discussing cams with a least a little familiarity. Damned Human Nature Rampant on the Idiotnet!
    #30
  11. RGregor

    RGregor Been here awhile

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    SS, cool down.
    I thought it was very simple. The question that arose here, whether BMW specs are right or not, will not be answered by talking. How could it?
    This simply takes some work: timing a 336.
    Now, who could do that?
    Know anyone having such a cam in his engine?
    And having the skills and knowledge .....
    Now, if you doubt the specs, then measure and prove they're wrong.
    What's so difficult to understand about that?
    #31
  12. supershaft

    supershaft because I can

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    Cool down? Give me a break! I am not the one going on and on with personal crap like you guys have been doing for months now. Cracking up is laughing, not steaming! Do you read my posts? I never said I doubt the specs. I said that I believe they are cam specs and the reasons why I suspect and hope they are. Meanwhile, you and others are up to your usual crap. Where do you come up with this stuff? I have told you numerous times now why I have as yet not timed my cam. Now that I want to I am going to have to get a degree wheel. Until now, I have just used the shop's working for hire or used a friends. Before I get one I want to decide what size I am going to get. I think I am going to get a monster one for now and just time them out of the frame.
    #32
  13. bereahorn

    bereahorn Long timer

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    While looking at Snowbum's site for something else, I ran across this section and thought it might hold some information of interest for this thread. And by the way, I'm just the messenger.

    7. BMW camshafts: This is a VERY confusing subject for many folks. Besides the confusion on camshafts, there are sprocket complications. There are several stock camshafts, and some available camshafts. For the stock cams, at .080" valve clearance, the timings are as follows, keep in mind that TWO types of these are available, the 3° advanced one and the NOT advanced one. There are a number of stock camshafts, 284°, 308°, and also a 336 degree.

    R50/5, R60/5, and R60/6 (to 1975): INtake opens 40 ATDC; closes 40 ABDC. EXhaust opens 40 BBC; closes 40 BTDC.
    R60/6 1976 and R60/7 1977: INtake opens TDC; closes 40 ABDC. EXhaust opens 40 BBDC; closes TDC.
    R60/7 1978: INtake opens 6 BTDC; closes 34 ABDC. EXhaust opens 46 BBDC; closes 6 BTDC.
    R75 and R90; R100/7; R100S; R100RS 1977: INtake opens 10 BTDC; closes 50 ABDC. EXaust opens 50 BBDC; closes 10 BTDC. (This is the symmetrical cam talked about a bit farther down in this section #7)
    R80/7, R100/7, R100S, R100RS (1978): INtake opens 16 BTDC; closes 44 ABDC. EXhaust opens 56 BBDC; closes 4 BTDC. (This is the advanced cam talked about a bit farther down in this section #7)
    From 1978, the U.S. models (R80/7 and larger) had INtake opening 10 BTDC; closing 44 ABDC; EXhaust opening 56 BBDC; closing 4 ATDC.


    note that sometimes cams are spoken about as the total degrees, and the 1978 would be 308°

    see: http://www.softcom.net/users/W6rec/duane/bmw/engine.htm
    also see Clymers, Haynes, the BMW books, etc.

    336 degree camshafts, the so-called sport cams are the ones ending in part number -053, -412, and -393, see below and note that the last batch of the 336 cams was for the square drive oil pump, and the cams come with the oil pump parts.

    NOTE #1: The 336 cam has about a .424" lift, soft ramps, and runs strongly between 5700-7700 rpm, with roughly 8000 max rpm.

    NOTE #2: BMW uses .080" of valve setting clearance ( 2.0 mm) as the reference point for cam timing, and the tolerance on timing is + or - 2.5°. Also note that if you are measuring at the CAM lobe itself, that the R60/7 had a 0.2417" lift; and the later larger bore engines had 0.2634" lift. NOTE however that the rocker arm ratio on all the engines is 1.39, so for valve lift you multiply the cam lobe lift by that 1.39 factor.
    Another way of saying all this is that the valve pockets in the pistons might have to be modified. The 284° camshaft has 8.62mm lift; the 308° camshaft has 9.40 mm lift, for some reference points here.

    11-31-1-258-053 has small cam seal, used on /5 to R90S (to 1976 model year); and was replaced by the -337-848 cam per book, in error, says K.
    11-31-1-263-412 has large cam seal, used on R60/6-R100/7 (to 1979 model year); replaced by the 337-843 for both /5 and /6.
    11-31-1-336-393 used on canister ignition models, from 1979, including the R65 (?). This cam has a slot on the front face.

    NOTE #3:...to further confuse the issue, there were TWO versions of the -053 and -412 camshafts. The difference is the KEYWAY for the gear. The later versions is advanced 3°, so the valve timing versus the crankshaft is changed 6°. The -393 flat nose cam is available ONLY in the advanced version.
    The cams are not easily identified by appearance, and must be measured. If an old cam is installed in a 1979+ engine, the slot is retarded 3 degrees.
    Here is the timing for these sport cams:
    ZERO degree cam: INtake opens 32 BTDC; closes 52 ABDC. EXhaust opens 52 BBDC; closes 32 ATDC.
    THREE degree cam: INtake opens 38 BTDC; closes 46 ABDC. EXhaust opens 58 BBDC; closes 26 ATDC.

    NOTE #4: UNconfirmed data for the sport cams, where P=(inches):
    4000 rpm, 3° cam, P= 46. For 6000 rpm P=30. For 7000 rpm, P= 25.
    for the zero degree cam, add about 2 to the P figures above.

    The entire camshaft story is very complex, and I am not going to put it all in this article, but, refer you to someone else's article:
    http://moragafalconers.org/BMW_336_cam/
    That is a link to an article that was translated and edited by David Paulus. I think that on the first page there is an error in the part number for the item 2 cam, which should be, I think, 11-31-1-263-412, and, that it is questionable that the cams won't fit the R45 and R65. One additional note: under figure @1, at C., it describes a 'suitable washer'. Try 11-34-0-026-186, as originally used on the R69S. NOT cheap! The washer is tough, made of fibre, and insulates the spring from heat, when the engine is suddenly stopped.


    NOTE #5: In 1977-78 BMW made changes, that amounted to a 6° difference in timing. This was done by changing the keyway in the camshaft sprocket. Because of this, if one uses the 1978 camshaft, and then uses a 1977 sprocket (11-31-1-250-253), then the timing is retarded. Engines/bikes imported to the U.S. from roughly January 1st of 1978 HAD to have the advanced timing, to meet the 1978 emissions rules. Many just before this date did NOT. Thus some "1978" might not have the emissions camshaft.
    Here is a sneaky way of determining things, an edited version of something passed on by Tom Cutter:
    Remove the spark plugs and valve covers. Put bike in 5th gear and rotate the rear wheel in the forward direction until the EXHAUST valve rocker arm pushes the valve inwards and then JUST returns ALMOST all the way outwards. As you rotate the wheel (jerks work fine on the gear backlash for that purpose) and the exhaust valve starts to come back out, the intake will start to go in. This is the overlap phase. Lay a straight edge across the adjustment LOCKnuts, from the exhaust to intake rockers. Looking straight down on the rockers, and on the straight edge from above, the straight edge will change angle relative to the valve cover gasket, as you turn the rear wheel. STOP when it is parallel. At this point, if OT mark is lining up in the window, the cam is symmetrical. If it is about 3/8" below the window, it is the advanced timing cam.
    #33
  14. Other Bob

    Other Bob Been here awhile

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    Would these tools help? -

    http://www.andrewsproducts.com/ezcam/key-features

    http://www.andrewsproducts.com/cam-design/cam-design-software

    I thought this tidbit from the Smooth4W (Cam Data Analysis Program) summary was noteworthy:

    "Smooth4W can also import valve lift data (not cam lift) and convert it to cam output. If you have a valve lift curve and need to generate data for manufacturing a cam lobe to produce correct finger follower valve motion for your engine, Smooth4W can do it."

    Constructive thoughts?

    Bob
    #34
  15. RGregor

    RGregor Been here awhile

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    The bulletin clearly speaks of valve lift. You believe it must be cam lift. So you doubt the bulletin. This point is crucial for timing and thus the specs. So you doubt the specs.
    This is very simple.

    All I mean is, if you doubt it, prove it to be wrong.
    Until then you shouldn't build an argumentation on your hopes, calling anyone an idiot not believing in you.
    Again very simple.

    So do us all a favour, time your cam and deliver data. Not hopes.
    #35
  16. chasbmw

    chasbmw Long timer

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    Berahorn,

    The snow bum information is interesting, but since it was last revised there is a much wider choice of camshaft available, in the old days it was either the stock 308 degree cam or a 336 and that was about it unless you were unlucky enough to fit an Andrews sports cam.
    Take a look at the Motoren Israel web site and you will find a much wider variety of cams.

    Snow bums article has reminded me that with airheads the devil is in the detail, if you are building a pre 81 engine out of parts, unless you check the cam timing, it would be easy to end up with a bike that runs badly and you would have no idea what caused the problem.
    #36
  17. RGregor

    RGregor Been here awhile

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    A friend has timed all airhead cams he could get hold of, measuring valve lift in 2° crank angle steps with digital gauges with a resolution of 1/100 mm. He measured lift at the retainers.
    He gave the data to me for my personal use, not to publish them in a forum, but today I'll make an exception.

    I took the data for the 336 and determined the angles corresponding to 2mm valve lift and 2*1,39mm lift (2mm cam lift).

    The angles are
    <table border="0" cellpadding="0" cellspacing="0" width="596"><colgroup><col style="mso-width-source:userset;mso-width-alt:4827;width:99pt" width="132"> <col style="width:60pt" span="4" width="80"> <col style="mso-width-source:userset;mso-width-alt:5266;width:108pt" width="144"> </colgroup><tbody><tr style="height:15.0pt" height="20"> <td class="xl65" style="height:15.0pt;width:99pt" height="20" width="132">
    </td> <td class="xl65" style="width:60pt" width="80">Ex-open </td> <td class="xl65" style="width:60pt" width="80">Ex-close</td> <td class="xl65" style="width:60pt" width="80"> In-open</td> <td class="xl65" style="width:60pt" width="80"> In-close</td> <td style="width:108pt" width="144">
    </td> </tr> <tr style="height:15.0pt" height="20"> <td class="xl66" style="height:15.0pt" height="20">Measurement</td> <td class="xl65">50</td> <td class="xl65">32</td> <td class="xl65">30</td> <td class="xl65">54</td> <td>(2mm valve lift)</td> </tr> <tr style="height:15.0pt" height="20"> <td class="xl66" style="height:15.0pt" height="20">Measurement</td> <td class="xl65">40</td> <td class="xl65">24</td> <td class="xl65">20</td> <td class="xl65">42</td> <td>(2mm cam lift)</td> </tr> <tr style="height:15.0pt" height="20"> <td class="xl66" style="height:15.0pt" height="20">BMW Spec</td> <td class="xl65">52</td> <td class="xl65">32</td> <td class="xl65">32</td> <td class="xl65">52</td> <td>(2mm ????? lift)</td> </tr> </tbody></table>
    Feel free to determine what the ?????? mean.
    #37
  18. chasbmw

    chasbmw Long timer

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    Thanks Rudi, you have proved your point thanks for all your usefull and pertinent info.

    I will also share my info on the 320 cam when I have done the work.
    #38
  19. RGregor

    RGregor Been here awhile

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    There was nothing to prove.
    My point was not that the BMW specs were right in any case.
    I didn't know myself prior to verifying.
    It simply was how to behave having little or null knowledge.
    #39
  20. RGregor

    RGregor Been here awhile

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    Yes I did. Not all but many.
    Re-reading the posts in the cam thread is very funny now.
    http://www.advrider.com/forums/showthread.php?t=804634

    Especially regarding the fact, that except PJ no one here has timed his 336. Not you, not the "crowd in the back".
    Again a very good example on how some people behave.

    Regaring the numerous times you told me ....

    I have told you a few posts ago that until then I didn't know it, in fact I have never read the slightest hint in that direction and I would be very surprised if we found these info in any of your posts here.

    So, I don't know whom you talk to and how.
    But stop it, it's not me.
    #40