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Old 01-10-2013, 01:58 PM   #16
supershaft
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Quote:
Originally Posted by RGregor View Post
The bulletin I have (the german one) also only says "gauge on the rocker", but then "after 2mm valve lift".
So they must mean to measure the valve side.
Thus the bulletin does not contain cam specs. All data are with respect to valve lift.
The rocker ratio ideally is 1.39, but what I'm not sure of is, if there's a constant ration between lifter travel and valve lift throughout the complete movement. So the question is if you simply can calc backwards to get the corresponding numbers for the lifter side if you want to measure there.

Thus the far from perfect method to measure on the valve side may be the better one.

All the data are with respect to valve lift? Your jumping to conclusions. 2mm valve lift very well could mean 2mm cam lift. It should IF the tech writers are following customary cam card spec practice. There are real good reasons for it just as there are for having specs that include a lift check point.

I don't see how lift is linear with our rocker arms. Yet another reason why most all cam specs are cam specs and not valve lift specs. It's not just me! Look at other cam manufactures of cams for OHV engines.
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Old 01-10-2013, 06:05 PM   #17
tofgasp
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Quote:
Originally Posted by supershaft View Post
All the data are with respect to valve lift? Your jumping to conclusions. 2mm valve lift very well could mean 2mm cam lift. It should IF the tech writers are following customary cam card spec practice. There are real good reasons for it just as there are for having specs that include a lift check point.

I don't see how lift is linear with our rocker arms. Yet another reason why most all cam specs are cam specs and not valve lift specs. It's not just me! Look at other cam manufactures of cams for OHV engines.
The ratio between cam lift and valve lift is inevitably linear, it's the multiple of the cam lift with the fixed 1.39 given by the rocker. For what I know the only possibility of a non linear ratio can only be found with radial valves driven by latch, because the contact areas are parabolic.

When taking measurement on the valves (opening and closing), you can establish a new usable chart and compare the collected data with the one you've got for your cam lift spec. You'll find some degrees less for opening, etc...

It's obvious that using valve lift implies all the potential mechanical plays in the different parts, but I'm quite confident that the most importants are in the cam crowns, camchain and tension spring. I do think also that it's most useful to get the same measurement on both side than everything else, what is directly related to the above statement and the cam shift.

Well... My English is not as good as I would like it to be, so I'm not really sure that all I've said is crystal clear...

tofgasp screwed with this post 01-10-2013 at 06:14 PM
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Old 01-10-2013, 06:47 PM   #18
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Originally Posted by tofgasp View Post
The ratio between cam lift and valve lift is inevitably linear, it's the multiple of the cam lift with the fixed 1.39 given by the rocker. For what I know the only possibility of a non linear ratio can only be found with radial valves driven by latch, because the contact areas are parabolic.

When taking measurement on the valves (opening and closing), you can establish a new usable chart and compare the collected data with the one you've got for your cam lift spec. You'll find some degrees less for opening, etc...

It's obvious that using valve lift implies all the potential mechanical plays in the different parts, but I'm quite confident that the most importants are in the cam crowns, camchain and tension spring. I do think also that it's most useful to get the same measurement on both side than everything else, what is directly related to the above statement and the cam shift.

Well... My English is not as good as I would like it to be, so I'm not really sure that all I've said is crystal clear...
Inevitably linear? It's a rocker arm, not a piston arm. You are forgetting that the pushrod is not just going straight up and down. It is also swaying side to side with the radius of the rocking of the rocker arm. Then you have the other side either rolling or sliding back and forth across the tip of the valve.

Most everyone agrees that checking when your intake is closing is about the most important thing. I wonder if the real tuners time every lobe? That would take some time on multi-cylinders engines with four lobes per cylinder!

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Old 01-10-2013, 07:21 PM   #19
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Originally Posted by Max Headroom View Post
Billy, you've missed the clues given by every engine manufacturer for generations including BMW, when they give cam specs. The usual information given is valve timing specs, along with total valve lift. The term "cam timing" refers to the drive from the crankshaft to the cam, and the relationship between the two.

The cam is primarily there to open and close valves at the pre-determined times, when it's not operating an oil pump or ignition system. This data is based on standard rocker arms, for one thing. A change to the rocker ratio is outside the parameters of factory timing specs.

All cams have specs arrived at by using a degree wheel on the crank to determine the crankshaft position when the inlet valve opens and closes, and when the exhaust valve opens and closes. NOT when the rocker arm, pushrod or cam follower moves.

The 2mm checkpoint is partly to get the cam lobes away from the opening and closing ramps, and partly to avoid valves tangling with pistons.

Valve timing has everything to do with the opening and closing of the valves relative to the crankshaft, therefore it is critical to know the correct check clearance (2mm in the case of an airhead) and the exact crank angle when the valves open and close.

Correct me if I'm wrong but it's my understanding that an increase in the rocker arm ratio would affect valve lift rather than valve timing, using the same check clearance. Any change in valve timing would be minimal..

YMMV etc
Lift ratio won't effect when the valve opens and closes but it will effect valve lift at the lift check point. Two completely different subjects! Because of the check point you are NOT checking when the valve actually opens and closes. You are checking the cams lift 2mm up the lobe so to speak for a variety of reasons. The biggest one being, as far as I understand it, an impossibility to manufacture cams accurately enough at the very beginning and end of a lobe to come anywhere close to standardized timing for the actual opening and closing of the valves. The specs from BMW give cam timing, cam lift, and valve lift with, of course, the stock rocker arms.

For OHV engines there are cam specs AND valve specs. All at the crank, of course. Big diff unless you happen to be running 1:1 rocker arms. Some performance cams do not include valve specs because the manufacturer has no idea what ratio rocker arms you are going to use. Our 336 specs might be valve specs. No one here knows for sure as yet. That doesn't change the fact that for OHV engines most cam specs are cam specs unless they are listed as valve specs. People time them before the heads are on for good reasons. Rocker arm ratios effect valve lift but not cam lift. Rocker arm rations effect valve timing at a lift check point but not cam timing at a lift check point. It is clear to me why most performance cam specs stick with cam timing specs. The term 'cam timing' refers to what position the crankshaft is when a cam's lift gets to the cam's spec's lift check point. That stays constant regardless of rocker arm lift ratio or likely variations thereof. It is not check 'clearance'. It's check LIFT. Big diff!

supershaft screwed with this post 01-11-2013 at 12:23 AM
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Old 01-11-2013, 05:47 AM   #20
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Quote:
Originally Posted by supershaft View Post
All the data are with respect to valve lift? Your jumping to conclusions. 2mm valve lift very well could mean 2mm cam lift.
No, I'm just reading the paper.
It says valve lift, nothing else. IMO it can NOT mean cam lift.
Additionally rocker ratio is not given in the paper. And as you wrote earlier, rocker arm movement is not necessarily linear to lifter/cam lift. So if you measure at the pushrod-side of the rocker you may see the same errors.

Quote:
Originally Posted by supershaft View Post
It should IF the tech writers are following customary cam card spec practice. There are real good reasons for it just as there are for having specs that include a lift check point.
Now we won't be able to change something they specified 30 years ago.
Additionally: cam specs alone will not help as it's always the combination of cam and lifter that defines actual movement (for a roller tappet you nead a completely different cam profile to get the same result as with a flat lifter).

Quote:
Originally Posted by supershaft View Post
I don't see how lift is linear with our rocker arms.
Agree, see above.

Quote:
Originally Posted by supershaft View Post
Yet another reason why most all cam specs are cam specs and not valve lift specs. It's not just me! Look at other cam manufactures of cams for OHV engines.
Probably the reason is that BMW is not a cam manufacturer.
Now, your argumentation about what should be is good but, what does it help? We will not get other specs than those that are given.
You can measure of course but measurements are no specs.
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Old 01-11-2013, 06:47 AM   #21
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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

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/Ca...DegreeCam.html
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Old 01-11-2013, 11:37 AM   #22
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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.


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Old 01-11-2013, 11:46 AM   #23
supershaft
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Quote:
Originally Posted by RGregor View Post
No, I'm just reading the paper.
It says valve lift, nothing else. IMO it can NOT mean cam lift.
Additionally rocker ratio is not given in the paper. And as you wrote earlier, rocker arm movement is not necessarily linear to lifter/cam lift. So if you measure at the pushrod-side of the rocker you may see the same errors.



Now we won't be able to change something they specified 30 years ago.
Additionally: cam specs alone will not help as it's always the combination of cam and lifter that defines actual movement (for a roller tappet you nead a completely different cam profile to get the same result as with a flat lifter).



Agree, see above.



Probably the reason is that BMW is not a cam manufacturer.
Now, your argumentation about what should be is good but, what does it help? We will not get other specs than those that are given.
You can measure of course but measurements are no specs.
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!
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Old 01-11-2013, 12:15 PM   #24
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Quote:
Originally Posted by chasbmw View Post
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

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/Ca...DegreeCam.html
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.
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Old 01-11-2013, 12:27 PM   #25
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Quote:
Originally Posted by supershaft View Post
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. ...and I hope they are!

.. There are basics that HAVE to be.
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.
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Old 01-11-2013, 12:32 PM   #26
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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 !

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Old 01-11-2013, 03:40 PM   #27
supershaft
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Originally Posted by RGregor View Post
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.
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.
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Old 01-12-2013, 03:36 AM   #28
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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

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Old 01-12-2013, 11:39 AM   #29
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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.
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Old 01-12-2013, 12:56 PM   #30
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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!

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