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Using a degree wheel to degree in your L series cams


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Hi Paul,

Thanks for this great info, as I am going to need it.

You mentioned setting the cam up say 0.25" and 0.30" advanced for the cam mentioned above, what would my Rebello cam advanced be?

 

Cheers,

Ian

 

Ian,

Since you purchased your Rebello cam elsewhere, I don’t know where it needs to be set. If you send me all the info you have on your cam, I would be more than happy to contact Dave Rebello and get that info for you.

 

Thank you for allowing me to use pics of your Cylinder head for pics in this thread.

 

Paul

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Paul,

My Rebello cam came direct from Rebello Racing. All the info I have is:

Quote " the cam specs are quite deceiving as the duration at 0.50 is about 226 deg, but the cam makes power like one of our bigger cams due to the unique lobe design. The lift is .487"

The only other thing is the cam is a 63D cam kit.

 

If you can find out the info, thats great.

Cheers

Ian

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Paul,

My Rebello cam came direct from Rebello Racing. All the info I have is:

Quote " the cam specs are quite deceiving as the duration at 0.50 is about 226 deg, but the cam makes power like one of our bigger cams due to the unique lobe design. The lift is .487"

The only other thing is the cam is a 63D cam kit.

 

If you can find out the info, thats great.

Cheers

Ian

 

Ian,

I talked with Dave Rebello today and he told me, with your cam and your large displacement L-series, (3.1) to set your cam up between .010” and .020” advanced. If you want more high RPM breathing he said he would lean towards less advance, i.e. .010” or even a little less depending on where you want your powerband.

 

 

Paul Ruschman

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So why do we degree in our cams? In hopes of getting the most out of our cams, right?

The exact cam timing specs as listed on the cam card or given by the cam grinder are really nothing more than a starting point. For most of the street crowd, they will set their cam to these specs and leave it, which is usually just fine for 90% of cars/drivers.

 

For those of you that are into fine tuning your power band to get as close as you possibly can to your intended goals with the car, just remember that there is NO “set” cam timing figures for any particular cam that works best on all L-series build ups. Your “ideal” cam timing specs will vary for reasons such as gear ratios, gear spreads, track conditions, driver comfort levels in street applications etc. For those of you that are anal about extracting every last bit out of your engines, those figures quoted on the cam card are merely a starting point, and depending on your induction and exhaust system, head work, type of track or street driving you intend to do, gear ratios and gear spreads, etc, you will no doubt be playing with advancing and/or retarding the cam from that starting point to shift the power band around up or down the rev range to maximize the power where you’ll be using it most. Just like finding that ideal ignition timing curve, ideal fuel map, ideal gear ratios, etc, playing with cam timing specs is another tool in the engine tuners tool box, used to “dial in” the engine for maximum performance for its intended purpose.

 

 

 

Good luck,

Paul Ruschman

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  • 3 weeks later...

I have looked and read, and no where did I find the lash adjustment issue addressed. On The L series cam adjustment, the lash adjustment is critical to get the cam degreeded in correctly.

I haven't spoken to Dave about this, so I am not sure if this has been addressed with him either.

 

The L series cam configuration requires that you establish the TOTAL duration of the cam with the valve lash adjustment. Changes in the adjustment will affect the cam opening/closing points, and the lobe centers.

The cam card says to go .010 hot for example. This was the case when I installed an ISKY cam in my car. So I made my adjustments and the duration was wrong, for both lobes. But more importantly, since the duration was affected, on BOTH lobes, guess what, the lobe centers were moved drastically from 114 to 120 degrees, not to good.

So the first thing to do is to establish the total duration of the cam lobe by taking readings with ZERO lash. Verify the duration with the cam card. You should get two sets of information, the cam grind information, and the cam timing based on the adjusted lash setting.

Once you have established that both lobes open/close as stated on the cam card, the overall duration should be dead nuts on the cam card. Good, now that you have checked the cam with the cam card, then you go to the second set of specifications taken @ .050 with the recommended lash setting. YOU NEED TO CHECK THE DURATION AGAIN to verify that the cam duration matches the cam card. IF IT DOES NOT! you will need to make to changes in the lash until BOTH the intake and exhaust durations match the cam card with the @ .050 setting on the cam card. A change of .001 in the lash will change the duration of the cam lobe by about 5 degrees of crankshaft rotation. You can see that a change of 5 degrees in the intake and the exhaust durations will change the opening/closing points of the cam, and when you run your nifty little cam calculator, you will see that the advertised lobe center will be off as well.

Now we have a problem, if you run the car, you could QUITE EASILY make a peeky cam, meaning power will come up at X rpm, but it will be short lived and start to fall off again. NOT GOOD AT ALL.

So find out what lash will bring the duration into the advertised specifications, check and verify both Intake and Exhaust lobes. Once the lash is set, then begin your degree testing of the cam timing using the @ .050 numbers. (AS A NOTE) I dont like to use the @ .050 numbers, because that will change the crankshaft realitive position as the ramp of the lobe is changed, so you still have room for error there. I use the ZERO lash adjustment, AFTER I HAVE ESTABLISHED THE LASH SETTING, and then degree according to the cam card. Once the cam matches the cam card on the intake, then go and verify the exhaust lobe just to make sure everything is still good. Always rotate the cam in a clockwise direction to keep the chain tight when making adjustments to the timing. This will ensure that you did not make an incorrect adjustment of the timing.

The last thing to do is then go and make the lash adjustments to the intake and exhaust lobes based on your previous data. You can then check the timing one last time on the intake or the exhaust lobe to ensure the intake is open at the advertised opening point on the cam card for the @ .050 settings. You should be just about perfect if you have completed the adjustment correctly.

VALVE LASH folks, this is KEY for ANY datsun cam period. When in doubt, check the cam timing with the degree wheel and verify your lash settings to bring the cam into the correct duration.

This adjustment will make or break ANY engine build no question about it.

 

So, I did not want to step on anyones toes here, but this is the CORRECT way to do L series cam timing. ANY other way is hit and miss in my opinion. One thing you need to realize about Dave Robello, is that he tests his engines on the dyno, and he does do the timing adjustments if required to find the SWEET SPOT of the cam in the engine. Granted doing a Nissan L series is not that easy due to the cam sprocket, and generally they are not to bad, but better knowing for a fact about something then to just guess that everything is good.

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First off, I want to thank Jeff P. for posting and adding to this technical thread. His insight is invaluable, thank you Jeff. Also, I would like to thank Jeff P. for bringing up the valve lash point. I went back and reread my posts and I did forget to mention adjusting the valve lash. That is VERY important for the reasons Jeff stated and I do apologize for omitting that.

 

Secondly. When degreeing your cam for an engine that will ultimately be fine tuned once running, (i.e. fuel, ignition timing, AND if you are going for every last bit of power, cam timing), while the engine is on the stand, there is no definitive right or wrong cam timing point to set to, so long as the cam timing is close to the card specs which is a good starting point for optimum cam timing and the valves don’t crash into the pistons. Remember that the cam timing specs as given by the cam manufacturer, are purely a “guideline”, they are not etched in stone specs that will deliver the most power for any given engine build. As Jeff said regarding how Dave Rebello times his cams, the cam will be timed according to where and how the engine makes its power and where the engine builder/tuner “wants” that power to happen within the rev range. This will happen on the Dyno, not the engine stand. Several pulls will be made on the dyno with the cam timing at various points retarded and/or advanced till the power being produced is as close to the desired result as possible. That cam timing spec could be way off from the “suggested” cam manufacturers specs that are printed on the card. The main goal is for the engine to produce as much power as possible within the RPM window the engine will be run, and that will be the ideal cam timing spec for that particular engine combination in that particular car.

 

 

Now back to engine stand cam degreeing. I agree with Jeff 100% in that you should verify ALL of your cam card specs, intake opening and closure points and the exhaust opening and closure points. Also of note, if there is a “small” discrepancy in the values measured vs what is printed, (1-3 degrees is normal), then focus on the intake valve closing point. Of all the cam timing events, Intake open, Intake close, Exhaust open, Exhaust close, it is the closing of the intake valve that has the most pronounced affect on where and how power is produced.

 

Jeff prefers not to use the .050” lift point for degreeing and that is fine. My thoughts differ slightly from Jeff’s as I prefer to use the .050” measurement because the ramps on the cam lobes are steeper at .050” than at the advertised spec or below that, and the readings on the degree wheel should be more accurate as a result, (more sensitive in regards to the crank position vs valve lift). I’m sure this can be debated the other way and I won’t argue my point any further. If you are able to get accurate and repeatable results using another lift spec for degreeing your cams, then by all means, use that spec. In using Jeffs ZERO lash procedure, I agree that is a more accurate means to center up the lobes than what I posted originally in this thread. The Zero lash procedure does add more work and complexity to this process. If we knew without a doubt that a particular cam timing spec as given by the cam manufacture will indeed allow the engine to produce the most power within the range we want, then that method is great. You then should verify that on the dyno as well. Other wise, as mentioned above, the cam timing will be fine tuned for that particular application on the dyno or at the strip, so as long as the cam timing is close to the manufactures specs for engine start up and break-in, you’ll be well served. Remember, these are old Datsun engines, not Ferrari Formula one or NASCAR Nextel cup engines.

 

Also, due to the fact that the Datsun Cams are Asymmetrical, be sure you are consistent in your cam degreeing methods or you could easily get really confused with conflicting readings from your degree wheel.

Cam lobe design is VERY very technical and as such should be left to the cam manufactures. A person could easily spend a life time and earn a PHD in Cam Shaft lobe design and still not know everything there is to know about cam shaft lobe design. Below are a couple of diagrams, (courtesy of David Vizard), one showing just the “basic” regions of a cam lobe and what they are called, the other diagram giving an example of the lift, acceleration, velocity, and Jerk curves, (Jerk curve is the rate of change of acceleration, this directly affects valve train harmonics). You can visually see that there is a LOT more to a cam lobe than just being a “bump” ground on a shaft that merely opens a valve to let air in and out of the cylinder. Cam lobes are VERY complex.

 

 

LobespecsSmall.jpg

 

Accelcrv1Small.jpg

 

 

 

 

The diagram below has two cam profiles overlaid on top one another, on is Symmetrical, the other Asymmetrical. Datsun cams are Asymmetrical. The picture below the diagram is a .520” lift Datsun Cam reground by Rebello racing and its Asymmetry is very clear. If you look closely at the profiles in the diagram, you will notice that if you measure for lobe centers and lobe separation using advertised duration, (typically around .002-.012”, all cam manufactures use different “adv” lift point), and then check at .050”, you will end up with 2 very different lobe centers and lobe separation angles because the cam is ground differently on the opening ramps vs the closing ramps, hence the asymmetry. The cam manufacture will specify at what valve lift the lobe separation is, so it is at those points that lobe centers and lobe separation should be verified. Remember, it could easily be as much as 2 degrees off from the cam card itself and that could be due to tolerances within the grinder itself when the cam was ground, angle of the rockers if you are cheating the wiping pattern etc. Not all cam grinders “calibrate” their grinding equipment on regular basis.

 

Assym1Medium.jpg

 

Lobe2Medium.jpg

 

 

 

 

Again, I would like to Thank Jeff P. For his technical insight and contribution to this thread.

 

 

Paul Ruschman

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I like the write up you did. I know that it took some time to get all of your information on this page, good work. I really like to see good data posted for everyone to use that is accurate.

I really had a hard time of it for a few days doing the cam timing the first time.

I spoke to Dave Robello, John Elgin, Ron Iskyderian, and Jim Wolf during this whole process. Lots of knowledge there, and it was very helpful to me in the process. Jim mentioned the fact that being a chain driven part the the chain and sprocket configuration will also change the cam timing due to the chain trying to ride up the theeth as it spun on the sprocket. So my solution was to get the chain to measureable tolerances with the tensioner I bought from Japan. I have a picture of it on my web page. So that took care of the chain slop issue. (I NEVER liked the tensioner Nissan used with these engines. I have had problems with the chain hitting the cover before when it was very cold outside. The oil just was not thin enough to provide the hydraulic pressure on the chain fast enough. So it was the idle rpm for a few minutes to get the part to work correctly. The second thing I did not like was the chain whip the engine would get from accelleration to decelleration, the chain has a tendancy to get a smooth bend in the trailing side of the sprocket, and again, you get the cam timing moving again. This was verified with the company that developed the tensioner. The were getting changes in hp because of the instability of the cam. so the cam in effect spends much of its time in a plus or minus cam timing situation. Plus the whine of the gears is cool LOL, loud, but cool.) So I got the stability of the cam timing with this part, and I think it is very helpful. The second thing that needed to be changed was the sprocket. This part needs to be adjustable as well. I bought the HKS part, no timing marks, but it adjusts like most of the belt driven adjustable sprockets/gears. Then I was able to acheive full adjustment of the cam, and control it better over the rpm range, accell and decell conditions.

The lobes, now here is the meat of the whole shootin match! Nissans have a nasty harmonic in the standard valve train setup from Nissan. Now with the new technology out there, companies like Sunbelt, Jim Wolf, to name two for the Nissan stuff have developed cam/spring setups that work very well together and reduce the friction of the assembly by almost 50% so that is a very good improvement. So now we have computer programs that can analyze the operation of the cam and rocker in operation. The biggest concern is to NOT get negative curvature of radious in the polynominal representation of the lobe and rocker operation. This is what creates the harmonics, and will create a bouncing motion of the rocker on the cam lobe on the closing side of the lobe, hense the use ofthe asymetrical cam lobe.

I got into this stuff hot and heavy when I was looking into doing a ROLLER cam for the engine, and I still want to complete that work. Maybe I will get it done here in a while, who knows. The cam guru that is working on the lobe configuration has not completed his work.

So yes the knowledge is alot to learn, and I agree, you could spend a lifetime learning all of the need to know information when it comes to cam lobe design. Anyway

good thread, I like talking technical information on a subject like the cam. The funny thing is that once I got sb ford, and chevy engine configurations out of my head, the problems I was experiencing with the timing became clear. I knew something was wrong, but it took a little thinking to figure out what it was. The thing timed very well after I had my head screwed on right.

have a good one.

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  • 1 year later...

I got into this stuff hot and heavy when I was looking into doing a ROLLER cam for the engine, and I still want to complete that work. Maybe I will get it done here in a while, who knows. The cam guru that is working on the lobe configuration has not completed his work.

 

I'm surprised that nobody has come up with a roller rocker for the L-series over the years. OR has someone done it and kept it their little secret?? Can't see why it couldn't be done.

 

Jim

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Sorry for such a late reply, but I learned a new way to check cam timing from my engine dyno guy and thought I would share it. It only requires and accurate timing mark on your damper, and it assumes the inlet and exhaust lobes are the same profile for your cam. It won't tell you the advance or retard in degrees just lift. The lash needs to be set correctly.

 

You can use the piston stop method Paul describes earlier in the post and a degree wheel to determine if you timing tab is accurate or not.

 

Imagine a cylinder of the engine at TDC but not in compression, but on the other stroke--overlap. Both that cylinder's valves will be open some amount. To measure those amounts set up a dial indicator on the closed inlet valve's retainer, zero it, and carefully bring the engine (turning it in the normal direction of rotation) to TDC overlap for that cylinder. The valve will have opened some amount. The indicator will tell you how much. Now, without rotating the engine, transfer the indicator to the exhaust valve retainer on the same cylinder and zero it. Once you are zeroed turn the engine in the normal direction of rotation until the indicator stops moving. The exhaust valve will have finished closing. The number on the indicator now is how much the exhaust valve was open at TDC. Compare the inlet and exhaust numbers. If they're the same the cam is neither advanced or retarded. If the inlet number is bigger the cam is advanced. And if the exhaust number is bigger the cam is retarded. There probably shouldn't be more than .005" difference between the numbers. This method requires only an accurate TDC mark on the crank to work.

 

Don't retard the cam without checking piston to exhaust valve clearance VERY carefully. For that matter don't advance it much without checking piston to inlet valve clearance. This is mainly if you are running a high compression engine with small combustion chambers and domed pistons. Remember that a small error in the TDC mark will double it's effect in the lift difference number.

 

 

You can still get these from Nismo I think:

 

13024-E4621.jpg

http://www.courtesyparts.com/nissan-motorsports-adjustable-cam-sprocket-s30-p-227555.html?cPath=7724_7758&

 

You can advance or retard in 3 degree increments. It is what I used on my recent build.

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  • 4 months later...

Getting ready to degree my cam again-since I have the head off right now for a HG issue. I was staring at my cam card yesterday and realized that the numbers were just numbers too me, no real understanding of what the cam designer was looking to do.. I been reading this lately--

http://www.datsport.com/racer-brown.html---- to try an educate myself on cams and engine building. I have a 270f cam from schneider and after doing some reading I was curious as to what changes were made by Schneider to modify the stock carbed cam. From reading this racer Brown article it seems that the stock cams used an arbitrary valve lift number of .020 for degreeing points. My cam card is at the more standard .050 number, so there is no way to make a direct comparison. I was wondering if any of you engine builders have translated the stock cam number using the .050 lift numbers? This way I could compare what Schneider did with their modifications.

 

I was hoping that someone could go put up a cam card and explain the contents of the cam card.

 

Another thing i got from reading this article was that one focused on getting the closing of the intake valve correct as the number 1 priority. It was stated in the article that the slack in the timing chain causes a retarding of the timing. So if I could only get close to the numbers on the card with my non-adjustable cam sprocket-it would be better to favor an advanced timing since the chain will only cause the timing to retard.

 

Any suggestions on measuring piston to valve clearance?

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In the last few days I had my head checked and it's flat, so time to do some degreeing. I set everything up verifying TDC before putting the head on(dial indicator directly on block measuring #1). As before the numbers on my Cam card are not coming up on the degree wheel. I set things at zero lash and measured the intake side and the timing is coming up retarded(atleast 4 degrees). The biggest concern is that the closing point is late-which I would like to rememdy and if anything be earlier then the card states.

I found a Nismo adjustable sprocket on line for less than 100$-so I jumped on it. Meanwhile, I thought I would adjust the timing with the stock sprocket since it does allow for advancement-or does it?

 

I realized at this point in time that I was stumped on how to relocate the position of the sprocket to the #2 hole. I did this about 4 years ago when i first put the motor together, but I'm not sure now. So at TDC do I remove the sprocket with chain intact to maintain my 41 link separation from the crank sprocket-then rotate the cam advanced to line up the dowel pin to #2??? Since the factory sprocket has this adjustment to allow for chain stretch-what if the chain has no stretch since it is new-can you still make the adjustment?

 

I reread this thread a couple of times and didn't read where it was spelled out on how this change was done. It might be beneficial to all that reference this thread to know the mechanics of actually changing the timing at the sprocket.

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In the last few days I had my head checked and it's flat, so time to do some degreeing. I set everything up verifying TDC before putting the head on(dial indicator directly on block measuring #1). As before the numbers on my Cam card are not coming up on the degree wheel. I set things at zero lash and measured the intake side and the timing is coming up retarded(atleast 4 degrees). The biggest concern is that the closing point is late-which I would like to rememdy and if anything be earlier then the card states.

I found a Nismo adjustable sprocket on line for less than 100$-so I jumped on it. Meanwhile, I thought I would adjust the timing with the stock sprocket since it does allow for advancement-or does it?

 

I realized at this point in time that I was stumped on how to relocate the position of the sprocket to the #2 hole. I did this about 4 years ago when i first put the motor together, but I'm not sure now. So at TDC do I remove the sprocket with chain intact to maintain my 41 link separation from the crank sprocket-then rotate the cam advanced to line up the dowel pin to #2??? Since the factory sprocket has this adjustment to allow for chain stretch-what if the chain has no stretch since it is new-can you still make the adjustment?

 

I reread this thread a couple of times and didn't read where it was spelled out on how this change was done. It might be beneficial to all that reference this thread to know the mechanics of actually changing the timing at the sprocket.

 

The only reason I can think of related to the discrepancy between the card and reality is if you're a tooth off on the chain. I would also verify TDC by using the method outlined in the sticky using a piston stop (I made one at home using a hollowed-out spark plug).

 

I'm not sure why you'd want to set the cam more advanced (open and close earlier) than what the card says. You can do that if what you're trying to do is shift the powerband down. I would set the cam 4 degrees retarded on the #1 cam sprocket hole and go from there since the stock sprocket advances 4 degrees at each hole. You'll have 4 degrees retarded, zero, and 4 degrees advanced to play with if using the stock sprocket.

 

Reference the manual for changing cam timing. DO NOT move the cam or chain when doing this. All you rotate is the sprocket, the cam may need a very slight rotation to seat the dowel in the hole.

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What head gasket are your using? What is the thickness of the head? These two items will effect cam timing. You should always time the cam "straight up", meaning exactly as the cam card states. Don't assume that by advancing or retarding the cam is going to make some HP magic. What pistons are you using? Flat tops with valve reliefs? Have you check piston to valve clearance? These are the things you need to be aware of when changing cam timing. You have to start somewhere, so start straight up.

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What head gasket are your using? What is the thickness of the head? These two items will effect cam timing. You should always time the cam "straight up", meaning exactly as the cam card states. Don't assume that by advancing or retarding the cam is going to make some HP magic. What pistons are you using? Flat tops with valve reliefs? Have you check piston to valve clearance? These are the things you need to be aware of when changing cam timing. You have to start somewhere, so start straight up.

 

It's not "HP magic", what you achieve by changing cam timing is altering the torque curve, essentially shifting it one way or the other. There is no requirement written in stone that you must time it that way. Best performance for the given requirements is found by using the adjustable sprocket and a dyno and it won't necessarily be what the cam card says. You should make sure that the valves don't hit, but if the cam is fairly mild then it shouldn't be a problem. I suppose you could time it "straight up" but make sure that you do so on the #2 hole if using the stock timing sprocket. That way you'll have 4 degrees of advance/retard if you want to play with your torque curve using the stock sprocket.

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Pete,

I am attempting to meet the cam card specs, but as I stated earlier, I am not reaching that goal with the stock sprocket setting-at least not #1 position. The readings are coming up retarded, which is the way I ran the engine the last 5k miles.Not looking for any magic, just to see if i notice a power change getting closer to stated specs on card. Schneider tech guy told me at the initial installation that my numbers were coming in slightly retarded, but running a manual gear box would help offset that and i would be losing some bottom end. So that's the way I ran the engine till this point. Now I want to dial it in closer to specs.Also, as I stated in reading Racer Browns article, it seems that you already get a retarding penalty from running a chain driven cam, so I don't want to leave the valve timing retarded. Though I must say the engine ran very good at lower rpms-lots of torque, so it will be interesting to see if feel any difference.

 

As far as valve clearance, I am ASSuming that my meager 480 lift cam should have ample clearance if I am close to specs on the valve timing.

 

As far as head gasket goes, the one I took off measures around 1.2mm and that is what the Nismo measures at once compressed(if I ever get it).

 

since writing the last post I have searched and found how to change the sprocket setting-thanks Leon. When you stated off by a tooth-do you mean too many links between the cam and crank?

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