How to degree your RBxx aftermarket cams

Discuss the RB20, RB25 and RB26 series engines.
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Carl H
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Since there is NO info anywhere on how to degree rb cams and the info that is out there is as clear as muddy water I decided that I would post a proper write up on how to degree your cams.Please note that I am using a ross metal jacket balancer with an integrated degree wheel, so the math isnt the same if you're using a traditional degree wheel but IS applicable if you're using the degree wheel which comes with some after market cam sprockets (my greddy gears came with a 360* wheel printed on a piece of paper).

Tools needed:1" travel dial indicatordial indicator standCoat hangerpiston stoppencil and papercalculator (if you dont like doing simple math)

Step one - locating true TDC on your crank pulley/wheel:This is the most important step of the process, do this wrong and you might as well not do it at all or possibly bend some valves, so be FORWARNED!Remove all spark plugs before you start, else you'll find its nearly impossible to get readings without a struggle.Crank the engine over by hand to the factory marked TDC using the notch on the lower timing cover as well as the marks on the cam gears on the timing cover backing plate.The cam lobes for both intake and exhaust should be facing outwards towards the fenders (cylinder 1).

Crank pulley @ 0*/ TDC

Cam gears @ 0* crank / TDC

Next you'll need to fashion a pointer out of the coat hanger wire, I chose to bolt my pointer to the power steering pump as it was a rigid surface out of the way of movement.You'll want to adjust the pointer to read 0* on the crank, you'll be most likely changing this later so it does not need to be exact.

Pointer made out of a short length of coat hanger bent to shape; note a slight bend in the pointer as well as the sharpened point on the pointer for accuracy.

Pointer aligned to 0* on the crank

An alternate method of finding tdc is to stick a 1' 3/8" drive extension down the spark plug hole and by finding the 'peak' height of the extension one can find the almost exact tdc within a degree or two, this is useful when setting your crank pulley to 0*.

Extension in cylinder head

Now you need to install your piston stop.These can be purchased commercially for around 20$ or if you have a few parts laying around (or are cheap/broke) then you can fashion one from an old spark plug.I chose to make one as I am impatient and did not want to wait till later this week to have a piston stop so I made one from an old spark plug and an m10x1.5 thread pitch bolt...sparkplug body was tapped for m10x1.5 and the threads on the purchased bolt extended using a tap, one should tap all the way to the head to allow a jam nut to be used but bottoming out the bolt works just as well.

Piston stop assembled

Piston stop body installed in head

Before the piston stop bolt is installed you'll need to turn the crank approx 60* BEFORE TDC, this will ensure that you'll have enough travel to install the bolt into the bore without hitting the piston prematurely.Install the piston stop bolt to desired height (in my case bottomed out) and lock it down with a jam nut.Rotate the engine BACKWARDS (counter clockwise) by hand using a socket on a ratchet, eventually the piston will make contact with the stop...do this slowly and stop rotating when the piston stop is engaged; you do not want a nicked piston.Make a note at what angle the pointer is resting at in this case it was 44* btdc

Pointer on first round of piston stop

Now for some simple math...To figure out what other degree we are looking for to ensure that we are at true TDC we simply subtract our first angle from 360.so 360 - 44 = 316

Rotate the engine now CLOCKWISE till the piston stop engages the piston; note the degree at which it rests at.In this case the pointer stopped at 315*, which is very close but still not exact...

Pointer at 315*

Adjust the pointer so that it reads tdc properly, my pointer required just a slight nudge to be spot on, you may find that you'll have to do the aforementioned process a few times to get your pointer lined up with true TDC.Remove the piston stop from the engine, FAILURE TO DO SO COULD RESULT IN DAMAGE TO THE PISTON IN PROCEDING STEPS!Once you've completed adjusting the pointer to true TDC you can proceed to step two.

Interlude - Setting up the dial indicator:For this step you'll need to make another special tool for the dial indicator to do its job, this is due to the lifter design of a cam on bucket setup.Since a dial indicator would normally rely on something pressing against it such as a rocker arm or crank run out we dont have the luxury of this with a cam on bucket setup.to get around this the dial indicator must be preloaded in order to induce a measureable change.For both intake and exhaust measurements the dial indicator was preloaded to .5" which gave good results and the ability to take measurements at several points during the cam's phasing.Due to the space constraints you'll need to fashion an extension rod from a coat hanger using a straight length (as straight as possible) and a small piece of shrink wrap.Most dial indicator tips can be removed from the dial indicator...you'll need to do this.Coat hanger wire by its self is too small to fit into the dial indicator but once some shrinkwrap is place around it and heated you'll find that it can be then screwed into the dial indicator resulting in a very tight fit and rather accurate extension.You'll also need to angle the tip of the extension rod as there is simply not enough lifter area available to place the dial indicator extension...Be sure that you round and smooth th end of the extension so as not to mar the lifter surface.

Here is the extension that I made for my dial indicator

Step Two - degreeing the intake cam:Here is where it begins to get fun, don't be intimidated tho its really not that hard (well after you figure it out).You'll need to mount your dial indicator so that the actuation rod is parallel to the valve stem, a good guide for this is the cam tower bolts as they are also parallel to the valve stem.Again as stated before be sure to preload the dial indicator before you mount it, do not have it set to '0' or nothing will happen when you turn the crank... I used .5" as preload which worked well I would not suggest anything lower.

Shot of the dial indicator mounted on the intake cam

Shot of rod placement on lifter

Make sure when placing the dial indicator rod that the tip does not get caught under the cam lobe...this is quite possibly the hardest part of the whole process.Once you have your indicator setup and 'zeroed' out (start with 0.50" for example, not 0.513") you are ready to begin.Begin by rotating the crank by hand CLOCKWISE while watching the intake cam lobe (cylinder 1) you will get to a point where the dial indicator will begin to move and DECREASE in measurement.Pick a nice round number such as 0.4" or 0.3" (I used 0.3" for my measuring) as a reference value for finding the center line, it is best to use this value for both sides to avoid confusion.Eventually the dial indicator will reach a minimum an 'bottom out' at which point max lift has been reached.Continue turning clockwise and the dial indicator should increase and eventually reach your initial preload setting.Go around again this time watching the dial indicator and when it gets to your reference value (again in my case 0.30") take note at what the degree reading on the wheel is, write this number down.Continue turning the crank till you reach max lift, again pay attention to the dial indicator and when it reaches your reference value again stop turning and record the number of degrees on the crank.

Once you have these numbers its time for some simple math...1) take both numbers and subtract them from 360.2) add both numbers together3) divide by 2

example - my degree numbers from my measurements (might have been 0.40" or 0.30", i did several iterations but they all should come out the same regardless of choice of reference value).318 and 172360 - 318 = 42360 - 172 = 188188 + 42 = 230230 / 2 = 115

Find out from your cam card what the degree value ATDC for the intake cam should be, for my tomei pro cams the value was 115 so no adjustment needed!

Should the cam need adjustment remember these three things:1) cam hash marks denote 2* of crank time unless otherwise specified (1:2 ratio)2) if your simple math worked out that the value was HIGHER than specified then you need to RETARD the cam3) 2) if your simple math worked out that the value was LOWER than specified then you need to ADVANCE the cam

It is best to check several times to make sure that you are on the right track...when I checked my cams with different reference values they all yielded 115* atdc so I did not have to change my intake cam at all.

You are now done with your intake cam.

Step 3 - degreeing your exhaust cam.Setup for this step is the same as for the intake cam except that we are looking for degrees BTDC.

Dial indicator setup on exhaust side

Once you have your degree values your simple math is a little different and is as follows1) add both values together2) divide by 2

example from my measurements using values of 191 and 45191 + 45 = 236236 / 2 = 118

Uh oh, we have a problem...tomei specifies the exhaust cam is spec'ed to 115 BTDC.There is a difference of 3* crank here between specified and what is shown.Since cam time is double that of the crank to get 3* crank we need 1.5* cam, and since this is advanced compared to what is specified we need to retard the cam 1.5* to get our 3* crank back.

After resetting the cam to 1.5* retarded I found the following values of 212 and 18So simple math ensues...212 + 18 = 230230 / 2 = 115

Perfect!Exhaust cam is now in phase according to tomei.

Remember to tighten the cam adjusting bolts temporarily while making adjustments and to torque to proper spec once adjustments are complete...you do not want your cams to slip as this can cause catastrophic damage to the engine.Remove the temporary pointer and be sure to reset your base ignition timing, depending how far out your cams were you may need to also retune the engine.

If you've followed all the steps properly your engine should now be in complete time as per the cam manufacturers specifications and perhaps on your way to more power, better idle vacuum, and drivability.


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placham
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that is some good stuff Carl. You got text and pics

----edit, thanks for answering my q's in your other thread-----

Also as I look throught your write-up.

What length did you get the bolt, its a m10x1.5pitch x _?_length for the piston stopper tool you made.

Where did you get that Pitwork timing belt, if you dont mind?

Modified by placham at 12:40 AM 5/19/2009
Modified by placham at 12:44 AM 5/19/2009

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virus77
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awesome post!!! great information

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cdorhout
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Yes Carl, awesome post. Darius and I have been talking about degreeing cams lately. Especially with my RB30 where my stock timing marks are probably wrong.Thanks!

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Carl H
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yeah, i'd imagine with the 30 that your cams are a few degrees out...I had never degreed my cams before, and the car pulled like a raped ape but after the rebuild it just never felt the same.It pulled worse vaccum and just felt laggier, the 1.5* advance on the exhaust cam was most likely the culprit as if anything the exhaust cam should be retarded compared to the intake.If you want to degree your cams I could proly 'rent' you my equipment...I dont forsee me needing to degree cams in the near future nor check run out of cams/cranks/small kittens.the writeup is pretty accurate but i think there are some errors concerning the direction of rotation when finding true tdc...I'll sit downt this evening and go thru the post again and check...what i get for writing this at 1a after working on the car all day.

Darius
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I felt the same way Carl. My car never ran as smoothly after the rebuild even after fixing valve length issues.

I have looked high and low on the internet for HKS 256 cam degreeing specs but I cannot find them. I have a question into an authorized dealer, but if I don't hear from them today, I'll call HKS USA corporate and see if I can get thru without being a dealer.

edit: Carl I am updating your link below since HKS must have moved some stuff around. Here is the new link: http://www.hks-power.co.jp/db/...D=605
Modified by Darius at 2:57 PM 3/30/2010

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Carl H
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darius - heres what you're looking for...http://www.hks-power.co.jp/pro....htmlthat is all of hks's cam shaft data so any nissan/toy/mitsu/mazda/subby cams that hks makes is on there.you'll notice tho that the center line for the rb25's cams are 115* I/E just like my tomei cams...but the rb20 cams have different center lines between the 256's and 264's.

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krayton
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thats awesome carl. im sure when i finally get cams ill dig this up to ask a billion questions and if u still rent out your tools.

mucho thxs

darksurfer81
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Very nice write up. Like the earlier question where did you get the new belt? We have the valve and cam covers off for painting and Im thinking of changing the timing belt so I should probably degree the cams espeically since we both know how the wiring was done...

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Carl H
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tim - a stock engine with stock cams should not need to be degreed...its over kill but you'll proly find that it wont be off. T-belt change is proly not a bad idea...who knows when it was last done.

placham - timing belt and other components related to timing AND the ross ballancer were bought from my good friend ricky @ raw brokerage...the pitwork belt is an oem belt apparently.

ANYWAYS, on to point.If you have aftermarket cams or have rebuilt your engine I STRONGLY reccomend that you degree them to reset them to spec.Car is back to what I remember it being years ago before the rebuild, I wish I had done it sooner.Engine pulls more vaccum now and is back to where it was before (-5.7 to -6psi at idle vs -4 to -4.5).Egts are MUCH lower under full boost, highest I saw was about 770*c vs the almost 875* I was seeing previous.Not sure if spool was improved any as one of the exhaust studs has kindly broken off so I have an exhaust leak which before degreeing I could tell a difference in spool time (longer).And the major difference here...the car hauls complete a**, its not laggy or doughy but just straight up balls out!Who would have thought that 1.5* cam time could change the way a car drove...

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cdorhout
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Carl H wrote:If you want to degree your cams I could proly 'rent' you my equipment
Thanks Carl, that's very cool of you. Right now I don't even have adjustable cam gears, but once I do i'll shoot you a pm.

Thanks!

mott6904
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I hope this is my issue also. I just bought the os giken gears that have been on ebay for a long time, I hope they are in good shape. Did you set it to cam card specs or did you readjust after that? I will be doing this soon, I cant wait to see if it fixes my issues.

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virus77
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what would a stock rb25det intake cam need to be at? also 115? Reason I ask it because I had my intake gear apart and its adjustable from the factory so I would like to degree it back to stock. I lost all reference points of the cam-to-gear allignment (stupid mistake). I did however modify the stock cam gear so I could adjust cam timing without having to pull the whole gear apart to access the bolts from behind so as long as I know what to set it at I should be ok. Car runs fine, pulls -9psi (-18 in)vacuum, but its more for peace of mind.

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Shocker
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Very nice walkthrough carl!

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Carl H
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mott - if you have cams and have had the head or block decked i STRONGLY reccomend that you degree your cams, i set mine back to the specified intial value that tomei stated and it is a night and day difference. you can readjust via a dyno if you care to but I am happy with how the car feels now.

virus - check out this website : http://www.tomei-p.co.jp/_2003....htmlr33 rb25det intake cam is set to 120* intial, i have found that a stock rb25/20/26 will pull around -20in/hg or ~-10 psi.

shocker - thanks, i know you were having cam issues before so perhaps when you get the beast back together doing this will yeild more favorable results.

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Shocker
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Carl H wrote:
shocker - thanks, i know you were having cam issues before so perhaps when you get the beast back together doing this will yeild more favorable results.
Definitally will. I will be posting some stuff up here in the next few months that you and some others might find interesting. I'm going a little different route this time. I'm getting exciting to start spending money again.. HA.

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virus77
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quick questions, what degree wheel should I pick up to go about this since I dont have aftermarket cams and how will my math varry as stated in the first paragraph of your post...

also does the link you provided in the last post have a significance in degreeing a cam or is it a wrong link perchaps... it seems like its talking about how tomei builds their cam profiles... thanks again.

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Carl H
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ah link was wrong, i've been on tomei's site all this morning and got link happy...its fixed now.

only difference in math is instead of subtracting the numbers from 360 for the intake you just add and divide like the exhaust side...i think, i'll dig up my notes on it later.

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virus77
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There we go, the link makes alot more sense now haha. Thanks for the help man I'd appreciate your notes if you can can dig them up later for sure.

Darius
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I just recently did this per Carl's writeup as well as another from hybridz. The hardest part of this whole thing was getting the degree wheel to stay on the crank in the same position while you tighten the crank bolt. Every time you go to tighten it, the wheel wants to spin and screws up your setting. So after trying about a dozen times and missing by 1-4 degrees each time, I was ready to pony up $550 for a Ross balancer. I finally lucked out and got it on exactly straight. BTW, I had to buy a stack of 5/8" washers to space the degree wheel out from the accessories and brackets.

Once I lined up the degree wheel, it was smooth sailing from there. I did the procedure twice and compared values to check for repeatability. I was within 0.2* of adjustment for both trials so I was satisfied. I adjusted the exhaust cam, double checked my setting, loc-tited the fasteners, and moved everything over to the intake cam for its degreeing. My HKS exhaust cam was dead nuts on 0* adjustment. I had previously adjusted the exhaust cam to 2 cam degrees retarded per internet lore and had to adjust it back to 0* to match my calculations.

I realize that the intake cam gear is not adjustable on the RB25 but I was curious to see how far off from 0* the cam and stock gear actually were. It turns out that the intake cam was off by a couple of cam degrees and needed adjustment. Not having an adjustable adapter on the VTC cam gear, I opted to say "screw it, it is close enough." Maybe I will dig into it this winter some time and go through the entire procedure again with an adjustable Greddy VTC cam gear.

I still need to do the idle re-learn on the PFC and do some fuel tuning, so I can't report on the difference just yet.

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virus77
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actually the rb25det intake cam gear is adjustable from the factory, you don't even need a aftermarket gear. Only problem is that the adjustment is made from behind the gear so you have to pull it off the cam. It has adjustment slots where the vtc actuator spins in relation to the cam gear which will allow you to change intake cam timing. I actually modified my intake cam so I can adjust it while having the gear on the cam :)

pic of said adjustment slots behind cam:
Image

Darius
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HAHA yah I know it is "technically" adjustable but it isn't feasible to try to adjust it while it is on the cam and then verify its position with the degree wheel. If you are off by a degree or two, you have to pull the timing belt again and redo the entire process and then make another guess at how far you should adjust it back since there are no timing marks on the stock gear. I say F*CK THAT! Spend the $165 on an adjustable cam gear for it or don't even bother.

Image

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Carl H
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awesome to hear you finally got around to doing this matt.
you'll proly find that your intake needs to be retarded a hair should you get around to timing the cams again...
I degreed the cams on the 30 and it made a noticable difference when i shifted them from their degreed settings to 0* while i was troubleshooting the install...had the whole head dissassembled in the car in 95* heat, ugh.
i'd imagine that your egts will be much lower now and it should feel stronger, however untill the intake cam is checked its hard to tell what your max gain will be.
Im a strong believer in degreeing cams after doing both my 20 and my 30,its free power for an hr or twos worth of aghervation.

240cp
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Since this thread is here and is focused on cams. I was wondering where/or what other cams are available for rb25's. I know the poncams are out there but lets just pretend someone was building a n/a motor and wanted a different profile than tomei's. Where would one find such????? I have looked and there just aint crap out there. So if there are no options off the shelf who would you recommend for custom grinds. I contacted comp and the rep literally said we dont deal with import stuff, sorry. :wtf2:

Sorry for the thread jack, just was wondering if anybody has looked into custom stuff.

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l0nestar
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Sticky?

Darius
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Carl H wrote:awesome to hear you finally got around to doing this matt.
you'll proly find that your intake needs to be retarded a hair should you get around to timing the cams again...
I degreed the cams on the 30 and it made a noticable difference when i shifted them from their degreed settings to 0* while i was troubleshooting the install...had the whole head dissassembled in the car in 95* heat, ugh.
i'd imagine that your egts will be much lower now and it should feel stronger, however untill the intake cam is checked its hard to tell what your max gain will be.
Im a strong believer in degreeing cams after doing both my 20 and my 30,its free power for an hr or twos worth of aghervation.
I totally agree, it is free horsepower and driveability for some headache and downtime on the car. I vow to replace the intake cam gear this winter and get the motor dialed in. If I can find a good deal on a Ross balancer and get a decent bonus at the end of the year, I'll use that degree wheel for pistol shooting practice. (.40 Sig P229 :bigthumb: ) I can't remember if the intake cam is advanced or retarded, but I want to say I need to retard it like you said. I'll have to redo it anyways so I'm not going to worry about it until later on.

As for EGT, mine never get high. They were always around 1400. Albeit, I'm running a little rich at 11.3 @ WOT, but I doubt it will pick up 200* with an AFR of 12.0.

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Carl H
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egt's sound good for the most part on your setup...im seeing ~790*C on full boost with an average afr of 11.7:1

flatrate
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I need to do this, both my head and block have been machined, im sure even having stock cams in there its off by a noticable amount..

julio
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Big thanks to Carl for lending me his setup so that I could degree my camshafts. RB26 was rebuilt (5 tho shaved from head, 7 tho from block), stock headgasket, and fitted with a set of Type - B Tomei poncams.

All in all, I had to advance the intake cam 2* and retard the exhaust cam 2.5*. Can't wait to fire it up and see the difference.

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HxC_Nismo
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this needs to be a sticky, great write up carl.


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