Cam Damage

[sonomaz]

I figure I have twelve hundred miles on my eniginge. At eight hundred miles the rockers sounded like they were loose. At about a thousand I adjusted them. I did this while it was hot so I put to much hustle in it to finish before it cooled. After there was no difference in the sound. I decided to adjust them when it was cold so I could tke my time and get them all the same. This turns out to be a good plan because the adjustments ranged from 0 to 0.012 and averything in between. I have a Crane cam and the spec card says 0.008 for Exhaust and 0.006 for Intake. While doing this I did a very close inspection and this is what I found.

 

 

I appoligize for the out of focus image but it was the only one I could get that showed the ridges.

 

 

As soon as I found the damage I came here and did some searches and found a thread where Paul Rushman had responded to someone else with cam damage and suggested they flush their oil system, drop and clean the pan, dissassemble the oil pump and clean it and of course change the oil filter. I thought that was a little dramatic. Then I pulled the rocker out and the thought of all that metal floating around in my engine and suddenly it seemed like more than a good idea, it seemed like a requirment.

 

So that leads to my question of "what happened"?

 

There was lots of moly lube on all lobes. The plug is in the back of the cam. All other lobes look beautiful. I had drilled the head oil supply jet to 0.125 as suggested by " how to modify your Datsun motor". I am using a spray bar that is new. The valve in question moves just like the others. The rockers where new. The wear pattern on other rockers is where it is supposed to be. There is no sign of spring stacking. All valves are at the same closed height.

 

I packaged up the cam and sent it back to Crane to get their input. It should get there about the same time huricane Fay departs. Any thoughts are welcome.

[Phred]

Scarfed cams in L engines is unfortunately one of the most common killers of rebuilt, modified engines. You're among a group of many, although I know that doesn't make you feel any better.

My only questions are to further the database of commonalities. (1) was the cam a reground original or an aftermarket core? Original cams will have "Japan" cast into the core between the third and fourth bearings. The most common aftermarket cam will have a CWC cast into the core. CWC cams have the worst record for failing. (2) were the rockers original or aftermarket. I can't remember the casting designation on the side of the rockers, but originals are about $30.00 each. So how much you spent on them is usually a good indicator.

After doing many post-mortem exams I have found the most common reason for failure is the difference of, or lack of, hardness of both parts. Datsun engineered their cam to be compatible with their rocker in terms of hardness. If the cams and rockers are hardness tested, there should be a difference of at least four or five points on the Rockwell "C" scale. It has been a few years since I last did these hardness tests, and I can't remember the excact numbers. However, the damaged cams/lifters that were checked always had a similar hardness, or there were only one or two points difference.

Point of interest, Datsun/Nissan is not alone when it comes to lobe failure. A similar cam/rocker design is used on the Ford 2000 four cyl. engine used in SCCA Sports 2000 spec engines. A few years ago there was a series of cam failures, all cams that failed had the CWC casting ID. And all that I checked had similar hardness numbers on both cam and rocker.

These are my personal findings, which have been corroborated by other racing engine builders who have also independantly done testing. I am not aware of any technical papers on this subject, but I would be very interested to find some. Although I have been building racing engines for thirty years, consider all of the above FWIW.

Phred

[2eighTZ4me]

Those are indeed aftermarket rocker arms. I'm going through the whole ordeal of setting up my cam/wipe pattern now. Look at the divot on the rocker arm. The wipe pattern is way up toward the pivot side of the rocker. "Correct" wear should be near the center. I've found differences on my cam setup between cylinders that must be addressed with different sized lash pads. It's all in the archives - in fact, I posted a long thread on wipe patterns not just last week and will be updating soon.

 

Secondly, since I ate up a Schneider cam, I did a lot of research on this. Even Schneider is now sending a note with thier cams stating to use an oil with zinc in it. There are several on the market out there listed in their note. I've been running Rotella diesel oil for quite some time now with no problems whatsoever. Oil companies have removed zinc from a lot of oils out there, and it's murder on aftermarket cams and such. Hence, Schneider is covering their assets by sending this big yellow note that falls out in your lap when you open the cam, telling you to use one of several oils that still has zinc in it.

 

Funny that Phred mentions the aftermarket cams have a CWC casting on them. My Schneider has this casting, BUT so does my Racer Brown cam dated back to 1986. I read that Racer Brown bought all their cam blanks from Nissan, but I could be mistaken on that. I think it was jeffp who pointed out this information.

 

Nonetheless, BEFORE you install your new cam, check the wipe pattern and adjust the wipe pattern accordingly with different thickness lash pads. I had to go from a .240 down to a .200. I'm nice and centered now, on all except 2 valves. I will have to go down to probably a .170 or .180 to get them centered back up. The geometry is just as crucial as cam hardness.

 

Do NOT depend on the cam manufacturer to supply the correct thickness lash pads. My Schneider was supposed to come with .170's, and it turns out they shipped the cam with stock (.120) lash pads, and I, like a dodo, didn't check the wipe pattern and "ass - u -med" they were correct. Ate up two lobes in a matter of 20K mi. They looked 20x worse than what you had going on there.

 

Keep us posted with your findings.

[Pyro]

Almost looks like the cam was running off the lash pad. If too thin a lash pad was used, the wear pattern will run on the side of the pivot ball. If the lash pad was way too thin, it will run off the pad.

 

FYI, a thicker lash pad moves the wear pattern towards the valve side of the rocker arm pad and also make the valve train quiet by reducing the slop at the lash pad/rocker tip interface.

 

The cam doesn't look like it was a regrind, so most likely a "cwc" casting which typically only require 0.160" lash pads (stock are 0.120").

 

Yes, todays engine oil's have much less anti-wear additives. Need to use oils with high zinc content or use an oil additive that replaces the zinc.

 

yes, the bearings take a beating when cams go flat like that. Most likely too late so plan on turning the crank and getting some new bearings.

 

Try breaking in the new cam with stock valve springs and EOS oil additive. and use both oiling systems (spray bar and an internally oiled cam).

[JMortensen]

I've said it before, but I think the zinc is a red herring. I ran Chevron Delo 15W-40 for years with my reground Nissan cams with stock unaltered rocker arms. It turns out this oil has no zinc at all in it, and yet my cams have held up just fine even though I autox and did some track days. Nobody I used to race with has ever lost a cam lobe, and we're talking about quite a few L engines with reground cams, only one guy ever bothered to replace the rockers, and that was only on one of his 6 or 7 motors he's built since I've known him. I think the metallurgy of the camshaft and possibly the rockers is the issue, and the oil is not really a factor.

[Pyro]

Chevron Delo 15W-40 is diesel engine oil. It has tons of zinc and phosphorous. (0.151% and 0.138%). The old engine oils we once had used around 0.12% to 0.15%, now they use 0.005%. Not a red herring, plenty of articles on high performance cam failures and oil anti-wear content (ZN and P).

 

here is the oil spec sheet

 

http://www.matweb.com/search/datasheet.aspx?matguid=8234601b8c6941e4bf8ba16e47da1b56

[JMortensen]

Wow. That's weird. I would swear that when the zinc thing originally came up I looked it up and it had no zinc whatsoever. I tried to find the post and see where I came to that conclusion, no joy. Well thanks for setting me straight, but I still think the zinc is a red herring.

 

How many stock cams do you hear about losing a lobe? How many Schneider cams do you hear about losing a lobe? Notice a correlation?

[sonomaz]

Thanks for the feed back. The Cam was ground by Crane Cams. It appeared to be a new core and not a regrind. I do not recall any casting alpha-numerics but there was a purple paint swatch on the shaft. I am refereing to past because I have sent it off to Crane for evaluation (and hopefully a replacment). I can't recall if the rockers were aftermarket or not but I have no recollection of them comming in a "Nissan" red and blue box. I may have gooten them from Motorsport Auto but I am not certain. I have the other eleven rockers so if there is some way to determine their origin I can look (I sent the bad one iwth the cam hoping it will provide more info).

 

Your statments about hardness makes a lot of sense. I could see how one rocker may be slightly harder than the others which would explain only one lobe failure. Any idea who could measure the hardness of the others? I would expect to close that question I would also have to have the cam measured.

 

Paul

[Pyro]

stock cam have very slow ramps and soft valve springs so their isn't nearly as much stress on the metal.

 

High performance cams tend to lift the valve much more aggressively and therefore require much stronger valve springs. This creates a double wammy, quick lifts and heavy springs really wear out the rubbing metal parts. Plus the new datsun cores are softer and the aftermarket rockers are not as good which isn't helping. It's better to get a stock cam reground and stock rockers resurfaced and not too use a very aggressive lift rate like schneider cams

 

This problem is also hitting the old v8 engines hard. People with flat tappet high performance cams are having huge problems especially with the newest flat tappet cam profiles that are overly aggressive in my opinion.

[JMortensen]

stock cam have very slow ramps and soft valve springs so their isn't nearly as much stress on the metal.

Good point. This is not a fair comparison. So how many reground cams do you hear about losing a lobe? These should be worse than the Schneider, because the base circle is smaller. I've still never seen it though. Did I mention that I'm using Schneider springs with my cam?

 

This problem is also hitting the old v8 engines hard. People with flat tappet high performance cams are having huge problems especially with the newest flat tappet cam profiles that are overly aggressive in my opinion.

Right. I think they're also using substandard metallurgy. I think this is also where you get the "run it at 3000 rpm for 1/2 hour" before you drive the car cam break in stuff from. Look at grumpyvette's posts and it appears that Comp Cams has the equivalent reputation as Schneider does with the L6 for soft cam lobes. V8s have always had a reputation for losing cam lobes, at least they've always had that reputation with me.

[sonomaz]

I'll try to get a photo up soon, but all other rockers have their wear pattern in the center where it belongs. I woundered about the divot being toward the back and for some reason I think it moved backward as the rocker wore. I work this through my head because I know the geometry changes as the pad wears away. Also my confidance is high that it was set right at the begging but I have no proof.

 

As to engine bearings, their going to have to hang in there. I'll take some precautions to remove what I can but an engine tear down is out of the question. As to changing valve springs for break in, that dosen't seem practical either because I would have to pull the head to change them and that also ain't in the budget. Don't get me wrong, I think your suggestion is very wise.

 

Please stay tuned because I will need advice when I get a replacment cam and it is time to go back together. You guys are great.

[sonomaz]

Jon,

 

you're making me anxious about reputations. I was intending to get a replacment from Crane (hoping they work a deal with me) but I definatley do ont want to repeat this. Who would you suggest and why?

 

The basic concept of regrinding a stock cam seams all wrong. As you mentioned, you have to reduce the base circle to increase lift and if you want a faster rise the base circe is even more compromised.

 

Paul

[JMortensen]

you're making me anxious about reputations. I was intending to get a replacment from Crane (hoping they work a deal with me) but I definatley do ont want to repeat this. Who would you suggest and why?

 

The basic concept of regrinding a stock cam seams all wrong. As you mentioned, you have to reduce the base circle to increase lift and if you want a faster rise the base circe is even more compromised.

I don't know Crane's reputation at all. I do know ISKY's, it is good, and they regrind cams for L series. The base circle issue is not really an issue as far as I'm concerned. Theoretically one is better than the other, but practically speaking unless you're running insanely high rpms you shouldn't have issues with valve float on a reground cam with the proper springs.

 

I should let Phred pick up the cam wear/zinc/metallurgy argument because I've already made a couple incorrect statements and he seems to be more on the ball in regards to this issue. Thanks again Pyro for showing me where I was incorrect.

[Tony D]

Yes, the Zinc (ZDPP I think is the acronym for the specific ingredient) is crucial for older cars with a high sliding load in their valvetrains. OEM's have seemingly seen this as well in some of their 'factory rebuilt' engines. More and more OEM's go with rollers, and Zinc is a 'bad for the environment' kind of thing, so API standards have changed over the years to accomodate the Environmental Issues. For us with stone age stuff, we're stuck. Diesels have high load inherent in their operation, much more so than our engines, and theirs is the last domain of ZDPP Rich Lubricants out there.

 

The 'run it for 3000rpms for 1/2 hour' is an example of a non-hardened lobe run in specification. This is for cams that are not nitrided, induciton hardened, or otherwise adequately treated to give the proper rockwell RC Hardness level on the cam lobe itself. It's a 'work hardening' situation where you run them like this to put heat into the lobe and get a surface hardness. This was common when I was going through apprenticeship training, but as far as I know this is more of a domestic engine (American V8) than import thing to do. This goes to reading the cam grinders breakin recommendations and following them to the letter. If they say 'do it' who am I to argue?

 

Far as I know, Isky hardens their cams after grinding and also puts a coating on them. And talking with Ron directly, he will recommend if you have a good regrindable Nissan Japan Core, to send it in for regrinding rather than using a new cam billet.

 

Paeco in Birmingham AL has welded 'Paecolloy' lobes and journals to their cams, cranks, etc. They offer a lifetime warranty on this hardfacing alloy, and for an engine where there is limited accessibility to spares, it bears considering. I would be interested in knowing if they would weld up a CWC core with this hardfacing alloy, and then have it ground... Hmmmmmmmmm...

[Phred]

This thread has evolved from cam damage, proper assembly, through metalurgy, and oil composition to....more questions. While I have no clear cut answers, it looks like its a combination of all three. On the oil issue, I have one more tid-bit to offer. A few years ago Joe Gibbs Racing started to engineer their own oils. http://www.joegibbsdriven.com/trainingcenter/index.html

They have very specific oils for each specific application. Now, many top racing engine builders have come to agree that it is the best on the market. I mention this only to point out how important oil composition is. And no, we don't use it, only because it is very high priced. However one So-Cal builder, Esslinger, uses it exclusivly, and won't warranty an engine if it is not used.

For the last three years, I have been building Porsche racing engines. (sorry) which have a similar type cam/rocker design as Datsun. During that time, as the oils lost their Zinc/Phos content, we have seen more lobe/rocker and bearing damage than when the oils had a higher content of Zinc/Phos. Makes you go Hmmmmm.

For the last year or so we have been using 15-40 Swepco with good results. http://www.swepcousa.com/lubesite/highperf.htm

Valvoline offers specifically street, and track oil. If you're a Valvoline Synthetic user, be sure to use the track oil, even if you drive on the street. I don't think the Feds will arrest you. If you are becoming paranoid about what to put in your new engine. At least break it in with some G.M. EOS, it will help. Then wait till the planets line up, howl at the moon, pour in some oil, and pray.

Phred

[jc052685]

As to engine bearings, their going to have to hang in there. I'll take some precautions to remove what I can but an engine tear down is out of the question. As to changing valve springs for break in, that dosen't seem practical either because I would have to pull the head to change them and that also ain't in the budget. Don't get me wrong, I think your suggestion is very wise.

 

FYI - Head does not need to be removed to pull the springs. Use a compression gauge fitting and an air compressor, turn the crank so the the piston for the cylinder you are working with is at the bottom. Now remove the rocker and apply presure. The presure should hold the valve closed for you. Still sux but you can do it.

 

 

[Silent]

i had that happen to my 3.1. i pulled the motor, took it all apart. haven't touched it since.

 

hell i even tried to sell the damn thing, and no one wants it

[Pyro]

there is a simple speciality tool for the L series engine that uses the cam as a lever point to compress the spring. This also requires filling the cylinder with compressed air to keep the valves up. I have done many spring changes this way.

 

Maybe some eos oil additive will do the job plus using a cam with both oiling systems (internal and external) would be extra insurance.

[jc052685]

there is a simple speciality tool for the L series engine that uses the cam as a lever point to compress the spring. This also requires filling the cylinder with compressed air to keep the valves up. I have done many spring changes this way.

 

Maybe some eos oil additive will do the job plus using a cam with both oiling systems (internal and external) would be extra insurance.

 

i knew there was I just found this pic first. chances are there is a spring tool out there for every motor

[srgunz]

ZDDP: Zink Dialkyl Ditho Phosphate.

 

http://www.zddplus.com/index.htm