Camshaft/Rocker Break-in

[Green993]

Assuming the break-in period (20 minutes 2000-2500 RPM) was NOT followed (i.e., engine ran for 20 minutes at idle), how can I check the camshaft and rockers to see if they can be re-used as is. Are there tell-tale signs the rockers need to be re-brushed and the camshaft re-ground or re-hardened?

[HawgRyder]

The most critical time for an engine is when it is first started.
All the assembly lube gets flushed into the sump...the oil has to feed into lots of places that might take a few seconds to reach.
Constant RPM is not the best (might not do much harm) but I always try to vary the RPM from just above idle to maybe 3000 - 3500 RPM just to be safe.
With a water cooled engine...I run it until the thermostat opens and the top rad hose gets hot.
With an air-cooled...perhaps the oil line to the front cooler or something along that line might be the best indicator.
In any case 20 minutes sounds about right.
Then....I change the oil AND filter!!
All the stuff that you missed when doing the rebuild will be out of the engine (and we all miss something...LOL).
This makes for the best chance of a long term engine in my opinion.
As to your engine...you can check the cam surfaces by taking off the top valve covers...if the cam looks OK...you might be lucky.
Bob

[Green993]

I have the cams out of the engine (i had to tear it down for other reasons). Both the rocker surface and the cam surface appear to have a slight un-evenness. For example, the left side shows the machining marks from re-brushing while the right side is shinny. I'll take a pic later a throw it up here.

[Green993]

Here is a pic of the rocker. Notice the left side looks different from the right:


Reverse pattern on camshaft:

[earossi]

It is my understanding that many rocker arms are out of parallel between the follower arm surfaces and the centerline of their bushings. This leads to the follower portion of the arm slightly out of being square with the cam lobes which leads to the asymetrical loading wear pattern that appears in your pictures. The solution is to have the rocker arms machined to true them up. I've been told that this condition can exist on new OEM rockers fresh from Porsche!

[burgermeister]

Originally Posted by earossi

I've been told that this condition can exist on new OEM rockers fresh from Porsche!

I can confirm that this can exist on rockers you have sent out for refacing also ... in fact, those rockers look a lot more even than mine did (they were sent out to a very well reputed shop).

[Lapkritis]

If you're reusing worn rocket shafts then it won't matter if the rockers are perfect...

[HawgRyder]

Considering the width of the surface of the rocker...it would only take a fraction of a degree when grinding to create a non-parallel condition of cam to rocker face.
Obviously the more "wear or coverage" on the rocker face indicates the more true grinding of said raocker.
I would think that even with a very acurate jig...you could still get a slight offset of degree.
If the bushing is replaced first...then honed to size...then the rocker is jigged and ground...you would have the best chance of maximum contact between the surfaces.
This all supposes that the cam lobes are 100% accurate.
I believe we all go for the best possible contact area...but given the geometry and accuracy of grinding...it will never be 100% to our visual liking.
The next step of course is to redesign the whole system...so that everything is perfect.
Not feasable for cost reasons...but it would make everyone happy...LOL
Bob

[Walt Fricke]

The slight unevenness of cam and rocker surfaces is the reason often given for keeping track of the rockers when doing a rebuild which does not involve refacing cams or rockers (and that is a very common rebuild), so that the same rocker can be put back on the same cam lobe.

Since hearing of this rationale, I have gone back to keeping track of the rockers, but I can't say I ever saw any bad results from the years where I just put them back in any old which way. What I looked for was pitting suggesting the hardening was wearing through, or something approaching a ridge at either end of the wear surface of the rocker, or some seriously uneven looking wear.

Me, I wouldn't worry about what you have. Chances are good that the wear process will continue to even things out as the two surfaces wear in together.

My suspicion is that short of a lack of oiling (which will quickly lead to machining the cam lobe down to its base circle), the motor will put up with quite a lot. Not that mismatches are good, but just that there is a tolerance.

Of course, you can spend more $ to get machine shop level matches - if the cam itself was ground exactly true. If the rocker grinding setup is a little off, it won't be true. If the hone for the bushing is a bit off, ditto. And there seem to be ways to use the hone to compensate for the surface if your bushings were sufficiently undersize in the ID to start with.

I don't think the shaft's wear has a lot do do with this, though. Most of us home brew guys just reinstall the shafts so the least worn part takes the load, and that part is the one which is the most true.

Here are a couple of pictures I have saved from this forum. First, a machinist checking rockers for true faces - one is, one isn't. Then pictures (from the same source) showing a precise method of grinding the faces. Then a home brew setup which doesn't look quite all that trustworthy, though if the feeble bracketry were replaced with something better it might be all that is needed. There is a U-tube video out there of a machinist grinding faces - what is needed is something which allows the pivot to be true while it is slid in and out as the grinding happens. Naturally the stone's surface also needs to be true, which means something like the diamond tipped rods used on valve grinding machines, and that is going to be difficult for those of us with inexpensive bench grinders.

[HawgRyder]

Walt...it is my understanding that the green grinding stones are the hardest...so would be the best for holding their trueness..?
If one were to make a jig that held the rocker by the shaft bushing...and had a off-set pivot...so that the pivot was the center of the circle of the rocker rubbing surface...then would that be considered the best we could do?
The rocker would be ground (hopefully) true with the rubbing surface in an arc based upon the off-set pivot.
This asumes that the rubbing surface is actually an arc.All the rockers I have seen look like they are.
Bob

[Walt Fricke]

You got me on stones.

The video I saw used the existing arc of the rocker as the method of retaining that arc. The rocker was moved by hand, and by twisting it and moving it in and out, its face was ground. The shaft kept the face parallel with the grinding surface at all times. The idea appears to be not to remove too much.

I've cleaned up some rockers with wet/dry 1200 or so grit sandpaper on a piece of window glass - sort of the same thing, though if the rocker surface is not parallel with the shaft axis this won't change that.

[HawgRyder]

Walt...unfortunatly I don't have access to a rocker to measure the curved surface.
Is it an arc?...or perhaps part of an elipse?
The jig needed to grind an elipse would be much harder to make.
Bob

[KTL]

Couple of videos from guys that do a nice job reconditioning the rockers

Costa Mesa R&D John Edwards https://www.youtube.com/watch?v=He1uhpV4mIw

G2 Performance cgarr here on Pelican https://www.youtube.com/watch?v=HxNiWy5of7k

[Walt Fricke]

Looks like an arc to me.



I once traced it onto a piece of paper, but was not satisfied with my accuracy to determine a radius or anything else.

[AlfonsoR]

Maybe someone could comment on the methods linked by KTL....

First, the methods used by those folks seem to introduce a slightly different pattern than the original if there were any appreciable wear.

Secondly, the distance from pad to shaft bore centerline is shortened, and now if you "keep the same profile as original", now the angle of attack to cam lob is slightly different.

Third, since material is removed by feel, then how do you keep accurate track of how much material is removed on each rocker? I would think you would like to remove a consistent amount from each.

Fourth, does the hardness of the pad surface get affected when grinding?

Maybe Chris_seven will chime in to tell us his solution for determining the pad arc on his rockers, would be intresting to hear.

Also i found this, page 10: http://www.chevalierusa.com/pdf/FSG-818_C1224CNC.pdf

[KTL]

John @ Costa Mesa actually got asked Q3 on his youtube video. His response was "In a manufacturing sense, yes because you would have a dedicated machine 4 doing this op, however in the real world of rebuilding, we use a machine that is universal to do all types of rockers, etc. and these work very well after refinishing." So it seems John didn't think the same exact profile was extremely critical.

Also got asked Q4 too. His response "The rockers are hardened to a dpeth of about 0.75mm (.030") which is way less then we grind them, we typically remove about .002"-.008" when refinsihing them"

Heh. How about that, eh? Porsche-like rocker on page 10.

[cgarr]

This is interesting: It is very difficult to get any surface perfectly flat, you can grind it, surface check it for square but when you check it with a diamond sheet on a surface plate you will see all the imperfections. When I say "imperfections" you would never feel or see them. Thats the reason for break in, you have to let everything get happy with each other.

In most cases if you get 80% rocker contact thats normally pretty damn good, all the above dont look too bad to me. Look at the pressures that are applied to the rocker. The cam pushes on the right side of the rocker center line and transfers to the valve foot left of the center line, this automatically puts a twist in the rocker and bushing, you can really see this if you ever remove old bushings. The only problem I have found is if they are out of square by too much you will get higher pressure on one area of the pad and it will start pitting much quicker and even more if there is any loss of oil most times at start up.

[AlfonsoR]

Originally Posted by KTL

Heh. How about that, eh? Porsche-like rocker on page 10.

Thanks for the responses Kevin.

If you notice, it says R36, which I believe that indicates a radius of 36mm. Which makes me wonder if the Porsche rocker is similar, just a simple radius, not anything more complex. That makes sense in that these rockers have been around since at least the early 60s, correct?

I apologize for the silly questions, I have two disorders, obsessive-compulsive and perfectionism. I am working on both issues. But I think many here share one or both disorders. Or for some reason, I just feel comfortable here.

I think the proof is in the pudding, if Costa Mesa and CGarr have been doing it with good success for years, then what is there to argue? I just wonder if there is a better way, that might also be as cost effective.

[afterburn 549]

My way of thinking...the factory got it as good as its ever going to be.
2 - Never send them anywhere cause the will change the the angle !
3 The used parts have Est. a wear pattern over time...SO Just polish everything and put them back (with new bushings if required ) where they were. (Thats Very important)
I did mine 10 years ago..everyone said it would not work.....It has been just fine 50000 latter.
Which leads to an other question -
On Rockers that have been reground....What is actually being measured at the 1st valve adjustment ?
Wear from misaligned grindings and polish ?

[Lapkritis]

Originally Posted by AlfonsoR

I just wonder if there is a better way, that might also be as cost effective.

Careful around here with that line of thinking. Some of this crowd takes suggestions of alternatives very personally.