Another rebuilt rocker question

[89turbocabmike]

I noticed that the bushings on my rebuilt rocker arms are not camfered at the two oiling holes like the originals. Is this something to be concerned about? Thanks

[Steve@Rennsport]

Hi Mike:

If it was my engine, I would put a chamfer on the holes. Be VERY careful that you remove all of the material shaved away from the holes.

[Wayne 962]

When I was in the machine shop during college, we had a deburring tool that would do this job nicely (instead of using a file that might create metal flakes).

-Wayne

[HawgRyder]

Wayne is correct...a deburring tool is only about $15 at the local discount tool places.
They come with different tips...get one that will fit into the hole.
Bob

[89turbocabmike]

Thanks for the help guys. It seemed like they should be camfered. Yet another parts-problem delay! Arrggh, I just want to drive my car!!!

I paid $16 an arm to a well known Porsche machine shop for rebushed/reground...should I have expected that this was already done? It would seem that better oiling would be desirable in any Porsche engine. I have a dremel tool with a ball carbide-type bit. Will this cut bearing material smoothly? After I cut, what grit paper can I use to deburr the edges of the camfer? In the picture I posted earlier you can see the current hole in the rebuilt rocker on the right. Thanks again

[Steve@Rennsport]

Hi Mike:

Unless you are VERY skilled using that dremel and have the right cutter, I would not chamfer the holes with that.

Get a deburring tool with the correct end and do it right. It leaves a nice finish that cannot tear away at the edges. Do not forget that the rocker arms live & operate at very high temps and are "lubrication-challenged".

[Wayne 962]

Also a note on the carbide tool bit - way overkill. The bearings are made of relatively soft metal. You could probably scratch them with your fingernail if you have hard nails. Use the deburring tool...
-Wayne

[89turbocabmike]

So this deburring tool will allow me to replicate the original rocker as seen on the right? I love learning new stuff, but I'd have prefered to pay not to deal with this! (I rubbed the old bushing with 1200grit so it would photo better)



I was at Andial today and they told me not to worry about it . I can see that with the factory camfering there was some wear. I can't imagine how good the oiling could be with the simple hole in the rebuilt one. Thanks for all the help guys.

[Wayne 962]

That's a pretty big chamfer there. Now that you mention it - the rods that I had done by Walt (Competition Engineering) didn't come back with a chamfer on them either (see page 117 in the Engine Rebuild Book). Chamfering the edge slightly can't help, but I wouldn't really worry about duplicating what you see in the photo above...

-Wayne

[Wayne 962]

Oh wait a sec, we're not talking about rods (duh - it's late). Well, on page 162, it shows my rockers from Walt as well, with no chamfer. When it comes to specific details of machine work, I usually go with what Walt recommends...

-Wayne

[William Miller]

Wayne, A new rocker comes with the bushing in it. Can you take a look at one and report? That would indicate what Porsche intended.
I can't recall what mine looked like.

[911pcars]

I would suspect Porsche doesn't chamfer this bushing; too much labor. I suggest doing it; can't have too much lube in this area.

Sherwood

[89turbocabmike]

My rocker arms are factory stock '89 turbo, so at least they use to chamfer them this way.

[oneblueyedog]

My old rockers have a chamfer. I'll check my new ones and get back to you. I think the new rockers are not drilled with as much care. Most of the borings are not exactly centered. I guess the adjuster will have to compensate.

[William Miller]

Now you got me thinking. What's the hole for anyway? There is no oil under pressure getting there.

[911pcars]

If factory rockers are already chamfered, that's great. Replacement bushings should be similarly chamfered. An oil groove in the bushing might be even better.

William,
You're right. This area is not pressure-lubed. It's "splash" lubed. More accurately, oil in the camshaft/rocker area dribbles into the hole and eventually lubes the rocker shaft. Pretty tortuous path, eh? Anything you can do to make this entry path a little easier is better.

Many builders recommend assembling the rocker shafts dry so they don't wander after installation. This also means the rocker and shaft won't be lubed until enough oil decides to enter. I suggest a compromise. Lube the rocker arm (Moly or some other high-pressure lube), then install a dry rocker shaft through one cam housing boss. The leading end of the shaft will pick up some lube as it goes through the rocker; the other end will remain dry. Center the shaft, then tighten. Alternately, assemble dry and force-feed lube into the oil hole with a squirt can. The critical high-pressure area is the underside of the shaft.

Sherwood

[William Miller]

Sherwood, Thanks!
My rebuild was only about 2500 miles ago and I had forgotten that the holes go all the way to the other side of the rocker. (Feeling pretty dumb now because I set myself up.)
The wrist pin bushings are the same way right?
I assembled my rockers dry with the seals on the shafts.

Ok, I'm stumped about the off center hole in the bushing. I would think that when they rebushed it they would drill the hole after the bushing was installed.

[ChrisBennet]

I put the rocker shafts in dry and then squirt some oil in the rocker oiling hole.
-Chris

[Wayne 962]

Originally posted by 911pcars
You're right. This area is not pressure-lubed. It's "splash" lubed. More accurately, oil in the camshaft/rocker area dribbles into the hole and eventually lubes the rocker shaft. Pretty tortuous path, eh? Anything you can do to make this entry path a little easier is better.

Yes, but these are very low-load bearing surfaces, and the load per square inch of bearing surface is low as well. In general, the rockers and shafts in these engines wear very little, so the system must work pretty darn well.

-Wayne

[911pcars]

The rocker arm is highly stressed despite being controlled by the camshaft that only rotates at 1/2 crank speed. At high rpm, the stress increases as the valvetrain inertia (rocker arm, valve, valve spring, valve spring retainer, retainer locks) increases as it tries to follow the cam lobe contour. Camshafts with mild timing and lift specs produce the lowest stress because of limited lift and slow lift rates. More radical cams open the valves more and keep the valves open longer which means the valves must open that much quicker. Higher engine speeds usually require higher valve spring rates to keep the valvetrain mass in contact with the cam lobe. This places more load (more friction) on the valve gear. No wonder F1 cars use a pneumatic valve train to allow the engine to spin up to 19,000 rpm. A conventional valve train using wire springs wouldn't allow this engine speed due to the necessary spring pressures and heavy frictional losses.

Sherwood