Cam Pitting, Piston Oil Squirter Testing Without Splitting Case

[boyt911sc]

Originally Posted by Trackrash

What Walt said. However, you need to be careful when re-installing the tube.

The picture in #14 only shows one of the holes for each lobe working. There are three holes in each lobe area.

If you had the restrictors installed, that may be the smoking gun...

Gordon,

Show me a spray bar with nine (9) holes. Never seen one before.

Tony

[Trackrash]

OK, maybe my memory is a little hazy.

Perhaps someone who has one OUT will show a picture and we will know for sure.

[Flat6pac]

They all have 9 holes except some of the very earliest castings
Bruce

[ahh911]

Just checked, didn't know there were two more holes spraying downwards for each cylinder. I'll check those too.
Phil

[boyt911sc]

Originally Posted by Trackrash

What Walt said. However, you need to be careful when re-installing the tube.

The picture in #14 only shows one of the holes for each lobe working. There are three holes in each lobe area.

If you had the restrictors installed, that may be the smoking gun...

Gordon,

Thanks for bringing up this up.You are indeed correct. Next time I perform another pressure test, I will focus at the other two (2) holes at the underside of the spray bars. I had to use my wife’s dental mirror to locate these hard to see orifices. I failed to identify the total number of holes on the spray bar.



BTW, have you found a procedure to refurbish a collapsed Carrera hydraulic tensioners? I was having some sort of problem finding a good way to disassemble the tensioner without damaging the critical parts. Thanks.

Tony

[Trackrash]

Since you have it this far, I would remove the plug on the end and have a look inside the tube. There could be some debris floating around in there. It would be worth while to check. However running fluid through and checking for blockage is the right thing to do.

As far as Carrera tensioners go. Porsche says if they are not firm you need to replace them. I had a thread a while back about trying to refurbish them and basically the one I thought I had fixed failed after a while. There are two check valves in them and if they are not working perfectly, the tensioner is doomed, sorry to say. No one to my knowledge has succesfully rebuilt one. Read all about it here. Carrera tensioner questions

[trond]

with three holes in each lobe area; how are they oriented ? As I remember it is possible to install the spray bars wrong.... hope I did not do that but I seem to remeber there was one hole pointing straight up towards the cover.... makes no sense but I thought that was less unlikely than the other options. So could anyone make a small schematic please, of how the three holes in each lobe area are to be oriented ?

[Walt Fricke]

Trond

There are 6 cam lobe/rocker spray holes, one per valve, in the spray bar. The intake valve holes face a bit above the rocker at the rocker shaft. It is going to hit the valve cover, though at max lift some of it will hit the end of the rocker. Volume II of the Porsche shop manual notes "separate bores must face upward toward intake valve covers."

The exhaust spray holes face pretty much straight down (well, as you assemble things on an engine stand - in the car they face in toward the head) to spray at the lobe.

There are three (pre 1978) or four larger holes which feed oil to the three/four cam journals. And two holes facing outward at each end, one for the locator on the flywheel end, and one for the oil line fitting at the cam chain end. The end holes face both ways, with oil coming in through one, and the locator plug blocking the one on the other end.

I can't remember if the center journal holes go "up" as well as down to the journal, but oil going up doesn't go anywhere because the holes drilled through everything for the middle journals are plugged on the outside

You can check the spray holes with the cam installed with compressed air and a finger - you can feel it coming out. You can't check the journal oiling holes with the cam in place, at least not that way.

[ahh911]

Gordon you asked how the rocker arms looked:
Here are the rocker arm pictures. Cyl6 worst lobe, rockerarm & bushing play. Cyl5 next, cyl4. Cyl 1 seems to have a little, I'll need to check if cyl1 I or Exhaust showed the start of pitting. All other rockers look like 2 and 3, clean. I don't think they've ever been re-worked, is there some way of telling?
I think I get it now, when the rocker arm bushing starts to wear, an off angle force is applied to the rocker arm lobe contact area, the oil film that would normally sit across the lobe gets squeezed to the part of the lobe and rocker area that has least contact pressure starving the corner most area of the lobe that has the most force on it of it's oil and the local heating begins there and starts to eat away at the material and an off angle wear pattern begins to occur. Then as that wear portion sinks deeper, the next area is exposed creating a triangular pattern of wear starting at the corner of the lobes and rockers, the additional wiggle room between rocker arm bushing and shaft accelerates the whole process.
(As well, I checked all 9 holes, clear)
Phil

[RedCoupe]

The areas with spalling or pitting on the cams and rocker arms are where the hardening is failing. Once the hardened areaa are completely worn through, it gets smooth again (and wears very rapidly). It you've ever seen a "flat" cam, the surface is smooth not pitted.

[ahh911]

Sorry for the bringing back from the dead.
I've edited where possible.
There is no cam oil restrictor in this car, I goofed when I looked down the barrel and saw the journal feed narrowing and took that as the oil restrictor. Not so. So cam pitting in my case can not in anyway be attributed to cam oil spray restrictors. I know the cam oil restrictors has a pro and con group and I don't want bad data in anyway to shift opinions.
Phil

[VFR750]

Replace the rocker shafts.

If they are not perfectly smooth they will bind up and cause the rocker bushing to wear.

This happened to me. Damage showed up quickly. Like 1000 miles or less.

[ahh911]

Replace the rocker shafts.

I hear you. I've noticed the shafts of the most badly worn rocker arm bushings and coincidentally associated cam pitting have a wear that are of a very curious pattern that the good rockers don't show. I read someone had said to flip them 180degrees, but I have in mind to order in any that show this U shaped type imprint. I'll not replace the shafts that showed no rocker bushing wear which are the same valves that show no cam/rocker arm pitting.

[VFR750]

John (DRC) reground the cam and rebushed the rockers. Took a look at the rocker shafts and said they were not usable.

Replaced all 12 in 2016. Just looked at the cam surfaces a few weeks ago during a valve adjustment. Looks perfect.

[dtxscott]

Originally Posted by Trackrash

What Walt said. However, you need to be careful when re-installing the tube.

The picture in #14 only shows one of the holes for each lobe working. There are three holes in each lobe area.

If you had the restrictors installed, that may be the smoking gun...

When you mention restrictors, are you referring to the smaller diameter connector (Number 34 in the diagram)

[Trackrash]

Yes, #34.

[dtxscott]

Thanks.

As a general comment on the function of that connector, I understand that restricting flow increases pressure in the system. It is reflected on the gauge. However, that also restricts flow to the cam/rocker oiling system so how does it improve the overall system in a street driven application?

[Henry Schmidt]

In my opinion the factory oil cam feed restrictor is too small.
From memory... 2.5mm. The non-restricted fitting is 6mm.
We modify the opening to 4mm. This gives us the best of both worlds.

[Martinlassmann]

4mm with an early 4 rip pump or 964?

[burgermeister]

I had similar pitting, though not as severe, on my 3.2 caused by improperly refaced rocker arms. The (reputable) shop's bad for doing crappy work, my bad for not blueing and checking the contact before installing them. Rather than a full width line of contact, some rockers only had 1/3 to 1/2 of the full width. Cams as well as rocker pads pitted in those cases.

I would imagine worn rocker bushings might contribute to uneven contact pressure, as Stowensen stated.

My 3.6 of unknown provenance also had some light pitting on the cams, though contact was even across the full width of the pad, and there are no rocker bushings to wear out as the rocker bores are pressure lubricated. John Dougherty suggested this pitting was not uncommon with high mileage engines, even with the 'right' oil and everything otherwise fine.