Cam Pitting, Piston Oil Squirter Testing Without Splitting Case

ahh911 · 11:41 AM

Hello Guys, 81 911sc
I have some questions please. While I await the decision on what to do with my newly received heads.. I have some concerns about what caused the pitting in the right camshaft and if possible how to test the piston squirters without disassembling the head. As you can see, cylinders 4,5,6 intake cam lobes are all pitted, all other 9 lobes are fine (cyl 1 exhaust very mild pit). Three things jump out, one, the previous owner used 5w-40syn, second there is No oil restrictor to the cam oil lines, 3 why all on one side? I am concerned that it may also be related to a stuck open oil piston squirter but with the case still intact, the only way I can think of testing them is with a vacuum of some sort attached right on the squirter and a clear tube to see oil drawn up. Does anyone know how to test with the case intact? Anything else besides this that might help describe how 3 intake lobes on one side are pitted and all the rest ok? Also, could a stuck open oil squirter result in low enough oil pressure and only cause the intake lobes to pit on one bank? Why then not the exhausts lobes and the other bank? Any ideas would be appreciated. (oil pressure was just under 1 bar, warm, idle)

Thank you,
Phil

ahh911 · 06:51 PM

Intake lobes of cyl 4,5,6 in that order, closeups.

Richey · 03-02-2020, 07:39 PM

Are any holes plugged in the cam housing spry bar ?

targa72e · 03-02-2020, 08:29 PM

If a piston squirter was stuck open it would lower pressure (slightly) every where in the engine. Since it is mainly one side I would side with Richey and check that the spray bar is not plugged. To you original question. You would have to remove at least the pistons and cylinders to see the piston oil squirters. You hypothetically could remove a thru bolt and fill cavity with brake cleaner turn the engine on its side. plug the lines to the cam towers and pressurize the thru bolt passage and look for squirter to work. With how small a hole is in the squirter even if it was stuck open you might never notice.

john

trond · trond's Garage

I have seen similar wear on two sets in my engine. Best oils only and no plugged spray bars, but many cold starts if that matter. Hope you find a reason and that you publish here

Peter M · 11:33 PM

I think we fool ourselves expecting to know the cause of some failure because there are far too many factors and too little data to separate the wheat from the chaff.

If it was oil related surely more lobes would be damaged and more randomly across the banks.

The fact that most of the pitting in on one cam only suggests the original heat treatment. Or did that cam somehow suffer from corrosion pitting? Google "lycoming cam spalling" for some truly horrendous photos!

Do your checks, do your repairs but don't sweat it, I don't think we will ever really know for sure

ahh911 · 11:42 AM

Thank you very much for the responses. The cylinders and pistons are off, currently replacing 2 head studs, 1 per side but at 95kMiles, I don't really want to open the case, maybe next time. I haven't checked the cam spray bar fully yet, I did gently stick a wire in each and it was clear of debris before removing it, I will do a more thorough job when cleaning the cam housing.

So basically, use good oil zinc/phos, clean the camshaft spray bars, (there is none edit: remove the cam spray bar restrictors?) Should I have DRC grind the cam and clean up rockers and go with that? Does this seem about right? I still wonder if it is possible to test the piston oil squirters using vacuum, a good seal and a clear tube to see at what pressure the squirter opens up. Anyone try this?

Thank you,
Phil

trond · trond's Garage

it is not trivial to test squirters and impossible I would think without taking it all apart. If you run engine at idle without valve cover and take a look ? Will be a bit of a mess obviously. But only if there is oil and squirters are not causing any issue. ... without headers would be better to avoid oil contamination

You are aware that the piston squirters are below the pistons and not visible ? You are not mixing up with cam squirters by any chance ?

stownsen914 · 03-03-2020, 05:48 PM

Cracking pressure for the squirters is like 30 psi. When I tested the ones in my engine as part of a rebuild, it took over 40 psi to open them. I'd be impressed if suction would work to test them properly.

For the cam oil line restrictors, you'll see opinions all over the place whether to use them or not. I'm not, but it's a race engine.

Flat6pac · 03-04-2020, 10:04 AM

SC and Carrera cams are inexpensive used compared to having them rewelded and ground To spec
Properly operating piston squirters need about 40 psi to operate. You’ll need to open the case to pressure up and observe flow. Stompski racing has a tool for sealing and testing.
I use the cam line restrictions on Carrera motors because a cam is cheaper than a crank or torn up case from a broken frozen rod on the crank from oil starvation.
A bottom end gasket set is about $60 and a few hours work.
Bruce

Walt Fricke · 03-04-2020, 04:27 PM

The "proper" way to check the cam oil squirter tubes is to remove them. Pull the plug at one end, pull the two fittings which locate them, and remove. You can now run brake cleaner through the whole thing, and eyeball the entire inside of the tube. And figure out various simple ways of blocking off the squirter holes so you can run fluid through each of them one by one (though by shining a light down the lumen of the tube you can pretty much just check the holes for blockage by eye).

Many of us opt to tap the hole where the end plug was, and screw in a plug, making pulling the squirter the next time easier (though it is mostly us race motor guys who anticipate doing this kind of thing more than once). It does away with wondering if the interference fit of the aluminum plug (pretty much bombproof from the factory) is going to work properly when done by a DIY guy (like me). I don't have a lathe to make new plugs, and am not sure I am good enough at measuring to check for proper interference fit before forcing the plug in.

Trackrash · Trackrash's Garage

On my motor, I drilled and tapped a small hole in the plug in the end of the cam housing, which allowed me to use a screw and washers to remove the plug. I could look down the squirter tube. IMO, no need to remove the tube. At that point you can fill it with carb cleaner and blow through with compressed air and it will be apparent if the holes are clear.
I reused my old plug. Used JB weld and peened around the plug for extra security.

I am using restricters BUT I drilled them out to 2,5mm.

ahh911 · 03-05-2020, 05:56 AM

Thank you guys. Looking at the cam wear pattern and the rocker arm bushing play in all the arms, it seems like when there is lots of bushing play, there is cam wear. But there was one exception. So 5 worn bushings, 4 cam lobes with pitting. The wear pattern on all the cams is on the same side. The wear in the rocker arm bushing looks like it allows the cam contact arm to go off angle when under load and cause the side away from the pitting to lift up or away from contacting the lobe. I see it in my case as simply rocker arm bushings that are wearing in step with the pitting. Replacing the bushings years ago in my opinion may have prevented this. I'm still interested in cleaning the oil spray tubes and wonder if the high pressure oil piston squirters are worth testing. What happens if one is blocked? The piston heats up, for short hard drives, does that matter? 45 second intervals of full load followed by regular street type driving?

Thank you,
Phil

boyt911sc · boyt911sc's Garage

Quote:

Originally Posted by Walt Fricke

The "proper" way to check the cam oil squirter tubes is to remove them. Pull the plug at one end, pull the two fittings which locate them, and remove. You can now run brake cleaner through the whole thing, and eyeball the entire inside of the tube. And figure out various simple ways of blocking off the squirter holes so you can run fluid through each of them one by one (though by shining a light down the lumen of the tube you can pretty much just check the holes for blockage by eye).

Many of us opt to tap the hole where the end plug was, and screw in a plug, making pulling the squirter the next time easier (though it is mostly us race motor guys who anticipate doing this kind of thing more than once). It does away with wondering if the interference fit of the aluminum plug (pretty much bombproof from the factory) is going to work properly when done by a DIY guy (like me). I don't have a lathe to make new plugs, and am not sure I am good enough at measuring to check for proper interference fit before forcing the plug in.

Walt,

You can test the fluid flow through the cam spray bars without any engine tear down. I have been demonstrating this procedure in the engine rebuilding sessions. See picture below:

For this test, I used a house garden hose and a typical residential water pressure is around 50 psi. You can do similar test with a complete motor using your choice of fluid. The camshaft was removed and replaced with a home-Made camshaft made of PVC tube from Home Depot.

Tony

Trackrash · Trackrash's Garage

What do the faces of the rockers look like? The thing is there are a number of factors to consider. Were the cams re-ground, that could remove much of the surface hardening. Were the lifters rebuilt? Ditto.

Neil Harvey · 03-05-2020, 09:08 AM

Porsche 2V camshafts are made from a cast Iron steel that is processed by chilling the steel very rapidly. A very basic explanation.

This creates a very hard surface but keeps the internal core a lot softer. Unfortunately, as with most steels, there are inclusions left in the core which are often just below the surface.

In most cases the surface hardness is compromised by lack of oil lubrication. The oils fundamental job is to remove heat from the sliding surfaces of the rocker arm pad and the camshaft lobe. Once the oil film is lost, heat is generated and the surface breaks down, exposing often the inclusions under the surface.

What also can happen without an oil issue, are other issues. A poorly ground camshaft lobe and or a rocker pad poorly repaired. This can add huge contact stress loading to one isolated area of the lobe and rocker pad, accelerating the wear.

What happened in this case? The only way to establish this is to check everything, but my first inclination would be a lack of oil.

ahh911 · 07:03 PM

Thanks Tony, that image shows one cam stream shooting off centre compared to the others, is that something that might affect how the oil splashes back onto the lobes? i.e. it ends up splashing the exhaust lobes more than the intakes for instance?

Thanks Gordon, the rockers corresponding to the damaged lobes have a little pitting in the corresponding location. The worst lobe 6, has the most bushing wear, and has the worst rocker pad wear with not only a little pitting, but also showing a little sloped wear as well. I don't know if they've been reground, I don't think so. A seperate question, could the pressure reducers cause an angle change in oil delivery of the originally intended cam squirter target, meaing the oil stream doesn't hit the orig designed location?

Thanks Neil, I undertand the message, but oil films would be across the lobe, not sequestered to the edges, although I do think there is a force that tends to apply more rocker arm pad pressure on the cam lobe edges that are wearing, so if not enough oil were present across the lobe, then potentially it might start to wear in those locations first. But why not the exhaust lobes right next to the damaged intake lobes, why are they fine?

stownsen914 · 03-05-2020, 07:12 PM

Wear can be uneven on the lobes if your rockers or shafts are worn, and the situation will be worse if there is any oil starvation due to blocked oil passages as mentioned.

You mention the PO used 5w40 oil. That is a bit low viscosity for these motors. And if it didn't have proper zinc levels, even worse. That could definitely cause accelerated cam wear.

Walt Fricke · 03-05-2020, 10:04 PM

Tony - I used to check the spray bars with brake or carb cleaner and air pressure. I could put some fingers over several of the holes for each fill and blow, and see that no holes were plugged. I agree, It is all a guy really needs to do for peace of mind when doing normal rebuild.

But once one end is tapped and plugged, super simple to pull the whole tube. Got to be confident you know its orientation for reassembly, but that's not hard to do.

If the engine "blowed up," then I'd think pulling the tube would be mandatory - you can't blow debris out the little holes.

Trackrash · Trackrash's Garage

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...