Partial Rebuild on Race Engine?

[jgparker]

OK, I missed a shift at Sebring in September and dragged the engine well over 9k, but the only apparent damage was one of my valve adjuster jam nuts backed off. I ran the engine again last week, and it ran great, but I noticed a glint of very small metal partials in the oil and found a very small amount of metal in the oil filter. Here is a picture of the filter pleats.



So, my question is do I tear it down and risk doing a whole lot of work and money for nothing or do I keep running it, watching it carefully and risk doing more damage?

A little more background info. The engine is a 2.5 single plug 10.5:1, S-cam, SC oil pump, based on a 7R case. it has 3 races on it, so it is still very fresh, but should already be broken in. I run J&B racing valve springs, and ARP rod bolts, J&E pistons with stock rods and rod bearings. So it should have some margin on an over-rev. It sill makes great power, oil pressure was perfect, and compression is perfect in 6 cylinders.

My suspicion is I've damaged one of my rod bearings, but the amount of metal is so small it might not be enough to worry about. If I do need to go through it, is it reasonable to do a partial rebuild and replace the rod bearings without splitting the case?

Any advice would be appreciated .

JP
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[Steve@Rennsport]

JP,

While I cannot tell from your picture (very nice, BTW) if those particles are ferrous or not, if it was our engine, I'd be pulling it apart to look at every rod bearing at the very LEAST.

Unless you have a filter on the pressure side (ala 964/993), you are only seeing some of the metallic debris,.....

If you do that, remember to check and correct the big ends for concentricity.

[Grady Clay]

I guess the caption after the Last Engine Rebuild Project link says it all:
“Now a coffee table.”

If you are willing to risk having another ‘coffee table’ then keep running it.

Judging by your careful rebuilding, I suspect you have a lot of your time and effort in the engine.
I would not willing to risk destroying an engine with a broken rod or rod bolt.

A ‘maintenance rebuild’ is an easy alternative.

http://forums.pelicanparts.com/911-engine-rebuilding-forum/569915-hours-between-rebuilds-911-race-engines.html

Best,
Grady

[lucittm]

Steve,
This is a topic that is dear to many of us so I am asking you to expound on your answer. What would you have said if JP had said the particles are all attracted to a magnet meaning they are ferrous?
Conversely, what would you have said if JP had said the particles are not attracted to a magnet at all?

The easy answer is rebuild it anyway, but I am more interested in what you think is the source of the metal particles and why would an over-rev cause this, if at all (is this possibly normal wear and tear).

I think the oil filter did its job and I would be curious to see inside the oil filter of a similar car under similar conditions. I may start opening my oil filters out of curiosity.

Thanks,
Mark

[jgparker]

Hi Steve, Grady,

Thanks for the suggestions. The particles are non-ferrous, no question. That rules out a lot of things, but point to the plating on the bearings to me. I'm thinking rod bearings. I'm leaning towards a partial rebuild without spitting the case. As an experiment, I've changed the oil and plan to lightly street drive it for fifty or a hundred miles and recheck the oil and filter. Any hint of metal and it comes apart. I wouldn't hesitate other than how minimal the amount of metal I found was.

JP
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[Grady Clay]

Bearings are usually three-layers: babbit, copper alloy and steel.
Babbit is very soft, the copper alloy is intermediate but much harder than the babbit and the steel is … well… steel.
A common mode of bearing failure is fracturing of the intermediate layer of ‘copper’. The fractured pieces can flake off the steel and go through the oil system.
This is the common bearing material in the oil when there is a failure.

This failure can be due to the babbit failing and the copper alloy running on the crankshaft journal. It can also be from overloading, like over-rev. The fracturing can also be from detonation where the shock travels down the rod and is absorbed in the bearing, overloading it. I have seen bearings with perfect babbit but the lines-of-fracture of the underlying copper alloy are showing through the babbit.

I don’t see any of this kind of failure in your filter.

The debris in your filter I would consider ‘normal’. An engine is always generating some debris. It can be sealant flaking off, wear of cams, rockers, chains, sprockets, ramps, pistons, cylinders, etc.

Best,
Grady

[aws]

The problem with over-revving a stock rod engine is that the big end will not maintain its concentricity due to (in my opinion) its weight. The stock rod engines I have rebuild due to serious over-rev (over 9000) have all had the big end .0008 to .00013 out of round. This will the cause the crush on the rod bearing to go away and the engine will eventually spin a rod bearing. In a race engine with open exhaust you will not hear it knocking and the time between it knocking (spinning) and the rod parting company with the crank is MAYBE 1-2 laps. Until the bearing spins it will not shed any debris into the filter----- The filter on the scavenge side of a 911 engine with a aluminum counter-shaft gear will always show a lot of aluminum debris--along with brass from the timing gear, your filter, if it was on the scavenge side was very clean. It is not a bad idea to run a screen on the scavenge side and a pressure filter where the oil cooler goes on the pressure side. (if you can get away with removing the pressure side cooler which is very efficient). You then check the scavenge screen after every session. I think Henry said 2 over-revs and you are done--- But I think peace of mind would make me want to tear it apart at least to the rods to see what you have.

aws

[ErVikingo]

JG, tear it apart and save the potentially larger bill later on.

Sounds like a ticking time bomb

[jgparker]

Any advice on where to send the oil for analysis to find out what the metal is?

Thanks,

JP
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[Steve@Rennsport]

Originally Posted by jgparker

Any advice on where to send the oil for analysis to find out what the metal is?

Thanks,

JP
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I use Stavely for oil analysis as their results are more consistent & accurate than others.

[304065]

I can't help you with the work part but what's a teardown cost?

Gasket set
574 and the other sealants
Miscellaneous single use hardware (DIN 985 nuts etc)
Main bearing set if necessary

Engine drop: 2 hours for a race car
Teardown to the crank: half a day if you take time
Dimensional metrology and inspection: a few evenings
Reassembly: a couple days

Peace of mind of knowing you won't blow a fist-sized window in the case: priceless

[Robert Shafer]

JP
I was behind you on the start of our last race at Sebring. Where did all the smoke come from? Bob Shafer

[jgparker]

Hi Bob,

The smoke was caused by one of my chain ramp studs falling out and oil was running out the hole in the back of of the chain housing onto my exhaust header. I've driven it 3 times over about 30 miles without a lick of smoke, so I think I have it fixed. I plan to run this weekend at the Moroso vintage, so we'll see if it's fixed or not. I'll have the oil analyzed as well to see if I have any other problems.

Thanks,

JP
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