Origin of Piston Failure (Advice needed)

[allaboutas]

Gentlemen,

Recently, while driving about 40-45 MPH in my 1929 Model A (Original engine, 47K miles) I lost cylinder #4--Confirmed later with compression tests (other 3 cylinders had quite good compression). Removed the head and found faulty cylinder with a burnt exhaust valve, and aluminum distributed (seemingly interstitially) throughout the bore (see attached pictures). I checked the volume of oil in the pan recently and measured 4 quarts, but I'm not sure If I added a quart (but certainly no more) to the pan when I was moving the car around before the investigative disassembly. I would have noted that the oil level was low right after the incident, so I don't think that was a factor, but I cannot completely rule it out. I knew I would be traveling about 30 miles, so I did check the radiator, which had adequate coolant at the beginning of the trip.

Two days ago I removed the piston, which revealed a heavily scored OD & Cylinder ID (again see attached ;-)) Big end and crank journal showed minimal evidence of wear.


Bore Micrometer measurements of all cylinders were taken, and indicated an engine with only moderate wear.

Two last things....I had just switched to Mobil Delvac 1230 straight 30W oil (after quite a bit of research), And also when I had hobbled
home, and exited the car....I found about a pint of oil had exited through the weep hole in the clutch housing.

Please take a look at my attached photos/PDF file, and if possible, could I ask anyone with the expertise and/or the inclination to recommend potential root causes for the failure. It would be troubling to complete the repair without a thorough understanding, and risk having the event occur again.

Some friends have suggested clogged water passages in the vicinity of the damaged cylinder as a potential root cause.


Many thanks in advance !

John M

[Joe K]

Oil out the rear main (clutch hole) might have been the additional sliding resistance of the 4th cylinder causing the crank to "wag like a dog's tail" and lift (and drop) the flywheel resulting in rear bearing "pumping." You may have damage here too - check the endplay/thrust and the bearing itself.

The galling certainly seems related to that seen by others elsewhere "hot spot" at the steering wheel quadrant of the 4th cylinder.

Keep in mind that 30W oil does not have the constancy of viscosity that more modern multi-weight or synthetic oils have. Were this engine lubricated with full synthetic I would wager this would not have happened. (Flat viscosity curve.)

Bummer.

Joe K

[tbirdtbird]

I would expect that of a new build with too tight a clearance to the walls. But this is not that situation. Plus you have a burned valve. I would be suspect of clogged passages myself. Plus, 3&4 run hot anyway. Should be easy enough to determine if the block/head are full of crap. Start there. Running too lean?
Delvac 1230 should not be an issue

[James Rogers]

Cause, lean run.Just look at how clean and light colored the deck, piston and seats are. #4 is the most susceptible to excess heat even when running good much less in a lean condition. Just about bet this happened at 50 MPH or better or pulling a hill. The oil from the rear main is a result of the bypassing of combustion gasses in the pan pressurizes the crankcase and oil is forced out the tube to the slinger which is overwhelmed and leaks profusely.

[Kohnke Rebabbitting]

At some time or other, that engine has set for a long period of time with out being turned over.

Cam shafts don't rust like if they are used or turned.

May be a leak of something some where.

That took a long time for the rings to get that way.

Antifreeze and water will stick rings like that, and also smear piston Aluminum on the cylinder walls.

30wt. oil causing that, not a chance!

[H. L. Chauvin]

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My first guess is that in order to "guess" at a cause, we are not hearing all of the history on this engine. For example, before this incident:

1. Was this engine/car ever stored without exercising the engine?

2. How long has this engine been in constant use, like started at least every 6 months or so?

My first "guess" without very much engine history is:

1. As mentioned above, if the block did not leak because of being cracked, and/or the head never leaked, & there was never ever any water in the oil, this camshaft indicates that this engine sat a long time without running to accumulate condensation & rust to cause rust pits like that on the camshaft.

2. If so, it is also highly possible that when the engine was at rest, no. 4 piston rings rusted in their grooves when piston no. 4 was near the top of the cylinder, where the largest diameter occurs. Then when the rust wedged the piston rings to where they could not flex inwards & outwards, with large "fixed" ring diameters overheating took place while running the engine & began contributed to wear.

A Model A diagnosis is like bringing a dog to the vet -- the dog cannot tell the Vet details so either the owner provides details or the Vet has to guess at a cause & remedy.

If you really want assistance for one or more root causes, appears it would help immensely to please furnish a few more "engine history" details.

[Tom Endy]

I had the exact same thing happen to my engine last November that had just been rebuilt. Traveling along at about 55 in overdrive, the engine failed. The #4 piston virtually melted. The other three were not far behind. it was a cold day and the engine water temperature was below 160F.

The engine went back to the builder. I asked where the pistons came from. He got them from one of the better suppliers, but they were made in Taiwan. The engine was re-bored and new US made Silvolite pistons installed. Fortunately the only damage to the engine was to all four pistons and cylinder walls. Valves, rods and mains were not damaged.

I have been told that several of the better suppliers switched over to the Taiwan made pistons a while back because they are cheaper. The Silvolite pistons were $60 a set more expensive. However, they are certainly available because that is what is in the engine now.

Tom Endy

[tbirdtbird]

Since a customer is pouring a few thou into a rebuild that he wants to hold up (none of us are doing this for kicks), I'll never understand why the builders are using the cheapo inferior crap.

[Kohnke Rebabbitting]

Any Piston will fail if they don't get the right clearance.

Every set I have seen has the paper work saying, fit at .002 thousandths total clearance.

No Aluminum piston can live at that.

[H. L. Chauvin]

In my opinion, when one gets half a story of the former history of a particular problem of any kind & that historical half appears somewhat "iffy", incomplete, & questionable because of lack of former historical details ........ like cause & effect, why guess at what happened during or after the problem?

A positive solution as to what caused the problem, if any, will usually be revealed "after" reporting the historical details that occurred "before" the problem, in what could be later called: "The Rest of the Story."

[tbirdtbird]

.002 in an A is way too tight. Maybe, in a modern car. There used to be a rule .001 per inch diam. At nearly 4" diam, that brings you close to .004. We use .0035