Packard Forum Index » Post-War (1946-54)

Have pulled the head and pistons from my 51 Patrician which had low compression on one cylinder and found very bad exhaust valve seat. I have found 4 or 5 top compression rings broken. What would cause this ring to break? Also, I was using non-detergent oil in this engine, but now that it's apart and cleaned out (in chassis), I am considering using detergent oil with a zinc additive. Any ideas regarding broken ring and oil issues? Thanks

Wayne

What about any excessive carbon buidup????
Broken top ring can be due to excessive bellmouthing of tje cylinder whoch is caused by cold running engone at high speed or load demand.
I.e not letting engine warm up and short runs.

Use 10w 30 or 10w 40. ESPECIAly if HIGH CARBON DEPOSITS ARE EVIDENT!!!

Arguments for running streight weight oil ARE varied but very shallow at best.
One argument is that engine not designed for streight weightt. Of course it wasnt. Multi grade did not exist until sbout late 1950's. Many used multi grade detergent in 50's cars well into the 1970's.

Cheque for excessive bellmouthing of cylinders within sbout one inch of thr top of cylinder. Up to about 0.008" bellmouth is ok.
I' m guessing your condition is at 0.018 or more.

Heavy duty or detergent oil was on the market by 1947. Multigrade introduced in 1951.

10W30 was the default choice in all garages and dealerships in the fifties, sixties, and seventies. We kept single weight for those who insisted on it, and non detergent bulk oil for the cheap skates with oil burning clunkers but every oil change was 10W30 unless the customer said otherwise.

Chances are any post war car has used nothing but 10W30 since it became available.

If the car had hydraulic valve lifters the maker most likely insisted on heavy duty oil if you did not want to void the warranty.

I don't know why the rings broke up but this seems to be a common fault in old long stroke inline engines. You can reuse the pistons if the cylinders are within wear specs.Check the top ring for wear or damage. The ring groove can be cut oversize and a shim put in if necessary. Pistons can be knurled oversize if they are a little loose.

This is known as a ring and valve job and was a common overhaul procedure when your car was new.

Non-detergent is better in a worn motor that has a lot of blow by. The water blow by doesn't emulsify and lays on the bottom of the pan. Non-detergent helps in heavily sludged motors that would otherwise turn detergent oil into waste upon startup.

Detonation due to carbon can break rings, as can revving fast enough to hit a carbon ridge. The same way as the excessive taper suggestion. If the ring grooves are worn and the carbon breaks away the force of combustion will not fall evenly and break the ring like a lever. If one side is stuck that can break them as well. I saw a number of motors that broke rings after sitting because the rings were stuck.

Piston rings can often do with more lubrication than they get nowadays, since lead was removed from petrol. Good/new rings tend to not let much oil pass to the upper compression ring and of course the valve seats, guides etc don't get lubricated as well as back in the leaded gas days. I personally think using upper cylinder lubricant is a good idea in older engines, especially in early days when newly fitted rings are tight in the bore. It is pure oil which will not burn off, but remains as a thin film on upper cylinder parts including the compression rings as it is delivered via the petrol. You're lubricating from 'both ends' of the piston so to speak.

Of course this is only a prevention measure, so not much help in your situation of having already broken rings.

You can also add a friction modifier to engine oil to reduce drag and therefore 'leverage' on rings. Costs a bit but it should lengthen the period between engine rebuilds.

I find this very often on these long stroke engines. Just want to underline that the new rings need to fit with proper side clearance in the grooves. Chances are your top ring grooves are all noodled out and you will not get a satisfactory job unless you recut them and install a shim.

If you have a lot of bellmouth you will need to rebore for a good job. But even .010 will be ok for a drive-around-for-fun car as long as you can get a good fit of the rings into the piston and they aren't flopping around in the grooves.

I have had excellent results using Grant piston rings. Their oil control even on worn cylinders is very pleasing.

Re top piston groove wear, here's one of several pages on ring and piston servicing from "Glenns" which IMO is the best book on general principles and practices on engine servicing. I hope this is helpful.

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