what oil do you use in an 1942 chev motor

I got a 216 which has just been rebult and i am trying to find out which oil is best .
The rear rag engine seal is leaking bad.

I have been using Castrol Magnatec in my 216 (in my '40) .
It is 10w40 I think.
I suspect a 15w40 might be a bit better in a worn 216.

I think todays oils are so good , compared to the '40's product, that just about any will be fine.

as for the leaking seal....

edit, I just re-read your post and see the 216 is rebuilt?

So the builder should have replaced the rope seal , eh.

Or did the rebuild consist of paint and plugs?

Either way , its not easy to change the seal with the engine in the truck, possible , just not easy. Then resealing the pan is a bitch from under the truck too. Better pluck it out and lay it on the floor to do the job if it really bothers you. That and sack the engine rebuilder

Emu - You'll find that many oil companies now produce "oil for older engines". It's generally advisable to use an oil designed for older engines, in older motors .. as new oils have a very high detergent level, which strips beneficial carbon from pistons, rings and oil seals, thus increasing oil burning and oil leaks. However, if the engine has only recently been rebuilt, it will probably run O.K. on newer oils.

Oil is rated by an API classication, which is broken down into diesel and petrol types, with some crossover between heavy duty petrol oils and light-duty diesel oils, and those crossover oils being suitable for both.
Oil for petrol engines is API rated under "S" classifications, diesel oil is rated under "C" classifications.
These ratings commenced before WW2, and run in basically alphabetical order.
Thus we had API "SA" classification petrol oils originally .. then SB, SC, SD, SD, SE, SF, SJ, SL, and the current SM classification.

www.aa1car.com/library/API_ratings.pdf

Each oil classification is upgraded every few years, as new and improved oil additives are found, and demands by engine manufacturers, for better oil performance, increase continually .
API claim that all new classifications are backwards-compatible with all older classifications.

This is not entirely true, as I mentioned above, and if you change from an older-classification oil to a newer-classification oil, in an old engine .. it will most certainly develop more leaks, and burn more oil, as a result of higher detergency.
Much sealing in worn engines, relies on carbon buildup in these engines, and the new high detergency oils strip out that beneficial carbon.

The current anti-pollution engines demand less pollutants go out the exhaust, so the pollutants are driven back into the engine (via EGR) or held back in the engine, via combustion methods tuning .. and these pollutants are driven down past the rings, and then neutralised and held by the oil.

Thus we have modern oils with much higher detergency than older oils, because the higher detergency is needed to cope with the higher level of combustion by-products (pollutants), that the oil has to strip out, neutralise and hold in suspension, in the newest model engines.

The other important factor in newer oils, is the reduction in the levels of an important additive, ZDDP (Zinc Di-alkyl Di-thio Phosphate).
ZDDP is reduced in newest classification oils, to protect and extend the life of catalytic converters .. and ZDDP is an important anti-wear additive, for older engine camshaft lobes and valve lifters.
Many modern engines use roller lifters or have modified cam lobe designs that can cope with lower levels of ZDDP.
Thus, you need an oil with a good level of ZDDP, or if using a newer-classification oil, you need to add additional ZDDP to the oil in an older engine.

The rope-style oil seal in the old GM-style motors (Holdens and Chevs), is a pretty crude arrangement, that has little "give" or tolerance to accommodate movement. Thus, if it's not carefully installed, and the component fit tolerances kept to the recommended minimums (thrust and main bearing clearances), you'll get the seal leaking very quickly after assembly.

These rope-style seals were originally made from asbestos, but are now made from replacement materials that are non-asbestos, and they are supposed to be equivalent to asbestos, but this isn't necessarily the case.

By far the biggest cause of leaks with GM-engine rope-type seals is careless installation, and a lack of careful attention to correct fit, proper compression/bedding down of the rope seal .. and a lack of adequate seal lube with installation. It's critical that there are no scratches on the crank surface. Some installers say it pays to soak these rope-style seals in oil prior to installing, but Fel-Pro disagrees. Fel-Pro state that just oiling their current rope seal upon installation, is adequate. I'd hazard a guess, that the old asbestos rope seals worked best when oil soaked, but the new materials don't.

Chev 216 rear main seal installation .. www.chevytrucks.org/tech/bobadler-1.htm

These seals nearly always still leak, even after proper installation .. as with every type of GM seal (GM and GMH always built the worlds worst oil seals and gaskets) .. so you must ensure that you pay careful attention to the installation procedures.

You can purchase an improved style of these seals from a company called Best, who are an American Company .. and you will probably only be able to source these Best rope-style seals from a local specialist engine parts supplier, or buy them direct from the U.S. The improved Best rope-style seal is called Best Graphtite.

www.bestgasket.com/

GM went to a rubber-style rear main seal after 1956 in the Chev sixes, but these rubber style seals are risky to use as a replacement in earlier engines, as machining tolerances are tighter for the rubber seal.

Original rope-style seal .. cgi.ebay.com/ebaymotors/37-62-Chevrolet-...ck_Parts_Accessories

Post-1956 rubber seal .. cgi.ebay.com/ebaymotors/40-63-Chevrolet-...ck_Parts_Accessories

Some excellent rear main seal advice (with pics) .. www.hemmings.com/mus/stories/2009/03/01/hmn_tips2.html

Here is an excellent forum discussion (link below), with pics, where some Yanks are discussing their rear main seal, leak problems, on old military Chevs. You can convert the rope-style seal to a lip-style seal, but the block usually has to be machined, to do so.

It's rare to be able to repair these rope-style seals properly, with the engine in the vehicle .. the only really effective repair method, is to whip the donk out, turn it upside down, and work on it with the crank lifted well out of the rear main.

Cheers - Ron.

www.steelsoldiers.com/early-deuce/38509-...-seal-gmc-302-a.html

Thank for that.
You have given me some thing to think about.
And oil is not just oil

Hi Emu ,I run in my 1934 Bedford and 1950 Landrover Shellsey 40 made by Prenrite.

As Onetrack said you have to be careful as most newer oils will eat bronze bearings and there is a older style oil made for the gearbox, diff, steering box, and motor. Dave

In both my 1955 Inter and 1965 Ute I run a Penrite oil designed for older engines. It was either 30w-70w or 40w-70w and is now the other way around. Seems to work ok