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Oldsmobile Flatheads

Discussion in 'The Hokey Ass Message Board' started by Zaloryan, Jul 30, 2012.

  1. Zaloryan
    Joined: Oct 13, 2009
    Posts: 25


    I'll be tackling a beautiful 1947 Oldsmobile 66 Series with a 238 L6 engine, Hydramatic. Also, a 1947 Oldsmobile 98 Series with a 257 L8 engine. And finally, a 1940 Oldsmobile Series 70 with an L6, not sure which displacement yet.

    Here's my question(s): I'd like to get as much information on these flathead engines Oldsmobile used before the Rocket V8 came out. Hopefully I could do another compilation for these engines like I did for the 303/324/371/394 engines. I've found has some very handy basic information for the flathead engines from 1946 on and that's all I've found. So please, if you have anything to contribute...

    Does anyone know where I could source a new starter for my 1947 238 L6? The previous owner's friend/brother/something took the housing apart with it still bolted to the engine and the internals have been exposed to the elements for the last several years. :rolleyes: I know Fusick's, Kanter's, and EGGE offer parts for these cars, but please add any other companies that you know of.

    I have a good understanding of OHV engines and how to tune them, squeeze more power out of them, etc. However, I am a novice with flathead engines. I understand the principle of how they work but I am not familiar with how to treat them as opposed to the newer Oldsmobile V8s I'm used to.

    Could one realistically mill the cylinder head to raise compression so long as the valve clearance to combustion chamber roof is checked?

    What kind of clearances do these engines need for the camshaft, rods, mains, etc?

    What other options do I have in the way of freshening up these old motors?

    Is it possible to have hardened valve seats installed in the block for daily usage of modern unleaded gasoline?

    Is valve recession a problem with unleaded fuel?

    Would it be a good direction to study articles on Ford flathead engines? What publications should I search for?

    How does one setup points in the distributor? (Sorry...I'm spoiled with HEI.)

    I'll be searching for an old Oldsmobile service manual, obviously, that will be my primary study guide. Before I turn any bolt or nut on any of these cars, I'll be juicing up all of these cars with PB Blaster for a few weeks to discourage broken fasteners and busted knuckles.

    Thanks guys!
  2. A flathead ford book would be pretty much usless for you.

    You should be able to have hard seats installed if you can find a machine shop to do it, but you need to be real careful of the fella installing them is not real sharp you will end up dropping seats left and right.

    I would imagine that hop up parts are going to be about as plentiful as hens teeth. I don't know that they were ever a popular engine with the hotrod crowd.
  3. Zaloryan
    Joined: Oct 13, 2009
    Posts: 25


    What could cause the valves to drop with hardened seats?

    I suppose I should have put a little more detail in my first post. :eek: I won't be hotrodding these cars, it's just a matter of trying to make the engines a little better than they were when they ran.
  4. If not installed properly the seats pop out. When installing a hard seat the machine work needs to be dead nutz, like in +/- zero dead nutz.

    I have seen a lot of thses old engines hold up fine without changing the seats, but to be on the safe side it is a good idea to just run lead subistitute.

  5. Look for a MOTOR'S manual that covers what you're working on, old book websites.
    GMC trucks used some of those motors back in the day.
  6. Dale Fairfax
    Joined: Jan 10, 2006
    Posts: 2,585

    Dale Fairfax
    Member Emeritus

    Old Motor's Manuals are available at swap meets and or I would imagine you might find shop manuals there as well. Motor's lists almost all the pertinent specs for all those engines--crank journal sizes, bearing clearances, bore & stroke, piston to wall clearance, compression ratios and others.
  7. Bert Kollar
    Joined: Jan 10, 2007
    Posts: 1,081

    Bert Kollar

    This may or not be relevant but in 1954 I had my Plymouth 6 head milled .060" and ran the piss out of it. I would think the Olds engines had similar compression ratios and it would be easy to check clearance of the valves
  8. F&J
    Joined: Apr 5, 2007
    Posts: 13,222


    I don't know if you tried for Olds 1940s engine specs, but I am in there all the time for the 50s and 60s specs they have.

    I am not sure if I can look up the starter number or not, if you need it? I can try if you want. Not sure I have the right book for 40s, but maybe

    I would not worry on a passenger car if not towing a huge trailer cross country :) It's the lugging that will aggravate the seats, so if no real load, it should be fine.
  9. belair
    Joined: Jul 10, 2006
    Posts: 8,802


    While I am hesitant to not agree with the beanner, I have never run hardened valve seats, and have never had a problem. These engines aren't going to see 10-12k miles per year are they? If not, I would not worry about valve recession.
  10. Butch11443
    Joined: Mar 26, 2003
    Posts: 353


    To start with, there wasn't leaded gas when these engines were built. That was from 49 up. You should have about .050 clearance above the piston after milling the heads. Your are starting with about a 6/1 compression ratio. As far as clearances, you will need a manual. Points probably are about .017
  11. Rusty O'Toole
    Joined: Sep 17, 2006
    Posts: 9,608

    Rusty O'Toole

    They may already have hardened valve seats, most cars did back then. The really heavily leaded, high octane gas only came in around 1954 -55.

    Most of your questions can be answered by a repair manual or web search.

    As far as performance goes they would respond to the usual old time hop up methods like milling the head, dual or triple carburetors, reground cam, lightened flywheel, and split manifold or headers.

    They were one of the least popular engines for hopping up. I don't know of any old time hot rods with Olds flatheads. Tom McCahill criticized the 1947 Olds for lousy performance. He said "when you step on the gas you get a squish instead of a swish" and other cracks. Years later an Olds executive told him that his article was the clincher needed to get GM to approve the 1949 V8 for production.

    Eddie Edmunds may have made a few heads and manifolds, he did for everything else. They would be pretty scarce though.
  12. Greg in Jax
    Joined: Jun 27, 2010
    Posts: 209

    Greg in Jax

    Check your PMs. One of those Edmunds intakes that I told you about is available for your six. Good luck with the project. Greg
  13. oldwood
    Joined: Mar 13, 2010
    Posts: 994

    from arkansas

    You can get a factory Olds manual for those years off of ebay. I have a '47 and a '48 Olds, 1 six and 1 eight.

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