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Technical Compression test numbers all over the place

Discussion in 'Traditional Hot Rods' started by thompsonwayne1, Sep 2, 2014.

  1. thompsonwayne1
    Joined: Nov 6, 2013
    Posts: 88


    Got a stock 283 in my roadster. The engine history is unknown. Did a compression test and came up with 115, 115, 140, 125, 125, 130, 140, 135, 100. Many of the plugs were oily when I pulled them. Engine goes through a lot of oil, and getting worse, a 200 mile trip and I was down a quart.
    Someone said maybe I had leaking valve seals also??
    Any ideas? And does anyone have a ballpark idea what a valve job would cost if I took the heads to a machine shop
    And has anyone had any experience with the aluminum heads that are sold on Ebay They are cast in Australia and finished here. They sure have sold a lot of them, $500 a pair
  2. AHotRod
    Joined: Jul 27, 2001
    Posts: 10,370


    The Heads for a 283 are not the same as those used on 350's.
    You can kill the power of a 283 by installing the wrong heads.

    Now, squirt 3 pumps of oil into each cylinder, and re-run the test. This will show if the rings are shot.
  3. Grahamsc
    Joined: May 13, 2014
    Posts: 466

    from Colorado

    Intakes gaskets can leak internally and suck oil from the valley.
    Return drains in the heads can fill with sludge , filling the valve cover with oil and sending it down the valve guides.
    If neither of these is the case , I doubt a quart in 200 is going through the top end.
  4. saltflats
    Joined: Aug 14, 2007
    Posts: 9,666

    from Missouri

    My guess the ring land on the pistons are worn out.
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  5. I may get crucified here, but I've seen high mileage engines with those kind of compression numbers still live a long and productive life. A cylinder leak down test will give you a better idea of why the weaker cylinders are, well, weaker.

    For the oil consumption you're reporting, if the oil is getting into the cylinders you should be seeing some blue smoke from the exhaust. If it smokes a bit on start up, at idle or during decceleration, valve seals and/or guides may be the issue. If there's little or no blue smoke you may have an external leak to track down.

    As mentioned, make sure the oil drain ports in the heads aren't plugged and while you're at it make sure the crankcase venting is working properly. Remember too that if you do have a little leakage past the rings and a little leakage past the valves, putting on a fresh set of heads or doing a valve job is likely to further aggrevate any problem with the rings.
    Last edited: Sep 5, 2014
  6. Don's Hot Rods
    Joined: Oct 7, 2005
    Posts: 8,319

    Don's Hot Rods
    from florida

    I have no personal experience with the heads you mentioned, but my machinist, who I respect completely, told me one time he likes them a lot and that they flow good numbers.

  7. Valve job figure 200 plus any hard parts.
    You'll want a small CC combustion chamber on your 283.
    You should do a leak down.

    The product "restore" can help and does what it says it will if the engine isn't too far gone. If that engine were mine I certainly would try it.
  8. With those compression numbers, a wet compression test is needed to determine where the culprit is.
  9. thompsonwayne1
    Joined: Nov 6, 2013
    Posts: 88


    Thanks everybody, I'll do the test again and do the 3 squirts of oil in each cylinder and see what numbers I get.
  10. jguff
    Joined: Jan 14, 2009
    Posts: 134


    That must be a very interesting 9 cylinder 283! Maybe the oil is leaking out of that extra hole.
    Ha Ha

  11. Fogger
    Joined: Aug 18, 2007
    Posts: 1,399


    Check the road draft tube at the rear of the block, is the tube there or is the hole plugged? The early small blocks, 265, 283 and 327 had the breather hole next to the distributor and they require a venting and an open type breather cap on the oil fill tube at the front. You can eliminate the draft tube with a PCV attached to the vent hole and connected to the carburetor base. The engine must have an air intake at the oil fill and vent out the draft tube, if not there will be an increase in oil consumption. As others have suggested do a leak down test.
  12. squirrel
    Joined: Sep 23, 2004
    Posts: 44,069


    I had a 283 with numbers a little bit lower than that, but similar was plumb wore out.

    using as much oil as it does, my guess is your engine is just really tired.
  13. oldolds
    Joined: Oct 18, 2010
    Posts: 2,818


    What Squirrel said.
    140 is about all a stock 283 would do when fresh, 100 is what they do when worn out.
    A bad cam can give numbers all over the place, measure the lift. But I would bet it needs a rebuild.
  14. aaggie
    Joined: Nov 21, 2009
    Posts: 2,529


    If you rebuild the heads you will need to install hardened valve seats for the unleaded gas. It can get expensive. Remember the newer heads are meant for 4" bores and putting them on a stock bore 283 will shroud the valves.
  15. 305 heads- wham bam & cheaper than spam. But you get accessory holes which will muck up the looks of your 283.

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