304 oil blow by...

Discussion in 'Member-Club Forums' started by NickyRotten, Dec 6, 2015.


  1. NickyRotten

    NickyRotten Farmall Cub

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    My 1970 Scout 800a is giving me a little trouble. Runs great, starts up, idles, makes head turning good noise! BUT I am getting blow by through my dip stick. I have checked my PCV valve (not sure what Im looking for there), new hose, new breather on the other cover. Not sure what else to do. I don't want to believe it is bad rings, does anyone else have this problem or a fix?
     
  2. gpa

    gpa Binder Driver

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    Is oil pumping it's way into the air cleaner ?
    In any event, you have excess crankcase pressure.
    Likely plugged vent/PCV or the dreaded piston ring delete option.
    PVC should rattle & tube should be free of obstruction. Remove the PVC & oil cap , rev the engine & look for fumes.
     
  3. Dana Strong

    Dana Strong Dreams of Cub Cadets

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    What is "head turning good noise!"?
    More details would be useful, for example which engine, what is the history of the vehicle such as mileage, modifications, engine rebuilds, previous owners and/or type of usage. Has it been running since new, or did it sit a long time in a vacant lot in recent years?

    If just one piston has stuck or broken rings, that can be checked by making an adapter for the spark plug, setting each piston in turn on power stroke-TDC, replacing its plug with the adapter and running compressed air into that cylinder. With all other crankcase entrances closed, compare how much air leaks out of the PCV port (valve removed for checking) from one cylinder test to another. You're not trying to crank the engine so be sure it's exactly on TDC, don't overdo the pressure, and if a manual transmission, put in high gear with brakes locked while pressurizing.


    .​
     
    Last edited: Dec 7, 2015
  4. NickyRotten

    NickyRotten Farmall Cub

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    Hey Guys,

    Sorry for the lack of info. It is a 304. No major modifications to the motor. 33 inch tires with a 6 inch lift. From what I was told the PO brought this Scout back to life but the engine and bay are gorgeous.

    As for the "head turning noise", I mean it sounds great and everyone loves it while I drive by.

    Should the PCV rattle while I have it out and shake it back and fourth? There is no oil in my air cleaner but I did find a small amount of oil at the base of the valve cover breather.

    Thanks for the help and suggestions guys, this is my first Scout.

    Nick
     
  5. NickyRotten

    NickyRotten Farmall Cub

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    *UPDATE*
    I took the PCV valve off, it rattles. I stuck my finger in the hose attached and there was some oil in it. Is that normal?
     
  6. Greg R

    Greg R Dreams of Cub Cadets

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    There is no oil in my air cleaner but I did find a small amount of oil at the base of the valve cover breather.

    It appears you have an "Open" PCV system, that is where make up air is coming from an "open" breather rather than the carburetor's or induction's air filter. You will have some condensed fumes that appear as oil at the PCV valve. I would replace the hose, look for blockage at it's connection on the carb's base, and clean the PCV if it's a take apart kind. If it's a newer stamped steel kinda thing, replace it. An impromptu test of the PCV system is with a warm idling engine; pinch off the make up air, or in your case block the valve cover breather, and place a thin cloth over the oil filler hole. The crankcase should have a few inches of vacuum and you can see this with a depression of the cloth over the oil filler hole. It's not enough to suck the cloth in unless you make it to small. I put a corner of a handkerchief big enough to cover and drape the hole a little and I can see a depression in the cloth on a correctly working system. It's not accurate or scientific, but it is on par with readings you can get from a regular PCV system tester such as was made by AC. Post a picture of your engine and the PCV items in particular. For a 1970, you should have a "Closed" PCV system with make-up air coming from the air cleaner and through a spark arrester.
     
  7. NickyRotten

    NickyRotten Farmall Cub

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    Breather.jpg PCV.jpg PCV hose.jpg Attached are some pictures. In my hand is the treaded PCV valve that rattles. The hose is brand new I just installed last week. The breather is still on the clean side. What I don't understand is other systems the PCV hose seems to go to the air cleaner, where mine goes to a 90 into the engine.
    Breather.jpg
     
  8. Greg R

    Greg R Dreams of Cub Cadets

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    Thanks for the pictures, it confirms my suspicion of your "open" system. To get to the root; with the PCV valve off of the rocker attach the manifold hose and run the engine, you should have a moderately strong suction at the threaded end. If you don't, clean or replace the valve. If you do, check the threaded port in the rocker cover; it may be choked or blocked. It also has a baffle under it, it might need cleaned too but that means taking the cover off. Try my test in my previous post, all in all we're looking to see if the system is working. When you get things working, I suggest Plan B and get that breather replaced with an arrestor and hose to the carb air filter. Then you'll have a "closed" PCV system. Those after market cleaners usually don't have any provision for breather hoses and you'll have to fab one. I did for my K&N air cleaner, and it's not hard with a bulkhead 90* flare or inverted flare fitting. A PCV valve only works under certain idle/load conditions. Above that, such as WOT, you're either dumping trash to your engine bay as in an open system, or it gets recycled and burned as in a closed system.
     
  9. NickyRotten

    NickyRotten Farmall Cub

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    GREG! You are a wealth of knowledge! Do you have any pictures of your set up or something I can look at with the arrester and hose? I will check for suction and any blockages tomorrow.
     
  10. Greg R

    Greg R Dreams of Cub Cadets

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    71 PCV valve.jpg 71 Crankcase air breather.jpg 68 266V8 PCV to valley.jpg 68 266V8 breather oil filler.JPG IMG_1504.JPG Okay here are some pictures. None of my engines are as snazzy as yours ;)
     

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  11. Greg R

    Greg R Dreams of Cub Cadets

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    The first two are off of the 71 345. The PCV valve is similar to yours, on the passanger side rocker bung. The breather is on the driver side. The next two are off the 68 800. The PCV valve is a stock take apart kind, and stock routed to the valley pan with fitting and grommet. The breather is a shop made oil cap breather for a 70's Ford I put a grommet and 90 ell in to attach the hose. (It is not open to the atmosphere or has holes on the bottom; it's totally sealed. a Ford PCV strategy) The original breather location was the front of the engine in the timing cover. Putting it high on the rocker cover I got a better blowby removal. The original air cleaner was an oil bath type with a hose connection for PCV, then I went to a K&N. Later I settled for a later model air cleaner with a hose connection. In all cases I maintained a closed type PCV system. Here are some pictures for the aftermarket air cleaner with alteration: IMG_1504.JPG IMG_1509.JPG
     
    Last edited: Dec 8, 2015
  12. Greg R

    Greg R Dreams of Cub Cadets

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    IMG_1515.JPG A more accurate way to check PCV valve/system function is with a vacuum gauge. Here is a compound gauge for pressure and vacuum and notice a range has been marked out for PCV. You block off all make-up air and let the PCV valve pull maximum rated vacuum on the crankcase. The gauge registers how strong a pull is. Low readings are from a weak, clogged valve or leaks such as deteriorated gaskets, bad leaky seals; or at the worst excessive blowby that compression and leak-down tests can confirm.
     
  13. Greg R

    Greg R Dreams of Cub Cadets

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    IMG_1516.JPG Here is a vintage PCV tester put out by AC. Various brands of this style were out there but I believe AC was the 1st and the rest was just rebranding the same device. You matched an orifice selection off of a chart based on engine size; though it was listed as make, model year and then a color band indicating performance was viewed through a slot when the device was put over the oil filler. A good PCV system keeps a clean engine by ventilating out the fumes that would otherwise condense on engine internals sludging and coking things up.
     
  14. NickyRotten

    NickyRotten Farmall Cub

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    Wow Greg, great pictures. I ran mine today...took the PCV off the rocker cover and had a ton of suction. I also did the bandana over the oil fill trick, it pulsated in and out.

    Do you think it matters which side my breather and PCV are on? Currently my PCV is drivers side and towards the front end, and the breather is passenger and towards the fire wall...
     
  15. Dana Strong

    Dana Strong Dreams of Cub Cadets

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    The breather and PCV valve should be on opposite engine sides so the fresh air flows through the entire engine, as yours now does. It doesn't matter if it's left-to-right or right-to-left, though; that depends on the easiest way to route the hoses.
     
  16. Greg R

    Greg R Dreams of Cub Cadets

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    I don't think it matters on these engines, I've seen it both ways. See if you can confirm with a vacuum gauge that at least can read 0 to 5 inches Hg in the lower end of the scale. The readings should be steady.
     

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