engine blow-by questions

Discussion in 'Engine, Fuel and Exhaust' started by mystryman, Oct 9, 2014.

  1. mystryman

    mystryman Member

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    Before I start, I'lltell what I have. A'98 wideglide with s&s carb, crane pushrods and crane ignition.. not sure what else might be in engine, bought it used.
    Ok, now to my story...lol. I left to go to a rally last week and a few miles out of town I smelled something hot. Pulled over and saw my oil cap popped open, oil all over bottom halves of all of the pushrod covers and on rear exhaust. babied it back home and took my trike. yesterday went to car wash to clean it off so I could determine what's happening. sprayed degreaser on everything and washed it off. got it back home, no leak. let it set and idle for a bit, then revved it a few times, no leak. Took it out on the road and opened it up, bingo! Started blowing out.
    Did compression check today. My clymer repair manual stated it should be about 90psi. I got 145 on rear and 100 on front. Apparently previous owner had more in this engine that isn't stock. Anyway, still a big difference between cyls. Put plugs back in, took air cleaner off so I can access breater tube. Has a LOT of air coming out at idle and none detectable when I rev it. First question is should this be normal with the breather tube?
    The other question being blowby in front cyl is obvious, could I put a can of engine restore in it to buy some time till I can rebuild it? Recently laid off and don't have the funds right now to do a rebuild.

    I apologize for the long drawn out post.
     
  2. tourbox

    tourbox Senior Member

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    On compression the norm. is only 10% difference. On your push rods, are they adjustable type. If so so then one may be to tight on the front cylinder causing one of the valves to stay open a small bit. Check them cold.
    tourbox
     
  3. BUBBIE

    BUBBIE Well-Known Member

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    IF that much pressure is lost thru the front piston, Blowing Oil is the results...:shock

    No, on the restore. Yon need to find Why that front cylinder is Low... IF going down the rings, A re-ring AND OR possible a new bored cylinder (Both) .

    IF you can hook up air thru the spark plug hole and find where that air goes? when valves are closed.


    signed....BUBBIE
     
  4. mystryman

    mystryman Member

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    I've got a compressor, i'll see if I can round up the fittings to put air to it.

    As an added note,...someone on another site asked about oil on the spark plug. Both plugs are normal color (tan) with no signs of oil or carbon.
     
  5. dolt

    dolt Senior Member Contributor

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    If the compression readings are accurate, the front cylinder is low. What Bubbie is suggesting by putting air in the spark plug hole is a leak down test. You really should use a proper leak down tester for the test. To do a proper test, you need to be able to regulate the application of pressure with one gauge and measure the leak down with another.

    Cylinder Leak-Down Tester
    Pressure is building in the crank case from the front cylinder blow by or from a blockage in crank case venting mechanism preventing venting of the crank case. Sounds like the front cylinder is the likely offender.

    If so, and you are short on funds, pull the rear cylinder and have the piston to cylinder wall fitment checked (in torque plates) and if excessive bore that cylinder to fit a .010" over piston and put her back together. There is no rule that says you have to bore both cylinders; you can bore one and you will never know the difference.

    BTW, get rid of the Clymer manual and get the real one; the H-D manual for your bike.:hii
     
  6. flst89

    flst89 Member

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    Hydraulic lifters...

    For the pushrod adjustment to cause this, the pushrod adjustment would have to be extended so far as to have the piston in the lifter bottomed out...
     
  7. tourbox

    tourbox Senior Member

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    That would be some what true. But do you have adj. push rods? Either way it's a simple check. Put both valves fully down and see if they both spin freely by fingers.
    I also agree with what Dolt and others are saying but I would check push rods first.
    tourbox
     
  8. Jack Klarich

    Jack Klarich Expert Member

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    If your leak down test turns out OK, I would open the nose cone and have a look at the breather If it is plastic I would replace it with a steel one I assume this is an EVO
     
  9. dolt

    dolt Senior Member Contributor

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    Both plugs looking good is a positive indicator that, at least, valve guide seals are working. The different CCP from front to back requires repeating the compression test to validate the first readings. If the same variance in CCP is verified, definitely a leak down test is the next step. Having said that, the CCP variance could well be a pre-existing condition that should be addressed but the oil puking is the result of a faulty breather. If it is plastic, do as Jack suggests and upgrade it to metal. This may stop the oil puking but, eventually, you need to address the front cylinder.
     
  10. mystryman

    mystryman Member

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    I tore down the top end on both cyls and taking them to shop to be bored and order new pistons. When I put it back together, do I need to use conventional oil for the break-in period?