QuestionQUESTION: Have a low oil pressure problem. Purchased car recently and never ran well,with SU's set to run rich, so I replaced with a Weber. However, as oil pressure is dangerously low am getting ready to pull engine and do an overhaul. Checked pressure with a remote gauge and there is a "knocking" so it seems to be in need of some work. Checked compression and it was in the range of 140-152 psig in all cylinders so thought I was looking at a bottom end rebuild only.
So, moving on, I started getting ready to pull engine and noticed quite a bit of antifreeze in oil. Can I rule out head gasket with the above compression test? If so, what do I look for next? Thanks.
ANSWER: Hi Brian,
No! you can not rule out head gasket with coolant in the oil. The only combustion chamber test I seen that can rule out a head gasket is to put the car in 4th gear with the hand brake on and the piston at TDC of #1 and put an adapter in the plug hole to fit shop air pressure (At least 125 PSI) hose to the combustion chamber. Then remove the radiator cap while the pressure is on and watch for the coolant to raise. This test will find even the smallest leak if it is there. It is also very good to check for valve leakage. Open the throttle and listen in the carb with either a stethoscope or a hose in the ear. Listen at the tail pipe too for the exhaust valve leakage. It is no use listening in the oil filler cap because ALL engines "Hiss" in to the crankcase past the rings, even a new engine that is just broke in.
Do all four cylinders for an exact sure test of a head gasket leakage. This test will pick up the smallest leak that doesn't show up on a compression test nor even show any signs of overheating.
That adapters are available from most mechanics tool trucks. We use to make them before they were available. We knocked the insides out of a spark plug and welded in an air hose fitting.
Your compression test shows good but it is foolish to only do the bottom end when the engine is out. It is not that much more to do a ring and valve job while it is out. First check the pressure relief valve in the side of the block and checking the filter before condemning the crank and bearings.
If the bearings are bad you need to clean all of the oil galleys and up to the rockers anyway and the oil pressure operated chain tensioner.
If the crank needs to be turned or not, be sure to Plasti-gauge ALL the bearings when you assemble them. Target is .0015" on the rods and from .0015" to .0025" on the mains. The "Green" Plasti-gauge is what is needed.
Howard
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QUESTION: Howard,Thanks. I did check the oil pressure relief valve, and spring free length was ok. Moss sells a stronger spring to boost oil pressure and am going to install with engine out. (tough to get that nut on)What else is there to check on the valve?
When I pull the head, if the head gasket is blown, won't I see light rust or signs of leakage on the cyl walls/piston heads? Are there other places to look for water getting in the oil?
Thanks,
Brian
AnswerHi Brian,
You can examine the valve for ware and it is very noticeable when it is badly worn. Also check it for free movement in it's bore. Unless the spring is weak or broken or the valve is stuck open a stronger spring will only raise pressure at higher RPM as the valve doesn't even open at idle. Except in the winter with cold oil.
Gaskets usually show where a leak was but not always. The worst is a leak that does not show because it could be a crack in the head or the block. Most auto machine shops can pressure test the head and even Magnaflux but not all can pressure test a block. Some can be hard to spot. That is why I always did the combustion chamber pressure test first when a head gasket leak was suspected.
It depends on how bad the leak is. Brown foam deposits in the valve cover and thick brown oil should be a large leak and should be able to be easily found.
Howard
