valve guides leaking?

[Don S]

How do I check for valve guides that may be leaking. While driving up our hill in second gear at about 25 mph,the engine sound changed a bit and blue smoke came out the back. I have done a compression check,all 4 pretty even at 118-120. I have a 5.9 hc head.Done the vacuum checks all good except the idle where it shakes between 18 and 22 inches vacuum. This is supposed to indicate a problem with valve guides. Mine are the new 1 piece valves and keepers installed only 3000 miles ago. Could oil be passing the valve stems when the engine is under load? Any ideas??

[Special Coupe Frank]

Usually oil getting sucked-past the valve guides happens on extreme vacuum, such as descending a long hill against engine compression, with the throttle closed.

If you're belching blue smoke on a pull, that sounds like loose bearings / worn rings...

You say you have new guides... how fresh is the rest of the engine ?

SC Frank

[Don S]

Only 5000 miles on a complete rebuild,bearing shells,valves,guides,hc head,cam bearings,Stype touring grind cam,bronze cam gear,etc.

[Special Coupe Frank]

Originally Posted by Don S

Only 5000 miles on a complete rebuild,bearing shells,valves,guides,hc head,cam bearings,Stype touring grind cam,bronze cam gear,etc.

My worn-out 88,000 mile un-restored A engine also has the vacuum gauge needle bounce bewteen 18-22 in Hg at idle... I think this is due to the Flivver idling so slowly... same gauge holds steady on my other old cars, which are all sixes...

Last compression test this fall, she was still pulling 55 - 60 pounds between all four cyls.


Is your car consuming oil or fouling plugs ? Engine done by a reputable / knowledgable A rebuilder ?

What year engine ? The '27-early '29 engines had a valve cover with a higher return-pipe outlet at the rear of the engine; this was changed in '29 with that outlet lowered, to cut down on oil level in valve gallery and reduce oil consumption.

[Don S]

Engine rebuilt by a reputable builder,I haven't talked to him yet. He is away for the holidays. My block is a Canadian late 29 5 bearing cam. When I removed the plugs for the compression check they were oily. This has not happened before. As I said earlier, the smoke blew out in second gear going up hill at about 25mph.

[SteveB31]

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118-120 PSI Compression? Seriously?

[mach0415]

Kinda what I was thinking. Its hard to get 110-120 psi with a 5.9 head. (14.7psi atmospheric pressure at sea level x 5.9 = 86.73 psi....max) Anyway, a compression test will only find a gross leak and give you a "general health check" of an engine

The most concise way to diagnose base engine issues is to perform a cylinder leak down test (It can be used to localize and isolate burned, bent, or unlapped valve(s) or cylinder leaks. For example, in your case, if oil is getting past the oiler/wiper rings, then the compression rings are also worn enough to let oil past to be burned in the combustion chamber OR there is an issue with cylinder bore/taper,out of round issues that never were addressed during a "rebuild." On an overheated engine, ring tension fails, causing blow by - also found with a cylinder leak down test.

I would think that valve guides on a flat head would not be so much an issue as it would be on an OHV or OHC engine because there is not nearly as much oil sitting on top of the valve stem, while running. In fact, on a flathead, the valve stem is inverted, so oil would have to blow upward, past the valve face and into the combustion chamber. This could happen, I suppose, if there was significant crankcase pressure, due to a plugged oil cap vent and/or worn, undersized rings. My 1947 Plymouth P15 flat head 6 had almost .030" clearance in the valve guides and it never smoked.

Was there any instruction on how to run the engine after you received it from the rebuilder. Is it possible the rings never were seated in properly?

[Don S]

Compression checks have been similar numbers since first tested. The gauge could read a bit high,but the numbers would be comparable.So the question is why did I get smoke on hard accelleration up hill in second gear.? It did not start at the bottom of the hill but about half way up. Same story on two different trys. Had severe overheat last May while going up hill on a highway,no where to pull off until near top of hill. Found the timing retarded. THe distributer screw had become just loose enough to retard the spark. I advanced it enough to get power to drive home. Did a thorough check when home,made several trips during the summer with no problems or loss of power. Never did burn any oil. Just before putting her away for the winter,I was taking her for one more drive when the blue smoke situation happened.A year after rebuild I returned to my rebuilder,where he replaced a wrist pin,but otherwise found nothing. I helped with the teardown and checked the block as well. Nice and clean,and still is. I have the pan off,could check shells if necessary.On the leakdown test ,how much air pressure is needed,and how much oil?
I appreciate your help

[mach0415]

Before I get into details, is the oil level correct? If overfilled and going up a steep hill, cylinder 4 could be really sloshing around in some serious oil past the skirt. Just a simple and probably irrelevent thought. Also, did you have this problem before the overheat? If not, thats probably what caused it, and I would lean toward loss of ring tension and would be most noticed under load and accelerating. Now for more detailed thought.

When I refreshed dad's 1929, I paid VERY particular attention to measurement detail. I carefully checked, rechecked, and checked again for cylinder bore taper, out of roundness, piston to wall clearance, ring clearance in the grooves (lands), end gap etc. I was able to get away with a quick hone and a set of rings and no need for going up a size on pistons or bore. The engine had been rebuilt in the past, as there was evidence someone other than me had been there. Most people simply throw a set of rings to it based upon the specs without even checking for end gap. It is amazing how different rings in the same set really can be when they are installed in the bore. So, I file fit ALL my rings on any engine I refresh/rebuild. Now, she's together with no smoke.

There are many variables that will not have a conclusion unless you take detailed measurements. Only then will you be able to arrive at a conclusion. "Rebuild" and "refresh" are two totally different things. AND "rebuilt" wears many different faces, I am finding out. I am not trying to discredit ANY "rebuilder," but I would think that if an engine were actually rebuilt, there would not have been a need to go back and replace a wrist pin IF the measurements were taken prior to assembly, thereby correcting a problem before it becomes one, unless the overheat somehow caused that.

Since we are at the diagnostic stage, a cylinder leak down tester will show a percentage of leakage. I would think that 100 psi would be enough. My gauge reads up to 120psi. Since the most yours would build is 86ish psi, that range is more than plenty. With both valves closed on each cylinder as you roll through the tests for each, listen for air rushing through the intake, out the exhaust, or out of the oil cap. You will most likely find it at the oil cap if it is ring-related. Otherwise it will be an intake or exhaust valve related leak.

It is possible that the rings are not seated. Some others can chime in, but I used Hastings cast iron rings when I refreshed Dad's. I hear the chromium rings are really hard to get to seat. Also, if the bores were close to the higher end of what the tolerance is and never bored up a size with new pistons, then the ring size for that would really be too small and probably have a heck of an end gap, not to mention less tension. Before its all over, you may have to pop a few/all pistons out and do the measurements to make sure it truly is within specs. Again, all of that would be irrelevent if the problem occurred after the overheat and not before it. I have never seen worn bearings lead to oil consumption, as bearings do not seal the oil from combustion gases.

[Special Coupe Frank]

Perhaps worn bearings contribute to oil consumption only on pressure-lubricated engines: excessive rod bearing clearance allows excess oil to be thrown on the cylinder walls, more than the rings can adequately control.

May well be a non-possibility in a splash-oil motor...

SC Frank

[Don S]

Thanks Marc for your thoughts. There were no problems with the engine prior to the overheat. No oil consumption,oil level kept at 3/4. Dipstick is original to the engine and close in measurement to what I have seen here on Fordbarn posts.I also used Hastings rings as recommended by my engine guy.With good compression numbers,the rings and valves should be ok,no? So where would the valves get the oil from? Don't want to pull the head unless I run out of options. Thanks again

[PC/SR]

Tough one Don. I think the best test of leaking guides would be smoke after the very high vacuum on decleration sucking up oil mist from the valve chamber. Then blue smoke when you re-apply the throttle. Does smoke happen after deceleration, or other times, or is there blue smoke even now only when accelerating up hill? This check would also apply to bad rings, but your compression check seems to rule that out, although a leakdown test is more conclusive.
My initial thought given your symptoms of sudden onset while accelerating uphill was detonation breaking a ring or piston. (HC heads are more susceptible to detonation.) Again, a leakdown check would be better than a simple compression test if the break was relatively "minor" and only on one cylinder. The short cranking time of a compression test may mask a "minor" failure on one cylinder.
Oil on all 4 plugs might be coincidence. If it were due to only worn rings, or guides, it would be a gradual onset, not sudden. I don't see how bearings would contribute to the problem.
It is the sudden onset along with smoke only on acceleration uphill that stumps me. That indicates to me that something suddenly broke and is repeated only under stress. Maybe a valve spring/guide or ring broke or shifted? Are you using modern guides pressed in, or original style guides? I will follow this thread with interest.

[mach0415]

Ring tension, or lack thereof, will present itself under load and higher RPMs more often than at idle or cruise. A compression test would not reveal this sort of issue, because the leak is a running compression issue with high crankcase and cylinder pressure under load at higher rpm's. A cylinder leakdown test would reveal the same thing, because you typically introduce higher than compression pressure into the combustion chamber. When I was working on Fords, our factory equipment and diag procedures included performing a running compression test.

Your experience does not exemplify a gradual onset because it is not a failure due to normal wear. It happened suddenly because of a high, prolonged overheat under load. You mentioned this in one of your first posts. One thing to remember about the Hastings rings, or any cast iron ring, however, is that they are more susceptible to failure quicker and easier than a chrome/moly ring. That makes sense, since a chrome/moly ring is harder to seat on break-in.

Excessive bearing clearance presents itself as low engine oil pressure and knocking. It is absolutely impossible for a bad bearing to cause oil blowby into the combustion chamber. In fact, if a bearing had that much clearance, it simply would allow oil to be dumped out of the journal and into the pan - pressurized or not, at which point, the engine should not be run at all.

If I were you, I would explore a leak down test first and then begin diag items from there. Unfortunately, the head will need to come off. Thats not so bad. Check the valve guide diameters with a ball gauge and mic it, measure the valve stems' diameter, and determine if that is a factor. If not, throw the valves back together...nothing lost there. I would also pull pistons and determine if there is a ring or more that is out of spec. Heck, for the $, I would just throw a new set in, knowing that it has been severely overheated and then "poof" the problem presented itself. This can all be done in the car.

One last thought...In a previous post, you mentioned the spark plugs were oily when you pulled them to do a compression test. My assumption is that the engine idled at some point prior to doing this test, and perhaps just after pulling a hill and smoking. But I would think that there was adequate run time to clear the plugs of oil, UNLESS there is oil leaking past rings or somewhere else even at part/closed throttle and low load.

[James Rogers]

The guides could cause a flathead to smoke but, probably not. Pull the pistons. When you overheated the engine the new pistons expanded and the cylinder walls and skirts of the pistons scored and the rings lost tension. It won't smoke perceptibly when running but at hard pull it will smoke enough to see. Been there, done that.

[Tom Wesenberg]

I was thinking the same thing as James, and while the head is off be sure all of the cooling chamber and radiator is clean. The overheat may have caused rust flakes to come loose.

[H. L. Chauvin]

Different Degrees of Engine Overheating ?

1. Overheating for a short period of time is not quite as damaging when the coolant level remains all the way up to the water neck whereby the head remains full of hot coolant.

2. Because of a Model A non-pressurized coolant system, coolant in lieu of becoming superheated under pressure does not get over 212 degrees, just 22 degrees over a normal 190 degrees .

3. Many old hopper fed hit & miss engines survived with original rings running over 25 years at their designed temperature of 212 degrees; however, later air cooled engines operating at their higher designed temperature of a little over 500 degrees never survived as long as water cooled engines running at 212 degrees.

4. "If" engine coolant level drops a bit below head gasket level, even for a short period, tops of cylinders get hotter than bottoms of cylinders & wear rapidly occurs at tops where one normally finds a cylinder ridge.

5. This higher temperature overheating at tops of cylinders can cause rapid cylinder taper whereby the top of the cylinder has a larger diameter than the bottom which was cooled with coolant & oil. Even though one still sees steam exiting the radiator, this is severe overheating

6. If this condition occured, with high heat & wear at tops, not only can rings loose tension, but one can get rapid carbon build up in piston ring grooves whereby rings get stuck in carbon filled grooves & do not expand fast enough when the piston gets to the top of the enlarged cylinder.

7. Many have witnessed a good example of a similar, severe engine overheating case such as following a car "cruising" along with a very light hint of blue smoke. Then this driver mashes on the gas pedal to pass another car whereby the engine speeds up, & all of a sudden this same passing car disappears in blue smoke.

[mach0415]

Keep in mind 212F is good for straight water's boiling point, but when mixed with ethylene glycol (antifreeze/coolant, green stuff that kills Fido and FiFi) or propylene glycol (not toxic) it raises boiling point up to 265F depending on the mixture ratio.

[H. L. Chauvin]

Thanks Mark.

8. And, in addition, please also note that to make matters even worse, after the coolant level drops enough, (with "any" mixture of coolant), the engine coolant temperature can no longer be lowered by flowing through the radiator whether while having a Model T thermosyphoning circulation system or Model A water pump circulating system. Vehicle engine overheating does not always sound too bad, but it if left unattendd for a period of time, it can cover a wide range of different very harmful temperatures.

[Don S]

I am pretty sure that over heat( boiling) may have caused some damage. I was running antifreeze at the time,a lot of which had to be replaced due loss. It took a gallon plus several drinking water bottles to fill. The question of did it idle after the hill climb,yes I live near the top and more or less idled down my driveway home.