dropped compression

[GARY F]

37 Olds, straight 8 flathead.  I know it needs work.  Did a comp. test, got 4 at 60lbs. 4 at 30lbs. tested the next day same.  checked it yesterday and today and two of the 30s come up zero. I never hear of such a thing. Would any of you have any thoughts why. I checked the valves and the setting is correct when closed. Thanks Gary

[Gunsmoke]

Try a second compression gauge first. Sometimes the valves in the gauges don't function properly. Make sure all plugs are out during check and that battery gives a good turnover. Usually takes about 3-4 compression strokes to get a good reading and ideally use a gauge with a re-set function (I don't know if they all do). I checked Compression on mine today, friend had a professional quality 2 piece tool, first part was a 10" long hose that screwed into each plug hole and had a quick release fitting to attach a second hose to the gauge, typically needle reading went up to 45 lbs on first stroke (that stroke fills the hose), needle went further to 65-70 on 2nd stroke (pressurizes the hose) and topped off at close to 80-85 on 3rd/4th stroke and stayed there. I'm not an expert on this procedure, others may be. 

[Bloo]

Sounds like sticking valves. Valve adjustment was ok I take it? Is it still ok? If something stuck there should be a huge gap. Is the gauge staying up until you reset it? There should be a valve core in there. Gauge should stay up until you release it. Sometimes the valve cores are special for a compression gauge. If the needle stays up, the valve works.

 

Did this get run on some rotten gas?

 

The next steps (IMHO) would be to verify that the valve timing hasn't jumped, and then do a leakdown test. You could proably do both at the same time, since you have to put each cylinder on TDC to check leakdown. It is going to be bad on at least part of those. Listen at the exhaust, take the air cleaner off and listen in there, take the oil cap off and listen to the crankcase. Some leakage through the rings (oil cap) is normal, but there really shouldn't be much out the exhaust or intake. Don't get fooled by the sea-shell effect, but you probably wont, because at 0 pounds, you have a hellacious leak somewhere. You will get to hear what that sounds like right off the bat.

 

[GARY F]

Answer to some of your question.The car has not run since 1975. New comp. tester. Like I said 4 cyl. had 60lbs. the other 4 had 30lbs.  new battery. I had the head off refaced the valves. In the beginning most all lifters were stuck up. Freed all  lifters, checked all valve settings according to shop manual. I did the comp. test many times on different days. The first two days were 4 cyl. @ 60lbs. and other 4 cyl. @ 30lbs.  Yesterday and today two of the 30lb. cyl. were zero.  All the plugs are out. My tester has the reset function.  My tester can be used by just pressing down in the plug hole  with the rubber tip and I have the adapter to screw in the plug hole and attach the gauge to it. I tried  both but I like just holding it on the plug hole with the rubber tip. I just don't know why I lost the two cyl. that showed 30ls.  I have tried them all many times because I thought I might have made a mistake. Valve adjustment is still on specs.

Thanks again for the replies.

Edited November 11, 2019 by GARY F (see edit history)

[Bloo]

So you have had the head off then? and you KNOW there aren't any holes in the pistons, right?

 

Stuck rings can cause low compression, but not zero. If there is no physical hole for the compression to leak out, you still have a valve problem. I cant explain it, but there it is. I doubt you could even get down to 30 pounds with ring trouble. Certainly not 0. Zero is valve trouble. A leakdown test will show where the big leak is, but it has to be valve related.

 

Since even the good ones are on the low side, I would also verify the valve timing. Do you have a shop manual? It probably has either a valve opening-closing diagram, or if it doesn't, some specs where the valves open and close. What you are interested in, to verify it without taking anything much apart, is the overlap. On most of these old engines it is centered VERY close to TDC, probably within 3 degrees or less.

 

Find the "opposite" cylinder of #1. For instance on an engine that has a 1-5-3-6-2-4 firing order, 6 is opposite of 1.

 

Example: If you have the engine run up to TDC #1 on the firing stroke, the tip of the distributor rotor points at #1, and the butt of the rotor points at #6 in this made-up example.

 

Plugs out, go on around almost 2 more turns of the crank, to almost where you were. Side cover off, you should be able to feel the #6 intake open and then the #6 exhaust close just as you cross the TDC mark. You can figure out exactly where it should be from the numbers in the book, but VERY close to TDC on an engine like this.

 

Go only clockwise with the crank to keep the slop in the valvetrain taken out. There can be quite a bit of slop in timing chains or gears after some normal use. If there is doubt whether it is jumped, find a picture of the timing chain and count the teeth on the sprockets. In my made up example, I am gonna say 10 teeth on the crank and 20 teeth on the cam.

 

Then either do:

 

1) 720 crank degrees divided by 20 cam teeth = 36 crank degrees  or

2) 360 crank degrees divided by 10 crank teeth = 36 crank degrees

 

So, in my made-up example the spot where the overlap occurs would have to be MORE than 36 crank degrees from where it should be (about TDC) to indicate a jumped tooth. Use your Olds tooth counts of course.

 

 

Edited November 12, 2019 by Bloo (see edit history)

[Gunsmoke]

When I first opened up my '31 Chrysler 8cyl flathead (had not been run in 60 years), it was clear a PO had been trying to solve a valve sticking problem without removing the head. I don't know if the '37 Olds valve setup is similar. The manifolds on my car were loose, and when I removed the side valve covers, all the valve spring retainers had been removed from the valve springs, again by a PO. When I then removed the head, which it appeared had never been off, I found the exhaust valve at #8 stuck solid (took a great deal of effort to pull it out), intake was also very tight, and 5 or 6 other valves were sticking. I had to ream out the #8 valve guide quite a bit (with proper valve guide reamer), less so on the others which were obviously carboned up from some sort of improper maintenance, and made sure all valves stems moved up and down freely.  Refaced valves and lapped them in, all is working well now, compression 77lbs-86lbs across the 8 cylinders. I agree with above suggestion that it sounds like a problem with a valve(s) not closing  properly. Insure timing is correct or that can also upset compression.  My engine calls for timing set when #1 cyl is a few degrees before TDC (piston .006 from TDC).

[dalef62]

Are the two dead cylinders side by side?  Possible that the head gasket is leaking between the two?

[trini]

Gunsmoke and Bloo, you guys are on track, the most likely cause is sticky valve stems. There is a but here . If the engine was running good before it was put to sleep then the timing is fine, but the valves in different position after so many years of in activity will definitely have a negative effect on the valves. I had a problem with a V8 engine on a 67 or so 5 ton Ford box truck. The valve train was noisy because the oil was not coming up the rods. The manager made me drain the engine oil and replace it with transmission oil and run the engine for ten minutes. The oil started to come up the rods one by one. Run the engine for 30 minutes, drain and refill with regular truck engine oil.   BACK YARD tricks works. carburetor cleaner and even voporust helps to remove carbon

[chistech]

I believe on the Olds flat head, you should be able to see both valves some. Look down the plug hole with a flashlight and watch the valves for movement. Simply putting your finger over the plug hole you should feel compression but if your gauge is reading zero, I suspect like others, your valves are sticking. Put some mystery oil down the two culprits and find the valves that are staying up during cranking.  push them down with a screw driver. Sometimes putting the screw driver on the valve and tapping with a small hammer does the trick. Only use the hammer when the opposite valve is open. This way you know the lifter is off the cam on the stuck valve.

Edited November 13, 2019 by chistech (see edit history)

[chistech]

On 11/11/2019 at 5:58 PM, GARY F said:

Answer to some of your question.The car has not run since 1975. New comp. tester. Like I said 4 cyl. had 60lbs. the other 4 had 30lbs.  new battery. I had the head off refaced the valves. In the beginning most all lifters were stuck up. Freed all  lifters, checked all valve settings according to shop manual. I did the comp. test many times on different days. The first two days were 4 cyl. @ 60lbs. and other 4 cyl. @ 30lbs.  Yesterday and today two of the 30lb. cyl. were zero.  All the plugs are out. My tester has the reset function.  My tester can be used by just pressing down in the plug hole  with the rubber tip and I have the adapter to screw in the plug hole and attach the gauge to it. I tried  both but I like just holding it on the plug hole with the rubber tip. I just don't know why I lost the two cyl. that showed 30ls.  I have tried them all many times because I thought I might have made a mistake. Valve adjustment is still on specs.

Thanks again for the replies.

Honestly, the 60 lbs is about the minimum you’d want to run the motor with. With 4 being at 30, it sounds like you have a ton of taper or stuck rings.  The old cast iron pistons used a super aggressive ring along with the long stroke and low wrist pin location all added up to cylinder wear.. your motor is most likely due for a rebore and some new pistons.

[JACK M]

On ‎11‎/‎11‎/‎2019 at 2:58 PM, GARY F said:

The car has not run since 1975.

 

Get the valves un stuck and get it running (a few times) and then start all of this again.

[GARY F]

When the zero compression is on that cyl. I put my feeler gauge in the lifters and I have my 11 tho. and 8 tho. between the lifter and valve. I agree it is time to pull the pistons and go from there.  I thank all of you for your replies.

[GARY F]

Disregard the no compression  for this question.  I dropped the pan. Inside was a little over an inch of  sludge in the bottom and a little less in other areas. The car has a 104,000 miles on it according to the speedometer. Question, with all that sludge why was there no ridge on the top of the cyl. walls, not even a trace of a ridge. Even the oil pick up screen is loaded with sludge. Any comments?

Edited November 17, 2019 by GARY F (see edit history)

[GARY F]

Btt

[Bloo]

Non-detergent oil, I imagine.

[Spinneyhill]

If that oil has been in there since 1975, it has probably oxidised while sitting there, not to mention whatever use it had before being parked. The anti-oxidants back then were less good than they are today. As well as that, it probably has some sludge  from earlier times using oil with not many or no additives, as @Bloo says.