1937 La Salle series 85 compression test help

[jet-tech]

Hallo, new member here. My dad owns a 1937 Cadillac with a series 85 engine. A compression test shows 80 psi cold. Then he repeats compression test with a wormed up engine and gets 50 psi on all holes. This sounds backwards to me. One more note, my dad bought this car about two years ago fresh from a full restoration. Any help word be appreciated.

[35-709]

Hmmm. We need to back up a little here, first year for the V-12 was in the 1931 Cadillacs --- LaSalle never had a V-12.  If it is a LaSalle, it has a flathead V-8.

To your problem, whatever you have, one place to look would be the valve adjustment.  If they are set too tight, the clearances only get closer as the engine warms and can hold the valves open ever so slightly effectively lowering your compression.

[jet-tech]

My mistake, 1937 Cadillac series 90 v12

[35-709]

   OK.  My answer as to your problem is the same.

[Bob Schuman]

The Series 90 has the V-16 engine. 1937 was the last year for the V-12, which was Series 80 and 85. Since the V-12 was essentially a shorter version of the V-16, comments about valves, compression pressures, etc. should apply to both the V-12 and V-16.

[jet-tech]

Thank you Bob and 35-907 for the corrections. As you guys can tell I'm not that familiar with these older Cadillacs. My Dad has had a few including a 1930 v12, 1931 v16 convertible and 1957 Eldorado Biarritz convertible.

On Monday I will fly to his home in Ft Lauderdale and check the valve adjustment. Redo the compression test and also do a leak down test. I will report back with findings. Any other suggestions would be appreciated.

[G Pennington]

The 1930 - 1937 V-16 is a completely different engine than the 1938 - 1940 V-16s.  Nothing in common with the earlier V-16s or V-12s.

[jet-tech]

I just got back from fort Lauderdale to help my dad with his 37 Cadillac series 85 V12. No luck with finding out what's the cause of the low cylinder pressure. All valves checked close to .030" with all Rocker Arm Silenser dash pot pushed down as per shop manual. The limits are .030" to 070". Then adjusted valves to .060", cylinder pressure checked as noted below at both settings.   

1) Performed dry cylinder pressure check on all cylinders cold. 90 psi. I think this is good
2) Checked pressure wet. 90 psi. no change.
3) Warmed up engine, check now shows 50 psi.
4) Ran engine with with pressure gauge fitting still in spark plug hole. increased RPM's. gauge drops to 30 psi.
5) Leak Down test showed 50%, this may be normal for this engine.   

We think the Silensers are pushing the rocker arms up too much on the pushrod side, and adding downward pressure to the valve stems. The Silensers use oil pressure for muscle and the more RPM's means more oil pressure in the silencer body.

Any suggestions would be appreciated. Tim

[fishnjim]

Not in evidence: Did this problem recently occur or was undetected since purchase?
(I realize you're steering from a distance, partially blind, emotionally invested, too.)

These are low compression motors to begin with 5.6-6 to 1.  eg; 6 x 14.7 = 88 psig (103 psia) max.   So at best going to make the 90 psig.  (It does, that's good!)

If all the cylinders are the same pressure, may not have a problem, per se, unless there's some underlying performance or interference issue - not described?   (No evidence given of coolant leakage at temp given - whitish exhaust, coolant in oil, etc.)
Since this 82 year old motor was redone with unknown previous history, there's no way, without a tear down, to accurately tell what the issue is, if one exists*.   Throwing it to the internet, you're assuming there's a simple fix you don't have knowledge of.   You're not going to get complete diagnosis from an internet forum.  You'll get 50 opinions.   So you have to gauge if tear down is worth the effort?  Always a chance things could get worse and you may not like the answer - crack, etc.. 

* - Someone expert in V-12s is best to resolve this and who you should seek out.   There's some unusual things that happen when you increase # cylinders, >8.
ps:Another reason I don't do pre-war.   A lot of iron to make a little HP.

[jet-tech]

Thanks for responding Jim. The car was at a restoration shop that specializes in these old cars. After a test drive they performed compression check and suggested a tear down & rebuild for $20000. But they had no idea what was the cause of low cylinder pressure. The motor has very low miles on it, maybe less than 2000 miles. So a rebuild did not make sense and my dad had the car shipped back to his garage. The problem really only happens after the engine is wormed up.

[Bob Hoffmann CLC#96]

Tim,
Maybe I missed it, but what are the symptoms of the low compression? 

[jet-tech]

Tim,
Maybe I missed it, but what are the symptoms of the low compression?

On test drive the car would only go about 30 mph. Test pressure gauge shows 90 psi cold, same wet. After warming up engine pressure  showed 50 psi. And with engine at idle with gauge still installed 50 psi and then above idle the pressure drops to 30 psi. 

[savemy67]

Hello Tim,

When you did the leak-down test, how much air pressure was applied to the cylinders?  Were all cylinders tested, and did all cylinders have the same result?

Did you listen for escaping air at the carburetor, exhaust, and crankcase or valve cover?  A pronounced hissing of air at one or more of these locations might point to the area allowing compression to escape.  If you are careful, you could do a leak-down test with a warm engine, but be careful.

Forgive my skepticism/cynicism, but if a shop ..."that specializes in these old cars." proposes to rebuild the engine for $20,000 in the hope that the problem might be fixed, the shop's "specialists" must not be very good.

Respectfully submitted,

Christopher Winter

[jet-tech]

Hello Tim,

When you did the leak-down test, how much air pressure was applied to the cylinders?  Were all cylinders tested, and did all cylinders have the same result?

Did you listen for escaping air at the carburetor, exhaust, and crankcase or valve cover?  A pronounced hissing of air at one or more of these locations might point to the area allowing compression to escape.  If you are careful, you could do a leak-down test with a warm engine, but be careful.

Forgive my skepticism/cynicism, but if a shop ..."that specializes in these old cars." proposes to rebuild the engine for $20,000 in the hope that the problem might be fixed, the shop's "specialists" must not be very good.

Respectfully submitted,

Christopher Winter

Hi Christopher. Good question. We did the leak-down test on all cylinders and instead of a using a stethoscope, we only had a long funnel to listen for sound. I believed that we could hear sound from both the exhaust and from around the heads were the pushrods are at. We could not detect sound from the carburetor, I just could not get in a good position being downdraft carbs. No sound from the radiator. The oil looked normal and no oil in the water.

The shop has a good reputation, but we did not want to tear down the engine without knowing the reason why. 

[Bob Hoffmann CLC#96]

Tim,
I still feel that all the facts are not being presented. Your dad bought the car 2 years ago. How did it run then? What happens if you start it cold & immediately drive it? Will it go over 30 MPH? That car originally had up draft carbs. What carbs does it have now? You mentioned down draft. Please advise.
Bob

[jet-tech]

Tim,
I still feel that all the facts are not being presented. Your dad bought the car 2 years ago. How did it run then? What happens if you start it cold & immediately drive it? Will it go over 30 MPH? That car originally had up draft carbs. What carbs does it have now? You mentioned down draft. Please advise.
Bob

You are correct, my error. The carbs are updraft. When My dad first purchased the car it ran just okay. A few months later it started to run poor, turned out to be one of the points in the distributor. The point got replaced and all was good again. Then about six months ago it started to lose power and was not driven or worked on because my dad was out of state at that time. Finally the car was sent to a shop to trouble shoot with no answer why it ran poorly. I don't know if the car has better power when driven cold. The last day I was in FL the starter gear would not engage, so thats off and getting looked at. I'm planning on returning to Fl in a couple weeks for some more quality time helping my dad figure this out. I do think it has something to do with the valve silencers not letting the valves fully seat. I might take them out for inspection. We adjusted the valves last time per the shop manual, pushing down the silencers and turning the ring that rest on the silencers before adjusting. Do you have a procedure thats works for you? Tim

[harvey b]

if the car will only go 30 mph?,i would look at the timing again to see if it is set properly.also check the carbs to see if the choke is working right.Is the gas in the car fresh?,i would add a bit of marvel mystery oil to the fuel as well.Does the motor smoke when it is running,a blue smoke is the rings or valves,a black smoke is a choke issue or a flooding problem.It could be flooding and washing down the cylinders as it is running?.I dont think the problem is serious,just needs a good mechanic to make it right. good Luck  Harveyb

[Brad Ipsen CLC #737]

Just got reminded of this again but old plugs cause all sorts of problems so just on general principles put in new spark plugs.  Do not use NOS plugs but new from the auto parts store.  One other thing that has not been mentioned is to test with a vacuum gauge.  Refer to manuals for symptoms versus readings.