VCCA Home Forums TECHNICAL - 1945 AND EARLIER 1929-1932 Vacuum test on 1932

Did a vacuum test on my 1932, and got these readings:
Vacuum test

Compared to this:
Vacuum readings

To me it looks like a loose valve guide, are there any way to find out which guide is loose, without removing head?

Compression test gives an even result around 85 PSI on all 6 cylinders.
Other threads recommend a leak down test, will it tell my anything here?

i would agree something is not right IF the valve is jumping all over.

since i just had a head job done on my 1929, to truly check the valve guides you would have to remove the valves, which have to be pulled from the inside. you do not want to play with the valves and drop them in the cylinder with head on engine.

my guides were shot, options were to replace them about $10 USD per guide or sleeve them, they opted to sleeve mine, was noted as a superior options for wear and tear and should outlast me. cost me $10 per guide, so $120 for guide job.

if concerned, I paid $350 USD for head job, that was magnaflux, sleeve guides, valve hob, machine head flat, & machine manifold face. well worth the security knowing everything is now correct :)

To check a valve stem to guide for excessive wear wiggle the top of the valve stem BACK AND FORTH. tHIS CAN BE DONE WITH THE ROCKER ARMS IN PLACE AS LONG AS THE VALVE IS IN THE CLOSED POSITION. wHILE NOT 100 PERCENT ACCURATE ONE VALVE CAN BE COMPARE TO ANOTHER. A
a STICKING VALVE COULD CAUSE THE PROBLEM ALSO.

A leak down test would check for valve leakage and your compression test says the valves are OK. The leak down would also test for worn or leaky piston rings wich would cause a ot of blow by past the rings.
Make sure no valve springs are broken also.

Great use of the link to OneDrive for the video and chart. I need to get out of the dark ages and start using that or Google Drive to post larger files.

Now to the real topic.

I agree that the rapid needle vibration is a strong indicator of leaking around the valve guides. I know this might be an embarrassing question. Are you satisfied that the rocker arm to valve clearance is within spec? And Gene's tip to check for a broken or weak valve spring is right on as usual.

I also note that the reading is somewhat lower than one might expect. Normally I see anywhere from 17 to 21 on these engines. I was thinking that maybe the compression was down but then I remembered that that this engine is in the 5 to 1 compression ratio range. 5 x 15 (normal atmospheric pressure) is 75. So that seems ok.

Overall I am not a big fan of leakdown tests. About the only real value is the relative numbers cylinder to cylinder. There are too many variables (temperature, incoming air pressure which keeps dropping during the test, and air volume) to support any valid engine to engine or test to test comparison.

I sometimes do a "cheater" leakdown test. I have a spark plug adapter with an air coupling on it. Turn each cylinder to TDC for that cylinder with the valves closed. Put the car in gear and set the brake/block the wheels. Then connect the air coupling to that cylinder and listen/look for where air is leaking. Is it coming out the carb, exhaust, or oil filler?

85 psi is very good compression. I assume you have the gauge attached to the vacuum fitting on the intake? I would look at the surface of the manifold and the gasket. Spray some WD40 around the intake ports and see if you get a change in rpm. Every car I do motor work on I have the intake planed level. I’m thinking your vacuum leak is at the manifold. It’s more common than most think.

Did you check with the line to the windshield wipers blocked off? On my 32 I had a leak in the windshield wiper steel line that is inside the pillar post .

Did this test, and none of the valves seems different from the others, and nothing feels loose.

Valve clearence is checked several times, and is ok.
I even tried to adjust valves with the vacuum meter, and ended up in same positions.

Tried both WD40 and starting fluid, no change in RPM.

Wipers are not connected to manifold, so connect directly to manifold.

I then tried to adjust carburator mixture and timing, only looking at vacuum meter, then I can get a higher and more stable reading, but don`t feel engine sounds correct, and response on throttle is slower.
As it`s wintertime here in northern europe, I can`t roadtest it now.
I don`t beleive (hope) there are any serious mechanic errors, so will continue with carburator/timing adjustments when I can do roadtests.

I did not see any specs above but most are gapping plugs at .040 and timing at 18 BTDC. The original spec is .024 and 12 but with todays better gas the previous gives better results.

Plugs are gapped at .040 but engine starts and runs best with timing at 15 BTDC.
Not sure why it doesn`t run well at 18 BTDC, but I see most recommend AC-C86/AC-C87, mine had new Champion D16 when I bought it last year.
Another issue can be that petrol here in europe might be different from yours.
I`ll try to find a set of C86/C87.

Note those specs for gapping and timing are for the AC Delco C86 or C87 plugs, if you use Champion, it is different... here is a post from a while back talking about the plugs and how to set them up:

I have used 0.040" gap with plugs other than AC-C86 or AC-C87. Works with the other plugs that I have used including Autolite 386.

Ok, I think I will fiddle with the gap and timing on my D16, but also get a set of C86/87.