Questions for engine experts
 

Yesterday a friend and I conducted a series of diagnostic checks to see what work the motor in my '30 Roadster needs. Currently the engine is using some oil, as seen on the dipstick as the oil level decreases, and a puff of blue smoke from the exhaust pipe during gear shifts. Here are the results of the tests:

Leak down test results(conducted on cool engine, starting with each cylinder in turn at TDC, verified with digital inspection camera, then pumping 20 PSI into each cylinder in turn):

#1 cylinder -0 % leakage;

#2 cylinder - 20 % leakage, piston pushed down and engine turned backwards, air coming out the carburetor;

#3 cylinder - initially less than 3 % leakage, with air coming out exhaust pipe, then the leakwent down to 0 %;

#4 cylinder - less than 5 % leakage, piston went down and engine turned forward, could not detect where air was leaking from, checked carburetor, exhaust pipe, and radiator.

Camera also revealed carbon buildup atop pistons, and around the edges of some of the valves.

Vacuum test results (conducted on warm engine):

Drifts rapidly at idle between 13 and 20, stabilizes at higher RPM between 18 and 20.

Compression test results (conducted on warm engine):

DryWet

#1 cylinder -6060

#2 cylinder -6060

#3 cylinder6063

#4 cylinder6060


The leak down and vacuum tests indicate to us that the engine needs a valve job.

The oil usage, and blue smoke indicate oil in the cylinders, but that is not indicated by the compression tests, except maybe in cylinder #3.

Also, we don't know why the leak down test caused the piston in #2 cylinder
to go down and turn the engine backward, or why it caused the piston in #4
cylinder to go down and turn the engine forward.

Could someone please help us understand the test results, and let us know if they indicate that the engine needs more than just a valve job?

Re: Questions for engine experts
 

The compression test results were:

#1 - dry 60, wet 60
#2 - dry 60, wet 60
#3 - dry 60, wet 63
#4 - dry 60, wet 60.

Re: Questions for engine experts
 

when you put each cylinder on TDC and inject air you cannot let the piston move any as this will open a valve which is what happened in your case when air came out the carburetor.
i hold the crankshaft still at TDC using a wrench on the crank nut...

do a retest holding the crank still.
this wont cause oil burning but also remove the radiator cap when doing the leak down looking for air to come up..

Re: Questions for engine experts
 

If the engine is free turning and the other three plugs are out, car in neutral, the 20psi in the cylinder is enough to push the piston down. which way depends on which side of TDC the crank is on. Put it in 1st gear and put on the hand brake.

Puff of smoke when changing gears can be a sign of loose valve guide clearance -- oil is pulled by the valve stems when the throttle is closed and burned when the throttle is opened again.

Sounds like a valve job to me, but hard to tell since the pistons moved. Perhaps an A&P mechanic among us can give a better opinion.

John

Re: Questions for engine experts
 

Third gear with the parking brake on gives more holding power than using first gear.

I like Mitch's idea of using a wrench on the cranking bolt.

Re: Questions for engine experts
 

I agree with Tom in that 3rd gear will hold better.

Re: Questions for engine experts
 

If you go that way chock the wheels also

Re: Questions for engine experts
 

Yes u need to stop the crank from turning

Re: Questions for engine experts
 

Compression's not THAT bad, me, I'd go a trifle heavier Synthetic Oil & DRIVE IT!
A "little bird" tole me that Synthetic burns CLEARER, if not, re name the car "SMOKEY JOE"
Bill W.

Re: Questions for engine experts
 

I don't see any problem with your engine. Perhaps guide wear, but an occasional oil puff, wouldn't make me dig into an engine, unless I was just looking for something to do and to spend some money. Your leak down is totally bogus, sorry to say. Pistons must be on top and unable to move. Your probably losing more by leaks than combustion.

Re: Questions for engine experts
 

Movement between 13 and 20 is usually indicative of a sticky valve.

Re: Questions for engine experts
 

I have completed many leak-down tests; if the crankshaft rotates during a leak-down test, the piston/crank position was not at top dead center. From your compression tests and leak-down results along with you noticing smoke, I would only complete a valve job to eliminate the smoking. If you can check, try to move the valve around in the guide to see if there is noticeable movement. If so, new springs, guides, valves and seat machining should take care of your issues. I also suggest...Check your bearing clearances while you have the engine open.
Good Day!

Re: Questions for engine experts
 

I agree with what others have said. The compression results are great if you have a stock head. I'd say the valves are OK too. If there was a significant leak at any valve the compression would be lower. A leak down test is usually done to determine the cause for low compression.
The vacuum fluctuation could be due to carb adjustment. You might try tweaking the low speed mixture screw in/out. If not it could be a sticky valve as others have mentioned. Do you notice any backfiring or popping? How is the overall power?

Re: Questions for engine experts
 

I too think your engine is OK.
Compression readings are good.
As said, the engine has to stay still on the leak test. I think your bad #2 cylinder leak reading is only because the engine turned and started to open the intake valve.

Now, to clean the pan and check the bottom end along with the side cover and checking the lash.

Re: Questions for engine experts
 

Just "THINKING",
If you had an otherwise good running engine, with stock valves & lifters, BUT 1 Exhaust valve was, say, .004" TOO TIGHT--Has ANYONE ever tried to SQUEEK in some type of "file" or Diamond strip, etc, to give it .004" MORE clearance, without pulling everything apart?
Bill W.

Re: Questions for engine experts
 

I's been a lllong time I know, but I am wondering how you made out with the smoking issue? My 30 has the same symptoms.

Dave Eddie

Re: Questions for engine experts
 

Its kind of a pain when folks don't follow up with a result isn't it.

Re: Questions for engine experts
 

it sure is.

I myself would have done nothing to that motor with those compression results. So what if there is an occasional blue puff? Worn valve guides....not valves... with 60 compression

Re: Questions for engine experts
 

Some synthetic oil will burn clear

Re: Questions for engine experts
 

If the engine doesn't foul plugs or spew a constant cloud of smoke, and the oil consumption is "reasonable" (not more than 1 qt in 300-500 miles), then I think I would leave it alone and keep an eye on the oil level.

A few puffs on shifting is nothing to be ashamed of with a 90 year-old car.

Watch some silent movies with cars in them, you'll be surprised out how much smoke some them spewed when they were less than 30 years old...

Re: Questions for engine experts
 

I know, leave well enough alone is proly the smart thing to do, but I hate cars that smoke. This motor uses next to no oil, runs great, and up untill a week or so , never smoked. I think I'll do a compression test, the spark plugs look good, all grey in colour. Might try an oil change,...could be oil leaking past the valve guides.

Dave Eddie

Re: Questions for engine experts
 

Check the compression tonight, low cyl is 60, high cylinder is 68, which doesn't seem terribly bad. Also did an oil change and went to a slightly heavier oil 15w-40.
Same result,...still smoking at gear changes. I think when time permits (probably this winter) I will pull the pistons and replace the rings,....sounds to me like an issue with the oil rings.

Dave

Re: Questions for engine experts
 

Yikes!!!!!
just like that?

why not a dry-wet test?
if the readings don't increase wet then the rings are fine.
Suppose the valve guides are worn and you are sucking up oil around the intake
stems

Your readings are respectable. if the compression rings are holding compression why would the oil rings be all worn out .

more diagnostics are needed before you take the plunge

Re: Questions for engine experts
 

If you pull the spark plugs and look at the tops of the pistons, those with worn rings and burning oil usually have clean edges around the top of the pistons.

I bought a NOS set of rings the other day for my 1950 Studebaker Commander, and the instruction sheet said the rings are fast seating and don't require cylinder honing.
I've seen that statement for some of the newer ring sets, but didn't know it went back to the 50's, which is when these rings appear to be made.

Re: Questions for engine experts
 

I just started two cars that have been setting for a while. I shut them done by putting oil in the carb. They smoked like crazy, never did stop smoking.
If I was you I would drive them and see what happens.

Re: Questions for engine experts
 

I'm feeling a little worried, my engine never smokes...what could be wrong?

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Does it have oil in it? :p

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Are u running synthetic oil:rolleyes:

Re: Questions for engine experts
 

I wouldn't be too quick to criticize the guy. Maybe he had a serious health problem and couldn't continue with his car. Or a family crisis. Sometimes life gets in the way of our plans.

And I don't mean to be taking you to task, Patrick L. I'm just reflecting on some possibilities for his absence. We're just an internet community and seldom know what's otherwise going on with guys here.

Re: Questions for engine experts
 

d'oh

Re: Questions for engine experts
 

OP hasn't been on here since January 2016