Exhaust from oilpan vent.

[Von Tiergarten]

Hey guys’n’galls

 

New problem with my 47 torpedo 8.

 

When cranking without ignition I get the “galop” - never had it before. When starting the engine it sounds like missing a beat and exhaust comes from the oilpan vent. and the filler neck (rhythmically).

I have a suspicion that cylinder 2 is the sick one 🤔 (right Einstein).

Comp-test.

 

1 - 115

2 - 35

3 - 130

4 - 130

5 - 130

6 - 130

7 - 130

8 - 128

 

I’m not a mechanic so now I need your help.

 

My gutfeeling tells me I have a broken or stuck piston ring (exhaust from Oil vent.). But before tearing the engine apart - could it be something else? Valves perhaps? Gasket?

 

Edited October 15 by Von Tiergarten
Comp. not vac. (see edit history)

[EmTee]

I think you're probably right.  Have you tried pouring a couple of ounces of oil into the cylinder and taking a 'wet' compression reading?  If a ring issue, that may increase the compression by 10 ~ 15 psi.

 

If you have air available you could try pressurizing that cylinder and listen for air escaping.  Based on your observations, the hissing will likely come from the crankcase rather than the tailpipe or carburetor.  In any case, it sounds like the head needs to come off...

[Von Tiergarten]

20 hours ago, EmTee said:

I think you're probably right.  Have you tried pouring a couple of ounces of oil into the cylinder and taking a 'wet' compression reading?  If a ring issue, that may increase the compression by 10 ~ 15 psi.

 

If you have air available you could try pressurizing that cylinder and listen for air escaping.  Based on your observations, the hissing will likely come from the crankcase rather than the tailpipe or carburetor.  In any case, it sounds like the head needs to come off...

Just tried the wet test and it did give me almost 80 psi more. But only for the first test - the  comp-test right after went back to 30 psi. So I guess it helps untill the Oil passes the rings - and then its back to full blowback mode🙁

 

I have found leaks on both sides of the head by cylinder 2 - I could see Oil weeping out when wet testing. But these leaks should not give me exhaust from the crankcase or? 
 

Edited October 15 by Von Tiergarten
Comp not vac (see edit history)

[Bloo]

5 hours ago, Von Tiergarten said:

I have found leaks on both sides of the head by cylinder 2 - I could see Oil weeping out when wet testing.

Time to pull the head. The head gasket is blown anyway if oil that you put in the cylinders is getting outside the engine. What is vac-test? Is this a normal compression test made with a pressure gauge in a spark plug hole? 35 pounds of compression is unbelievably low for worn rings. That is a big leak, probably indicating a broken or holed piston. A head gasket could do it on some engines, especially overhead valve ones, but offhand I don't think there are any ports to the crankcase in a Pontiac Eight head gasket.

 

Normally compression that low would indicate burned or stuck valves, but then the pressure would be escaping through the intake or exhaust, not the crankcase. The next step would normally be a leakdown test to see where the pressure is escaping, but it sounds like you already have the answer if you have a rhythmic puff from the oil filler neck and the draft tube.

 

[Von Tiergarten]

14 hours ago, Bloo said:

What is vac-test? Is this a normal compression test made with a pressure gauge in a spark plug hole?.

 

Yes - I meant compression test from the spark plug hole. I’m still learning - and you guys here are helping a lot 👍

 

I will pull the head and inspect the damage.

[Von Tiergarten]

I dont think that the head’s been off since production - 76 years.

 

Anything I need to know before picking up the tools and go in? Should I torch the bolts? WD40?

 

All help is Gold to me 👍

[EmTee]

Some penetrating oil on the head bolts can't hurt, but won't really do much for the threads in the block.  Go slow and work each head bolt back-and-forth (i.e., loosen a little, then tighten a little) to help clear the threads until the bolt begins to turn freely.  Not sure how heavy the head is, but the issue will be awkward handling, so best to have a helper or at least go slow and watch your fingers.  Before you clean anything, post pictures of the sealing surfaces of the head and block.  Careful inspection should reveal any leaks that were present.  Also look closely at the #2 piston crown.  As Bloo said above, there may be visible damage to the top of the piston or the outer circumference.  Rotate the crankshaft by hand to lower the piston to the bottom of the bore and inspect the cylinder wall for damage.  What happens next will depend upon what you find...

[Von Tiergarten]

It took me a while finding correct wrench heads for the bolts - our tools here are in millimeter.

 

I was rather surprised how “easy” the head bolts came off. Took me less than an hour to pull the head off.

 

When looking at the piston in cyl. 2 it clearly is damaged at the rim. The sides on all cylinders feels smooth and without mayor damage - thats good.

 

No Big cracks or anything on the block or in the head. Its dirty and filled with soot - but to my untrained eye, it looks good.

 

Now - I’m sure I need to remove the damaged piston, and as a bold non-mechanic I might need all the guide from you guys that I Can get.

 

I have read on this Forum, that replacing pistons is possible without pulling out the engine (Thank God). But as I have never done anything like this before, I hope for you experienced people to look at the pictures I will post during this quest I’m starting - and perhaps kick me hard before making a complete fool of myself 😁

 

Next step is going under the engine pulling the oilpan and have a look where the number 2 piston arm is connected.

Edited November 11 by Von Tiergarten
Typos (see edit history)

[Von Tiergarten]

[Von Tiergarten]

[Bloo]

You need to clean the inside of the cylinders all up and take measurements before deciding what to do. From the pictures, it appears you have vertical scoring in the cylinders. If so, that will leak combustion around the rings.

 

Clean it up and see if you can catch your fingernail in the scoring. If so, it won't disappear with simple honing for standard size pistons and rings.

 

While you have it apart, measure the bore size in several places. Measure at the most worn spot at the top at 90 degrees to the crank (highest wear), inline with the crank (to check for oval), and as low as you can get in the cylinder. Do this both 90 degrees to the crank and inline with it (to estimate taper). You can't accurately measure taper with the pistons in, but since the worst wear is always overwhelmingly right near the top you can get a good idea. Measure all cylinders.

 

"Inframe" overhauls were common in the old days, and if it does not need boring, you may be able to do it. If it does need boring, you probably need to take the engine out. Back then, people did bore engines inframe, using a portable attachment. It is not as good as a modern boring machine, and I doubt you would find anyone to do that today.

 

 

 

Edited November 11 by Bloo (see edit history)