Borescope results - diagnosing cylinder, exhaust leaks

[alexiskai]

In this thread I discussed the results of a leak-down test that showed leaks into the crankcase on all 4 cylinders, plus a leak into the exhaust on cylinder 2. This, combined with a compression test on cylinder 2 of 40 psi, led many folks to suspect a burnt exhaust valve. I was able to get a borescope and take some pictures, so let's see what we found.

First, here are images of all four cylinder bores. They all look about the same to me. What do folks think about the visible condition of the piston head and the cylinder walls?

[alexiskai]

Here are the valves for cylinder 1 as a reference. To me, these look pretty healthy.

[alexiskai]

Now here are the valves for cylinder 3. Clearly something amiss with the exhaust valve, but this didn't show up in the testing as leaky.

[alexiskai]

Now here's cylinder 2 at TDC. This valve looks to me like it's in the early stages of burning. Fully discolored, asymmetric coloring. To me it also looks like the valve isn't flush with the block. Is that normal?

[alexiskai]

I cranked the engine around to get a photo of cylinder 2 with the exhaust valve open, so here's that and a second photo zoomed in on the stem. You can see that the stem is also discolored.

[alexiskai]

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As I said, it doesn't look to me like #2's exhaust valve is cracked yet, but it's clearly not normal. If you look at the other exhaust valves, it doesn't seem like any of them sit fully flush with the block. Is this something anyone's seen before? Is there anything else you can tell about the engine from these images?

[dumb person]

The valves often don't sit flush with the block, as long as they seal is what matters.

As for what else i can tell from those images.
The bore scope is good quality.
Your engine is in good shape up top.
The only time i've seen valves like that on my engine, was when i ran slightly lean on all cylinders. Didn't harm it but was leaner than it should have been?
Have you used a test light and measured piston position to see if the distributor cam is slightly worn on one cylinder? Because i can't really think of an air leak on the intake causing that on saimesed ports.

[BRENT in 10-uh-C]

The hash marks typically mean the engine is not been run that much since it was rebuilt. It does appear it has been stored in a damp climate where the rings has "rusted" against the walls and during start-up, they cleaned up however they left a faint line. In a race engine, this is a problem however your engine not so much.

The valve you are questioning could be one of several things. A worn or excessive clearance(d) valve guide can cause a valve not to 'land' on the seat in the same location each time. The other possibility is the valve face does not have concentricity with the seat.

Personally, I think what you are seeing is much like looking into the kitchen at your favorite restaurant. Sometimes you really do not want to know all the details. Unless you are having a major issue, I would drive it and be happy.

[alexiskai]

Thanks Brent, I appreciate your perspective. I'm conscious of the tendency to fix what ain't broken. The borescope investigation was driven by two things: (a) a rough idle that I had been unable to resolve through the usual carb/intake methods and (b) several commenters in the previous thread urging me not to drive the car until the problem was fixed. I'd hate to be a bad caretaker and damage the car by driving it while the engine was in bad shape.

[BRENT in 10-uh-C]

Originally Posted by alexiskai

Thanks Brent, I appreciate your perspective. I'm conscious of the tendency to fix what ain't broken. The borescope investigation was driven by two things: (a) a rough idle that I had been unable to resolve through the usual carb/intake methods and (b) several commenters in the previous thread urging me not to drive the car until the problem was fixed. I'd hate to be a bad caretaker and damage the car by driving it while the engine was in bad shape.

You probably already explained it and I have forgotten but refresh my memory, ...define 'rough idle'.

[alexiskai]

Oh man, I've been through like five threads on this board about it over the course of six months. Not surprised you don't remember. Basically:

• Car idled nice and low when I got it two years ago, then at some point I found that it would stall if I didn't keep the throttle lever high
• Also started stalling at stops and you could tell the idle had a gallop-y quality to it, like some of the cylinders weren't at 100%
• Replaced the intake/exhaust manifolds, did all the gaskets, checked for leaks, replaced the carb twice
• Spark plugs, timing, you name it, I tried it
• Then I ran the compression test that showed 40 psi in cylinder 2
• Then I ran a vacuum test that indicated "worn/loose valve guides," but I didn't know whether it was all the guides or just a few
• Then I ran the leak-down test and that's basically where we are today

[rotorwrench]

If number 2 stays low after running it with a load a while, I would suggest pulling the head and getting a closer look at the valves & guides. This would allow you to turn the engine over and watch the valves for signs of sticking. The #2 exhaust valve could be removed to check it and all the parts out if a person pulls the valve chamber cover. Check for a loose guide, problems with the seating surfaces, and for a broken spring. All it would cost is a few gaskets and some elbow grease. The bore scope is a handy tool but it won't always give the whole picture of what's going on in there.

If everything turns out to be workable after cleaning things up a bit, you would likely be able to get some miles out of that engine.

[alexiskai]

OK, so it seems like the conclusion is:

• Borescope shows relatively normal cylinder condition
• No serious damage to valve heads
• Problem is likely with the valve motion, interface between valve and seat, or both
• Only way to diagnose is to pull the head and the valve cover and inspect closely

[johnneilson]

From the limited diagnostics available with a bore scope images, here is my opinion, remember, just an opinion.
Cyl #2 shows some rust stain in the bore near the top of stroke. This indicates water was in the cylinder, not much. This can cause the rings to stick in the piston or contaminate the ring lands. But, I also see the ex valve seat surface is not uniform, what we can see. This along with knowing there was water in the bore lends to the fact that there could be a rust damage to the seat or valve face. The fact that the valve is showing warm could be an indicator that valve is leaking some.

All that said, 40 psi cranking pressure on #2 compared to what on others, 55?
Will it get worst, probably, it will not heal itself.
It has probably been that way for some time, the rough idle is more than likely something else.
If you are worried, it is time to pull the head and drop the pan. You might even get away with just a light lapping on the valve. The bores don't look that bad, maybe a light hone and clean up the rings.
John

[CC-Mo]

In another thread related to this, someone mentioned running MMO in the gas. I use seafoam on occasion. How much MMO per gallon/tank are most using?
Thanks in advance

[alexiskai]

Originally Posted by johnneilson

40 psi cranking pressure on #2 compared to what on others, 55?
John

60-65 on the others

[30 Closed Cab PU]

Originally Posted by CC-Mo

In another thread related to this, someone mentioned running MMO in the gas. I use seafoam on occasion. How much MMO per gallon/tank are most using?
Thanks in advance

4 oz. per tank. This is what others had recommended.


If you do searches on MMO and Marvel Mystery oil, there is tons of info. Some believe it is snake oil, some strongly believe in it. Read the strings and you can decide. Another subject like what's the best oil - lots of strong opinions.

[Bob Bidonde]

From all you have shown and said about this engine, my opinion is to run it for a 100 miles and recheck the compression.

If you windup taking this engine apart, I highly recommend that you junk the OEM valve train and replace it with a modern stainless steel system. By the way, valves should not be flush with the block because such valves have knife edges that get too hot and warp. Look at the modern valve train in the photo. This engine powers my Victoria.

[alexiskai]

Originally Posted by Bob Bidonde

From all you have shown and said about this engine, my opinion is to run it for a 100 miles and recheck the compression.

If you windup taking this engine apart, I highly recommend that you junk the OEM valve train and replace it with a modern stainless steel system.

Haha, I don't think I've run it more than 10 miles at a time since I bought it. I hear you, though, that's a good call.

Just to clarify, you recommend not just the SS valves but the modern-style SS valves?

[Patrick L.]

The pic of #2 exhaust seems of good quality and it looks to me like there is some damage to the valve seat. So, I would take another close look.

You seem to not want to remove the side cover but it won't get fixed without doing that.
If the lash is good then the next step would be to remove the valve and take a look at the guide, seat and face. You may be able to borrow [ or have someone do it] a seat cutter set and have the valve faced and then adjust the seat to where it needs to be. Then reset/ grind the lash.
With the compression as good as it is on the other holes I'd be inclined to leave them alone.
I'm thinking that engine could then run for decades.