This is my Cylinder 8 piston, a few months ago it sucked down a lifter and hasn’t ran right since even after top end rebuild. It’s currently not running. All other cylinders are good, aside from cylinder 2 being overly clean.

Are these cracks or something else? They run all over the crown of the piston.

 

They sure do look like cracks..... what happened? you can suck a lifter down the intake, did it drop a valve? The head needs to come off.

 

If I understood the OP correctly, head HAS been off since valve ingestion? Did rebuilder see these marks? Look like marks from a valve face bouncing around for a bit.

 

looks like a borescope pic. #2 too clean. head gasket. steam-cleans the piston top...and look more like damage than cracks. like something small jamming between piston and head digging into the crown. compression still good? more pics of piston? and #2...
but i will wager heads coming off. followed by engine coming out.

 

The head hasn’t been off since the lifter, I started college and haven’t been able to get to it I just started looking at it again after it wouldn’t start.

I’m going to pull the head after work today, and get some more news. But you are probably correct.

 

2-8. 2 at the lowest stroke.

2 aka the really clean one.

4. Also pretty clean compared to others.

6. Looks normal.

8. “Cracks” were just scratches in the carbon.

2-8 valves

2

4

6.

8. How to determine if bent?

 

Side note: Can anyone tell me what pistons these are?
Stamped:
W631CP .030 33614-02-C

 

Yeah, I didn't think anything looked cracked. Your local machine shop can evaluate the valves.

 

.030 over speedpro hypereutectic

 

There is nothing alarming here but the pics are tough to see due to the reflection.....

Jebby

 

I wish I saw this earlier. If the fear is a head gasket I would have suggested pressure testing the radiator system to see if you got fluid in any of the cylinders, or a pressure test of a cylinder to see if you had a fast leak down before pulling the head

 

Yeah that probably would’ve been a good idea to check but of course me being inexperienced with working on cars I didn’t think of it. I’ve already taken the head to the machine shop and will hopefully figure out if it’s anything head wise within the next few days.

 

I don't think there is much damage at all on the number 8 piston. You do have a bunch of carbon on those pistons and heads. When you get a carbon buildup inside an engine like that spraying cold water into the intake air allowing it to get into the combustion chamber can break up the carbon deposits and then they get blown out your exhaust. I used to do this VW engines running low compression but still detonating due to the carbon glowing red hot and pre-igniting the fuel charge making it detonate/ping. I am not suggesting anything more than a light spray out of a spray bottle filled with cool water, do not flood your motor with water. I would spray as much water as it could take without stalling the engine.

Had I been in your shoes I would have performed a Leak down test as that is a more precise way of finding a specific problem. They are not too hard to do and the results are awesome. Piston powered aircraft have s Leak Down test done during the annual maintenance. It can tell you IF there is a problem and it even helps point the problem out by following the air leaks with good hearing. The main reason they use them is to determine when the engine needs to be overhauled before something catastrophic happens.

Say for example your #8 exhaust valve was bent. During a leak down you would have noticed an air loss on cylinder number 8 compared the rest of the cylinders. Then you would listen for any air leaking out above in the head indicating possible leaking valve guides or valve seals. If everything is quiet up top then you listen inside the oil cap for air leaking out which might suggest leaking rings or a scored cylinder bore. Lastly if you listen to the exhaust and if you heard air escaping there it would tell you that #8 exhaust valve that is not sealing.

The tools to do leak down testing are a good sized air compressor that can deliver 100 psi and hold it while the air is leaking. The tool itself is not too expensive either and available at Eastwood or Amazon. If and when I pay someone for a leak down test I watch the test being done to satisfy myself it was done right as not a lot of car mechanics are used to performing the leak Down test. My airplane mechanic taught me all about this type of test and she is good at it, she can do a 6 cylinder aircraft engine in less than 1/2 hour as she has lots of experience doing the leak downs.

That is a beautiful Corvette you have there young man! Hopefully the heads will be fine and you can re-install them. If you have a machine shop clean the heads and re-lap the valves while they are out it could help your performance a bit. Just remember to do the same work to both heads!

Best regards,
Chris

 

So I went back and looked again at your first post, and it shows that you can't always trust what you see in those borescope cameras.....nothing like pulling the head and seeing it with your own eyes. I went back and forth trying to find the area the camera was looking at, but couldn't see it.

So did this engine collapse a lifter? Still can't understand what the original issue was.
With the funny burn patterns on the pistons something was going on here. Did the engine do allot of idling before it was torn down?

 

Yessir, it was kind of a relief to pull it and it not actually be cracked, but not so much because I’m back to square one of why I can’t get it to run. The camera is looking at the scratches in the carbon on cylinder 8, you can kind of see it, it’s just those lines on the crown on piston 8 the last piston picture.
The original was it had I guess collapsed a lifter I’m unsure of terminology, all I know it half the lifter was just gone. Not in the intake valley where pushrods are just gone. I went back through did a whole top end rebuild, except for replacing the valves which looking back now i probably should’ve done but live and learn I guess. And after that it ran for 500ish miles maybe more enough to break in the new cam, broke down and wouldn’t start since. I checked all lifters and everything was fine. So I got a borescope and looked down and that’s where the post starts. Before tear down it wouldn’t even start.

 

ok, crank the engine over and eyeball the 16 lifters. disconnect fuel line from pump first. you are watching to see if all 16 move the same. this is eyeball, not dial indicator but if you have a flat lobe you will see it. then when you get head back and installed, do the same with the rockers. looking to see if all moving essentially the same amount. now, the head. if the shop says 600 bucks, it may be time to float test the heads. by float test i mean throw them in the river and see if they float.old heads are not worth spending money on unless numbers-matching, etc. then do compression test. that is a rebuilt engine and pistons look ok. that much soot is fairly normal and nothing looks too clean like water ingestion steam cleaned it. did you drain the oil? no water in it? usually when you do something and something else goes wrong you just did it. but when a car won't start, start with fuel and spark before tearing it down...

 

All lifters according to eyeball look like they are moving correctly none look like they get stuck or anything. And I know for a fact they wouldn’t float they a tad bit on the heavy side lol. And I’ve done all the normal tests before I started tearing down, I’ve posted a couple times in the past few months about the no start. As well as when the lifter originally deleted itself and when I rebuilt the top end afterwards. Like I said it drove enough to break in the cam after the lifter situation and then broke down on a nice day I decided to drive it to work. I ran through all the normal tests after inspection, spark, fuel, checked the oil, it was still pretty clean no water or metal in it, checked timing I even pulled the distributor and reset the timing to 0 at tdc, didn’t work so I tried advancing it, and then that didn’t work so I tried retarding it, at first we thought it was the ignition coil and replaced it, that wasn’t it. Gave up for a few months while I was at college considered selling it. Then went on spring break, looked at the borescope then tore it down 2 days ago. I know what I’m doing to some extent.

 

I had something happen once while driving normally at highway speeds. I was near a Corvette shop so I limped there and left the car with them. Since I never really saw what they saw, I have to guess as to what happened. I think I let the lash on my solid lifter cam get too loose and for a brief moment the valve hit the piston. I did not have damage to the head nor to the piston and I drove it for some time afterwards without apparent problems. However, when I pulled the engine for a rebuild, I discovered the incident had bent the connecting rod fairly significantly. I mention this on;y to suggest that if no further work is required to the rotating parts, and you still have the head off, rotate the crank and double check that all four pistons in that bank achieve an equal top of stroke height. A bent connecting rod will leave the piston deeper in the hole and you'll lose compression in that cylinder. I did and never knew it.

 

At this point, I would pull the other head as well! I'd have that one checked and cleaned too....what kind of valve seals do you have? I'd make sure they all get get some good positive-lock seals installed if not already. The majority of the disassembly is done, I'd check both heads and clean all of the piston tops! Something to consider👍

 

Hard to imagine an interference strong enough to bend a rod wouldn't leave a mark on the piston or bore.