Name that problem-SB Chevy noise

[Oh Haha]

FIL and I are tracking down an intermittent clunk in his 400 CI Chevy. We thought it was a cracked flexplate but that was not it. We ended up pulling the engine and trans out together as the bellhousing bolts were a total PIA to loosen in car.

When we pulled the plugs we found this(number 8 cylinder). Obviously, something has been hitting the end of the plug.

In all my years of working on hot rods and running Chevys hard I have never seen a plug this beat up.

Anyone want to hazard a guess as to what we will find once we open the bottom end?

[herr_oberst]

A foreign object?

[Norm K]

Originally Posted by Oh Haha

Anyone want to hazard a guess as to what we will find once we open the bottom end?

I'd be as interested in seeing the what the top of the no. 8 piston looks like as I would in seeing what might or not might be in the pan.

[Oh Haha]

We tried to see the top of the piston through the plug hole but couldn't see anything.

At that point we were ending work on it for the day. The starter bendix was jamming on the flexplate and not retracting so we bought anew starter and had the same issue.

Yes, we shimmed both but the issue remained the same. The noise started a couple of weeks ago out of nowhere, according to my FIL.

[BeyGon]

can a rod/main bearing get that bad?

[flyenby]

Have you tried a bore scope ?

[chapo]

Pieces of the plug that was in there before that one. Had that happen on a used Jetta I got.

[Oh Haha]

Originally Posted by flyenby

Have you tried a bore scope ?

Don't have one but I will suggest the purchase to my FIL.

He bought the car about a month ago. The seller has documented everything that was done to the engine and vehicle.

I'm just helping my FIL out. What he does to fix the issue is up to him.

[Laneco]

Originally Posted by BeyGon

can a rod/main bearing get that bad?

Yes...

Many, many variables in Chevrolet engines for displacement, head design, stroke, compression, etc. But I did have one that I killed many years ago that threw out this type of warning sign before the worn bottom end made a brilliant connection with the valves in one cylinder hard enough to shove the pushrods and lifters for one cylinder into the crank case. Well into...around...etc. Same cylinder that had the "odd" damaged spark plug previously. The engine autopsy revealed a horribly worn crank with the bearing entirely missing for that connecting rod. Almost a half of an inch of play on the connecting rod interface with the crank.

Though in this case, if you hear hoofbeats, think horses not zebras. More likely something was in the cylinder bouncing about and is either fabulously embedded in the piston or has worked its way out of the exhaust.

angela

[1990C4S]

Originally Posted by flyenby

Have you tried a bore scope ?

They are ridiculously cheap now...

5m 5.5mm 6LED USB Borescope Waterproof Inspection Snake Tube Camera Sale-Banggood.com

[asphaltgambler]

Def mechanical damage / foreign object causing interference. At this point you should just pull that cyl head for CSI and consider the good possibility the engine will need to come out because of further damage that was the cause or result of this.

BTW - if this was a late model engine it would have already bent / broke the connecting rod or punched a hole in the cylinder...............

[pavulon]

I seem to remember SBC 400's had an issue with staying cool. If so, could that have contributed to whatever the issue might be here?

[gtc]

These are awesome. But I'd look for one with a better camera.
Amazon.com: CrazyFire® 2.0MP HD 720P Coms 6 LEDs USB Snake Inspection Camera Waterproof Digital Endoscope Borescope Inspection Camera Pipe Locator: Computers & Accessories

Originally Posted by 1990C4S

They are ridiculously cheap now...

5m 5.5mm 6LED USB Borescope Waterproof Inspection Snake Tube Camera Sale-Banggood.com

[Oh Haha]

The noise we heard wasn't consistent with RPMs which led us to believe there was interference with the flexplate/starter.


I'm just glad that it isn't coming out of my wallet for the repair although I will probably help with teardown and rebuild. I'm pretty sure I still have my "How to rebuild your small block Chevy" manual somewhere in my collection of books.

[Norm K]

^^^ There's probably not a cheaper & easier engine to build.

[911SauCy]

The flexplate stater issue sounds consistent with main bearing play as the entire crank would be able to move, no?

Good news is parts are cheap and work is relatively simple.

[Josh D]

Originally Posted by pavulon

I seem to remember SBC 400's had an issue with staying cool. If so, could that have contributed to whatever the issue might be here?

They had siemese cylinders and steam holes in the block into the head. They made good low rpm torque, but the long stroke, short rod and siemese cylinders did not favor longevity.

[Oh Haha]

today we stripped the engine down to the block and rotating assembly.

When we pulled the 2,4,6,8 cylinder head off a piece of metal was on top of the piston, obviously beaten to smithereens. (I have pics but am waiting for my wife to email them to me cause my flip phone sucks.)

We couldn't figure out where it came from but know that it is the culprit of our noise and smashed plug.

We had the heads on the bench looking over them for anything that was broken but seeing nothing. I noticed the intake valve(2.02) on cylinder 8 seemed to not be flat against the seat.

Sure enough, using a light down the intake port I could see it getting past that valve.

I believe the bits came from the valve seat and will confirm tomorrow when we get back at it. We didn't have a spring compressor and he had to bowl tonight.

The heads are 1968 so they should have had hardened seats installed for use with unleaded fuel. If they didn't, the seats will beat themselves to death. We will have them done if needed after we check the PO's receipt pile.

[Oh Haha]

Here is the debris:

[fastfredracing]

Is the bore/block o.k? I have seen this a few times, and it can make a real mess of things.