Dave W 1971/240Z rebuild

[grannyknot]

I got the engine and trans pulled this morning, up to the shop on the engine stand.

Dave, looks like you got your moneys worth out of the clutch, the release bearing was kind of crunchy, not sure the flywheel can be saved either.

All the lobes on the cam are in very nice condition, no real wear, underneath 50+ years of grease and dirt is some of the assembly line marker paint.

[davewormald]

You really don't mess around! Awesome to see the engine coming out. Were you able to do a compression test before pulling it? I did a couple two years ago, but didn't trust the results, which weren't consistent with each other.

Can you tell whether that's the original clutch? It definitely looks to be at the end!

I found quite a bit of the original marker paint when I started cleaning it up a few years ago. The car had clearly not had much done to it before I got it, and I didn't touch it. Before it started to deteriorate from lack of maintenance, the engine was really strong. Hopefully it soon will be again!

[grannyknot]

Some bad news, did a compression test today and cylinder 1 and 2 are leaking badly, then did a leak down test and all the air is coming from the exhaust valves.  I didn't hear any escaping air in the crankcase so fingers crossed that the rings are still good, I'm hoping it is just a build up of carbon that's keeping the exhaust valves from closing.

I'll pull the cylinder head in the next couple of days and will know for sure.

The oil pump is in good condition, no scratches, and someone in the past modified or repaired the shifter, maybe shortened it?

 

[davewormald]

Oh well. It's good to find these things early. I guess we'll soon know how bad a problem it is.

I can't remember the exact details around the shifter, but Ken (who I bought the car from) had a Z with a very short shifter, that I really liked. I asked him about it and he said he'd change mine if I wanted. If I remember correctly, I didn't like the one he made for me, and by the time I went back to him to get the original back, it was gone (Ken's shop was an interesting place). I ended up with the one you've discovered (which I don't think I was all that fond of either).

[grannyknot]

Removed the head today, no obvious signs but the exhaust runners are covered with a thick layer of carbon so will know more once the valves are removed.

 

[Zed Head]

Those dimples around the edge here could be detonation damage or foreign object.  The damage looks the same, but it's only at the edges in your case where the detonations would be.  Not a big deal, just an observation.  What's the top of that piston look like?

[grannyknot]

That's the #4 piston and it has the same marks but I'll have to clean the carbon off first to see how extensive the damage is.  If it was a foreign object, it didn't stay in there for very long, a few seconds then broke apart or exited through the exhaust valve.

Hard to imagine pre ignition detonation with a compression ratio so low, as I remember the early engines like this one were around 9 -9.5: 1

[Captain Obvious]

Are you sure the exhaust valves in cylinders 1 and 2 were not being held open by too little (less than zero) valve lash? The whole thing doesn't look caked with exhaust carbon that would cause such poor leakdown results.

I know... I know... I just have to ask.

[grannyknot]

8 hours ago, Captain Obvious said:

Are you sure the exhaust valves in cylinders 1 and 2 were not being held open by too little (less than zero) valve lash? The whole thing doesn't look caked with exhaust carbon that would cause such poor leakdown results.

I know... I know... I just have to ask.

Good point, I still have to measure all the valve lash before tearing the head down.

[davewormald]

I was the last one to adjust valve lash, so all bets are off!

[Captain Obvious]

Haha!! 

I know it's a longshot, but the insides of the cylinders really don't look that bad. In order to leak that much past the exhaust valves, I would have expected everything to look worse. Longshot, but here's hoping it's something simple like a valve lash issue!

[grannyknot]

Lash measurements before disassembly,

I've never knowingly seen detonation marks but seen lots of marks from nuts and screws and when one of those get into the cylinder both the piston and head are just hammered with marks equally all over both surfaces. I've never seen marks on either side like they are in this engine.  None of the other cylinders have these marks, just #4

This is the exhaust valve and seat for cyl #1  with 160psi, the next 2 pics down are valve and seat from cyl #2 with 100psi

On the #2 those crusty bits are hardened carbon that I had to scrape off with dental pick, I'm pretty sure that is the cause of the low compression.

Edited July 11, 2023 by grannyknot