loud knocking noise 2.7

[rotor562]

I just rebuilt my 1976 2.7. New pistons and cylinders, Line bore, rebush rods, magnaflux crank and rods, rebuild & rebush rocker arms, etc. etc.
Upon first start it ran fine with some smoke for a few minutes. Engine was turned off after a few minutes. The following day when I tried to start it, it had developed a loud ticking noise and it was immediately turned off. Later on the day when trying to diagnose the source of the knock, we turned on the engine and the noise was gone (only difference is the day was warmer (80s as opposed to 60s in the morning when it knocked). The following day in the morning, I cranked the engine without fuel or ignition, and the knock was back. It will randomly make the noise when first started, but once running without the knock, it will remain without it . I have only ran the engine for 6 or 7 minute intervals. Never ran the engine with the knock for more than 4 or five seconds. The knock seems to be coming from bank 4-6 tensioner area or valve covers. Any help would be greatly appreciated.
I have attached a youtube video link with the noise while cranking


https://youtu.be/ff1n02VnuBY?si=ydNPllmLfnfc_ZTP

[Tom_in_NH]

Very irregular cadence while cranking. Sounds like a compression loss in at least one cylinder. Do a compression test. A leak-down test will be more informative.

[911 SLANT]

Sounds like starter. Have you tried turning motor over with a socket on alternator nut. Use a impact gun. Also disconnect coil wire.

[proporsche]

i would start with a stethoscope or a long screwdriver to exactly pinpoint the sound location.
It is metal sound ,hanging valve in valve guide possibly..
Also , on new engines i like to run them longer by driving them right-away.Not just start and shutting it off.
let us know about the location...

Ivan

[ant7]

Sounds like severe compression leak to me, but if that was the case, it would run like a bag of crap, i.e.; missing and spluttering on that cylinder, notice how its not every revolution of the crank ? it seems to be every other revolution, which seems to indicate its cylinder related or cam gear components.
Hope this helps.
Ant.

[Schulisco]

Remove the valve covers and check the head stuts. Start with the bottom ones. Still using Dilavar or switched to steel? Did you enforced the case threads with Heli coils?

Thomas

[rotor562]

Thanks to all that have chimed in. I had not noticed the irregular cadence, which leads me to believe it is a compression issue as suggested by proporsche, Tom in NH and Ant7. I will tackle it during the weekend removing the valve covers, and using a stethoscope. I do not believe it is the starter since it has made the noise while running with the starter disengaged. I haven't dared driving it until I find the source of the problem. This morning it started no problem and no noise as can be seen on video.
https://youtube.com/shorts/grOcbMzxfXU?si=1BrZ4yC8TodPD3f7

[proporsche]

Originally Posted by rotor562

Thanks to all that have chimed in. I had not noticed the irregular cadence, which leads me to believe it is a compression issue as suggested by proporsche, Tom in NH and Ant7. I will tackle it during the weekend removing the valve covers, and using a stethoscope. I do not believe it is the starter since it has made the noise while running with the starter disengaged. I haven't dared driving it until I find the source of the problem. This morning it started no problem and no noise as can be seen on video.
https://youtube.com/shorts/grOcbMzxfXU?si=1BrZ4yC8TodPD3f7

As i suggested ..go for a ride --really! it will only be good for the engine instead of on and off..trust me;-)

BTW sounds nice..do at least 50- 100 miles nonstop do not go over 4K rpm ..brake with the engine for the piston rings...
when i finish engine i go right away to Germany on autobahn ...or at least around here in Czech for a while..before i stop the engine..
like here
https://www.youtube.com/watch?v=vniHFvd7WSo

https://www.youtube.com/watch?v=e6AFN7rrPSM
https://www.youtube.com/watch?v=EGWlKtAwdTs
https://www.youtube.com/watch?v=YTSM-FYxUKU

[ant7]

It does sound fine on that vid, I wonder if there is an issue with one of the valves sticking, or something in the cylinder getting under the valve seat, otherwise it makes no sense why it can come and go, if it were a head to cylinder issue, it would be there continuously, anyway, keep us updated with your findings.

Originally Posted by rotor562

Thanks to all that have chimed in. I had not noticed the irregular cadence, which leads me to believe it is a compression issue as suggested by proporsche, Tom in NH and Ant7. I will tackle it during the weekend removing the valve covers, and using a stethoscope. I do not believe it is the starter since it has made the noise while running with the starter disengaged. I haven't dared driving it until I find the source of the problem. This morning it started no problem and no noise as can be seen on video.
https://youtube.com/shorts/grOcbMzxfXU?si=1BrZ4yC8TodPD3f7

[Till Krueger]

The irregular knocking could be related to compression or maybe something with the valves.

[porsche930dude]

Originally Posted by 911 SLANT

Sounds like starter. Have you tried turning motor over with a socket on alternator nut. Use a impact gun. Also disconnect coil wire.

You're kidding right!? Great way to snap your alternator shaft

[911 SLANT]

No, not kidding. That's what I used to spin my motor without using starter. I put on least amount of torque and spun motor over slowly without sparkplug. I was able to determine that I had a bad starter gear that was making noise.. I had no issue with alternator. . I see your concern though.

[porsche930dude]

Well if you are going to be doing that use a drill not an impact. As a small engine mechanic I know alot of people snap their crankshafts off with an impact. They learn one way or another.

[911 SLANT]

Did you ever find where knocking noise is coming from?