First motor start, terrible knocking
 

Fired up the motor today for the first time to hear a horrendous, fast-paced knocking. We quickly shut her down and pulled off valve covers, but didn't see anything obvious.

Engine was partially rebuilt. I pulled the heads off for a valve job but didn't touch the cam or pistons. This sound did not exist prior to tear down.

I'll be pulling the pan tomorrow but was wondering if anyone knew immediately what may be producing this knocking?

https://youtu.be/VAxGZIOPXL0

Re: First motor start, terrible knocking
 

Did you soak / fill the lifters before you installed them ?

Re: First motor start, terrible knocking
 

Total shot in the dark, but you might check as a last resort that the fly wheel is tight. I built a flathead once and the bolts on the flywheel were just a little too long and bottomed out. Could be the flywheel needs tightening.

Re: First motor start, terrible knocking
 

Are you missing any nuts? A nut bouncing around on too of a piston sounds just like that. (Ask me how I know.)

Re: First motor start, terrible knocking
 

Or the sound of a valve touching a piston!
Likely valve adjustment done wrong.

Re: First motor start, terrible knocking
 

I did soak the lifters for a couple hours before installing. Then the motor sat for a couple months before firing up.

Re: First motor start, terrible knocking
 

We aren't missing any that I know of and were extremely careful to avoid this when putting everything back together. I would be really surprised if this was the culprit but it's worth looking into.

Re: First motor start, terrible knocking
 

Did you pull the distributor and prime the oil system before firing?

Re: First motor start, terrible knocking
 

Is there a way to check this without pulling the motor? The valve job was done at a pretty reputable machine shop but I'll be calling them immediately if this is the case.

Re: First motor start, terrible knocking
 

Any chance the valves are adjusted wrong?

Re: First motor start, terrible knocking
 

If you disconnect the coil wire, then crank the engine, does it sound normal? If it does, I'd then do a compression test to see if the piston and valve action is correct.

If all that pans out, you might want to try starting it with the rocker covers off, to see if oil is getting up to the top, and isolate any sounds.

If you are the really careful type, you'll disassemble the engine, and check everything, including the stuff mentioned above. This is the slow, but possibly cheapest way to go.

Re: First motor start, terrible knocking
 

I turned the motor over a few times while working on electrical before priming the oil system and firing the motor up for more than a few seconds. Is it possible I damaged something doing this?

Re: First motor start, terrible knocking
 

I actually never removed the flywheel but I'll check today to see if it's loose.

Re: First motor start, terrible knocking
 

Sure!!
Whatever amount of turn you last put on the rocker nuts, just back them off half that amount. If you did one turn, back them off 1/2 turn.
That way the lifters are still quiet.

Or it might be just as easy to re run them.

Re: First motor start, terrible knocking
 

I wouldn't think it would since the bottom end wasn't rebuilt, but you could have had a dry start with the lifters since it sat so long?

Have you drained any of the oil to look for "glitter" (metal shavings).

With everything you've described, I'm wondering if you have a bent rod or valve.

Re: First motor start, terrible knocking
 

I drained the oil last night and didn't see any metallic flake. I'll look again in the light today.

When I tore down the engine, I found a single bent push rod and replaced it. I wonder if I should have just replaced all the push rods.

Re: First motor start, terrible knocking
 

I will give this a try today!

Re: First motor start, terrible knocking
 

I second this advice. I would pull all the spark plugs and inspect them then crank it over and listen for noise. I suspect you will hear it. If you don't, I would do a comp check, put the plugs back in and start/run it with the valve covers off but damn, something is getting the snot hammered out of it.

What did you all have done to the heads? If he cut the valve seats did he shorten the stems too? Did he deck the heads, how much? What is your quench distance? What pistons are you running, flat/dished/dome?

Re: First motor start, terrible knocking
 

I will try cranking it over without the spark plugs today. I ran the motor last night with the valve covers off but didn't see anything obvious (the knocking was still there).

I had the original heads magnafluxed and they were found to have hairline cracks, so the machine shop give me a different set of heads and performed the valve job on those.

Re: First motor start, terrible knocking
 

Do you know the casting numbers of your old heads and of the new heads? What pistons are you using, flat/dished/dome? Do you know how much deck clearance you had..? Are you running an aggressive cam?

Re: First motor start, terrible knocking
 

I do have the old heads' casting numbers. I will check these against the "new" heads casting numbers.

Using flat top pistons.

I do not know how much deck clearance I had or what the cam is.

Re: First motor start, terrible knocking
 

Ok, compare the numbers and let us know.

What head gasket did you use (thickness)?

The frequency of the noise seems relatively high. My fear would be pistons contacting something but I wouldnt expect it to run long like that if it was.

Re: First motor start, terrible knocking
 

I'm having trouble figuring out the head gasket thickness. I used the heads gaskets from this Fel-Pro KS2600 kit: https://www.summitracing.com/parts/fel-ks2600/overview/

Edit: according to the description, the kit comes with these head gaskets: https://www.summitracing.com/parts/fel-7733pt2 (4.125 in. Bore, .039 in. Compressed Thickness)

Re: First motor start, terrible knocking
 

.039 thickness as stated

Re: First motor start, terrible knocking
 

Always start with the easy low cost stuff before tearing everything all apart;

In order -
1) Rent a bore-scope. Pull the spark plugs and look inside all of the cylinders for loose parts and scarred pistons from valves touching. Also check the oil pan if it's emptied of oil for loose parts.

2) Confirm all of the valve retainers are in place. Confirm the pushrods are equal length and in place.

3) Use a long screwdriver and electric drill to prime the oil system from the distributor shaft hole.

4) Re-adjust the rockers - adjust all to zero lash plus 1/3 turn, turn the motor 45 degrees and re adjust. Do this 6-8 times turning the motor 45 degrees each time you adjust.

5) Confirm firing order / plug wires.

6) Check all ancillary equipment (alternator, A/C, power steering, flywheel, clutch or torq convertor, etc) for proper installation or loose parts.

7) Check oil level. Try starting 'er again.