Engine Knock on a 1950 8ba

[Flat head charley]

Well after picking up a crate engine from a deceased friends family member we assembled it on a platform stand with radiator, guages and start stop switches. Engine runs like a clock but has this annoying knocking sound from the rear. It is resonating the loudest when we place a stethoscope between bell housing and pan.
Removed flywheel no rubbing, removed fuelpump rod no noise reduction, pulled each plug one at a time no noise reduction, removed starter no marks on gear from hangup, all lifters are set properly, no broken springs, no bent or sticking valves, plenty of oil pressure. Tore engine back down- everything looks fine and mikes within specs.
I have seen a couple of threads with members having similar problems but no one has printed their solutions. Any other ideas?

[George/Maine]

You want a guess check rods for being bent.

[Flat head charley]

Will keep that in mind if/when we tear it back down again. Thanks.

[Binx]

Elongated flywheel bolt holes or worn rear piston pins? Cam/oil pump idler gear would be my next suspect.

Lonnie

[corvette8n]

I had a ring gear get cockeyed and it hit on the block, tapped it back on and had it tacked in a couple of spots.

[WestCoast]

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possibly a flywheel bolt is to long and hitting the back of the block

[Ol' Ron]

Check the frequency of the knock. cam runs 1/2 crank rpm.
D0z knock increase or decrease with load? RPM?
Good luck

[Tinker]

Fuel pump rod makes a lot of noise too. And can sound like an engine knock.

Edit: you covered that... My bad

Please post the resolve

[RalphG]

Did someone accidentally install one wrong piston? I recall that happening years ago on the 52 Merc. All new pistons but one was slightly taller than the rest and nobody noticed it until start up and the knocking started. Hope it didn't bend a connecting rod.
Just a thought.

[Flat head charley]

Thanks for the feedback. I need to explain, the "Crate Engine" is a Stroked .030 over domed piston engine with Edelbrock 65cc heads, isky cam and a triple deuce Edelbrock intake with 3 Stromberg 97's. All rods are new, all bearings are new along with waterpumps. As you can see, the normal problems have been addressed. We are thinking of tightening up the lifters to .010 & .013. That is all we have left for ideas. Again thanks and maybe someone can hit upon a subject that has not been thought of. A thousand minds are good to have.

[Flat head charley]

This is for Ron, we do not have it in a vehicle therefore cannot put a load on it.

[Ronnie]

Piston to head clearance. Valve lash won't do anything.

R

[swedishsteel]

I rebuilt a '36Lb, had the rods reconditioned and new wrist pin bushings put in. Upon start up had a knock like you describe that was most noticeable when idling, but went away at higher rpm. Long story short, I tore it back down, and only seven new wrist pin bushings had been put in, one rod had the old one and it was the source of the knock. Good luck, Rod

[RandyZ]

Originally Posted by Ronnie

Piston to head clearance. Valve lash won't do anything.

R

I'm think that a piston is tagging the head too. The heads may well have been milled at least once before and the maybe there is some interference. Your going to have to pull those heads anyways, so start by looking for contact There.

[George/Maine]

If your engine is stroked with after market rods your bore may NOT be big enough.
Rods hitting bore, also lay head with no gasket and turn over and see if head is dancing a bit.

[Ol' Ron]

Now anybody building an engine now days checks Piston to head clearance to get the ideal .050". So I doubt the pistons are hitting.

[George/Maine]

Speedway has new rods and require 3.250 bore or better. the stock could hert you more.
I think not to bore but get a drimal tool and grind some clearance.
Maybe get 3/8 grinder and get some clearance.
Isky is that a high idel ,flathead like slow idle loose the cam.

[RandyZ]

Originally Posted by Ol' Ron

Now anybody building an engine now days checks Piston to head clearance to get the ideal .050". So I doubt the pistons are hitting.

If it was check, Ron. Maybe not.

A rebuilt motor I picked up didn't have the front plug put in the oil gallery. Ran for years before the bearings slowly started to give out. Mistakes do happen.

[Flat head charley]

No rods are hitting bore skirts, need to pull pistons I guess, check wrist pin suggestions. will get back to you guys soon.

[Mart]

Some pistons have a more "pointy" dome than others. I had my stock french (pointy dome) pistons hitting my edelbrock heads. I'd look there next. the stethescope would pick it up directly over the middle of the bore.

Mart.