Technical Fresh rebild, clunk noise from flexplate

Hey everybody. I just did a rebuild on my 350. 30 over, flat top pistons, new crank/rods/bearings/flexplate etc.

Anyway.. compression is now .75 higher than before (10.25:1) and the motor is definitely harder to turn over with the fresh hone and rings. I got the engine in the car and got ready to fire it up today, and decided I'd check the starter after I primed it to listen for odd noises... sure enough I found an odd noise. The starter engages the flexplate and it cranks over fine.. slightly slower than before, but, it still turns over. I noticed a sort of noise, best described as maybe a clunk or maybe a click. It's not crazy loud or hard, but you can hear it over the starter. At first I thought it was an issue with the flexplate/torque converter so I pulled the bolts and made sure the torque converter was seated in the front pump, then pulled it out a bit and shimmed it up and torqued it down. Then I thought maybe it was a rod knock. Pulled the pan, checked torques and clearances again then cranked it over... noise went away. There's no signs or evidence of contact on the oil pan, and the new crank and rods are stock dimensions. I'm pretty lost here. Any ideas??

Yes I did check PTV clearance and set cold lash.

Any help would be greatly appreciated. I'm lost on this.

 

What kind of oil pan ?? new or old stock chevy pan, some of the after market oil pans don't fit right on the drivers side and the crank will hit the pan

later kb

 

Cracked in flexplate? Or loose flexplate bolts? I've seen both before.

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shimmed it up?

 

It's a moroso 5 quart pan. That is a good possibility, considering i have a different crank. It worked fine with the stock crank though... and I hope it isn't lose flexplate bolts haha. Brand new ARP bolts that I step torqued to spec.

In regards to shims on the converter: I have a 1/16 thick washer between the flexplate and converter on all 3 bolts so It isn't pulled too far out of the front pump.

 

Pull the plugs and crank it. Listen
Then while the plugs are still out, turn it with a bar. Listen.
You sure the valves are adjusted ?
2 days ago a fresh overhaul got started. Tacky tacky tacky tacky wtf!!!
Dude left 1 rocker nut finger tight.
Double check it.

 

Hahahahahaha feeling your pain man! The joys of building your own s**t eh? I will check again. I have a solid cam and roller rockers. Hot lash is .022", I usually just cold lash them to .017". PTV clearance was .140". But it looks like I'm checking everything again!

 

What is the purpose of listening while the plugs are out? Just listening for odd noises without compression applied to the motor?

 

Is the noise constant or just when cranking the engine? HRP

 

Only when the engine is cranked over. I put a mark on the flexplate, and the noise happens every time at a specific location of crankshaft rotation. It's weird though, once the oil pan is removed the noise goes away (which would lead me to believe contacting oil pan). But it has no signs of contact. Also, it's a stock stroke. We tried loosening the starter bolts a bit to see if it were an issue with the starter, when we cranked it up with the starter bolts a little bit looser, the noise got quieter. I disassembled the starter to see if it were internal, but it all looked to be working properly.

 

Could it be the dust shield rubbing?



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That could be a possibility if i had one lol

 

I had a 472 Cad engine with a deep knock when starting. Turned out that the new torque converter was just different enough that using the original TC bolts, the bolts bottomed out in the new TC. Put in shorter bolts and the knock was gone.

 

Too long as in they would bottom out on the torque converter leaving it room to wiggle side to side?

 

I'm really considering just checking my valve lash again, maybe shimming the starter differently, and saying screw it lets go and break the motor in and see if the knock goes away.

 

Crank hitting the dipstick?

 

If you drop the pan again, clean off the counterweights and inside of the pan, paint the counterweights with a grease pencil. Slap the pan back on with a few bolts, give it a spin. Take the pan off and look for marks. It takes very little interference to make a noise.

 

Yes, bottomed out in the new TC and did not tighten down on the flex plate.

 

Good idea bob. I'm gonna check a few other things and give that a try.

 

Had an issue like yours once. It was from sitting a 4X4 under the very front of the pan and tiying it down for the truck ride home. Put a very small flat spot in the pan that looked factory. That was my tick on every revolution in the same spot on the flywheel.
The Wizzard

 

The purpose would be to eliminate strain on the starter, strain in the flex plate and it will increase the speed.

If noise should go away you'd know it was related to starter or flex plate.

In light of the noise going away without the pan, it could be contact with pan or related to the oil pump.

 

Give the ring gear teeth on the flex plate a good look too. Might just have a tooth with a burr on it.

 

Ah I see. Valid point. I'll do that this evening when I'm off work. I'll remove the plugs, prime the engine again, and crank it and see how it goes.

 

Hey everyone. Found the problem....

Feel free to make fun of me.

The starter was shimmed too tight and it was popping and binding the flexplate.

Yeah. I'm a rookie

 

had that happen as well on recent 40--found it immediately while I had wife crank the car with me under it-new starter was out of wack--got another one--all fine now.--also had flexplate rubbing on trans cover--made an awful racket. Glad you found it

 

Nobody is gonna make fun of you.
But I'd like to hear this explained.

It's weird though, once the oil pan is removed the noise goes away (which would lead me to believe contacting oil pan)

 

I think that with the oil pan removed there was less resistance on the motor so it turned over a little easier, which eliminated the popping noise.. but then again, I'm just guessing haha.

 

And by less resistance I really have no idea what I mean by that, but, for whatever reason it didn't strain as much without the pan on.

 

Until I read the whole thread, I was going to jump in and say that perhaps the starter had the incorrect shims.
We had a Pontiac in for repair once that had "some strange noise" according to the owner. After adding a few thin shims between the starter and the block; the noise abated. IDK how the noise got there.
Although not all GM-built 350s had them, I'd also look to see if there's a brace on the forward end of the starter.

 

I think it is an issue with the diameter of the new flexplate that came with the rotating assembly... it's an eagle kit, and it came with a Mexican made flexplate. I think it is just slightly larger in diameter than the stock chevy flexplate I had on before.