Hi Guys,

A while back, I had a local machine shop build me a 355 shortblock. I took it home and finished assembling it then filled it with Antifreeze & oil, primed the oil via distributor, and fired it up. It sounded good and no problems.

However, after a while, I noticed a knocking noise coming from the #3 piston area. I thought it was a rocker, so I readjusted them and its still there. It sounds like a knock coming from cylinder.

I took the car to the machine shop and they said it could be a 'galled' piston? I asked what this meant and they said it was metal-on-metal contact as a result from improper lubrication. Of course, they said it was my fault and now I'm needing to pull the engine again

Since I'm new to this type of problem, I was hoping to get some advice on what to look for? I'm guessing it's a bearing or rod problem. Assuming I pull the engine out, what do I need to look for to determine the source of the problem? Will the bearing have a big scratch/groove cut in it if its bad?

Any advice would be greatly appreciated!

Thanks!

 

If they did the assembly, there's nothing you could have done wrong that could cause the problem.

 

Thanks Apeiron! That's what I thought as well. Unfortunately, I'm stuck fixing it. Any guesses on what is wrong? You can hear the knock at idle but it seems to go away if you rev the engine.

 

I hope it wasnt bobs in NKC missouri.I have been stuck twice by those guys.Very unprofessional.They messed up a wrist pin in one of my engines before not to mention dropping a forged piston and mashing the ring groove half closed.Got the pistons home seen that damage called them and wouldn't you know it they played dumb.
Your issue kinda sounds like a wrist pin to me kinda.Pull the plug wire to that cylinder and see if it stops. Wrist pin will be more close to the upper/mid engine area rod would be pan area for best listening.

It sure sounds like bobs in nkc to me. Im in missouri as well.

 

Thanks formulax4! I went to Mike's Automotive in St. Louis. When they heard the noise they said, "this isn't a warranty issue". Ugh. I was going to have them fix it for me but I'm not so trusting of their work now.

It does sound like it's closer to the top of the piston to me, so I will pull the plug wire and see if it stops.

 

I forgot to ask - If I pull the piston and there is play in the wrist pin, can I simply replace the wrist pin and that's it? Also, can I reuse the existing rings?

Thanks guys!

 

Play in the wrist pin will be a defect in the rod or piston. Rings are so cheap they're not worth re-using.

 

I know the engine builder reconditioned my factory rods. Not sure what kind of pistons they used. So do you recommend replacing both the rod & piston then?
Will there be a part number somewhere on the piston?

 

I recommend taking it all apart and finding out what the problem actually is first.

 

Ha! I guess I got ahead of myself... it's easy to get excited about cars

Thanks guys for all the advice!

 

Hi Guys,

I finally got the motor out and partially apart. I don't have the pistons out yet but I haven't seen any scuff/scarring in the #3 cylinder.

Also, the driver head is off and the only thing I notice is the exhaust valve is bright white on #3 exhaust port. The rest of the valves on both heads are a darker color. Does this imply the motor is running lean on that cylinder?

Thanks!