lower end knock

[63Falconconvert]

Well yesterday was the day to finally turn the key on my 63 convertible. Rebuilt 200, rebuilt C4. Had everything ready to go. Car started right up, ran it for 20 minutes to break in the cam, oil preasure was good, water temp hung at 190. Shut it down, let in cool for a few hours while I checked for leaks etc. Started it back up ran great until it got to running temp of 190-200 then when I hit the throttle I get this knocking sound. (note I still have not driven the car yet) It doesn't to it at idle only when I rev the engine. The thing I'm confussed on is that it doesn't do it when the RPM's are going up but when they are coming down and when the engine is hot. I think it's either a cracked piston or a broken ring.
Tonight I will drop the pan and take a look.


I was so bummed out I shut the garage and went to bed.
Any thoughts.......

 

[maverick75]

what comp ratio do you have? what fuel are you using, check for exhaust leaks...when i broke my piston the engine seized up so i don't think its that.

 

[BUZZ]

Did you put this motor together or someone else? Could be a bolt or something in a cylinder. Did you have the rods resized and install new pistons? If not it could be slack in a wristpin. Was the engine bored over?

 

[48fordnut]

use a stick or hollow tube to listen to the area where you think its comming from. it could be an exhaust leak as this is where it would show up slowing down. good luck

 

[Patrick66]

maybe its pinging, retard the timing and see if it goes away.

 

[73GreenMachine]

Hmm this brings back memories. If it is a deep slow knock you might find it as a damaged big end bearing or another knock I had in similar circumstances was piston slap, although something would have to be majorly wrong for these to happen straight away. My piston noise was caused due to the engine overheating and the number 6 piston getting hot, expanding and being scraped away by the cylinder bore. The low knocking noise that is only noticeable under falling revs I think turned out to be a combination of this and the big end bearing damage, which was caused by a lack of oil at startup due to a very stupid person (me) leaving out the oil pump driveshaft (I was 17 and it was my first attempt at an engine rebuild). The other oil related failure that caused the deep knocking was when the seal between the oil pump and the pickup tube failed and I started pumping air through the oiling system. Hopefully that will give you some things to check anyway and help to isolate the noise, lets just hope its an exhaust leak!

 

[63Falconconvert]

Ok I found the problem. Of course I am to blame. This engine was out of an unrestored 66 Mustang. Well when I tore it down I was really meticulous about looking at each bearing, piston etc. I noticed on number 6 rod the bearing was .020 over size. So I noted that fact and went on with the rebuild. None of the other rods or any of the mains had over size bearings. So fast forward to the rebuild. I had all of my bearings, 5 sets of standard and one set .020. I plastic gauged each rod and got .002 clearance in all 6. I take out all of the rods/pistons for one final cleaning and a shot of assembly lube. Fast forward to last night. I drop the pan and tap each rod cap with a ball peen hammer, 1 2 3 etc, I get to number 6 and BINGO, rattle rattle. As soon as I tapped it I remembered the .020 over size bearing. When I reassembled the rods to the crank I grabbed a standard set of bearings for number 6 instead of the .020 set. Major brain fart. Any way I installed the correct bearing and the knocking is gone and the engine perrrrs.

 

[RagHead]

glad you found the problem without having to tear down the whole engine again.

 

[Bort62]

Ok I found the problem. Of course I am to blame. This engine was out of an unrestored 66 Mustang. Well when I tore it down I was really meticulous about looking at each bearing, piston etc. I noticed on number 6 rod the bearing was .020 over size. So I noted that fact and went on with the rebuild. None of the other rods or any of the mains had over size bearings. So fast forward to the rebuild. I had all of my bearings, 5 sets of standard and one set .020. I plastic gauged each rod and got .002 clearance in all 6. I take out all of the rods/pistons for one final cleaning and a shot of assembly lube. Fast forward to last night. I drop the pan and tap each rod cap with a ball peen hammer, 1 2 3 etc, I get to number 6 and BINGO, rattle rattle. As soon as I tapped it I remembered the .020 over size bearing. When I reassembled the rods to the crank I grabbed a standard set of bearings for number 6 instead of the .020 set. Major brain fart. Any way I installed the correct bearing and the knocking is gone and the engine perrrrs.

Lol, great save. I'll bet you feel pretty relieved right now.

 

[woodbutcher]

Lucky don`t even begin to describe your NEW name.hehehehehe.
Leo