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C263 knock

F

farmall pete

Member
Looking for advice. Bought a 656 with a c263 motor. Motor has a knock in it. Motor checks out good otherwise: oil pressure steady 30 psi, does not smoke, all cylinders compression test at around 150 psi dry. Motor runs smooth, just knocks. Set the valves but no change in knock. Tried pulling the plug wires one at a time to isolate the knock; no change. Pulled the oil pan, bearings Ok.

Was thinking it could be a piece of carbon broke loose & is sitting on top of one of the pistons. Maybe wishful thinking on my part as an alternative to a piston pin or skirt slap. Heard of an old remedy: splashing water into the carb intake with motor running to steam clean and maybe break up the piece. Sounds a little risky.

Any other ideas for diagnosing short of pulling the head to take a look see?
 
Pull the carb & see if all the choke & throttle screws are there. If ok then pull all the plugs & turn it over by hand. Maybe you can feel it when a piston comes against something. If it is carbon it can be softened with ATF.
 
Not there to hear the knock , as said it COULD BE this or that and one thing for sure it ain't ah going to fix it's self . You can bore scope the pistons thru the spark plug holes if ya have a bore scope , you can look at the skirts from the bottom and unles you clean and dry the crank and bearings and use plastia gauge on each throw we are guessing on rod and main clearance . BUT if ya keep on running it things will get acquainted and all that is left is a big hole in your check book.
 
(quoted from post at 17:08:21 02/15/17) Not there to hear the knock , as said it COULD BE this or that and one thing for sure it ain't ah going to fix it's self . You can bore scope the pistons thru the spark plug holes if ya have a bore scope , you can look at the skirts from the bottom and unles you clean and dry the crank and bearings and use plastia gauge on each throw we are guessing on rod and main clearance . BUT if ya keep on running it things will get acquainted and all that is left is a big hole in your check book.
Click to expand...

Good ideas, thanks to all. I do have a bore scope, and will look at the piston tops tomorrow. I also plan on pulling the oil pan again to disassemble and check the bearings one by one, and check for play in the pins, take a closer look at the the piston skirts & sleeves.

One thing I forgot to mention, a #1 cylinder push rod was slightly bent. Repaired that, but seems like that cylinder is the one to focus extra attention on.

Question: would removing the side push rod cover be worthwhile? Can't think of a reason the knock would originate there.
 
Nope . Also take a long screwdriver with a wood handle and hold it to the block and put your ear to it and move it around to see if you can pin point the knock . That is a OLD SCHOOL motor stethoscope . Also look for scoreing on the cylinder walls . This is a siign of piston swelling due to usen the wrong grade of gas and improper ing timing and this is a problem on the C263 and C291's .
 
Well this is what I found. Exhaust valve on #1 cylinder is hitting top of piston. Valve Seat has some wear on one side. Valve has rotator on it. Piston & sleeve look fine other than that. Rod bearing pastigauged within spec.

Next will remove the valve to see if bent.
45695.jpg
45696.jpg
 
(quoted from post at 14:35:03 02/16/17) That would explain the knock and the bent pushrod. Now what explains the valve hitting the piston in the first place?
Click to expand...

THAT is a good question! I hope to learn something when I get around to removing the valve tomorrow. I could imagine it getting held open by a piece of carbon and hitting once, but it had good compression and was knocking all the time. I am stumped.
 
I'd send the head into the most recommended shop to have it cleaned, mag'd, and rebuilt. It shouldn't cost that much, would fix the issue, and you will likely be six feet under by the time it needs to be done again.
 
Mystery solved. Removed the valve, and found that its seat had loosened. A little JB weld and it should be good to go.

Seriously, the head is going off to the machine shop for a complete going through.
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