Engine knock.

[Charner (MS)]

Unknown history on 48 8N. I bought it to restore. Rebuilt engine, turned crank, new kit, inserts (rod and mains), pistons, pen, rings, sleeves, etc. Cranks, runs fine. After warmed up you can hear a faint metal knock toward rear of engine. No. 4 maybe. Dropped pan. checked torque on all fittings - right on. Micro crank and inserts - right on. Oil lift tube clear of no. 2 and tube is tight. I feel all interior engine is proper. Reassembled engine - same problem. Pull no. 4 wire and sound much less??? Have read messages where could be camshaft butting engine. I don't see where that could be as no thrust factor. If you had 12 seasoned mechanics listen to the engine you probably get 12 knocking rod answers. Any suggestions would be appreciated.

 

[duey]

One thought might be piston-to-head contact....

 

[Den N Ms]

-Charner (MS) ,The first thing I would check by your description
would be for a exhaust leak around #4 exhaust port and the manifold.Check with a 2-3 foot length old garden hose or the like ,hold one end to your ear while moving the other end around #4 manifold port.Next thing it could be after warm up is a wrist pin with excessive clearance. Next would be possible piston to head slap from the head being milled to much.Again use hose to listen for knock on top of head.Hope it is a exhaust leak for your sake.

 

[Bill M. From Illinois]

Knocking rod noise may subside with slight load on engine I have found, if its not too bad.

 

[kossuth]

(quoted from post at 20:06:17 11/04/21) -Charner (MS) ,The first thing I would check by your description
would be for a exhaust leak around #4 exhaust port and the manifold.Check with a 2-3 foot length old garden hose or the like ,hold one end to your ear while moving the other end around #4 manifold port.Next thing it could be after warm up is a wrist pin with excessive clearance. Next would be possible piston to head slap from the head being milled to much.Again use hose to listen for knock on top of head.Hope it is a exhaust leak for your sake.

d be certain of this first. Not uncommon at all for there to be a leak on the very back most port on these. Sometimes manifold leaks make weird noises so Id triple check this particularly given that youve dropped the pan and noted nothing weird.

PS. Did you pull a cap to see what condition the bearing was in?

 

[Charner (MS)]

Thanks for replies. In reply to exhaust leak possibility. Block was painted and new manifold and gaskets. No residue smoke or other indication of leak. Also, while engine was stripped with head and pan off could still hear slight knock when spinning motor with hand crank. Cam is my only thought but how? I would run this tractor with knock if I were to personally be using it but its for sale (no, 55) No one would pay the $2,500 to $3,000 for it and I wouldnt put it on the market like this. Yesterdays Tractor should buy it as much parts as I have purchased over the past 20 years,

 

[teddy52food]

My thought too, being it comes after it warms up & expands the piston.

 

[Charner (MS)]

I may have found the source of the knock. I pulled the head, manifold and valve covers. When I spin the engine with the hand crank the intake valve on no. 4 was making a must louder noise than the others. Oddly enough it was knock sound. I stuck a tool under it when up and noise stopped. The valve clearance was correct. I changed out the complete valve assembly. Set the gap and turner the engine. No more noise. I've never heard of this before. This could be the problem. I'll post result after engine reassembled and running. The valve looked fine and had no distortions that I could see. Strange.

 

[Jim L WA]

Charmer, glad you found the knock. That's a new one for me. Sounds like that valve wasn't following the cam lobe back down, was hanging up and then slamming down.