F head burning pistons

I am rebuilding a 1957 CJ 5. The engine has been completely redone but has burned the #3 and #4 piston shortly after starting. We replaced the pistons and rings and water pump, and had the same problem again. The moter ran fine at idle but as soon as we tried to drive it in 3rd gear it overheated and shut down. The machine shop thinks it is because the distributer was not advancing. The distributer was about the only part not replaced. Has anyone run into this problem or have any suggestons. The motor was completely stripped, tanked bored and rebuilt with new parts.

 

I would have said timing also.
I've burned a few VW drag race motors that way.
Any labor knock?

 

Thanks for the info on cooling. They have check and added the bypass and are confident we are getting circulation.

Jerry, what do you mean by labor knock?

 

Labor knock is called pinging some places.

 

Dumping fuel spark late.
Just a thought. What part of the piston is cooked?
I've burned holes in the tops near the side in race engines from to much timing.

 

To much advance will burn pistons but I have never seen a motor that would burn pistons from not advancing, to much advance will also induce heat into the cylinders and if advanced to far it will induce alot of heat!!!

 

Thats how mine burned WAY to much advance trying to run quicker ETs.
Thats why I wondered about labor knock. Maybe cracking instead of melting.

 

Thank you for continuing the discussion. I will talk with the machine shop to find out about the timing setting. I do not belive we had any pinning at idle. not sure about when running at speed on the road. Too much other noise to notice. The weights in the distributer were rusted but moving. One of the springs was stretched. I do not know if this would cause to much advance or too little at higher rpms. The pistons melted on the sides and smeared across the rings. It was just the back 2 so I wonder if it is a combination of the cooling problems that have been corrected and a bad distributer. I bought a new distributer and it is being installed as we talk.

 

Not sure about anything at this point! top was not burned just sides seemed to be melted. Engine just shut down but did not lock up.

 

From FSM " Assemble piston to connecting rod with the piston skirt T-slot on the opposite side from the oil spray hole in the bearing end of the connecting rod"
In other words, when installed properly, the conn rod oil spray hole will be away from the camshaft; the skirt T-slot will be facing the camshaft

From FSM: "When the rods are installed, the offset in the rod is placed away from the nearest main bearing. The oil spray hole should be on the follow side or away from the camshaft, toward the right side of the vehicle. Because of the offset and oil spray hole, #1 and #2 or #3 and #4 connecting rods cannot be interchanged, for if they are reversed, the oil spray hole will be on the wrong side. #1 and #3 and #2 and #4 can be interchanged."

Got access to a factory service manual?
might be worth looking into, if not already done
sounds like lubrication problem to me, to happen so suddenly
my o.2 worth

 

Thats letting it advance to much.
Is it on the side near the top or the skirt?
You would only have labor knock under load, not at idle.
Be sure you have the bore checked also you could have scored the cylinder.

 

That comes under heavy load. Man I'm glad my wife is asleep. I'd just got punched.