This engine, with only 4000 miles on it since rebuild, has always overheated and locked up when shut down after overheating, which is usually when driven at 45 or less for 30 minutes or more. (This did not and does not happen when driven under 35 and/or just around town for less than 45 minutes). I thought I had this problem fixed. But apparently not.
Here is the history: On 3/16/14 I installed an engine which had been boiled out, sleeved back to standard, new pistons and rings from Snyder's, new valves, exhaust valve seats, new lifters, and new babbit by Bill Barlow. It was tight, but I figured it would loosen up during breakin, which I did very carefully, as I have done with all my previous engines.
After 2000 miles it was still overheating and locking up on shutdown. I took it apart to check measurements. Ring gap, rod bearings, and piston clearance were just where they should be, according tbirdtbird, Bill Barlow, Tom Godish, and several other commenters on the Barn. But when reassembled it had the same troubles.
At 3500 miles I went through the disassembly again and rechecked the clearances, just to make sure I had done it right before. I had (so I thought). So I put it back together, timed it to a gnat's eyebrow, thinking that might be the issue, drove it with the spark rod exactly where everyone agrees it should be in a stock engine. It still overheated and locked up.
Today I took it apart again, and again checked my piston clearances. I checked with my engine guru, Tom Gosish. He informed me I had been checking the piston clearance incorrectly. I had done it front and back. I was getting .004 that way. But side to side, the correct way, today I got .012 on all four pistons, except the driver's side #4, which was .016. These all seem excessive, so I don't see how too tight a fit resulting in expansion could be the situation causing the lockup.
Other notes: all spark plugs (Champion 3X) have perfect tan coloring.
There is very slight partial accumulation of carbon on the tops of 2 & 3.
This engine has always had a knock on deceleration, but after this last overheating, it is present in both acceleration and deceleration, but not a cruise speed. It's not like a rod knock; more like a loose wrist pin.
The cylinder walls show no signs of scoring or damage from the pistons. They are clean and shiny, though the crosshatching is gone.
It is not burning oil; the rings seem to have seated properly, though there is some minor blowby when under heavy load, like going up a steep hill.
There were no metal flakes or pieces or other metal indications present in the oil when drained.
I noticed today, which I hadn't noticed before, that I have a '28 head with no center hole in the middle between 2 & 3 for water circulation. This might affect the overheating issue, but to the point of causing it to lock up when shut off seems unlikely.
Tomorrow I am pulling the pistons and having the rods checked for trueness and balance. That is the only thing I have not done, even from the beginning, because Bill Barlow provided those rods and assures me they were trued and balanced, and he is a reputable engine rebuilder.
So, if anything occurs to any of you much more experienced engine guys that might be the cause of this, I am ready to try anything. I have run out of my shade tree ideas. I flat don't know what else to do, and neither do any of my local engine guys.
Thanks for indulging my long post.
Here is the history: On 3/16/14 I installed an engine which had been boiled out, sleeved back to standard, new pistons and rings from Snyder's, new valves, exhaust valve seats, new lifters, and new babbit by Bill Barlow. It was tight, but I figured it would loosen up during breakin, which I did very carefully, as I have done with all my previous engines.
After 2000 miles it was still overheating and locking up on shutdown. I took it apart to check measurements. Ring gap, rod bearings, and piston clearance were just where they should be, according tbirdtbird, Bill Barlow, Tom Godish, and several other commenters on the Barn. But when reassembled it had the same troubles.
At 3500 miles I went through the disassembly again and rechecked the clearances, just to make sure I had done it right before. I had (so I thought). So I put it back together, timed it to a gnat's eyebrow, thinking that might be the issue, drove it with the spark rod exactly where everyone agrees it should be in a stock engine. It still overheated and locked up.
Today I took it apart again, and again checked my piston clearances. I checked with my engine guru, Tom Gosish. He informed me I had been checking the piston clearance incorrectly. I had done it front and back. I was getting .004 that way. But side to side, the correct way, today I got .012 on all four pistons, except the driver's side #4, which was .016. These all seem excessive, so I don't see how too tight a fit resulting in expansion could be the situation causing the lockup.
Other notes: all spark plugs (Champion 3X) have perfect tan coloring.
There is very slight partial accumulation of carbon on the tops of 2 & 3.
This engine has always had a knock on deceleration, but after this last overheating, it is present in both acceleration and deceleration, but not a cruise speed. It's not like a rod knock; more like a loose wrist pin.
The cylinder walls show no signs of scoring or damage from the pistons. They are clean and shiny, though the crosshatching is gone.
It is not burning oil; the rings seem to have seated properly, though there is some minor blowby when under heavy load, like going up a steep hill.
There were no metal flakes or pieces or other metal indications present in the oil when drained.
I noticed today, which I hadn't noticed before, that I have a '28 head with no center hole in the middle between 2 & 3 for water circulation. This might affect the overheating issue, but to the point of causing it to lock up when shut off seems unlikely.
Tomorrow I am pulling the pistons and having the rods checked for trueness and balance. That is the only thing I have not done, even from the beginning, because Bill Barlow provided those rods and assures me they were trued and balanced, and he is a reputable engine rebuilder.
So, if anything occurs to any of you much more experienced engine guys that might be the cause of this, I am ready to try anything. I have run out of my shade tree ideas. I flat don't know what else to do, and neither do any of my local engine guys.
Thanks for indulging my long post.
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