The aluminum head debate

dougson

I am having my '56 308 rebuilt by what many consider to be the best engine builder in my region and we recently went over the aluminum head ('51-2 H-145) I purchased to use with the engine. It turns out that the head has been milled 0.105 and from information posted here and elsewhere is too much and the head will fail. As I understand it, 0.060" is the most a head can be safely milled. My standard is that all aluminum heads were 2" thick from the factory. There is on the upper surface, near a corner, "105" stamped, which we think was deliberately done to indicate that the head had been milled 0.105". The head is in otherwise great shape, straight, flat, not warped and has obvious signs that it was on an engine, obviously without failing. The builder is willing to do a sonic test but from experience he's had with engine heads he doesn't feel concerned. I know that some feedback I get here will be negative but assuming the engine is well built, normally driven, and maintained that the head will work. The presence of the deep valve reliefs in the '56 block should lower the compression below 7.2, so whatever compression increase caused by the milling will be offset. Any good news out there?

Browniepetersen

I have been down this road before and even if you do not want me to be negative, that just is not going to happen. It is much like putting worn out tires on your car and driving 90 miles per hour. They seem ok when you put them on. They hold air and stuff---but, they are going to fail. I cannot say when, but they are going to fail. That is the same with the head that you are going to put on a good engine. When I did it, it failed within an hour after I installed and started the engine. (The head that I used had been machined .050. We had every reason to expect that it was good. Problem was that there was a thin spot in the head from the factory. When we measured the spot where the head had failed there was .040 material remaining.) When it happened we spent the next 5 hours pulling the engine apart to try to save the work that had been done on the engine. There is no way that I would do the same thing again. When folks tell you that .060 is max for a head. I would not go over that. I would be out looking for a new head... Just my opinion.

dougson

"We had every reason to expect that it was good. Problem was that there was a thin spot in the head from the factory. When we measured the spot where the head had failed there was .040 material remaining.) "



How did you determine the thin spot? Through sonic testing or some other method. I agree that if through testing a thin spot shows up in the combustion area, the head should be replaced.

Browniepetersen

We did every kind of testing before we put the engine togeather. It did not give way until I was driving it home from the shop. When the head blew it threw oil into the radiator and water into the engine. When we pulled the head was when we knew that it had failed between the second and third piston. It blew a hole in the head almost two inches long and a half inch wide. All I had to do was measure the material and we knew what had happened. We were lucky that it did not damage anything else.

[Deleted User]

dougson wrote:

I am having my '56 308 rebuilt by what many consider to be the best engine builder in my region and we recently went over the aluminum head ('51-2 H-145) I purchased to use with the engine. It turns out that the head has been milled 0.105 and from information posted here and elsewhere is too much and the head will fail. As I understand it, 0.060" is the most a head can be safely milled. My standard is that all aluminum heads were 2" thick from the factory. There is on the upper surface, near a corner, "105" stamped, which we think was deliberately done to indicate that the head had been milled 0.105". The head is in otherwise great shape, straight, flat, not warped and has obvious signs that it was on an engine, obviously without failing. The builder is willing to do a sonic test but from experience he's had with engine heads he doesn't feel concerned. I know that some feedback I get here will be negative but assuming the engine is well built, normally driven, and maintained that the head will work. The presence of the deep valve reliefs in the '56 block should lower the compression below 7.2, so whatever compression increase caused by the milling will be offset. Any good news out there?

If you use that head make sure you do not rev that engine over 2,000 for then you will bend every exhaust valve and hope one valve head does not break off for there goes the piston and cylinder wall. A friend of mine built a drag engine and set to revs at 5,200 and I told him not to go over 4,900, he didn't listen and when he hit 5,200 and took his foot off the gas pedal, #6 rod, block and starter were on the ground. He now runs 4,900 and has no problems. Walt.

Ol racer

I like aluminum heads since they polish up so nicely.

If you think the head was used on an engine milled.105 with no sign of problem spots perhaps take a chance using a 'Best' Gasket to ensure it seals and re-torque cold a couple of times.



Un like alumimum heads today it 'may have' thin erosion spots from using early types of antifreeze (and alcohol blends) during its long life so I would inspect the passages closely using a small mirror and look for any elongated holes. It may never fail or it may eventually like mentiomed previously, but I think it would give some advance warning signs like seepage or antifreeze in the oil.



If decide to use I would use an inhibitor and perhaps double up the sparkplug washers or use shorter reach to keep from closing the gaps because milled.105.

dougson

I appreciate feedback on this, but still have questions. So in Browniepeterson's case, as I understand it, milling the head reduced the weak spot to 0.040, meaning that the total original thickness at that spot was only 0.090", or less than 3/32". That head was going to let go no matter what you did, right? Walt's Garage-53 says that the exhaust valves will bend above 2000 rpm. Is this because of contact with the head? Woundn't they hit anyway? Or does milling, by increasing compression ratio, produce too much exhaust heat? Milling a Hudson head 0.105 would increase compression, all other things being equal, 1 point, or from 7.2 to 8.2, not a huge increase.

50C8DAN

If you want an aluminum head get a Clifford. A bit pricey but you never have to worry about it blowing!

Richard E.

I would love to find a aluminum head for a narrow block 262. My '50C6 came with one from the factory. That head, unfortunately is corroded in the water passages and is very thin, so I replaced it some years ago with an iron head. That head now is cracked in two combustion chambers. If someone has a "good" narrow block aluminum head that they are willing to part with, please contact me. I am having a difficult time finding any good narrow block 262 head. I have had 4 iron heads crack checked and everyone of them was cracked in multiple places. Help!



Richard E.

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