Head Milling

You can mill your head all you want..it wont make you any smarter....and whether you have hair or not does not seem to matter.

Seriously I would not try to raise the compression on a bone stock T much...the crank is just to flexible to take much more than what Ford put into the compression pressure.

IMHO



Friend Dennis O
 
Mr. Oberer, I need my head the standard size for when I "mill about" at a swap meet, hair or no hair. Let me 'splain the question again. I want just a little more power if possible. Your point about the crank makes sense though, even to my pointy head.

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Thanks, tmodelman, that really helps. I pulled the head because I thought the gasket was blown but it turned out to be the exhaust manifold gasket that went bad. I am replacing that with the original gland and copper ring setup. The cylinder and head looks good and I figured that if I wanted a little more HP without forking out almost $400 for a hi-comp head, then a milling might help and now was the time to do it.

So your comment and the links gave me all the info I wanted. I think taking off 0.125 is in order.
 
The only problem with that is: How many times has it been milled already?
How much has already been taken off? Heads are quite frequently milled to remove warpage and no two 90+ year old heads are exactly alike. Most corrode from the inside. About the only way to tell is to cc the head. Anything less than 275cc and you' may be pressing your luck. Also check the steam holes. If you don't have at least about 3/16" of iron left, you're pressing your luck.
 
CCW, the machinist just had the same question. I am going to cc the head again before doing anything because it didn't look like there was 3/16 left.
 
From what I have been told, the issue of increasing the compression ratio is risky with a stock crank shaft. Many of the aftermarket heads do increase compression. Thr Ricardo-Waukesha head does not, but through an improved combustion chamber design it reportedly gives a noticeable improvement in performance. Perhaps there are others that are similar???
 
I put 312 Thunderbird pistons in several T engines years ago. I only did it because they were nearly identical in deck height to iron T pistons and the bore size was the same and they were readily available for cheap. I don't think they raised compression a bit but the oil control ring was better than a T. These aluminum pistoned engines had idling characteristics that were better than stock and they revved up a little quicker for what that is worth. I would never go out of my way to increase compression on a T. Better performance is gained from making things flow better on the manifold side of the engine and with less chance of damage to the crank. Someday I will build a full bore T engine with a real crank and real oil pressure but you can have a hell of a good time with a well tweaked T motor that is mostly stock. If you really want to go fast take a good running T engine, drop the frame as low as you dare and have no bodywork at all. I have done it and my oversize go cart scared the hell out of me at 58 MPH. (and I was MUCH younger then).
 
CCWKen, I rechecked the combustion chamber and I came up with 270 ml so I guess the head has already been milled to the max. Thank you for the specs.
 
More compression pessure from milling the head, even to the max, is NOT a problem for the 'T' crankshaft! What will hurt it is COMBUSTION pressure. Think about it: (these are ballpark numbers) say we go from 50 or 60 lb. compression to 80 or 90 lbs. We almost doubled it BUT, what about pressure in the cylinder when it fires? It goes much higher, maybe to 400-500 lbs? (I would have to research this to be anywhere close to actual numbers.) But the point is that compression pressure is not the culprit. We also raise combustion pressure whenever we do anything to get more power: camshaft, exhaust, porting, bigger valves, etc. The effect on the crank is the same. And if we get into detonation from higher combustion pressure and temperature, the crank will get a real beating! That probably has killed a lot of crankshafts.
 
Increased compression (whether static or combustive) is NOT going to break a T crank. What will break a T crank is stress. Compression does not significantly increase stress (remember, it is rotational force, so any increase in compression force does not result in the same amount of increase force directly on the crankshaft).

However, as 40 Deluxe said, if you get into detonation, you can break the crank. With the octane rating of modern gas, increased compression alone will not cause detonation. However, driver error can cause it! That would be by way of incorrect spark setting. Also, too much run out will cause a T crank to break. This MAY be the most common reason for broken cranks.
 
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