Head shaving: For the motor, not me! How much?

[phartman]

Thanks to the quick work of David, I now have a very nice set of 21-stud iron heads. The machinist was able to remove much of the scale and rust from my aluminum heads using his ocillating cleaner. They look quite nice. This week he did cc'd the original alloy and the replacement cast iron heads I left him.

And it is shocking what he found....no wonder the motor ran so well with those alloy heads!

The aluminum heads that the motor loved so much turned out to be 58cc's. The Ford script iron replacements are 84 cc's. With the other specifications of my motor that works out to 8:1 compression on the aluminums; and 6:1 on the iron.


How much can I safely shave off the mating surfaces to increase the compression of the iron heads? My guess is .030-.060". And that will bump the compression to around 7:1, which would be a good step. It doesn't need to go to 8:1, but the motor likes compression so any step up from 6:1 would be a step in the right direction.

Valve clearance is not an issue. The iron heads have more than 2x the clearance of the aluminum ones. I would have to shave an eighth off the iron to equal the pocket on the alumunum ones, and I know they cleared just fine.

So how much should I take off? The head thickness at its thinnest point is a little less than a quarter inch. .060" and call it a day? Too much? I just don't know.

[Walt Dupont--Me.]

It looks like your only problem is shaving them enough to have .040-.050 clearance over the pistons. Usually if you mill much over .050 the piston will hit the head. Walt

[ford38v8]

Here comes the Plast-Gage!

[David J]

Pete , You didn't tell the troops they were flattop type . Kinda important detail . Dunno nuttin bout how much to shave off but there's folks on here that will . Glad to see them getting back on the road where this stuff belongs . David J

[phartman]

David, the heads are beautiful!!! Wow, really nice. I had the other set over at the machinist's. He couldn't believe what fine shape the ones you sent were in. But we don't want to screw them up.

I don't think the valve clearance is going to be the issue. It seems more to be a thinness of the head itself issue if you shave it too much. Many, many of the flattop heads are cracked in the center where the coolant circulates, so I don't want to take off too much and weaken the overall structure.

But that being said, .040-.050" seems about right. My buddies are urging me to do more, but then, they're all kind of crazy and don't always know what they are talking about.

So, how about it? What say you, oh sage bards of the Fordbarn?

[JWL]

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If the heads have not been cut at any time previous, I would stop at .060. It will be important to avoid excess torque and to be sure the clamping is done evenly in several steps. There is no reason to exceed 45 ft' lbs. with properly cleaned and lubed fasteners.

[bbrocksr]

I just done a set for a 37 engine. I could only take .050 due to valve clearance. Measure both banks, the valves protrude a little more on one bank than the other.
Bill

[phartman]

I promised an update on the heads, and here you go:

Took several sets to Ballos Machine here in Richmond, courtesy of Doug Walker at Joe Smith Early Ford. Stewart there at the machine shop was quite confident that a simple "shake and bake" would thoroughly clean the original alloy heads...and he was correct! Here's what they look like after cleaning and a slight dress up milling:



Stewart cc'd the heads and they came out to 52. With the overbore and the way my block is set up, that came to an 8:1 compression ratio! No wonder the truck ran so well with these heads!

As you can see, the chambers are very shallow:



Next up were an original gennie Ford set of cast iron replacements from Doug's shop, also here in Richmond. Stewart cleaned them as well. Same combustion chamber design, but these cc'd to 86. That works out to a compression ratio of 6:1. Pretty much dead on what I expected.



Now the critical question: how much to mill the cast iron replacements to best work on the motor. To make the cast irons the same compression as the alloys, they'd need to be milled an eighth. We felt that was too much and would compromise the integrity of the heads. So based on the recommendations here, Stewart shaved .050". That gave a final cc of 70, and a compression ratio of 6.85:1. Not exactly the same as the alloys, but a notch above stock. And I note that the chamber design lacks the feature that is intended to direct the flame travel. But a nice set of heads nonetheless. Here is a pic of that set. Thank you, David, for sending me such a handsome pair of gennie heads to work with. Magnafluxed perfect.

Note the diffence in this head and the other stock gennie Ford iron head, particularly around the plug hole.



I left with Stewart one more set to cc, and I'll post the results of his findings. That set is a non-Ford cast replacement that is a different configuration that the Ford oval design. It is more symetrical, and the sparkplug is not biased toward the exhaust side of the chamber. He'll have them ready next week. I'll post up what I find.

Meanwhile, I have a set of heads to install on the teddy bear. No more running dome heads on a flattop piston motor! Yuzzaaaah!

[Adam/Mill Valley CA]

I shaved the cast iron heads on my '36 21 stud motor (flat top pistons) 100 thou without any problems; it runs really well-I've been running this motor for several years.

Adam

[phartman]

Originally Posted by Adam/Mill Valley CA

I shaved the cast iron heads on my '36 21 stud motor (flat top pistons) 100 thou without any problems; it runs really well-I've been running this motor for several years.

Adam

Adam, that was quite the debate at the machine shop! Shaving .100" as you did would have put the compression ratio at a bump over 7.5:1. The concern was the number of cracked heads that we saw in stock configuration. Most failed in the very center, around the big coolant holes there in the middle. Consequently, we decided to go very conservative with the .050" clip.

Also, I have on order a set of the Don Orosco repops of the Eddie Meyers heads. They are 8:1. So there wasn't much point in trying to go that far since his are already ordered and will be delivered by the end of the summer (I hope).

But it's good to hear that we could have been more aggressive. Yours is exactly the type feedback I'm looking for- to see precisely what will work and what won't.

Why be so conservative? Well, the nature of risk is that you won't know you've taken too much until after the fact. I'm a "belt and suspenders" kind of guy, it turns out.

[Adam/Mill Valley CA]

I have a couple sets of the cast iron heads, I think you can get away with such a deep cut if they start at stock thickness. They're pretty inexpensive since everybody wants the aluminum heads. The Eddie Meyer heads, I'm sure, are fantastic. For me, with a stock 21 stud motor in a stock truck, I definitely was not looking for very high performance, least of all with the babbit bearings-just wanted to bring it up towards the level of the cars. I did see the .100 figure mentioned somewhere in an old book on hotrodding flatheads and so I thought it wasn't completely nuts to try it. I know when I cc'd the heads before cutting them the chamber volume was very large

Adam

[cdan34]

Back some 35 yrs ago, I ran a 21 stud babbit bearing engine in my '34 Cabriolet. The engine was bored .060 over, flat top pistons, 3/4 isky cam and the heads were milled 3/32 or .094. This was done by a great flathead shop in San Jose, Ca. Was always pleased with the performance.

Chuck

[Ol' Ron]

Notice the location of the spark plugs. This would be a natural for power tip plugs. Might even give better mileage.

[phartman]

Ron, thank you for bringing up the subject of sparkplugs.

Power tip plugs? What are they? Don't know what that is. Some guidance, Dr. Flathead?

How far into the chamber should the tip properly extend??? Should the tip be into the chamber, but not the threads? The tip should be up in the hole? How do I know what the proper length of the plug should be???

Thanks, guys, for your guidance here from a reformed Y-blocker.

Pete

[Ol' Ron]

For these heads you'll have to experiment, most engines yse the power tip design, but only the tip should extend into the chamber. You'll need an adapter to 14mm style plug then using a friendly nAPA counter man find a plug that will fit.
Why?? the reason the plug is placed in the path of the exhaust flow is because , back in the old days plug fouling was a common occurrence and placing the pluf in the path of the exhaust burned off excess "junk". Modern engine place the plug in the center of the combustion chamber to have an equal flame front in a hi compression engine this is one way of reducing the octane requirement of the combustion
chamber.

[Ol' Ron]

I thought there might have been a comment on this??

[phartman]

Ron, we're gonna look at it. My motor man wants to play around with a couple different plug ranges. He wondered at this compression ratio whether it made much difference in horsepower, but he immediately agreed with the mileage impact. We'll just have to see. Thanks for the suggestion.

And if anybody else has some thoughts here, please chime in.

[phartman]

Another head chamber configuration I found. Repop heads from long ago. Note the late model, 8ba style chambers (but this is a 21 stud head). Symmetrical and the plug hole in the center of the chamber. CC'd out to 58 ccs, putting the compression ratio at a notch under 8:1 on my motor.

Unfortunately, this set (and every other set Doug had at Joe Smith Early Ford) were cracked in the centers. Quality just not there. But the manufacturer sure had the design down.