Flathead deck height

[frnkeore]

Originally Posted by Bored&Stroked

Well just to muck the waters up a bit. Piston manufacturers usually don't talk about deck height at all - it is really not their problem. Also, they may or may not talk about crankshaft stroke and rod length. What they almost ALWAYS talk about is CH - or compression height. This is the distance from the center of the wrist pin to the top edge (in the bore) of the piston. This is NOT to the top of any crown or raised area (almost as if you were measuring a flattop piston).
Here, you preaching to the choir, I included that info in my first post.

From a piston manufacturer's perspective, all they care about is where is the piston pin centerline going to be . . . in relation to the top of the piston. It is up to the builder to determine HOW to get the piston pin centerline to that location. In modern OHV stroker applications there are all sorts of rod lengths, deck heights, etc.. When you order custom pistons, they will always require the CH number.
Yes, if your ordering custom pistons but, if they list pistons that they stock, they HAVE TO know the deck height of that engine to know if their compression height will fit the application. Note that they list the CH and usually the deck clearance, for the many rod/stroke combo's available and in order to do that, they have to know what the deck height of the engine is, from the factory.

When I build a custom engine (high end), I have my decks trued/aligned first and I have my crankshaft and mains work done (in case I'm align boring the thing) and then I install the crankshaft, one rod and a piston pin (in the rod end). Then I bring the rod up to TDC (measured with a dial indicator), then I measure/calculate the actual compression height that is required to put the piston edge/dome exactly where I want it.
If I ask to have a block decked at my local auto machine shop, he will give me the finished deck height and starts from the factory setting as his decking machine reads the deck height from the main bore.

On a flathead, the CH will be calculated so I'll be about .010 above the deck (edge of the piston). I do this because standard head gaskets compress to about .050 to .052 - and I want a .040 quench distance between the dome and the head chamber. I then order my custom pistons with exactly the right CH number. Rarely is the number the same as a "stocking piston".
How can you calculate the CH, if you don't know the deck height? Do you assemble a rotating assembly, then measure the deck clearance and adjust you CH from that measurement?

This is the only way I can get exactly what I want . . . and it increases the cost of a set of pistons and rings. Sometimes I move the ring package around a bit as well - depending on the type of rings and whether a NA engine or blown and also the depth of a relief (if I'm using one).


Here is an example of a Ross flathead piston specification on Summit's website - shows a compression height of 1.374 . . . which is supposed to be for a 4.125 stroke crank. In my world, the off-the-shelf pistons rarely seem to do the trick . . . but I'm a bit picky! LOL

Attachment 402845

Maybe I just answered my quest as how to get the deck height of a FH. I'll have to see if my local shop has that info.

Frank

[frnkeore]

I'm not trying to act superior, I'm just trying to get some basic info. I have deck heights for most all major American OHV engines from the '52 Lincoln (10.94), on but, not the FH.

I know some general info on FH's as I have always loved the look of them and my very first car (1959) was a '48 Merc, with a 3/16 over bore. If you'll read my bio, you'll see my dad worked for a authorized Ford rebuilder from '46 - '51. I started out as a mechanic, at 18 with his tools. I've built many FE's and 289-302 (even had a Edsel, 410 MEL) but, this is only my second FH.

My back ground for the last 45 years, has been as a machinist (not auto motive) and I look at all things from that perspective.

Frank

[GOSFAST]

The number you all may be wondering about is 10.438".

If we do mill the decks (most builds do get milled) we remove the bare minimum, even though these blocks weigh over 200# they are still "flimsy". It's also the very reason every block gets plate-honed.

Thanks, Gary in N.Y.

P.S. Haven't found too many to be "dead-on" but they are relatively close considering the machining was done a long time back!

[Bored&Stroked]

Hey Frank - not trying to argue with you - we actually agree on most things. You and I both know that we can measure something many different ways - as long as we're working from the same starting point, we can get to the same answer. If you want to know what the deck height should be, then all you had to do was read the drawing I posted - it is all right there.

From the Drawing:

a) Crankshaft stroke = 4.125
b) Rod Length = 7.000
c) Compression Height = 1.3745

So - the deck height = (4.125 / 2) = 2.0625 + 7.000 + 1.3745 = 10.437

Knowing that Henry tended to use standard increments, the spec was probably 10.4375 or 10 7/16.

Now - what I can't say is what tolerance the various flathead production locations actually held.

And you asked the question up above:

How can you calculate the CH, if you don't know the deck height? Do you assemble a rotating assembly, then measure the deck clearance and adjust you CH from that measurement?


In the paragraph above that - I explained that this is exactly what I do. I don't have the luxury of having a block/crankshaft jig all setup for a flathead - to measure from the crankshaft saddle, so I do it the hard way and then I give the machine shop the instructions as to what I want done on both sides and I give the piston manufacturer the corresponding CH.

Good luck!
B&S

[40 Deluxe]

OK, I have a basic question: How do you determine the main bearing bore centerline, in order to get an accurate deck height measurement?

[frnkeore]

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You lay the deck on a flat surface, a surface plate in my case, with a main bearing cap installed, you measure to the center of the main bearing bore. You get the center by measuring to the bottom of the main bearing bore and adding 1/2 the main bearing diameter. I use a height gauge for that type measurement.

You would then measure the other end, to determine if the main bearing bore is in alignment to the deck. If it isn't, it's a good reason to deck the block.

Frank

[JSeery]

Originally Posted by frnkeore

You would then measure the other end, to determine if the main bearing bore is in alignment to the deck. If it isn't, it's a good reason to deck the block. Frank

Need to really take it easy on a flathead, the decks are too thin to begin with, not much to work with.

[Yoyodyne]

Originally Posted by GOSFAST

The number you all may be wondering about is 10.438".

If we do mill the decks (most builds do get milled) we remove the bare minimum, even though these blocks weigh over 200# they are still "flimsy". It's also the very reason every block gets plate-honed.

Thanks, Gary in N.Y.

P.S. Haven't found too many to be "dead-on" but they are relatively close considering the machining was done a long time back!

Originally Posted by Bored&Stroked

Hey Frank - not trying to argue with you - we actually agree on most things. You and I both know that we can measure something many different ways - as long as we're working from the same starting point, we can get to the same answer. If you want to know what the deck height should be, then all you had to do was read the drawing I posted - it is all right there.

From the Drawing:

a) Crankshaft stroke = 4.125
b) Rod Length = 7.000
c) Compression Height = 1.3745

So - the deck height = (4.125 / 2) = 2.0625 + 7.000 + 1.3745 = 10.437

Knowing that Henry tended to use standard increments, the spec was probably 10.4375 or 10 7/16.

Now - what I can't say is what tolerance the various flathead production locations actually held.

And you asked the question up above:

How can you calculate the CH, if you don't know the deck height? Do you assemble a rotating assembly, then measure the deck clearance and adjust you CH from that measurement?


In the paragraph above that - I explained that this is exactly what I do. I don't have the luxury of having a block/crankshaft jig all setup for a flathead - to measure from the crankshaft saddle, so I do it the hard way and then I give the machine shop the instructions as to what I want done on both sides and I give the piston manufacturer the corresponding CH.

Good luck!
B&S

Many thanks, both of you. I've also been looking for that number for years. Would a 221 block be the same?

That's a great drawing, Bored and Stroked, thanks much for sharing it! Is there a chance you did the same for an early engine?

[frnkeore]

S&B,
I saw that in the PDF but, if you look at my addition of the crank throw, rod and CH, it adds up to 10.503. That would put the piston .065 out of the block.

The CH I use, is the replacement piston, that TRW made in 1978, L912F.

So, something isn't right.

Frank

[Bored&Stroked]

Originally Posted by 40 Deluxe

OK, I have a basic question: How do you determine the main bearing bore centerline, in order to get an accurate deck height measurement?

Depends on the engine, the shop and what equipment they have for a given engine type. For many engines, the block goes into a fixture that picks up the main bore - with a big steel bar that the saddles/bores lay on. The fixture also is used to determine what is 'square' to the mains.

The fixture is used to not only square-deck the block, but for all decking operations - as everything is based off of the mains . . . which are indexed/mounted into the fixture.

Some fixtures allow you to rotate the block (one deck to the other) - such that you can easily deck one side, rotate it and do the other side the exactly the same way.

[Bored&Stroked]

Originally Posted by frnkeore

S&B,
I saw that in the PDF but, if you look at my addition of the crank throw, rod and CH, it adds up to 10.503. That would put the piston .065 out of the block.

The CH I use, is the replacement piston, that TRW made in 1978, L912F.

So, something isn't right.

Frank

It all depends on the stroke - the piston you're using has a different or wrong CH. If I modify my CAD model to use a different crankshaft stroke, then the CH has to change in order for the piston to be zero-decked. The end deck height remains the same.

Note: Their dimension for 'Comp Dist' is wrong - here are the basic numbers for the different strokes - which are easy to calculate - just add/subtract from the numbers in my drawing (based on 1/2 the stroke change/difference):

3.750 = 1.561
4.000 = 1.436
4.125 = 1.374 (what my drawing shows - as that is the crank I'm using)
4.250 = 1.311

PS: The drawing is correct - the math works out and matches the 'stocking' pistons that Ross and others supply. What is your math?

[Bored&Stroked]

Originally Posted by Yoyodyne

Many thanks, both of you. I've also been looking for that number for years. Would a 221 block be the same?

That's a great drawing, Bored and Stroked, thanks much for sharing it! Is there a chance you did the same for an early engine?

Ask and just sometimes you might receive! Guess I've given a couple 'gifts' to the Barn today. LOL

I don't have the detailed early drawings from Ford (32 - 42 production) - have never seen them. BUT - from the drawings that I have seen, these are the numbers. I did use these dimensions to validate my 42 Merc block - as best as I could manually measure the valve angles, they were extremely close (which was what I was after).

Note - this CAD model also shows a 4.125 stroke crank - as I wanted to compare things to the later engines and my particular setup (42 Merc). So - obviously there is some simple math to do to calculate CH - given any stroke.


FlatheadFordEngineCrossSection-32-42.PDF

[JWL]

The drawing I have here at my desk does not have the crank CL to deck dimension. It is listed in a different view and that drawing is out in the shop. However, the dimension from camshaft CL to deck is 7.0654 to 7.0704

[frnkeore]

B&S,
What is the origin of your drawing?

Frank

[Tinker]

Originally Posted by frnkeore

Look guy's, I didn't join this forum, looking for a argument. I specify joined, to ask this question. \

I don't think anyone is arguing just adding info.

[Yoyodyne]

Originally Posted by Bored&Stroked

Ask and just sometimes you might receive! Guess I've given a couple 'gifts' to the Barn today. LOL


Attachment 402868

Thank you Dale! You are generous! Most folks won't appreciate what you just gave away in terms of hours spent to create and validate that.

[Bored&Stroked]

Important! Okay guys - was pondering this last night when I went to sleep (you know how it goes) and decided to think back at the purpose of my drawing (which was to look at valve angles and show the CH and crankshaft offset).

For the purposes that I used it for (easy calculation of compression height - given crankshaft stroke and experimenting with rod lengths), it is fine. It doesn't show the block in relation to the crank - which is offset about 3/16. So, the math I previously showed (and the drawing) is fine for determining CH, but not deck height . . . as until I actually add "the block" into the picture, you won't know the number.

Hope I'm making sense here - and I owe an apology to Frank! It was not correct to extrapolate deck height . . . when there is no deck to be found in that drawing.

[rotorwrench]

If your a machinist, I'd suggest measuring your deck height on both sides and ask others if they get similar dimensions. Ford had big machines that planed multiple engine blocks at the same time. The 68 series or LB blocks were the last of the pump in head blocks but as I mentioned earlier the deck is thin on all of them so Ford machinists likely set them all up for the same deck height so as not to make them too thin. Not too many folks out there are concerned with the dimension other than they want the deck square, intact, and as crack free as is possible.

If a person has a mandrel to fit the diameter on the main bores in the block, it can be measured from the deck down to the mandrel to get a dimension that can be calculated. The LB was the larger bearing than the previous engines and the first to have removable bearing shells.

[Yoyodyne]

FWIW, as a quick and dirty check I measured a 37 block this morning. I used a pair of dial calipers from the main bearing saddle to the deck, then added half the bearing bore. The bearing bore looks like 2.590", the saddle to deck looks like 9.150" This is not a great way to measure, and I could only reach at one spot, the front of the driver's side of the block because of the length of the jaws on the dial calipers. So 2.590 /2 = 1.295. 1.295 + 9.150 = 10.445. I'm confident that this is accurate on this block to ±.005. I bought this block disassembled and cleaned and don't know it's history, but it doesn't appear to have been machined at all.

[Ronnieroadster]

Heres my simple thoughts which is similar to what others have written. The actual deck height standard dimension is of no concern to most of us. What is a concern pertains to the decks being exact heights side to side from the crank center line. On every block I have built this dimension side to side has always been different. Seeing your interest is in the rebuild of your engine relatively stock at that to help you get what your looking for you simply need to contact the Ford archives. The Flathead block prints are located there and for a small fee you can get the print which of course will show the dimension your looking for if the print still exists. I have a couple of NOS flathead blocks and they to are not accurate side to side the variations reflect the machining process at the time and the huge amount being produced daily.
Ronnieroadster