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Old 07-28-2019, 04:58 PM   #1
frnkeore
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Default Flathead deck height

Does anyone have a factory reference of Fords Deck Heights for the Flathead engine and are there any variation of the deck height for 32-36, 37-39, 40-48 and the last version of 49-53?


As far as the math goes, 1.875 (half the stroke) + 7.00 Rod length) + 1.627 (piston compression height to start of the dome) = 10.502. The dome is .154 but, I can't find a reference to the deck clearance.

Also, I know that the valve angle was changed, did that have a effect on deck height?

Frank
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Old 07-28-2019, 05:08 PM   #2
rotorwrench
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Default Re: Flathead deck height

The connecting rod length stayed the same for most of the v8 production. Only the pistons changed for the two different strokes. If a person registers off of the crankshaft centerline, the deck height can be checked since there are likely plenty of old engines that never had the decks cut down. I would imagine variations would not be very much if any since the deck surface is rather thin. They can only be planed off so much. Most machinists that do plane them only take enough to true them back up. The valve angle change would not have been enough to warrant any change that I'm aware of.

Last edited by rotorwrench; 07-28-2019 at 05:18 PM.
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Old 07-28-2019, 08:04 PM   #3
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Default Re: Flathead deck height

The valve angle change doesn't have anything to do with the deck height - as deck height is strictly based off of crankshaft centerline.

Since all of these engines came with the same length rod and the compression height was the same for all 3 3/4 stroke engines, the deck height "should be" the same for all years.

With that said, I typically see a variance between one bank and the other - so I usually figure out which side is lowest, then use it to determine how much more to take off the high side -- to get them both even.
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Old 07-28-2019, 08:23 PM   #4
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Default Re: Flathead deck height

Does the crank off-set come into play on that?
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Old 07-28-2019, 09:24 PM   #5
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Default Re: Flathead deck height

Quote:
Originally Posted by Bored&Stroked View Post
With that said, I typically see a variance between one bank and the other - so I usually figure out which side is lowest, then use it to determine how much more to take off the high side -- to get them both even.
I take it that you've measured the deck clearance then?

What measurements have you gotten, when you measure the deck clearance?

Frank
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Old 07-29-2019, 08:32 AM   #6
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Default Re: Flathead deck height

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Originally Posted by JSeery View Post
Does the crank off-set come into play on that?
Not really - in that the block dimensions (the overall casting) takes it into account. If this were not true, then you'd have "side specific" rods or piston combinations.

The crankshaft offset (about 0.265") does influence the valve angles as well as exactly how the pistons are located in relation to the crank pin at certain rotation angles (rod angles - relative to the centerline of the rod are different at TDC).


Attached is a cross-section drawing I made that shows a bit of what I'm talking about - hopefully you read it (this is 59x through 8BA - is different for 32 - 42):

Enjoy!

FlatheadFordEngineCrossSection-59A-8BA.PDF
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Old 07-29-2019, 08:57 AM   #7
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Default Re: Flathead deck height

Quote:
Originally Posted by frnkeore View Post
I take it that you've measured the deck clearance then?

What measurements have you gotten, when you measure the deck clearance?

Frank
Now sure what you're asking??? Clearance to what???
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Old 07-29-2019, 01:52 PM   #8
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Default Re: Flathead deck height

The deck clearance, is the distance from the top of the piston (on domed pistons, it's measured from the start of the dome) to the top of the block.

In more modern, OHV engines, it's usually between .025 in the case of the sbc and .016 on SBF.

It's a needed dimension when setting up a engine to calculate compression ratio.

That's why I'm asking about the block's deck height. You would take the dimensions that I listed in my first post, and subtract the 10.502, from the deck height and that will give you the deck clearance.

The other thing that it effects is the distance from the piston to the underside of the head. For OHV engines, you need at least .040, to insure that the piston, doesn't hit the head at higher RPM. In the case of the FH, you have to add the dome height to the deck clearance and compressed head gasket thickness, to insure you have that clearance. Of course you don't have the dome on the early flat top pistons and so, you don't use it on those engines.

Frank
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Old 07-29-2019, 02:10 PM   #9
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Default Re: Flathead deck height

It is much easier (and I would think more accurate) to measure it directly. The top of the pistons are often not a perfect dome, same applies to the area of the head over the piston dome. That is why it needs to be checked in several locations on each cylinder. There is also variation cylinder to cylinder. I'm not sure trying to figure it mathematically is the best approach. Takes some work to get the heads matched up to the pistons, the target value is normally in the .040 to .050 range.

Last edited by JSeery; 07-29-2019 at 02:16 PM.
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Old 07-29-2019, 02:22 PM   #10
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Default Re: Flathead deck height

Quote:
Originally Posted by frnkeore View Post
The deck clearance, is the distance from the top of the piston (on domed pistons, it's measured from the start of the dome) to the top of the block.

In more modern, OHV engines, it's usually between .025 in the case of the sbc and .016 on SBF.

It's a needed dimension when setting up a engine to calculate compression ratio.

That's why I'm asking about the block's deck height. You would take the dimensions that I listed in my first post, and subtract the 10.502, from the deck height and that will give you the deck clearance.

The other thing that it effects is the distance from the piston to the underside of the head. For OHV engines, you need at least .040, to insure that the piston, doesn't hit the head at higher RPM. In the case of the FH, you have to add the dome height to the deck clearance and compressed head gasket thickness, to insure you have that clearance. Of course you don't have the dome on the early flat top pistons and so, you don't use it on those engines

Frank
Edit: For FH's, you have to also measure the depth of the cylinder head depression.
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Old 07-29-2019, 02:38 PM   #11
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Default Re: Flathead deck height

Quote:
Originally Posted by JSeery View Post
It is much easier (and I would think more accurate) to measure it directly. The top of the pistons are often not a perfect dome, same applies to the area of the head over the piston dome. That is why it needs to be checked in several locations on each cylinder. There is also variation cylinder to cylinder. I'm not sure trying to figure it mathematically is the best approach. Takes some work to get the heads matched up to the pistons, the target value is normally in the .040 to .050 range.
I'm a machinist by trade and yes, there are very many variables. All production parts have a tolerance and those tolerances can accumulate i.e. stroke length, rod length and compression distance. You can also add to that, individual clearance of the parts. BUT, there will be only one tolerance for the block, itself to be concern with.

I don't know what Ford would have used for tolerance on the FH but, more modern tolerances is .005. Ford would have had to list that info (deck height and tolerance) somewhere or the engine could not have been built. The block is the basic "Building block" to the whole engine and everything is built to it.

Frank
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Old 07-29-2019, 02:47 PM   #12
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Default Re: Flathead deck height

I'm sure there are original blueprints if you are that interested. You can contact the Ford facility that keeps the original copies.

"The block is the basic "Building block" to the whole engine and everything is built to it."

That is true, but if you have the block in front of you, you have that information. Short of a NOS block, almost all blocks have several rebuilds on them which my or may not have included decking the blocks. Flathead blocks are very thin in the deck area to begin with, so any decking needs to be kept to the bare minimum.


What are your objectives with the engine? If it is all out competition there are some world recorded holders here on the barn that may or may not be willing to share some of their secrets.

A lot of us have considerable high performance/race experience in the non-world record category. A little more information on what you are after might help.

Last edited by JSeery; 07-29-2019 at 02:54 PM.
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Old 07-29-2019, 02:50 PM   #13
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Default Re: Flathead deck height

Since I'm a machine shop owner, I can measure any component to a engine. For most w/o that ability, what JSeery suggests, is the best that that can be done but, if you can measure each component, you can place them (or replace) to match OA lengths as evenly as possible, before assembling them together.

If you order pistons, you need to know the stroke length, rod length and the deck height, to get a accurate fit, for you application. That will inlude a acurate compression ratio, that is so important in a FH.

Frank
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Old 07-29-2019, 02:58 PM   #14
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Default Re: Flathead deck height

Quote:
Originally Posted by frnkeore View Post
Since I'm a machine shop owner, I can measure any component to a engine. For most w/o that ability, what JSeery suggests, is the best that that can be done but, if you can measure each component, you can place them (or replace) to match OA lengths as evenly as possible, before assembling them together.

Frank
I really don't agree with your prospective, it will be interesting to see what some of the expert builders have to say on the subject. And just for the recorded, I and just about any, hp builders have the ability to measure just about anything that can be measured, LOL.
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Old 07-29-2019, 03:29 PM   #15
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Default Re: Flathead deck height

Unless you are ordering special pistons, deck height is not listed for flathead pistons. I find that most of the pistons bought these days end up with the edge of the piston below the deck. Not ideal, but that is what you get these days.
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Old 07-29-2019, 04:12 PM   #16
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Default Re: Flathead deck height

I know that in at least one case the block was shaved INSTEAD of the heads because if you were a winner they would tear down the engine right after the race to check the bore & stroke etc. before you got paid!!!
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Old 07-29-2019, 04:23 PM   #17
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Default Re: Flathead deck height

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).

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.

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.

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".

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

2019-07-29_16-57-12.jpg
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Old 07-29-2019, 04:30 PM   #18
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Default Re: Flathead deck height

Quote:
Originally Posted by flatjack9 View Post
Unless you are ordering special pistons, deck height is not listed for flathead pistons. I find that most of the pistons bought these days end up with the edge of the piston below the deck. Not ideal, but that is what you get these days.
This is especially true in modern SBCs, SBFs, etc.. By having the piston "down in the hole" a bit, they didn't have to worry about quench as much and pistons won't be hitting heads (especially the 'smog motor era'). It is kind of a "punt" by the manufacturers - starting with GM and Ford themselves.

I 'zero and square deck' almost everything I build - because I want my quench to be exactly what it needs to be. I usually run about a .040 quench on SBC type engines as well - and with a stocking piston, that usually means the block has to be decked. In the higher quality forged pistons, they will specify the exact Compression Height - end the builder must figure out if they want to use that piston, deck the block or find another piston (if it is down in the hole a bit).
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Old 07-29-2019, 04:35 PM   #19
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Default Re: Flathead deck height

Look guy's, I didn't join this forum, looking for a argument. I specify joined, to ask this question. I asked on the face book site, Flat Spot and couldn't get a answer there so, I thought that I might find it here.

I come from the manufacturing world and may think differently than others.

My motive in this is the '35 truck pictured in my avator, it has a 68 engine that I want to rebuild to my spec's, to get the highest compress possible, with some aluminum, 21 stud heads and intake, that I recently bought, possibly modifying them to use domed pistons.

Frank
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Old 07-29-2019, 04:50 PM   #20
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Default Re: Flathead deck height

Don't think you are getting arguments, your getting information from folks who know and build flatheads and have for years. If I knew the deck height number I would give it to you, I don't. Don't need it and don't use it. You are on a site with some of the top flathead builders in the world. If people post on your thread it keeps it near the top of the listing, if they don't it tends to get buried. If there are any builders that have that information and use it they will see the thread and most likely comment. Just a hint, there is no reason to come across as superior in the way you do or go about an engine build. Again the top flathead experts in the world are on this site! I have years of experience in building late model drag and circle track engines and understand exactly what you are referring to. That is something I am concerned with on OHV builds, flatheads are different. One of the biggest differences is how the heads are manufactured, there is a lot of variation from cylinder to cylinder. If you are wanting top performance you are going to have to modify each combustion chamber to match the piston. You might be able to machine the head for consistency or start with a billet head, but off the shelf they are going to need work. And as stated, custom pistons would help.

Last edited by JSeery; 07-29-2019 at 04:57 PM.
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