Flathead deck height

[Bored&Stroked]

Originally Posted by 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.

You did well with that - I just reviewed some original prints and the "official number" is 10.440 to 10.445 (checked both 59AB and 8BA prints) . . . so a .005 tolerance.

I will update my CAD model to include a rough block outline and some of the other critical dimensions. Though everything previously mentioned about CH and the values for stocking stroke lengths remains the same and the drawings that I show and the associated dimensions (for the geometry depicted) should be correct.

[flatjack9]

I've got a box of Silv O Lite pistons for a 3 3/4 stroke engine. The box says CH is 1.702. The actual measurement is 1.507 which would put it below the the deck by .054.

[Bored&Stroked]

Originally Posted by flatjack9

I've got a box of Silv O Lite pistons for a 3 3/4 stroke engine. The box says CH is 1.702. The actual measurement is 1.507 which would put it below the the deck by .054.

Interesting - this is exactly why knowing the CH needed for a given crank, rod, stroke combination is the key number. It is all I've ever used in ordering pistons (or designing them in CAD and giving the prints to the piston manufacturer). Well to be clear - that is referring to the location of the top of the piston . . . there is a lot more to know for the rest! LOL

[frnkeore]

Thank you everyone, especially B&S and Yoyodyne. I'm going with 10.440/10.445.

I believe the Ford 9N,2N & 8N, 4 cyl engine, also used the same piston. I collect tractors and I found a set, this morning, for the 8N. Measuring from the pin edge to the start of the dome, I got 1.155, that makes it 1.530. Based on that, I believe that TRW had a typo and their dimension should have been 1.527, instead of 1.627. That would give a factory deck clearance of .038/.043 (sounds reasonable)but, that needs to be verified.

B&S, how do you access the factory drawings?

Frank

[frnkeore]

Originally Posted by flatjack9

I've got a box of Silv O Lite pistons for a 3 3/4 stroke engine. The box says CH is 1.702. The actual measurement is 1.507 which would put it below the the deck by .054.

Are your pistons oversize?

If someone requests a particular compression ration, using o/s pistons, they have to adjust the C/H to compensate for the C/R.

Frank

[Bored&Stroked]

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Originally Posted by frnkeore

Are your pistons oversize?

If someone requests a particular compression ration, using o/s pistons, they have to adjust the C/H to compensate for the C/R.

Frank

Typically the CH is not modified in the flathead world to setup compression - neither is the dome. Not that it couldn't be, but most folks buy stocking pistons in an off-the-shelf stroke combination. Sometimes I will modify the CH to get MORE compression - popping the piston up a bit (to setup a tight quench).

What we tend to do is manipulate chamber volume to setup/control compression. Truth be told, most of us wish we had more - hard to do with the typical aftermarket head - unless you have a large cubic inch engine OR we're running a blown application on gas (then we might buy heads with larger chambers - which are available from a few folks).

[JSeery]

Originally Posted by frnkeore

If someone requests a particular compression ration, using o/s pistons, they have to adjust the C/H to compensate for the C/R. Frank

That's back to what I was referring to on working on the cylinder heads. If you measure the clearance between the piston crown and the chamber roof (it has to be measured in several locations per cylinder) you can then modify the cylinder heads to match the piston. Then mill the heads to achieve somewhere in the .040 to .050 clearance range.

There are CR tables for different configurations, but they are somewhat of a guess, there are a lot of variables. Hard to do much CR wise with stock bore and stroke.

[flatjack9]

The problem is if the piston is below the deck, it's tough to get the tight quench at the edge of the chamber.

[Yoyodyne]

Originally Posted by Bored&Stroked

You did well with that - I just reviewed some original prints and the "official number" is 10.440 to 10.445 (checked both 59AB and 8BA prints) . . . so a .005 tolerance.

I'd love to see what tools Ford used to check that dimension and some other difficult features on the flathead in the early '30s.

[frnkeore]

Originally Posted by Yoyodyne

I'd love to see what tools Ford used to check that dimension and some other difficult features on the flathead in the early '30s.

Deck Height is one of the easy things to measure on a engine, you only need a surface plate and a height gauge, nothing else.

Those things existed in the 30's and before. As I posted before, this is how it's done:

You lay the blocks deck on the surface plate, modern surface plates are measured in the millionth of a inch for flatness and modern surface plates are made of lapped granite but in that period, cast iron surface plates, were more common. They would be made by surface grinding and lapping.

You then, measure the distance, from the surface plate, to the bottom of the main bearing bore and add 1/2 of that bore to your measurement. If your height gauge, measures in millionth's, you then have that accuracy in your measurement.

To maintain that kind of accuracy, it also has to be done, in a temperature controlled room. The standard measuring temp, is 20C.

All those thing don't sound like much but, steel and cast iron, expand at a rate of ~.000006, per inch, per degree F. If you, while machining a part, increase the temp of a part by 100F, that is 20" long (like say a engine block), that makes a difference of .012. The deck height would increase .006, also. So when they are measured the temp is important. Aluminum expands at about 3 times what steel does so, that has to be dealt with when using metals with different expansion rates, such as pistons.

Ford's manufacturing wasn't done with automotive type equipment, like you find in a automotive machine shop, it was done on milling machines, lathes, horizontal boring mills and planers, as well as other common, manufacturing machines.

Frank

[Bored&Stroked]

Originally Posted by Yoyodyne

I'd love to see what tools Ford used to check that dimension and some other difficult features on the flathead in the early '30s.

I have no clue, but I can imagine some "Go - NoGo" type of measurement tools. I've never seen the manufacturing equipment of that scale and of that day - so I'm totally talking out of my rear end!

Now - would be interesting to know how you officially measure the deck on a 409? Where on the deck???

[Yoyodyne]

Originally Posted by frnkeore

Deck Height is one of the easy things to measure on a engine, you only need a surface plate and a height gauge, nothing else.

Those things existed in the 30's and before. As I posted before, this is how it's done:

You lay the blocks deck on the surface plate, modern surface plates are measured in the millionth of a inch for flatness and modern surface plates are made of lapped granite but in that period, cast iron surface plates, were more common. They would be made by surface grinding and lapping.

Right, I understand, I have granite surface plates and the related equipment and use them daily, but I can't see Ford pulling blocks out of production to put them on a plate and installing a mandrel in the saddles to check the adjustment on the machine(s) that cut the major surfaces on the block. There must have been some hand carryable tools to measure that dimension. I've seen photos of spring calipers and scales used to measure some features I'd never attempt with those tools, perhaps that was what they used, or some job-specific vernier tool. I don't even know if the mains were cut first before the decks. I've seen precious few photos of Ford's machining processes, I wish there was more of that info available.

[40 Deluxe]

Originally Posted by Yoyodyne

Right, I understand, I have granite surface plates and the related equipment and use them daily, but I can't see Ford pulling blocks out of production to put them on a plate and installing a mandrel in the saddles to check the adjustment on the machine(s) that cut the major surfaces on the block. There must have been some hand carryable tools to measure that dimension. I've seen photos of spring calipers and scales used to measure some features I'd never attempt with those tools, perhaps that was what they used, or some job-specific vernier tool. I don't even know if the mains were cut first before the decks. I've seen precious few photos of Ford's machining processes, I wish there was more of that info available.

Have you surfed YouTube? There are lots of videos of engine production lines from the 1930's and '40's.

[rotorwrench]

There are some good films converted to digital video but you don't see a lot about the machine shop at the Rouge. Ford had some of the best tooling in the industry so they could mass produce. I'd figure with a strong percentage of certainty that they had gauges made to check stuff like that. The measuring equipment would have been designed for the specific job. Whether it was done at a line inspection station or actually in the machines that did the work would be unknown to me but everything was designed around the quickest possible check of a dimension so that the line could keep on moving at a steady pace. Those big planing machine cutting blades they used wear down over time so it would be important to check up on that so that tooling could be quickly serviced with minimal discrepancy to the finished parts. Charles Sorenson mentioned in his book that they had serviceability rates that were among the highest in the industry with very small percentage of discrepancies in the finished product.