Why did Henry or his engineers, design the Model T piston with a semi-pop up design? I'm referring to the top of the piston that extends above the block deck at TDC. Model A's and all flathead V8's that I am aware of, used a flat top piston that did not extend above the deck. If Ford had used a true flat top piston in the T, he could have reduced the weight of the cylinder head by casting it with a smaller combustion chamber and shorter overall height, and still maintained the same low compression ratios.
Maybe they didn't have ridge reamers in those days and the top ring came to the top and eliminated the ridge. When a ridge is created you can't get the piston out with out reaming, just maybe.
my thinking is any protrusion above a flattop piston would cause the downward force to loose part of it's energy being forced to the cylinder wall, instead of straight down?, or maybe there should should be a slight dish in piston top? just a thought.
I think most all Ford flathead V8s had domed pistons. Dave in Bellingham,WA
Easier to clear the carbon off (due to the poor gas back the day)?
I like Howard's answer.
David, You are correct. Some flat head V8 pistons may have been true flat tops, but rethinking my statement, and remembering my days working at Specialized Auto Parts in Houston in the 1970's, most V8 pistons did have a rounded dome on the top, but not near as much as today's T high compression pistons. As I remember, the dome on a flat head V8 piston, isn't even as high as the semi-pop up dome of a T piston.
As to Fred B's answer, that involves too much physics for my mind to comprehend.
As to Howard's answer, I doubt the quality of gas varied much between 26-27 and 28-31, so if your answer is to be accepted as truth, Model A owner's got screwed by Ford, because they didn't have a piston that extended above the block deck to scrape the carbon off of, making the job perhaps, harder.
In 1908 most engines used separate cylinders bolted to a common crank case. The Model T engine was cast en-block, one block for the T's four cylinders. The head is cast separably and is detachable from the block. Having the piston with the bevel that extends above the block helps align the head, head gasket, and block during assembly with two pistons at TDC. Model A's and V8's use head studs instead of head bolts to align things.
Kevin: "Winner, Winner- Chicken Dinner" I think you have hit on the correct answer; at least, I'll accept it.
The early T Fords used flat top pistons no bevel and maybe models before the T. Seems to me they were flat topped up to 13 or 14.
(Message edited by redmodelt on March 19, 2018)
Building engines in which the top ring partially exits the bore is not exclusive to Ford.
Mark: Now that you mention it I have seen pistons out of a 1909-10 T that were flat top. I don't know about the 1913-14 T's, but that would match the years of the assembly speed up due to the using of assembly lines for sub-assemblies like the engine, so the use of the bevel piston to speed assembly fits.
Seems to be a lot of guessing going on. I didn't know the early T's had flat topped pistons so mechanically there's a reason for the change over. Some thing new every day. The easier assembly and easier cleaning answers don't do it for me. must be something technically closer to the truth.
It looks like changing the pistons from flat top to the pop up style would raise the compression ratio. They pop up at least 1/4". I know the compression ratios were changed to compensate for the poor gas quality but I've never heard much about the effect of piston design change other than the heavier-lighter versions, nothing that would affect compression.
You're probably closest Corey. I really feel it was a mechanical/design type change.
Anyone who has pulled the head to scrape carbon will tell you it's easier with flat-top pistons.
The '15 engine I reworked (as opposed to being a true rebuild) a few years ago had what appeared to be original almost flat top pistons. They have a very slight convex arc to their tops, as opposed to the angle shape of the common later ones that appear to pop up slightly above the surface of the block. The outer edges of the pistons seem to rise slightly higher than the later common pistons do. However, the top surface appears to not rise quite as high. Without taking the time setting up some sort of displacement measuring device, I could only estimate that the difference between the two types of pistons was not significant. And since all the pistons and bore looked to be in excellent condition? I used them (besides, I like original stuff even if it can't be seen, and like cast iron pistons if they are in good condition, and are not some of the excessively heavy type).
If anything, from my simple observations, I would guess that the earlier almost flat top pistons might have a slightly lower compression than do the common later ones.
However, the only "facts" I am familiar with from Ford engine changes in that time frame is that due to the poor quality of gasoline (in part due to the early stages of the Great War), Ford lowered compression a couple of times between 1912 and 1917 (I don't have the dates of those changes, although I have read them here before). That makes my observation of the lower top of the piston appear to be in reverse of the technical changes known for the time frame, as the later higher dome would have instead raised compression slightly). So take all that as a "for whatever it may be worth"? Which in this case, may not be much.
Flathead v8 pistons went from flat top to dome during the 36 model year.
Jim Eubanks do you know when the flathead V8 had the very thin iron pistons, I think they were Ford issue, seen a few. Thanks for the refresher on the dome pistons, I worked in an engine shop through the 60's worked on many flatheads, hardly any before 36. Dave in Bellingham,WA
For you mechanics that are discussing carbon removal, there was a company in the early 20s that designed / manufactured and sold 3 tools for cleaning (scraping) carbon deposits from valves, piston tops and heads without removal of the head. Their advertising specifically called out that they were made for the Ford Automobile. The company was the Buffum Tool Company of Louisiana, MO. I have 2 sets in my tool collection. One set is stamped "ORD" meaning it had been manufactured and supplied to the Army.
Kim, Could you please post pictures of the 3 tools you mentioned above? Also, do you have any sales literature on them, and if so, could you post pictures of that also?
Thanks very much as I for one have never heard of tools like this and I'm anxious to learn more about them.
I would think that if the piston was flat and the head was shaped more like a flathead briggs 30 to 35hp could be possible?
So they went from flat to domed to what I'll call angular. Perhaps the angular ones were easier/cheaper to make ? They kept the pop-up over the block feature but changed the shape of the top of the piston. The same effect with a different shape.