What is the correct distance between the cam and the crankshaft centers?
100mm or 3,937" (Yes, the guys that made the drawings were european - Hungrarian, in fact)
Yes it is 100 mm European size .
Another perspective from this side of the pond:
Timing gears were originally 8 DP spur gears, with 21 and 42 teeth respectively. Standard center distance for this pair would be (21+42)/(2*8)=3.9375". This is not 100mm, its 100.0125mm. Does it really matter in the big picture? Nope! Have a great day!
I just looked at one of Ford's blueprints and there are no metric measurements that I can see. 3-15/16" (which for all intents and purposes = 100mm) sounds like a more likely measurement to me. Where did this 100mm thing come from?
If that is your fixture shown above, can you show some more pictures?
Tom C. - As long as Jack's question seems to have been answered, I'll make an "OT" comment here pertaining to your comment,..."Where did this 100mm thing come from?"
I think Rogers' immediate answer to the question was expressed in metric measurement (correctly of course as is usual for Roger) merely because that is just probably what he is used to where he lives,....and understandably so. What I don't get is why some things of long-standing in our country seem to change for no absolutely good reason. For example, all my life, torque (at least in this country) has been expressed in "foot-pounds". All of a sudden in recent years, I hear it expressed as "pound-feet"! Maybe there's some good reason, but I just don't get it! Sorta' like Colorado seems to have become "Cola raahh do, and Nevada has become Ne vaahh da! I'm wondering if probably Montana will become Mon taahh na...? I don't know,.....maybe if Mazda is M aahhs da,....maybe Cadillac should become Caahh d aahh laahh c!
Okay,....end of rant, but I still torque Model T head bolts to 50 ft/lbs,....yes,....."foot-pounds"! And I certainly can accept decimal equivalents where it makes sense, but I still express measurements as much as possible in English,.....like "an inch and a half", or "an inch and five eights", and leave them milligators and alligators to the Europeans,......harold
JD Wichita , as soon he is ready I put some pictures on the Forum
OK, I looked at the blueprints and did a little math. The two measurements are 2.875" and 2.6875". So using the Pythagorean theorem and significant digits, the center to center distance from the cam to crank is 3.935", which is 99.49 mm.
But the recommended tolerance for the cam to crank distance has been quoted to be from 3,9367" to 3,9375" or 3,9376" here at the forum.
And the 25,4 mm per inch standard wasn't set until 1933 by ASA, after some lobbying from C.E. Johansson, the gauge block guy.
I don't suppose a thousandths or two is going to make a whole lot of difference, but the correct actual measurement is. 3.935"
Whether that translated to 100mm in 1908, I couldn't say.
A little off Tom, 9.935" is actually 99.949mm and .051mm back to "s is .002" so setting the distance by Rogers tolerances puts it back to 100mm
Sorry that should read 3.935"
Frank, I calculated the center to center distance from the Ford blueprints. It is 3.935", not 3-15/16", not 100mm.
It only matters by an 1/2 a thou if you call it 3.375" or 3 15/16" or 100mm
Unless your books for imperial to metric are different to ours?
Australia had the fun of converting to metric some 35 years ago so us old farts have been swinging between new and old for a long time, setting the line borer up for the right back lash on the T timing gears works well at 100mm.
Frank, I understand that 3-15/16 and 100mm and so on are all the basically the same (and probably close enough). What I am saying, is that none of those are are actually correct (as calculated from the actual Ford blueprints).
The correct (more accurate) number is 3.935"
IMHO Dan McEachern has provided the correct answer. Here is why I think so.
The Model T was designed by an international design team. This team had a heavy contingent of Hungarians, in fact there were four of them: Joseph Galamb, Charles Balough (the grandfather of forum contributor Bruce Balough) Jules Hartenberger, and Eugene Farkas.
Galamb, Balough, and Farkas were all educated in Budapest Hungary. Galamb and Balough were graduates of the Royal Technical Institute in Budapest. now a part of Obuda University. The school is still housed in the same building that Galamb and Balough attended classes in 113 years ago. I have visited this university, and have reviewed the transcripts of both of these men. They studied Engineering from a very practical perspective, and they studied gears and gear design as part of their curriculum. Students there today still do.
Eugene Farkas spent most of his time in the drafting room on the third floor of Piquette. Parkas was a graduate of Budapest University, the main four year engineering school, and worked directly under Banke Donat, a professor at Budapest University. Donat was working on steam powered hammers at the time. I have also examined Farkas' college transcripts, in order to understand better the engineering subjects he studied.
Jules Hartenberger has been much more difficult to track down. We know he was ethnicity Hungarian, but then as now, the ethnicities crossed national borders, studies at a college or university in Hungary or Czechoslovakia and at some point immigrated to America. He was a well trained engineer at the time the Model T was designed, and remained active in the automobile design industry for the rest of his life, even though he left Ford in the summer of 1908.
Engineering in Hungary was based on existing knowledge and newly acquired engineering knowledge. In the case of gearing, there were well established tables on gears, meaning that the number of teeth, the pitch diameter, etc. was obtained for the most part either from tables, or formulas for that purpose. As Mr. McEachern points out, Model T was originally designed to use straight cut timing gears, not the helical gears we use today when rebuilding Model T motors today. The tables and formulas would take into account the number of teeth in two meshing gears, the clearance between the teeth where the gears meshed, and generate a diameter for the gears. In other words, the design of the gears determined the center to center distance between them, not the other way around.
In addition to the Hungarians, the design team also included C.J. Smith, C. Harold Wills, Henry and Edsel Ford. Wills played a key role in the design of all the gears found in a Model T. In the oral reminiscences of Joseph Galamb, he remarked on observing Wills quickly use his slide rule as they tried out different ratios for the gears in the transmission.
One final point, the Fords before the Model T also used straight cut timing gears. They were designed, most likely by Wills, before the arrival and active participation of the Hungarians in the later models design processes.
Sometimes, coincidences occur. The center to center distance between the large and small timing gears was determined using the standard formulas for straight cut gear design. It just so happens that in the case of the Model T timing gears, that distance works out to being almost exactly 100mm.
"The center to center distance between the large and small timing gears was determined using the standard formulas for straight cut gear design. It just so happens that in the case of the Model T timing gears, that distance works out to being almost exactly 100mm."
Yes, 100% correct! The gear math, and nothing else, generates the center distance. It's just as much a coincidence that the figure is almost 100mm as it is that it's exactly 3-15/16". And, with all due respect for the engine block drawing dimensions, these are not the timing gear drawing dimensions, (not that I know what those dimensions are). If the original gear tables indicate what the operating distance was, or if they suggest a gear that was modified from standard gear design, (which is a common thing), in such a way as to modify the operating distance, then we can only to apply and trust in the same gear math today that the designers of 100 years ago used.
I don't understand what the argument is here or the point Trent is trying to make. The cam centerline is 2.875" up from the crank centerline and 2.6875" over from the crank centerline. The calculation 3.935" is just a matter of geometry. It has nothing to do with European engineers or gear mesh or anything else.
I could care less what dimension it is or what Hungarian came up with it. It is what it is and it works and has for 100 years so why worry about it.
Oh my gosh, if we didn't worry about this, then we'd have to worry about something important.
You're right of course. I guess we're still bored, waiting for the weather to agree with our cars. (Maybe not a worry in CA)
Glen, the question was asked: "What is the correct distance between the cam and the crankshaft centers?"
Doesn't Jack deserve the answer?
The discussion is about how was the center distance between the crankshaft and the camshaft determined when the Model T engine was being designed. It falls into the same discussion category as "which came first, the chicken or the egg?"
In this instance our European members are pointing out that since the the Hungarian engineers on the design Model T design team grew up with and studied under the metric system, the fact that the center to center distance was 100mm indicates that the center to center distance was determined first, and the gears were sized to fit the 100mm distance. In other words, the chicken came first.
Dan McEachern pointed out that given the straight cut gears that were originally used on the Model T, the design of the gears in terms of number of teeth and the pitch diameter is what determined the the center to center distance between them. That is to say, the gears came first, and the center to center distance came from the design of the gears, or the egg came first.
My comments were intended to support Dan McEachern's argument, and yet also explain why the Hungarian trained engineers ended up with a final center to center distance that comes out to almost exactly 100mm without actually using the metric system to determine the distance or the gears.
In some respect, this whole discussion is a lot like arguing over how many angels can dance on the head of a pin. (Right now, I am thinking the number of angels that can dance on the head of a pin is somewhere between 3.935-3.937 and 100).
For Jack Putnum, all that matters is what the distance should be, not about how the distance was determined. From a practical standpoint, whether the distance between the centerline of the crankshaft to the centerline of the camshaft is measured in fractional inches, decimal equivalents or in metric measures, so long as that distance comes out to 3-15/16, or 3.935-37, or 100mm, you should get the right clearance for the mesh of the timing gears when rebabbitting the block.
This distance is built in to the tools we use to bore the new babbitt for the crankshaft, regardless of whether you use KR Wilson, Hempy-Cooper, or Gene French tools. The distance is inherent in the design of the tools and can not be easily changed by the user.
I hope this clears up why I posted what I did.
You have a blueprint measurement of 3.935", that's fine but we also have the Ford Power plant checking standards, which gives the vital parts of clearances.
Now to set the right back-lash on the timing gears there is only one way and that is set by the centre to centre which is 3.9372", if set to close you have a problem you can't fix with out starting all over again with babbitt and line boring.
So in relation to answering the original question, to go by the blueprint would be a formula for a lot of pain!
Just like setting the triple gear pins at Fords .0015" clearance, we all know that doen't work!!
I just found another drawing that has the crank centerline to cam centerline height as 2.877" rather than 2.875". It lists the center to center radius as 3.9375" So there you go! 3.9375" is definitely correct.
That's good Tom, so are we all happy with, 3.9375" 3-15/16" and the 100mm being the same specs.
Tom, do the original blueprints give any clearance specs on any parts of the eng/trans?
That was an informative and very interesting writeup Trent. Thank you very much for taking the time to write it all for us.