MTFCA Forum

The triple gear pins in my 23 runabout are shot and need to be replaced. I've recieved some new pins in the past where the surface where the gears run was rough. Are there any good quality reproduction pins available that are the proper size so that they will not crack my flywheel?

Thank you,
Stephen

I think I have read that Bob's model t parts makes good ones. I also need a set.
If I don't like the surface finish I will polish them. Good luck and let us know what you find.
Philip

I can't see how you could crack your flywheel the pins are made to press through from the rear side and press out from the inside. The last 1/2" of the pin about .0015 larger than the working area, with the pin in place, you should be able to press it through by hand then the last 1/2" will require some force but not tons, I set mine in with a block of wood and a heavy hammer. Some pins have an additional collar on the bottom so they can not be pushed through and some don't. You should always push the pins out from the inside and reinsert them from the out side. It would be good practice to measure the pins and the holes firstly to avoid any issues.

I bought standard size pins from Bobs. I measured the hole and the pins had a .0015” press fit. I got a set from one of the Vendors that was too large.

John

John, Did you check the hardness of the new pins with a file? How do they compare to your originals?

Altair wrote: ↑

Sat May 09, 2020 2:41 pm

I can't see how you could crack your flywheel the pins are made to press through from the rear side and press out from the inside. The last 1/2" of the pin about .0015 larger than the working area, with the pin in place, you should be able to press it through by hand then the last 1/2" will require some force but not tons, I set mine in with a block of wood and a heavy hammer. Some pins have an additional collar on the bottom so they can not be pushed through and some don't. You should always push the pins out from the inside and reinsert them from the out side. It would be good practice to measure the pins and the holes firstly to avoid any issues.

I don't know exactly what all was involved, but folks have in fact broken flywheels by pressing in triple pins.

The pins without the "additional Collar" referred to above by Altair are aftermarket pins not made to the Ford design. The purpose of that "collar" or slight step at the crankshaft side of the pin is to trap the pin between the flywheel body and the magnets.

I bought three new pins and they do not have the collar on the end and have a rough surface finish.
Stephen

Adam wrote: ↑

Sat May 09, 2020 7:02 pm

John, Did you check the hardness of the new pins with a file? How do they compare to your originals?

I did not check. They did not have the step in the end.

The ones that I got that had the step and looked like good quality
Were .004 bigger than flywheel hole which I thought was too much interference fit.

John

I see to remember that at one time Glen Chaffin made oversize pins. By this I assume the oversize was on the taper where it inserts into the flywheel and was 0.003”. I am not aware of any marking on either original or oversize replacements so accurate measuring is essential.

The late RDR and myself and a few of his friends spent a ton of time and money on this subject about a decade ago. We did a blind volunteer study of piles of matching used pins and bushes...we bought new pins and bushes from everybody...and I sent the whole lot of them to a facility certified by Mercedes Benz to inspect and accept directly for MB. That's another story...

At the same time I also sent for original prints and record of changes for all but the flywheel and had someone who had the CD of the piece parts used in the T-100 project read me the applicable info contained on the actual flywheel drawing as to dimensions and finish.

The original fly wheel press fit was really an interference fit as the range on the pin body (not the rim) was to be 0.004-0.005 interference fit.

As to the flywheels themselves and them breaking when pins pressed in. I shudder to say it but I did the calcs many times over because I never believed my found answer, then had one of my people do it from scratch and yes he came up with the same, if you do a full stress analysis on the flywheel with a 0.005" interference and at rotating speed, something very strange does pop out...it's allowed to spider crack as the stress limit for Class 20 cast iron is exceeded. Don't worry, the drawing may say 20 on it for the flywheel, but in those days when most grades were really just 'select stock' from one batch...I think the material came out much stronger than what Class 20 Cast Iron would actually be. I'd suggest that there may be a case of two or three where the flywheels did spider crack in use but not enough to worry Ford, and if a break did occur they apparently didn't grenade as I have never head of that in anything Ford. These these later reports of cracks and/or breaks are more probably the result of someone not knowing what direction the pin rim needs to be pushed out from and that extra 0.007/0.008 of diameter would take the localized force way above the so-called stress limit for the lower grade iron in theory.

The drawings of the flywheel when compared to the drawings of the pin show a 0.004-0.005 interference fit between the flywheel and a pin. I also have a personal theory that the speed at which a hydraulic press moves has bearing on stress buildup as it passes through iron and iron willingness to softly surrender. So fast press, more of a tear/stress riser wave. Slow press, load has time to normalize out of the way. (Yeah, I know...guys have beaten the crap out of these things with ball peen hammers and sledges and they still work without spidering...most of the time! )

Oh, back to the pins...in that lab on the new ones test there was one vendor who was absolutely stellar as to size and form and finish...the pin could not have been made any better...all 3 pins read exact in every plane...to the 4th decimal place...so using my choice of words, let's call them blue-printed and they might be my own preferred choice. Others' pin sets had some 'egg' in diameter and some dimensional deviations, but in fairness were still in 'tolerance' according to the print. Ralph and I were going to come up with a code name for the perfect ones that might imply location bought, but then Ralph heard from some of his steady gomba that the re-sellers sometimes aren't exclusive as to who their own suppliers are (meaning mix and match from batch to batch) so we took it as a single point in time solution and dropped any recommendation forward on supplier.

In the day Dodge supplied flywheels for Fords who probably had one or two manufactures, also Ford had several suppliers of flywheels. Most manufactures work to a + - tolerance anything from .0005 - .0020 depending on the part, the very fine tolerances would be difficult to maintain and therefore may vary somewhat. One flywheel may require moderate pressure and another somewhat higher.
Additionally unknowing mechanics may have disassembled the pins from the wrong side of the flywheel and enlarged the holes in the flywheel (that is where the oversize pins appeared) now it is only a guessing game as to fit. When a pin set is wrongly pressed out it would require custom made pins to fit.
It is amazing in the day without robots and computers how well they worked for a lot of miles without too many broken transmissions. Most of the horror stories are after we have messed with them.

A few additional comments on this. if you purchased pins with no end shoulder, send them back for a refund! They are simply not made correctly.

On edit: I just had an interesting conversation with Dave from Chaffin's on this subject, and one of the things we discussed was the end shoulder. Chaffin's has the factory print for the replacement pin, and it has no shoulder at the end like the production part!

For the record, the press fit diameter of the replacement pin is .682/.683. Neither Dave or myself can understand why the shoulder was removed and we both agree that the lack of a shoulder is less than ideal. We may never know why, unless someone obtains the change record for the replacement pin from The Henry Ford. But this does answer why there are pins currently on the market with no shoulder. They ARE being made to the factory drawing! Would I use them? Probably not, but that is my decision

I just checked the Ford factory drawing and the flywheel end diameter is 0.679/0.680

Again on edit: Dave also has a later copy (1923) of the standard pin and the press fit diameter was changed to .6800/.6805 , probably in an attempt to better control the amount of interference in the assembly or better manufacturing practices made the tighter tolerance possible

Over the years, I have installed a fair number of pins and much more than .0025" interference is a really bad idea. Less than .0015" interference and I would not trust the pin staying where it belongs. More than that and you stand a really good chance of pushing flywheel material out of the hole. I can't imagine trying to install a pin with .004 or .005" interference- even with heating the flywheel and shrinking the pin.
If by chance a pin gets pressed out the wrong way, you should scrap the flywheel, or save it until you purchase a set of my 20mm needle bearing conversions so we can rebore the flywheel for the larger size pins.

As I have always understood it, the SERVICE pin was larger than the FACTORY pin (Meaning the pins sold as parts to dealers and meant to replace existing pins were slightly larger than the pins originally installed at the factory). I haven’t seen the prints, but if this is the case, I would guess the factory number for the pin in the original parts books might be different than the factory number for the pin on the flywheel assembly drawing?

In any case the pins should feel right when installed they shouldn't take any more than a three pound hammer and a block of hard wood to install, if they require tons of pressure something is wrong. Except for the last 1/2 - 5/8" they should press in through the flywheel with no effort.

Bumping to the top - see my edited posting above. Thanks, Dave!