MTFCA Forum

Today I went hunting for "new" triple gears, and these are all I found.

I've arranged them here in three sets: left, center and right. The weights within each set are all quite close, so balancing them should be easy. But some have loose rivets. In a couple it's obvious. In some others, if there's any looseness it's so little that I can't be sure. The question: can loose or suspect rivets be hammered tight enough to make the gears usable?

Steve, all those gears will be "new" to your already run transmission that had the one piece gears. So, they will have to get to know your drums as they settle in. I can see no particular advantage in keeping them in their sets, unless they are quite worn, which is not usually the case with three piece gears. Selecting any three with tight rivets is not really going to make a lot of difference, so long as you can still balance them.

If you had a transmission apart and found a gear with loose rivets, then I would re-rivet that gear to keep the triple gear/transmission gear family together. If the gears have not "worked" to be quite loose. I would turn up a collar to support the rivet heads on one side of the gear, and use a press to load each rivet individually, rather than hammering on them.

Others may have suggestions which differ.

Allan from down under.

If the choice is between using the original gear which got "blue" in the center vs using a retightened riveted gear, there would simply be no choice for me...I'd go with the one-piece design, keeping the set of 3 a set of 3.

SpeedyT gave perfect advice as to how to test the gear which had the bushing spin. I find it very hard to believe that testing showed it to be anything but completely serviceable.

If the concern is that the gear is slightly oversized, well, I have yet to purchase a bushing which did NOT need to be machined DOWN to fit a gear (even gears which had spun bushings previously). As sold, even the best bushings on the market are slightly large. I have a favorite trusted source but will not open myself up to what would invariably follow.

Scott,
If I read your response correctly, you use a triple gear bushing that has a slightly smaller OD than what is sold by the usual catalog sources. Can you divulge what this diameter is or what the resulting fit is.
Maybe an improper OD fit has something to do with triple gear seizures / failures.
Art Mirtes

I have always pressed the new bushes into the gears. Never have I found one that fits right away. They need to be reamed to size to fit the pins. the problem comes when the reaming leaves the gears a too neat fit on the pin. They need to have clearance.

Allan from down under.

Art

what I was saying is that every source of bushings I have found in the hobby are (at least the last time I purchased some a year ago) selling triple gear bushings which are somewhere around .0025 - .0040 (at least) over the nominal diameter of the gear. I believe that this is to account for older gears who have had the bushing spin in them. Actually the same goes for front axle spindle bushings too...if you want to split and ruin an early spindle, the bushings sold by EVERYONE will do that job for you just fine unless reduced to the proper interference fit.

I measure the bushing OD, accurately measure the gear ID and select a press fit allowance per Machinery's Handbook or similar, and then alter the OD of the bushing to suit.

Yes, you can use the new bushing as-is and horse it into the gear with a 10 or 20 ton press, but as you watch the shavings boil out of the assembly, you don't really have any idea what the fit is now, as material is being removed rather than compressed, and there is no telling what structural damage is occurring to the bushing itself. Looking OK and actually being OK are two entirely different things.

In the hobby, we have parts offered to us that range from great to inferior. They are being placed into service in parts which range from NOS to totally worn out and not meeting the original dimensional spec. The parts purchased cannot possibly fit properly into both NOS and worn out parts, too. Thus, many are made in a Maximum Material Condition and beyond. Many or perhaps most folks don't realize that and don't fully realize what they're getting into. If suppliers were made aware of these things from the manufacturer, and then made it clear to the retail purchaser, I think a lot of problems would be avoided...this is why one guy just smashes a bushing in with a big press and another guy sets the bushing up on a tapered mandrel and takes a bit of material off. Either method works in the majority of cases, but when it comes to transmissions and particularly triple gear bushings, the two methods often have dramatically different results in practice.

Steve, I talked to Dan Hatch when I needed to ream new bushings and ball burnished mine as I didn't have reamers. Pressing sequentially larger stainless steel balls through the bushings hardens the surface as well as makes a tighter fit of the bushing in the gear. You need to press slightly larger balls through as there is a spring back of the bronze of about .0015". I went to a 0.681 ball to get the right clearance in my slightly worn pins. I believe Dan sizes with a ball of about 0.682 to get the correct clearance with new pins but the spring back varies a bit.

Thanks Scott for your answer. If I had an extra triple gear, I could calculate the hoop stress versus press fit. My guess is a press fit if .0004 in to .0015 in would be adequate. I could check my old tooling and machining books. But they are old and possibly obsolete.
If the triple gear pin is worn, it is out of round and is not a good shape as a bearing. Why not not just change it. They aren't expensive and not too difficult to change. Just follow instructions as previously discussed in the forum.

Steve Jelf wrote: ↑

Thu Jul 01, 2021 5:17 pm

Today I went hunting for "new" triple gears, and these are all I found.


IMG_6136 copy.JPG
I've arranged them here in three sets: left, center and right. The weights within each set are all quite close, so balancing them should be easy. But some have loose rivets. In a couple it's obvious. In some others, if there's any looseness it's so little that I can't be sure. The question: can loose or suspect rivets be hammered tight enough to make the gears usable?

No.