Transmission

[hayleyl]

Hello all - can I use an Ironhead transmission in a set of non-trapdoor K series cases? Cheers Hayley.

[EKHKHK56]

Hello. Yes you can. Use the entire transmission. You will need a sleeve to go around the countershaft right side bearing. OD is smaller than the one on early case. Mine had a bronze sleeve pressed in to take up the difference. Erik K

[sportsterpaul]

This is good to know. There must have been a lot of problems with the early K transmission- I have read there were some weak gears and you can see the factory redesigned pretty much everything by 1956. Be sure you set the spacing between the gears while assembled into the left case, and you have to do a few dry runs to make sure the endplay on the shafts are OK. I don't drag out the dial indicators any more-- I just tug on the sprocket shaft to hear tink tink instead of thunk thunk, or worse yet, binding. Is there a hole in teh left case to get to the countershaft to check its endplay? A quick check of the technical section shows a picture (pdf) and yeah, there is a nice hole under the sprocket shaft to get that dental tool in.

[hayleyl]

Thanks Erik - thought as much but never tried it. I have a near new tranny to use for my 53 project. And yes - SportsterPaul - very aware of end float etc. Have seen many AMF produced Sportsters vomit gearbox bits everywhere. Cheers Hayley.

[sportsterpaul]

Vomit parts, yeah, when I worked at Ford we had a saying: "Measure it with a micrometer, mark it with a piece of chalk, cut it with an axe."
I wonder how long Harley still made parts with hand-crank Bridgeports?

[EKHKHK56]

Some of the early gears are really bad looking. Like I mentioned in the History, looked like they were formed with a cheeze whiz can compared to Andrews or 58 and later gears ....

[Simon]

FWIW I had a shop rebuild one of my transmissions on a K, and had to split the cases again when I received it.
I don't think the spacing was correct for one (no movement in the countershaft sprocket whatsoever), but it also had a mix and match of earlier and later gears (assuming -52, vs -54 or -58, or later).
The gear box seemed to have a "run" or surge in the gears when ridden. Problem was solved before case damage by replacing with gears from one era.

I have heard of hardening problems in the very early gears that possibly led to the puking transmissions when fragments got caught up in the speedo drive gear.
Can't prove this, although maybe early shop dopes or dealer literature may be able to confirm.

[EKHKHK56]

Yes Simon the first run of changes is documented in the January 1954 Shop Dope Service Bulletin #345. "Servicing the 52-53 K, KK & KRM Transmission." New gears are provided for this recommended service for old and new Ks but not 54 KH. Five gears are replaced with new ones that have better tooth profiles, stronger steel & heat treating. Also better designed dogs I noticed. Those 5 gears are mainshaft 3rd and Low and countershaft Drive, 3rd & Low. Book calls them that. Low is 1st and Drive 4th of course. Interestingly it calls for either 25 or 26 tooth CS 3rd gear to be replaced.

[EKHKHK56]

Service Bulletin #356 June 1 1955 concerning KH, KHK & KHRM Only. 2 gears were updated with stronger, better designs. Mainshaft 2nd and countershaft 3rd. New gears have a 4 stamped on them. Interestingly the new gear first came out as 24 tooth than switched to 23. Both interchange directly as the tooth pitch remained the same. Motorcycles built after 55KH1706 came with the new gears. Before that some were built with new C/S 3rd but not M/S 2nd. And updates continued. The 58 and up is probably the strongest. I know some later years had bad batches of gears. I purchase Andrews transmission parts for anything other than stock. Careful setup is critical to smooth operation, & gear, bearing, and overall life.

[Tim The Grim]

This is what I was told when I worked at an H-D dealership in '73...the original K gears were heat treated to 56/58 Rockwell C and had great wear properties but we're very brittle in the dog/cog area. Lots of shattered gears and cases. Different tempering processes brought the hardness down to 52/54 and improved impact resistance on the gears.
This heat treat methodology continued long into the Ironhead era, until AMF came in.
That's when AMF/H-D allegedly forced the aged heat treater guy into retirement and the QC guys went back to the harder gears according to written specs.. Many broken later '72-73 gears resulted and we actually had a gear blow up through a case and cut the riders femoral artery. He almost bled to death at the roadside but was saved by a passing Doctor. If I remember right he got a settlement of $65k in a lawsuit.
Allegedly, AMF had to re-hire the heat treater to get his process back into production.

Things back then were so bad, all I did was warranty work in the shop and it soon went bankrupt and closed. We had some amazing, skilled wrenches there but the parts just sucked. I replaced 8 sets of faulty lifters in a new Shovelhead before the new owner was finally happy. My tenure as an official H-D mechanic came to an end not much later.