Topic: HM300's on K2?

[y2kc0wb0y]

Picked up a crusty rusty dusty 1 owner K2 (titled 73) with 1100 miles on the clock. Sat since 84 in a poorly insulated barn. its rough - locked up but all there. The pipes on this bike were in remarkable solid condition considering their rusty appearance. Started cleaning the shifter side pipes today and found something interesting. The outside pipe was the as expect HM341 but the inside pipe was an HM300.

Know I know enough to be dangerous with regards to the equipment history of CB's but I thinking the HM300's were for the early bikes 69/70...and a cross over happened in early 1971? Given the miles and owner history is this possible it came that way from Honda? I was under the impression that HM341's would be expected. IDK would love to hear your thoughts on this interesting mystery.

[newday777]

Yes K2 should have all 341 pipes.
What is the manufacture date on the vin plate?
The original owner could have had a ding in that pipe and the dealer or someone could have put on a 300 pipe that was available, though it could present a little different tuning variation.

[y2kc0wb0y]

What is the manufacture date on the vin plate?

8/72. 205XXXX VIN Tag and 206XXXX engine. I had to go outside and look but kicker side has 341 and inside 300 too.
The bike has crash bars and sissy seat but otherwise stock. weird.

[seanbarney41]

Yeah, i just bought a rough k4, for what I expected to be a set of 341...but to my surprise, they are stamped hm300.  All 4.  I am assuming the 341s must have gotten replaced long ago.  I found it odd, because the po did not see fit to select such nice parts for the rest of the bike...4" extended forks, king queen sissy bar seat and rear lowering blocks...other than that very unmolested.

[HondaMan]

Interesting!
I remember some tourers who rode behind full fairings (Vetter Phantom, Avon, et al) on the K0/1 bikes remarking they would prefer to listen to the HM341 at interstate speeds (which were 70+ MPH at that time). Maybe they started changing them out?

[y2kc0wb0y]

The baffles are missing and I"m now remembering it had velocity stacks when I picked it up. (airbox was included). I'm guessing someone tried to hotrod the bike at one point. Who knows, hard to say in its 50+ year history what tweaks happened and why. I'm planning to clean the carbs on Monday and will note any jetting differences and report back. If these bikes could talk; right?

[newday777]

Yes the stories they could tell.......
If the guages are original and not been swapped out, that poor bike was neglected......motorcycle abuse 101.
You know that the 300 pipe baffles were removable and the 341 baffles are not removable? It will be interesting to hear what you find in the carbs for jetting. Write it all down as you take them apart and clean up. Maybe the jets are all the same and the owner was just disgusted with how it ran not knowing how to fix it and just parked it??

[y2kc0wb0y]

Squirrels had the pipes and battery box packed full of nuts. Maybe that is what saved the pipes. IDK.
Gauges look correct.

[Don R]

 I've always thought parts swapability is the best/worst thing about the cb750, best thing to get one running, worst when you want one that's original appearing.
 I have a set of the reproduction 341's on a K0 only because it was in the thick of covid and they were all I could find.

[Prospect]

Nice score. Love the K1. Mine both came with 341 (I have an early k1 and an later k1). I was told they should be 300. I've switched them to 300 on one and left the other with 341. Awesome sound on the 300 with no baffles.

[Stev-o]

Gauges look correct....

...for a late K2.  My early K2 had K1 type gauges, which was somewhat common.

Do you have the K2-only turn signal switch on the left control?

As for the 300 pipes, it most likely just got changed out for some reason? Maybe a crash and then he installed the crash bars?!!!

[Terry in Australia]

The lower pipes copped the brunt of damage in low speed crashes, rusted out more than the top pipes due to battery acid dripping on them and chain grease and road grime blocking the drain holes. Someone probably just swapped them out when CB750’s were a dime a dozen, not knowing or caring about the difference.

[MauiK3]

I’d prefer a full set of pipes that are the same design, no telling how well a mismatch could be tuned. Sound would be weird too.

[beemerbum]

Have 300 repops on my K2. That was all DSS had at time. Lucky me. Very happy as they sound great.

[y2kc0wb0y]

Do you have the K2-only turn signal switch on the left control?

I think so

[Terry in Australia]

Have 300 repops on my K2. That was all DSS had at time. Lucky me. Very happy as they sound great.

Yep, the HM300’s were the best “stock” pipe for any of the K series bikes, except the K7/8, of course. I just bought a set of Yamiya repops (the best you can get) for my K0 and am just waiting on the rear footpeg bolts to arrive so I can install them.

[MauiK3]

Waiting to see them installed!!

[Terry in Australia]

Thanks Steve, well of course I've been busy fixing Subaru turbo's and Triumph Rocket 3's of late, but yesterday my bolts arrived. Now Honda, in their wisdom uses a special bolt 14mm OD, but with the end necked down to 12mm. Don gave me the measurements, so i bought the minimum 5 14mm bolts on Ebay assuming that I'd probably bugger one up, at least.

After work I waddled out to my "shop" (patio) and opened my bag of bolts. They're grade 8, so to heat the threaded ends I used my new cool tool, a "Vevor" magnetic heating coil thingy, that heated the end of the bolt in a jiffy, to red hot.

Honda Exhaust bolt 23 October 2023. 2 by Terry Prendergast, on Flickr


I then just let it air cool (quenching in water would have been faster) to "anneal" the end of the bolt so that I could put it in my lathe and cut the end down to 12mm, and thread it.

Honda Exhaust bolt 23 October 2023. by Terry Prendergast, on Flickr

The original bolt probably had a fine thread on it, but as I only had a couple of 12 x 1.75mm nuts, I just cut a standard thread on it, and shortened it by 10mm to 140mm, wich is apparently the stock length. I'll spray some "cold galvanising spray" on the threaded end so it doesn't rust, but I'm pretty happy with the result.

 Honda Exhaust bolt 23 October 2023. 1 by Terry Prendergast, on Flickr

[Kelly E]

We tried one of those magnetic heaters on a stuck case cover bolt with the head drilled off holding on the stator cover on the 80' GS 1100E. We took off the cover to make room for the tool. It wouldn't heat up the bolt, my buddy that owns the tool said that it was too low grade of metal for it to work. He uses it at work mostly to remove broken exhaust studs. He's a Ford diesel master tech.

[Terry in Australia]

We tried one of those magnetic heaters on a stuck case cover bolt with the head drilled off holding on the stator cover on the 80' GS 1100E. We took off the cover to make room for the tool. It wouldn't heat up the bolt, my buddy that owns the tool said that it was too low grade of metal for it to work. He uses it at work mostly to remove broken exhaust studs. He's a Ford diesel master tech.

That’s interesting Kelly, I had a problem removing a stud from the exhaust flange of a Subaru Turbo using it, I got the Stud red hot in seconds but still couldn’t get it out, so welded the nut on the stud, and while that was still really hard going, eventually got it out. I haven’t found a bolt yet that this thing can’t light up in under a minute.

[willbird]

The original pipes on my K2 rusted out pretty quickly as I recall. My dad put an action 4's 4:1 on it then :-).

[Kelly E]

We tried one of those magnetic heaters on a stuck case cover bolt with the head drilled off holding on the stator cover on the 80' GS 1100E. We took off the cover to make room for the tool. It wouldn't heat up the bolt, my buddy that owns the tool said that it was too low grade of metal for it to work. He uses it at work mostly to remove broken exhaust studs. He's a Ford diesel master tech.

That’s interesting Kelly, I had a problem removing a stud from the exhaust flange of a Subaru Turbo using it, I got the Stud red hot in seconds but still couldn’t get it out, so welded the nut on the stud, and while that was still really hard going, eventually got it out. I haven’t found a bolt yet that this thing can’t light up in under a minute.

 

As we all know the case cover hardware is a bit on the soft side. The 6mm that we had trouble with ended up taking 1 1/2 hours to drill and pick out the remains. It is the one spot that there's not enough metal around the hole to even repair it with a Helicoil.
An exhaust stud is harder steel than case cover hardware and Kevin said that it was the first time it didn't make a bolt or screw glow in less than a minute.