Topic: CB750 triple clamps onto 350K frame

[emlupi]

Good evening,
I am looking to use the triple clamps from a ‘77 CB750K on a ‘73 CL350K frame. The sticking point is the longer stem of the 750. I know this conversion has been done, just wanted to know if anyone knows what can be done to make this fit?
It has been suggested to cut down the 750 stem and weld it at the correct length. If there is a way to make this work without cutting the stem I would prefer to do it that way. Thanks.

[scottly]

A 550 lower triple has a shorter stem than a 750, but has the same offset as the K7 750. I think it's about 7/8" shorter??

[seanbarney41]

Usually, the stem is pressed into the lower triple and then spot welded.  Iirc, 70's Honda's are quite a bit more extensively welded than just a spot.  Many have still been able to grind the weld off and then press the stem out of the triple.

[willbird]

Usually, the stem is pressed into the lower triple and then spot welded.  Iirc, 70's Honda's are quite a bit more extensively welded than just a spot.  Many have still been able to grind the weld off and then press the stem out of the triple.

From the perspective of being almost born in a machine shop :-) If I had to shorten that without using any fancy machine tools I would try to find a mild steel rod that slid snug inside the tube, then I would shorten the tube and use the inner sleeve to keep it aligned, and plug weld it. I saw some video about the NHRA approved method to do this and they require solid round bar to be used and what I am seeing in google search says 6" solid round bar extending 3" either way. The task that the  part performs demands the utmost in strength and security of the work IMHO.

Bill

[emlupi]

Usually, the stem is pressed into the lower triple and then spot welded.  Iirc, 70's Honda's are quite a bit more extensively welded than just a spot.  Many have still been able to grind the weld off and then press the stem out of the triple.

Yeah, I thought that would be a solution but the spacing of the threads on top of the stem for the steering head thread and the stem nut are different between the two bikes. If I were to just swap the stems out between yokes there wouldn’t be enough thread left on top to catch the stem nut.

[emlupi]

From the perspective of being almost born in a machine shop :-) If I had to shorten that without using any fancy machine tools I would try to find a mild steel rod that slid snug inside the tube, then I would shorten the tube and use the inner sleeve to keep it aligned, and plug weld it. I saw some video about the NHRA approved method to do this and they require solid round bar to be used and what I am seeing in google search says 6" solid round bar extending 3" either way. The task that the  part performs demands the utmost in strength and security of the work IMHO.

Bill

I was considering using a sleeve and a butt weld with a v-groove using the sleeve material as a backer. I can weld but I’m not an engineer, would this joint layout not be appropriate?

[emlupi]

A 550 lower triple has a shorter stem than a 750, but has the same offset as the K7 750. I think it's about 7/8" shorter??

Thanks Scottly, I will definitely look into this avenue. The 750 stem was a suggestion from another builder. Fortunately, there are plenty of these around and they are relatively inexpensive.

[willbird]

From the perspective of being almost born in a machine shop :-) If I had to shorten that without using any fancy machine tools I would try to find a mild steel rod that slid snug inside the tube, then I would shorten the tube and use the inner sleeve to keep it aligned, and plug weld it. I saw some video about the NHRA approved method to do this and they require solid round bar to be used and what I am seeing in google search says 6" solid round bar extending 3" either way. The task that the  part performs demands the utmost in strength and security of the work IMHO.

Bill

I was considering using a sleeve and a butt weld with a v-groove using the sleeve material as a backer. I can weld but I’m not an engineer, would this joint layout not be appropriate?

Only you can say really, but we would presume that the NHRA did testing in order to establish their approved method :-). I can weld but by no means would I call myself a welder :-). The plug welds add something to the finished structure for sure. I saw the video showing the method on Hot Rod Garage. They were modifying a chassis part too, not a steering/suspension part as we are talking about. The middle of the steering tube is not highly stressed probably but it is important :-).

[Don R]

  I have a CB500 triple that was lengthened to fit a 750 by cutting two stems to make a single weld in the middle with an interior sleeve, it's not up to the NHRA spec but that bike was raced all over the streets of Central Illinois and made more than a few passes down the drag strip.
  When I got it, the top tree was broken by the pinch bolts being overtightened, but it never came apart.

[turboguzzi]

The sticking point is the longer stem of the 750.

"longer" by how much?

some taper roller bearings are taller than the OEM ball races, might be worth checking

[Tim2005]

Do you have the CL350 triple? If so then could you grind the stem out of that and swap it into the 750 triple?