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So I probably should have started this thread a little sooner as I have already begun tearing the bike down and working on the engine. I am not so good at documenting while working but I do have a couple pictures of what I have done so far. Right now I am in the middle of re-building the engine with new gaskets, valve springs, new exhaust valve (old one was bent), new exhaust valve guide, new engine top bolt to replace old one with broken oil seal, new clutch springs, and that's it I think. I have also sourced a new seat and hoop for the rear subframe. The hoop was pretty dope with the LED wrap around light already integrated into the hoop. I am now trying to decide how I want to attach the new hoop. My original plan was to do away with the stamped steel coming off of the subframe bend that catches the suspension and then weld on a new tube frame member to replace it. However, my buddy came over to take a look and said to just go ahead and do away with the hoop all together. I'm a little nervous taking that much out of the frame but I think it is do-able. QUESTION: Does the rear subframe bolt onto the front frame near the footpegs, or is it welded on? It looks to me that if I cut just above where the footpegs mount the frame can pivot at this point. Also, just looking for some advice or recommendations on what to do with the subframe. I have attached a pic of what I am thinking but am definitely open to suggestions. Thanks in advance!
 

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I'm surprised no one has chimed in....I haven't had as much time lately to spend on the motorcycle. Still working on rebuilding the engine as wells as the carbs. I've decided i'm going to build the bike with all my modifications/updates and then tear it down again to paint and everything cosmetic. I did find another guy somewhere online who was trying to do the same thing I want to do and I think I will pretty much mimic what he did. See attached picture. Any comments on whether or not this is a good plan?

Proposed Frame Idea.JPG
 

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The more you look around, the more ways you'll see that this has been done. Be sure to use good quality DOM tubing, it means Drawn Over Mandrel and its what motorcycle frames are made of. Good materials and good fabrication work will go a long way, but a bad design will fail no matter what so be sure your design is well founded before you begin.
 

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The more you look around, the more ways you'll see that this has been done. Be sure to use good quality DOM tubing, it means Drawn Over Mandrel and its what motorcycle frames are made of. Good materials and good fabrication work will go a long way, but a bad design will fail no matter what so be sure your design is well founded before you begin.
I was planning on going with chromoly. Would you recommend DOM over Chromoly?
 

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I'm not particularly qualified to make that comparison, but I'll take a few minutes to research it. There are however plenty of documented cases where someone used some type of 'pipe' for frame material instead of tubing, you do see a few of those projects finished, but you never hear how well they worked out.

Brb.

Yes, it seems chrome moly is also a very good choice. One key difference is that chrome moly is alloyed to a specification and DOM is not. This makes it a better choice for aviation and aerospace while DOM seems to stay on the ground.
 

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I'm not particularly qualified to make that comparison, but I'll take a few minutes to research it. There are however plenty of documented cases where someone used some type of 'pipe' for frame material instead of tubing, you do see a few of those projects finished, but you never hear how well they worked out.


Brb.

Yes, it seems chrome moly is also a very good choice. One key difference is that chrome moly is alloyed to a specification and DOM is not. This makes it a better choice for aviation and aerospace while DOM seems to stay on the ground.
Alrighty, thanks for the response! We used chromoly to build mini Baja car frames back when I was in college. It's certain characteristics made it a favorable choice for the amount of welding required. You don't happen to know of any build threads on here you think would be helpful do ya? I'll do my own search too, just curious if you had any in particular in mind.
 

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Like Alan says about the design, it's so important. Make sure you have everything drawn on "paper" before you start to cut and weld.
It might be easier to take a photo and find the right angles in Photoshop ;-)

We have very strict rules where I live when it comes to vehicles. We have to get the build inspected were one of the many tests is the strength of the steel and it can't be too stiff or too soft. This inspection also costs many hundres of dollars so you better make sure you do it right the first time. There are other types of steel that works but I was recommended to use EN 10305-4 E235 +N. I've seen that EN 10305-1 E235 +N has the same specs so it should work too. 22mm or 25mm x 3mm but 2mm works, maybe 3mm is preferable if you're going to attach the the rear shock mounts on it but I guess it also depends on the construction. It's called Seamless cold drawn hydraulic steel tube.

Edit: You might only find this steel in Europe and Asia by this specific name.
 

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I'm not too up on build threads but if you search I made a thread on how to use the advanced search on this forum, with that you can search for frame mods on cm400s.
 

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Like Alan says about the design, it's so important. Make sure you have everything drawn on "paper" before you start to cut and weld.
It might be easier to take a photo and find the right angles in Photoshop ;-)

We have very strict rules where I live when it comes to vehicles. We have to get the build inspected were one of the many tests is the strength of the steel and it can't be too stiff or too soft. This inspection also costs many hundres of dollars so you better make sure you do it right the first time. There are other types of steel that works but I was recommended to use EN 10305-4 E235 +N. I've seen that EN 10305-1 E235 +N has the same specs so it should work too. 22mm or 25mm x 3mm but 2mm works, maybe 3mm is preferable if you're going to attach the the rear shock mounts on it but I guess it also depends on the construction. It's called Seamless cold drawn hydraulic steel tube.
Yeah I seriously doubt I would have to get the build inspected here in Virginia, USA. I'm sure I could probably go through the proper channels to get the frame "certified" but unless I was going to sell this bike I don't really think this is necessary. I've typically always gone with the saying "ask for forgiveness rather than permission, or just plead insanity". I'll take a look at those steel types you suggested. If I were to build the entire frame from scratch I think some testing would be necessary, but because it's the sub-frame and I won't be changing any suspension angles/heights I think I'm okay.
 

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That's great. The only point I had was that I wanted you to know that the steel I'm recommending is most likely good enough for your states requirements if there was any. You're good to do whatever frame mod you want and feel safe. Good luck with the bike.

Edit: it was hard for me to look it up on US sites so you probably have a different name or standard. I only get hits from Europe and Asia.

Could it be Seamless Mechanical Tubing?
Cold Drawn Seamless (CDS) normally made from SAE 1018, having precise tolerances and good surface finish – Superior machinability – Increased dimensional tolerances – High strength to weight ratio
https://www.metalsupermarkets.com/difference-between-erw-dom-and-seamless-tube/
 

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I'm surprised no one has chimed in....I haven't had as much time lately to spend on the motorcycle. Still working on rebuilding the engine as wells as the carbs. I've decided i'm going to build the bike with all my modifications/updates and then tear it down again to paint and everything cosmetic. I did find another guy somewhere online who was trying to do the same thing I want to do and I think I will pretty much mimic what he did. See attached picture. Any comments on whether or not this is a good plan?

View attachment 274304
I think you want to add a cross brace above the shocks that will stiffen side to side movement caused by the shocks. Other than that it looks good.
 
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