Motorcycle frame inserts??

[scotto75]

Hi,

I'm doing some minor modifications to a Honda motorcycle frame. I've cut the rear of the frame to weld on a loop, not too much cut off to start with, but it looks like the frame is made up of two lengths of tubing, with the OD of the inside tubing being tight on the ID of the outer frame tube.

I can't find anything that references this except a very brief blog post here...

http://www.chinonthetank.com/2013/01/how-to-cb750-rear-frame/

I tried to get a chisel on one, as per the advice in the blog, and see if anything happened when I hit, but it's pretty determined to stay in there. I'm not even sure how far it goes? The only other idea I have is about making a small cut around the frame half an inch in and knocking off the outer frame tubing to expose the inner?

Does anyone have better ideas on how I could get it out?

 

[Wendelspanswick]

Why do you need it out?

 

[scotto75]

Sorry, I'm welding a loop that is the same OD and ID as the outer frame and I want to use an insert/slug that goes a couple of inches inside the frame and the loop tubing. The plan is to drill a hole in each side and plug weld, before welding around the gap. I want to get the inner tubing out so that I can get the slug in.

If I leave it, it means that the ID of the frame is much thicker than the loop I'll be welding, and I would have to make an insert that could fit in two different IDs.

Hope that makes sense?!

 

[Wendelspanswick]

I would drill it out in that case, you could judge the length of the insert by using a length of welding wire with a small hook bent on the end and feeling for the end of the insert.

 

[Seadog]

Sorry, I'm welding a loop that is the same OD and ID as the outer frame and I want to use an insert/slug that goes a couple of inches inside the frame and the loop tubing. The plan is to drill a hole in each side and plug weld, before welding around the gap. I want to get the inner tubing out so that I can get the slug in.

If I leave it, it means that the ID of the frame is much thicker than the loop I'll be welding, and I would have to make an insert that could fit in two different IDs.

Hope that makes sense?!

I would suspect that the inner tube goes in at least as far as the bend and may well be plug welded itself. Have you slipped a length of metal coat hanger, with a small hook at the end, down the tube to see if you can determine how far is does actually go?

A stepped plug wouldn't be too much of a problem to make otherwise.

 

[scotto75]

A coat hangar with a hook... of course!

The blog post says that Honda just used it as packing for the pinched ends of the frame that I've just cut off. If it doesn't go too far into the frame, maybe I could make a stronger version of the coat hangar and hook.

I wasn't sure that if I made a stepped plug, I would effectively have three layers of tubing at the point where I'm welding and wasn't sure if this would be a problem, as my welder can only happily deal with 2mm, 3mm with some prep.

I thought about straight butt welding it, but had just read lots of posts on other forums claiming plugging was the proper method.

 

[outofthefire]

It could have been from a previous repair and is probably plug welded in so i'd drill it out. Generally if your joining tube on a bike, plug it with tube, with the same wall thickness as the outer tube and radius the ends of the plug. Plugging it again could make it the tube crack where it goes back to a single piece of tube.

 

[Chris Stevens]

Purpose of double wall tube I would guess is to add strength to shock mount area. Not a great idea to remove it at all really. I would guess that unless your new frame loop has to take quite a lot of weight, butt welding directly to existing tubing, or reducing one end of you slug on a lathe would be a better idea.

 

[pedrobedro]

Cut a step in the tube and one in your piece you are welding on so you get like a half lap joint which takes you past the piece with the insert and gives you more weld area.

 

[addjunkie]

I agree that the double tube is to add strength for the shock mounts. Old kawasakis used to do that.

Why is the new part your welding on thinner than the od of the frame, will that not look odd.

Id machine a stepped slug. Or use the same od as the frame and go with the lap joint idea above.

Ive cut up a few bikes in my time, each time i do it, it always amazes me just how thin and poorley stuck together some of them are.

Drill before knocking in your slugs, two holes in each joint at 90 degrees to each other, then plug weld then. Also prep the jube ends, at 45 degrees not a straight but. I usually pre heat the joint too, before welding.

 

[Chris Stevens]

Most older bike frames are cheap ERW tube, and to be honest this works perfectly well, also easily joined with MIG welding. Old Brit stuff was in the main also heavy gauge ERW, but most often joined using hearth brazed lug system, with tubes held into the right place with nails. No real point in messing with slugs or scarf joints on a rear loop, unless its intended to take far more weight than it would have originally.

 

[addjunkie]

The main advantage of the slug for me, is keeping it all nicely lined up. Lets you twist and wiggle it, then weld in the hole. If its wrong just drill it out, till its right then fully weld.

Common when triking, hard tailing and stretching down tubes.

I bought an old bonnie yesterday, I may have a mess about with that in the near future. Once the que of projects in front of it recedes

 

[scotto75]

Thanks for all the advice. It's been a great help getting some focus.

The frame wall is pretty thin. I won't be removing anything if it's providing strength to the shock mounts.

The loop is the same OD as the frame tube so should look good when the weld's have been ground down, as long as I don't balls it up too much. It's the ID that's different and I was planning on using a slug for the exact reason that adjunkie mentions above.

I really like the half lap idea. Saves machining a slug and if I can cut it accurately enough I'm hoping it should be possible to clamp it in the right position.

 

[scotto75]

Sorry... what bonnie did you get addjunkie?

 

[addjunkie]

78 t140 thing, no where near standard, its a project bike, to go with my t100 project bike and my shovel head project bike. I like projects.

 

[addjunkie]

Heres one i fixed a while ago, got it free as a non runner, fixed it up, made it run, gave it to a bike club to raffle for charity. They raised 1200 quid from it. Guy who won it, then sold it for 800 quid. After having bought his ticket with his last pound.

 

[scotto75]

A seven fifty twin? My lockup neighbour has a brownish '71 t100. I said I'd have it off him if ever decides to sell, but it's immaculate I'm sure it's out of my price bracket!

The irony is that as soon as I start a project I want to finish it, but then I have no project to do. Maybe having several on the go is the solution

Nice work on the Z550. That's a lucky guy, even if he did sell it!

 

[scotto75]

Also prep the jube ends, at 45 degrees not a straight but. I usually pre heat the joint too, before welding.

Sorry, just to clarify... Do you mean I should give both ends a beveled edge? Thanks

 

[addjunkie]

A 45 degree champher, so that when you weld the joint it picks up the slug too. Also when you then smoth the outside with the flap disc there is some weld left to keep it all together, when your other half and camping gear are behind you.

An imaculate t100 wont be cheap....at a guess 3 k possibly 5 or 6. Plenty advertised at daft money, but it doesnt mean they sell for that. Sad but true some are worth more as bits, and get broken.

 

[scotto75]

Thanks addjunkie! That's great advice which I will definitely follow.

Oh, I made a typo. It's a T120, but still a few grand all spotless and shiny. I like knackered rusty bikes that need welding and electrolysis! No fun just polishing chrome