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Author Topic: Project CB690 (KTM 690 engine in a CB550f frame)  (Read 8966 times)

Offline Rat_ranger

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Re: Project CB690 (KTM 690 engine in a CB550f frame)
« Reply #50 on: Feb 23, 2018, 10:30:12 »
Around washington it seems to average around $60hr for waterjet. 
Xs650

Offline goodoltup

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Re: Project CB690 (KTM 690 engine in a CB550f frame)
« Reply #51 on: Mar 05, 2018, 12:09:48 »
^^ XS750AU,
I received quotes for the following.
Laser cutting, qty 2 swingarm plates in 10mm, qty 2 engine mounts in 6mm, £95
Water jet, qty 2 swingarm plates in 10mm, qty 2 engine mounts in 6mm, £44
Frame tube, qty 2, £75, PLUS VAT
Frame tube, qty 2, £54.26

This being the case, I believe I will buy the water jet frame parts, as I am not concerned about the draft angle. The frame tubes are both the same, so I will buy the cheaper of the two.

Lots of snow here in England, maybe this weekend I will be able to get out to the garage and do some work!

Offline XS750AU

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Re: Project CB690 (KTM 690 engine in a CB550f frame)
« Reply #52 on: Mar 06, 2018, 03:53:19 »
Those prices are much better that we would get down under. Very reasonable.
“Engineering is the art of being approximately right rather than exactly wrong.”

Yamaha XS750-2D
Yamaha XS896
Husaberg FE550
Yamaha TT250
Yamaha IT200N

Offline goodoltup

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Re: Project CB690 (KTM 690 engine in a CB550f frame)
« Reply #53 on: Apr 01, 2018, 11:58:21 »
I have returned from a business trip in the US and am ready to get back to work. Still cold here in the UK though. Even if you can get the garage to a good temperature, all the tools and anything metal remains cold to the touch, and it really soaks into your hands. In the first picture, my boss has gifted me a heater, the type with a large electric coil in it, like a big hairdryer. I will put that up in the shop somewhere and duct out of the outlet and try to direct the air around properly.
Also in the picture is my new air compressor. Super cheap, but it is 10 bar and 14 cfm. Problem is, all my air tools have Milton Type M fittings, shown in the second picture. These fittings are 1/4" NPT, so I can't just go and replace all the fittings, as the fittings sold here are 1/4" BSPT. SO, I had to order a Milton Type M quick connect from the US, and I will use an NPT to BSPT adapter to put it onto my hose. A trial of the air compressor must therefore wait until I receive that.
Third picture is just a reference of how the garage is shaping up.

Offline goodoltup

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Re: Project CB690 (KTM 690 engine in a CB550f frame)
« Reply #54 on: Apr 01, 2018, 12:08:49 »
So I've been thinking about it, and I welcome people's opinion on this. I have to remove the original swingarm pivots, in order to move them. The only way I can see to do this would be to fixture the frame in a jig, align it with reference to the original pivots, then the pivots can be removed and the new ones welded in with reference to the jig. I figure I can make a frame jig fora couple hundred GBP, it just seems like a lot of work to go through for one operation. I could reuse parts of the jig to construct the swingarm, but a lot of it would never be used again. Is there any other way to do this?
I bought a swingarm from an FZR, hoping that maybe I could modify it work on this project. Upon inspection, however, I think it would need heavy modification in order to straddle the swingarm pivot bushing in the 690 motor, with the construction of new bearing assemblies on both sides. And, it would need some kind of solution for the axle, and the length and diameter would be different. I think maybe that I will just make a new swingarm from scratch out of tube or box section. Not sure yet.

Offline jpmobius

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Re: Project CB690 (KTM 690 engine in a CB550f frame)
« Reply #55 on: Apr 01, 2018, 13:47:56 »
I think there a couple of important issues to consider here, as usual they are competing difficulties.  First, as you have touched upon, is the original pivot point in relation to the engine.  The ideal pivot would be concentric with the output shaft/countershaft sprocket.  That of course is to make life easy for the drive chain.  This is very complex/expensive to implement manufacturing wise, so engineers place the pivot as close as practical that center.  There is an additional strong benefit to having the pivot actually be part of the engine case, as all the loads can pass directly (more or less) into the swing arm and not have the engine mounts/frame work as a middleman.  While moving the pivot back behind the sprocket center is undesirable, it's not too bad if it is very close and the arc the arm passes through is small, which brings up the second point.  Moving the pivot further back, say where the original frames swing arm pivot is, places it quite a ways behind the sprocket, and the resulting change in chain tension as the suspension works becomes unacceptable.

Moving the existing frame pivot forward also creates some issues.  If you move it to align with the engine pivot, you will be rather a long distance away from the existing frame.  That places the loads input from the swingarm on the end of a much longer lever and will likely add flexibility to the system, though how much and how real world important is hard to tell.  Increased likelyhood of vibration fatigue cracking also becomes something to consider.  Swing arm pivots are placed as close as possible to the frame structure for a reason - look at the originals.  Certainly relocating so far away will add some weight, but being coincident with the engine pivot would definitely be a plus.  Personally, I would have the aesthetics in mind as well - I think a lot of flat frame real estate in this area is not too desirable.

Discounting other issues with moving the engine back (fitment, weight distribution), you would ideally align the engine pivot with the frame pivot and alter the swing arm to fit in between.  Looks like you have spent some time figuring out where it is now so moving it may not be practical.  Also, looks like there is enough distance here to consider the wheelbase and tire clearance with potentially moving the swing arm so far forward.

If that is the case, I think the job will not require any sort of major frame jig.  Get the engine aligned exactly where you want it and mount it so you can get the swing arm fitted to it.  I've made temporary mounts on occasion.  Probably less trouble than you expect to fit the swingarm.  The thing to remember here is that swing arm rotates on a fixed, solid, structural frame element comprised of the through bolt, inner bearing races (or bushings), any sleeves or spacers (including the engine) and the two frame elements.  The swing arm is captured by these components and shimmed or otherwise fitted to eliminate any play.  With this in mind, and with the swing arm fitted to the engine and the engine in place, you only will need to build structure between the new frame mount and the existing frame.  I would think you could get this all mocked up with the existing swing arm mounts still in place, and use them as a benchmark to ensure all the new work is properly aligned.  Once you are certain everything is lined up, you can remove all of the existing swing arm mountings and simply tack weld new structure in its place.  Take the engine back out, put the pivot bolt and bushings, sleeves etc back in and tighten it down.  In your case, you probably will have to make a long spacer to replicate the engine, any spacers and bearings in the actual assembly.  With a bit of care you should be able to finish weld everything with out too much trouble.  There will be some distortion, but no more than you would suffer with a complete frame jig.
« Last Edit: Apr 03, 2018, 18:40:40 by jpmobius »
Mobius


On a long enough timeline, the survival rate for everyone drops to zero.

1973 RD350 Yamaha build  http://www.dotheton.com/forum/index.php?topic=66498.0

Offline goodoltup

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Re: Project CB690 (KTM 690 engine in a CB550f frame)
« Reply #56 on: Apr 05, 2018, 14:33:41 »
Hello jpmobius,
Thank you for your input, that gave me a lot to think about. I just quickly made a CAD model of what I think it is you are talking about. The frame in the model is CB400F, and the motor is a KTM 525, so it is representative only, this is not what my bike will look like. To be honest, this combination looks like it would actually work better than the 690 engine, but that is the engine I decided on!
- Image 1 shows the engine in the easiest position, no frame modification required. The swingarm pivot bolt goes through the engine and the swingarm. The swingarm would have to be constructed to straddle the engine bushing in this case. On the bike that I am building, I'm not sure this is possible, but I will check again. It does leave a LOT of space between the motor and the front frame downtubes, and it looks kind of funny. Also it positions the motor pretty high.
- Image two shows another possibility, which is the motor mounted forward of the original position. In this case, the original swingarm pivot would still be utilised, but the swingarm pivot bolt would no longer go through the motor swingarm bushing. This could make some undesirable geometries with the swingarm and chain. The original swingarm could be used in this case.
- Image three shows what I was thinking, which is positioning the motor forward a bit, 70mm, and creating a new plate that would be welded to the frame.

I will try and see if I can move things around and mockup the motor per Image 1 and see if looks alright.

Offline jpmobius

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Re: Project CB690 (KTM 690 engine in a CB550f frame)
« Reply #57 on: Apr 05, 2018, 18:14:39 »
If you still have the KTM swing arm, you can determine where the engine sat within the KTM wheel base and compare that to your new project .  I think that would be a big driver to help me decide where I wanted to locate the engine in the Honda frame if this were my project.  I would expect the KTM  to have steeper steering geometry and a more forward center of gravity that you will have a hard time reproducing in the Honda chassis without - well making it into more of a KTM chassis than a Honda and thereby spoiling the retro look I assume you are going for.  You have said the KTM arm is too long.  Can you say why?  I get the aluminum being a stumbling block if you don't have the capability to do the fab work, but it might be worth comparing those difficulties with those generated by using an alternative swing arm.  I am sure it would be quite long (and in general I don't like increasing a bikes wheelbase), but if you decide to move the engine forward to the current proposed location, how much too long is it?  Is it viable to move it forward to resemble the KTM's engine location?  That would certainly make the swing arm length ok (at least if you ask KTM!), but it might not be practical or good looking for your application.  That could also potentially cause a lot more surgery of the frame at the swing arm pivot,  but at least it would all be in steel.  And of course there would be at least some aluminum fab for the rear shock set up, but that would likely be fairly painless.  Certainly the swing arm is plenty robust for the twin shock conversion so all you will need is the actual shock mounts.

Apologies for adding complexity to a pretty straight forward endeavor.  I personally find it easier (not to mention cheaper!) to think a little more about something before having to build it (over!).  And, at risk making things worse, it is none too early to consider the overall balance you are shooting for, and getting comfortable with the compromises you will have to endure.  Since you are keen to end up with a bike you like to drive, keep in mind the limitations of the chassis you are using.  The Honda frame will thank you for retaining the twin rear shocks.  But be thoughtful when you consider changing the front end.  Most new front ends have very much reduced offset compared to the ol' CB, which will result in a much bigger trail number, which will noticeably slow down the handling which you really do not want, as it isn't exactly a switch blade to start with.  The cure would be to steepen the rake (like to whatever the new front end came off of). That very likely will input loads very much equally, if not more so disliked by the Honda frame than the reduced offset, not to mention adding all sorts of additional fabrication/design work.  (noting how ultra rigid the KTM steering neck to swing arm pivot connection is exactly like the Honda's is not!)  So consider keeping VERY (read identical) similar offset in the triples, similar wheelbase and weight distribution (read engine center of gravity - if you live long enough, I DO get around to the point!) if you want to end up with a bike with similar manners as the 550 - not a bad thing at all!  I'd bet if you keep the stock steering geometry and focus on the suspension itself and keep the wheel widths reasonable you will come very close to hitting your bulls eye for building a great driving "old" bike!
Mobius


On a long enough timeline, the survival rate for everyone drops to zero.

1973 RD350 Yamaha build  http://www.dotheton.com/forum/index.php?topic=66498.0

Offline irk miller

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Re: Project CB690 (KTM 690 engine in a CB550f frame)
« Reply #58 on: Apr 05, 2018, 20:49:01 »
Don't forget carburetion and air cleaner locations, too.  Where it sits in the frame, forward and back especially, effects both carburetor and exhaust.  It's always fun to be forced into trying different carbs based on how and if they fit into the frame.  My F650 was a special kind of puzzle to find a good carb upgrade that also fit into it's wishbone frame.

Offline goodoltup

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Re: Project CB690 (KTM 690 engine in a CB550f frame)
« Reply #59 on: Jun 01, 2018, 17:08:51 »
Ok time for some updates. I bought a Tig welder and have been using it for some projects. It came from Amazon and it was very cheap, £250. In fact, I bought one and received it, and right out of the box it was broken, LCD screen would not light up. But, upon reflection, it was the right model for the right price, so I decided to go ahead and buy another one despite the first one being bad. I received the second one, and it works great. It has a dial on the front where you can dial in the starting amperage, the ramp rate, welding amperage, ramp down rate, final amperage, etc. It really works well. My first project, after some initial testing, was welding some new mufflers on my CD175. I got some aftermarket slip on mufflers, but the diameter of the new muffler was 8mm larger than the head pipe, so I used the lathe at work to machine up a spacer. Then I welded the spacer to the head tube, and the muffler to the spacer. Came out real nice.
The welder will be used in this CB690 project to create the frame jig, weld frame tabs and things, and maybe even fab the swingarm.