Diff'rent Strokers

arlurt · Posted: Thu Apr 16, 2015 2:56 pm Post subject:

The ‘crosser probably had ten inches of wheel travel on that swing arm and shock, there’s nearly four inches of travel on the shock itself. The CBR has under five inches of wheel travel with a little over two inches of shock travel. With the CBR shock fastened to the ‘crosser swing arm, moving the swing arm through its expected range of travel from full droop to full compression (where the wheel is close to bottoming out on the frame) looks to use all of the shock travel, and therefore all of the spring rate. That’s why I think it’ll be OK.

I need to mock up a load bearing top mount for the CBR shock, stuff the back wheel in the bike and bounce up and down on it to confirm that what "looks OK" so far is actually a practical proposition. I’ll break the welder out over the weekend and chop up some steel box that as a first attempt will pick up the exiting (MX) shock top mount and extend this to hold the top of the short CBR shock. It'll be a good ide to try to make it adjustable for ride height and shock angle so I can experiment a bit.

If it works then I have to make spacers and top-hat bushes to mount the (small bolted) CBR shock to the large bolted swing arm.

You're right about the "shocking" difference between the MX shock and the CBR one, but there are good reasons for that. The MX shock is re-buildable, and has to work really hard over rough ground and jumps to control and bike and rider giving rock all. The CBR road shock doesn't have to dissipate all that much energy because it's running over smooth roads, and is built to be sealed for (an easy) life.

I’m still pretty confident it’ll be OK.
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Gillinghampaul · Joined: 15 Aug 2012 Posts: 655 Location: Kent

Can i be cheeky and ask what the eye to eye measurement is on that cbr shock?
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arlurt · Posted: Sat Apr 18, 2015 3:11 pm Post subject:

I think it was 260mm Paul, I'll check when next I go down to the bike. That's the figure that was mentioned in the eBay listing.

I've had a look at what's needed for the shock top mount this afternoon. That's about where it needs to sit, and I've found an old 3XV top mount that will allow me to have some ride height adjustment, either with spacers of different length, or a couple of nuts.

The first rough-cut of the bracket to fasten the top mount to the frame is coming on.

This will be welded between the frame rail that carries the top-rear engine mount (visible in the first photo to the right of the top of the shock) and the top mount for the old MX shock that sits between the frame top rails just behind the tank.
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arlurt · Posted: Sun Apr 19, 2015 7:53 am Post subject:

This is a good idea:

All of the connector shells and crimps you need to remake a KH250 loom. Mine is pretty ratty, with some of the connector shells missing and some cheap/nasty crimps. Rebuilding it with this would make the bike more reliable and let me make the wiring changes I need for the re-located horn, different brake light switch, and for the other wiring adjustments.
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arlurt · Posted: Sun Apr 19, 2015 12:17 pm Post subject:

With the shorter rear shock, and new top mount, I can use the original battery box again. This also carries the regulator, rectifiers and flasher units which is useful as I'd otherwise have to make brackets for them all. Only problem is that the battery I have is a sealed lead/acid unit that's slightly bigger than the battery box!

I know the battery is up to the job because I used it when the bike was last on the road, so I'll mod the battery box to take it. Spot welds drilled out and here's my source of parts:

A bit of steel origami to take the bigger battery and then I can weld it back together.

I'm starting to understand why some people who aren't in to bikes stand about in a field for hours watching 22 other blokes kick a ball backwards and forwards. That might be more enjoyable than wire-brushing rusty old steel and modifying things for the sake of it.
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arlurt · Posted: Sun Apr 19, 2015 1:55 pm Post subject:

Now modified to fit around the bigger sealed lead/acid battery. You get the idea...

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1975-S1C · Joined: 25 Feb 2013 Posts: 22 Location: Bristol

Hi Karl,

Kojaykat that you are buying your wiring connectors from also does a very good A3 size colour laminated wiring diagram, for a few quids. I bought one for my S1C. Cheers, Paul

arlurt · Posted: Tue Apr 21, 2015 6:27 am Post subject:

I dragged the welder out last night and tacked the modified battery box together.

There's still a bit to do when I decide how high to mount the battery, and to close off the last joint. Then a spalsh of paint.

Once this is out of the way I'll get back to my other welding job, the rear shock mount.
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Cal · Joined: 20 Dec 2012 Posts: 62 Location: Bristol

Great progress mate. Much more than me!!!!

I have just got home from work, absolutely knackered.
We are a bricking it at the moment as the bosses have said 1/3 off us are out the door soon. Restructuring.
My mind really isn't on the bike.
I need some garage time. That will help me focus.
Hopefully at the weekend.

arlurt · Posted: Wed Apr 22, 2015 6:45 am Post subject:

Hi Cal,

Sorry to hear work are messing you about. Good luck with the restructuring.

I look forward to seeing anything you manage to do on the bike.
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Cal · Joined: 20 Dec 2012 Posts: 62 Location: Bristol

Thanks mate.
Sorry I downloaded there.

I'm going to try and get to Stafford for a bit of retail therapy Very Happy

arlurt · Posted: Fri Apr 24, 2015 6:51 am Post subject:

It's been a busy week, away from the bike unfortunately, but I found enough time last night to finish welding up the modified batter box. Next step is to take it to the bike and see what has to change on the battery box mounts to make it work there and to confirm it clears the new rear shock top mount.

I'll measure up the eye-to-eye CBR125 shock length too. I haven't forgotten...
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arlurt · Posted: Fri Apr 24, 2015 5:03 pm Post subject:

CBR125 Rear Shock is 260mm long centre to centre of the eye-bolts.

Eye bolts are 10mm Diameter, and eye-bolt bushes 25mm long.

The CBR125 Rear Shock is not a bolt-on replacement for a 1976 KH250.

Hope this helps...

I've brought the rear shock, bottom linkage and bolts home so I can make the spacers, bushes and bolts needed to fasten the CBR shock between the Suzuki MX swing-arm and the KH250 frame.
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Gillinghampaul · Joined: 15 Aug 2012 Posts: 655 Location: Kent

Thats perfect thanks Very Happy

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arlurt · Posted: Sat Apr 25, 2015 12:31 pm Post subject:

It is 260mm long, don't know why I typed 250. Brain fade...?
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