CB550F Double Disc's

[Trigger]

Sorry Graham but your wrong here. If the parts were identical then it would have the same part number, there are NUMEROUS examples of Honda using the exact same part on lots of different models but they still kept the original part number. There are websites dedicated to cross referencing part numbers, showing all the models that part number was used on. The 250N master cylinder was a single disc MC not a double disc,  if you look at the 400N (45500-443-614) which did have a twin disc setup it didn't use the same part number as the 250N (45500-442-612) yet they would have looked identical, yet they were designed to do a different job. So it looks like you put an MC onto some CX500 which if they'd had been in an accident, and it was blamed on the wrong one being fitted, you'd have been liable 

I'm not saying that sourcing where the parts were manufactured originally means your wrong to fit them as they don't have the Honda part number on the bag, clearly they are the same part, as such they are fine to fit. However it's wrong to assume that just because a part looks the same as another it's the same part with another part number, Honda just didn't do that, especially in the 70s.

I took on board what you said about part numbers would mean it was a different part but, i have 3 fuel tanks sitting in front of me: a CB550K3, part number 17500-404-670, a CB550F1, part number 17525-390-000 and a CB550F2, part number 17525-390-708. I have removed the paint code from the part number. All these tanks are identical in every measurement and shape.

[Bryanj]

They are identical in shape but are the stripes and badge fixings the same?

[Trigger]

Now you are getting it Oddjob. Yes, the tanks are identical apart from what is added to that part to give it a different part number. The only difference in the master cylinders was the brake light switch. And i think it was down to the manufacturer of the switch. One was made by Alps and the other by Mitzubi. Nothing to do with the bore size of the master cylinder  .
Engine parts are another story.

[Trigger]

Oddjob, you mentioned the 400N up against the 250N, not me. I was on about the CX500 custom. The part number for the piston/seal kit is different between the CX500C and the 250N (i can't explain why) But, as you say the piston may be longer.
All i can explain is we fitted the 250N to the CX500C with no problems.

[matthewmosse]

I thought one nice solution might be found on the bavarian wheelbarrows from the 70's, they put the master cylinder (easily capable of moving sufficient fluid for twin disks with big pistons - one of mine is running gt750 kettle calipers) anyhow, the actual master cylinder lives under the tank, with a cable operating it from the handlebars so you could get a much cleaner look to the handlebars. I think the gt750 calipers would probably have very similar fluid requirements to cb550 dual disk which work well of this setup, even when asked to stop a heavy bike, 100 kiloof sidecar and 4 adults  riding said contraption (with a drum rear brake on the bike  - no brake to the chair so lots to ask of a dual disk setup) Just a thought.

[Trigger]

Your confused Oddjob. I haven't a clue what you are going on about Mat. Are you farming magic mushrooms? Have seen a wheelbarrow with a brake but, that was in Bulgaria and Albania. Never seen one in Germany.

[matthewmosse]

Bavarian wheelbarrow - a rather odd nickname for bmw aircooled boxer twin motorbikes, sorry, a bit obscure.

[Trigger]

I thought you was on about this type:
http://www.youtube.com/watch?v=bqzu1_NqK_Y

[Ewan 500 K1]

could have been a Moldovian washing machine

http://www.youtube.com/watch?v=sMYRf5Ap72k

[matthewmosse]

I don't know who first refered to bmw boxer airheads as bavarian wheelbarrows, but for me that is what they will always be. They handle really well but boy are they an aquired taste looks wise and I found them disappointing quality / cost wise after a honda sohc4. I'm afraid being out in the sticks I may get better riding roads to go to work on then most but I cannt view the vids, just a plughole of doom loading icon.

[LesterPiglet]

This may help you Matthew. http://download.cnet.com/YTD-Video-Downloader/3000-2071_4-10647340.html
Lets you download and save youtube vids.