Topic: 1981 CB650 Caliper Piston

[zeech]

Mine are pitted and I need some replacements, but I can't for the life of me seem to find them. They are 38x38 and I can't seem to find that size anywhere. The only thing close is a GL1000 which is 41x38. Any ideas?

[MiGhost]

Lets start off by making sure we are working with the same parts, The calipers are different.
81 650 Std. single disc, wire wheel, or
81 650 Custom dual disc, comstar wheel?

Are you sure that the piston is 38 x 38, and not 38 x 35?
http://www.cyclebrakes.com/K&L%20Caliper.pdf

If 38 x 38. Here is a piston that will match size. Not sure about dust seal fit.
K&L 32-4184 BCP-305 38 x 38mm
SUZUKI
GS750ET /EX/ EZ 80-82
GS850GT/GX 80-81

http://www.ebay.com/itm/Suzuki-GS-850-GZ-82-Front-Caliper-Piston-Seal-Kit-/150875771671?pt=UK_Motorcycle_Parts_13&hash=item2320e59317&vxp=mtr

If 38 x 35
K&L 32-1168 BCP-102 38 x 35mm
HONDA
CB750F 77-80 Front & Rear

http://www.ebay.com/itm/Honda-CB-650-CB-Custom-S-O-H-C-81-Front-Caliper-Piston-Seal-Kit-/140821751481?pt=UK_Motorcycle_Parts_13&hash=item20c9a166b9&vxp=mtr

[zeech]

Thanks for the detail reply Ghost.

This is from a CB650C w/ dual front disc. I am positive they are 38x38.

This is the right part number though their measurements are off, I emailed them to confirm what they actually are. http://www.hvccycle.net/honda-cb650-cb750l-k-79-81-brake-caliper-piston-45107-425-003/

[MiGhost]

That part# is for the 79-81 650\80 650C single disc caliper. It will not work in the 81 650C dual disc caliper.

The correct part# for the 81 650C caliper piston is 45107-413-003

It sounds like the brake caliper, or forks might have been changed on your bike.
81 650C should be a lead axle fork

[zeech]

What a clusterflock I seem to find myself in. I can't believe I can't find a single one for sale in the new part number you listed. This sucks. Maybe the pistons were replaced at one point and the 38x35s will work fine. They seem to have more than enough seat depth at 38 right now.

[zeech]

They were air forks, and the caliper style matches another 1981 CB650C I have exactly. I just find it confusing that there doesn't seem to be a sngle Honda 38x38 piston out there...

[zeech]

Detail photos, maybe this will help...

[bryanj]

One of the Wing's has a 38 x 35 piston as well, got a new one in front of me and you can use them in a 500 four as long as the pads are not brand new as they have the dust boot groove at the top.

If the 413 middle part number is correct that is the same as a 400 twin from 78 to 80 so there should loads of used ones out there---hopefully in better order than yours

[fishtoft]

try David Silver Spares for P/N 45107413003

[fizzlebottom]

I went through something similar with my 82 CB650SC. I had to replace all 4 brake pistons, but none were available anywhere. Even eBay was showing nothing.

So I took the old pitted ones to a local machine shop, gave them the specs provided in the Honda Service Manual, and had them make me some brand new ones out of stainless steel. It cost a good chunk of change, but they work perfectly and will outlast me.

Keep that as an option, because you might drive yourself completely mad trying to find Honda replacements.

[zeech]

Here's an interesting observation. If I push the piston ALL the way into the caliper, if completely covers the input hole for the banjo bolt, there is no room for air space or to push the piston forward. Is that normal or more of an indication that I should be using a 38x35 rather than the 38x38? Thanks.

[bryanj]

Is this the case with the end of the piston level with the casing? if so its definately too long. Don't forget the farthest in it will go in service is the top level as the pad can't push it any further than the alloy casting

[trueblue]

http://www.davidsilverspares.co.uk/CB650C-CUSTOM-1981-USA/part_83773/

[zeech]

Is this the case with the end of the piston level with the casing? if so its definately too long. Don't forget the farthest in it will go in service is the top level as the pad can't push it any further than the alloy casting

Yep, that's with it level with the casting. I will source some 38x35s.

[trueblue]

38x38 is correct for your bike.  They need to hang out that little bit with the 650 calipers, if they don't you'll have trouble with your piston wanting to jam as your pad wears.  Here is another source for them. 

http://www.cmsnl.com/cb650pz_model8209/piston_45107413003/#.VDUCVhbTI3w