'79 XS650 caliper piston, brake lines, engine numbers and other ramblings...


XS650 Enthusiast
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North East USA...
Hey all,
Happy Thanksgiving...

Is this too soon to replace...? o_O


So I pulled the front caliper off the '79 650 to install a rebuild kit that I bought a year ago... can't rush these things ya know. lol

It all came apart ok, the seals and retainer went on easily enough, but the piston was just a little pitted on the very end, against my better judgement I put it back in but I think I'll find a new one.
On a quick search I did not find a new one for the '78...

I continued to assemble the caliper and put in some new fluid to see if I could pump up a decent brake anyway. Not happenin'

I then took a look at the hoses... Wow. Original, just wow..! I had come to learn when working on the '69 VeeDub that old hoses can collapse and subsequently a brake caliper would not let go. So, I figured that was what had happened here, plus the sticky piston.

Another quick look and I was hoping to find a "Kit" of new lines, upper and lower... No.

Should I be looking somewhere special to find these parts...?

Oh, BTW, the Frame # is 2F0 021231 and the only Engine # that I find is 4M4 - 004426. These things do not have numbers that match...? The engine number was found on the right/front of the engine, stamped vertically, just under the cylinders.

Sorry for the ramble...

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It can be tricky to get the pressure back Keeeeeee ..pppp on Pumping and it will most likely come
Can take loooong time .. I suppose there are tools available. But with patience i belive it happens
Brakes is a safety item. ,But I dont think I would change much hoses or so.
Best way I've used to bleed these brakes is to remove the caliper, pull the piston all the way out, fill the caliper with fluid and push the piston back in. That forces all the fluid... and any trapped air up out of the reservoir.
Brake lines are plentiful and cheap on Ebay. Get the aftermarket braided stainless one.
Pistons also readily available over there.
Yes, for the most part frame and motor numbers matched out of the factory. Sounds like yours has been swapped out.
Well re: caliper, you can have the brake hose on, the caliper off the bracket, push piston in just far enough to engage on the seal. Start with an empty MC reservoir. Now pour brake fluid in through bleeder port, replace bleeder, Push in the piston, slowly,. Use a c-clamp if needed. install caliper.
A squeeze bottle makes this easy.
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Once assembled and bled, the piston doesn't move much. So, you can have pitting on it as long as it's not on the section that moves through the seal. But if you do replace the piston, I recommend getting a stainless one. They only cost a few dollars more than the original chrome steel type and they will never rust .....


Most of us replace the 2 original lines with one long single line. It simplifies things and eliminates that splitter mounted on the lower triple tree. As mentioned, lines are available on eBay dirt cheap, less than $10.
Hey guys,
I am usually pretty good at rebuild kit for calipers and bleeding, but I was somewhat concerned about the tight-fitting piston and should have stopped right there.
I'll pull it back apart and check for whether it is stainless or not, prolly now as it is pitted...

@gggGary and @Jim
Liking the idea of filling the bore and pushing the piston in to move the fluid up to the reservoir, I'll give that a spin. I have a small syringe to use or filling.

Yup, good idea to make one line vs the two. I come up with ~ 32" from the master to the caliper with decent sweeping ends. Is that a good length do you happen to know...?

Frame & Engine Numbers:
Can anyone here tell me what I have for an engine with the number 4M4 - 004426...? I do not find that numbering convention Anywhere in the charts.
And am I looking at the actual engine number or where would that be located...?

Thanks much, all.

Ooops, I found the engine in question. It is from and 80-81...! Well, makes me wonder what happened to the F engine...? Not a big ta-do, it runs great.
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The engine not being original isn't really that big a deal unless you're planning a restoration or otherwise worried about the dollar value.
The smile value is unchanged. :wink2:
32" from the master to the caliper with decent sweeping ends.

lay it out with copper wire, length needed depends on what handle bars you have.
Many of us like the 11mm MC from some later model Yamahas to greatly improve brake feel. Early disk brakes had VERY conservative hydraulic ratios, that lead to high lever effort.
Search fleabay, use (xt225,tw200) master cylinder
They are plug n play into your brake handlebar mirrors brake switch best to use the lever from your old MC.
sometimes you can snag a nice one for less than $30.00
hotrod resto 006.JPG
I run slightly lower than stock Euro handlebars and a 90cm line (just over 35") is perfect .....


That may be about the best you can do. Most sellers sell them in 10cm increments and an 80cm line would be too short.
I run slightly lower than stock Euro handlebars and a 90cm line (just over 35") is perfect .....

View attachment 230655

That may be about the best you can do. Most sellers sell them in 10cm increments and an 80cm line would be too short.

Standard US variant bars and I like them actually. I have been finding a 37" stainless line that would be nearly correct, a little shorter would work but hey, is what it is.
Plus, I'd rather the line not have the fittings anodized in blue but whatchagonna do...? :rolleyes:


There are lots of sellers on eBay and I think some do offer a 95cm (37.4") line.
The only issue I've had with the eBay lines is if I try to fit one to a stock type MC with the line connection on the end. This needs a line that has the ends affixed 90° to one another or it puts a pretty bad twist in the line. All the eBay lines I've gotten so far have the ends affixed parallel to one another. That works fine if your MC has the line attached to the front like so .....

I also recommend drilling your disc. Not only will it perform better, it just plain looks cool, lol .....



This is my '83 and after a few seasons, I've got it looking about how I want it. One of the first things I did when I got it was swap an 18" wheel on the back because I heard they handle better. Well, I found that isn't true. I put the 16" back on, tentatively just to wear out the almost new tire that came on it, and found I like the look and ride better. So, I'm going to stick with the 16" out back (mostly). An 18" will probably go on from time to time (when I do work on the 16").
The master I found and ordered has the same exit as the one pictured.

That rotor looks great. I would love to drill the rotor but, Man, that is a ton of work. Maybe if I had a template for the pattern I could do it here with the drill press that I have but... good winter project.
US 1981, would have had TCI ignition and BS 34 carbs.
The line starting XS-SH (US)

So this must be the 1980 issue.

While waiting for brake parts, I pulled the two covers to have a peek and found the advance mechanisms on the right side and points on the left.
Runs great, I'll leave it alone... for now. ;)


The last year for points was 1979. 1980 got TCI.

Well, the plot thickens... Do any of you folks know of mis-matched frame and engine numbers or the use of the next generation of an engine series having been installed a previous year model frame...? Or do frame and engine numbers Always match from the factory...?

Of course, this could simply be a situation where the person that swapped out the 4M4 engine also replaced the TCI with the points plate. Odd.

Little confused here.
If the pics in post #11 are your bike then what you have is a 1979 Standard model, last year for the Standards and somewhat rare.