So I'm building a thumper....SR500

[blackbetty]

Not an XS650.....but still cool if you like big singles....

Bought a pair of 78 SR500s, I'll be making a cafe bike w clip ons etc. Don't worry, it'll be cool....

One of them is bone stock engine but PO did a little frame tab shaving and added a godawful ugly rear section. I'm gonna pull the motor apart and check out the guts later.

In the meantime I tore into the other guy. This bike has 6K miles and at some point there was some moisture in the cylinder. It got a fresh 1st overbore and 88mm wiseco. Never run!

Anyway, regardless of all that, I'm gonna hot rod this motor just short of a stroker crank.

I've got the motor pulled apart and I'm splitting the cases. I'm not sure if I want to do a ground up build with this engine, replacing all the bearings and seals, or simply use the bottom end off my other motor. Here's my planned engine mods:

540 kit w JE piston
162 Megacycle cam
RD springs
Bronze valve guides
Minor head work + new seals
Megacycle hardened rockers
Vernier cam sprocket
VM38
Copper gaskets

Gonna be building along the lines of this that a dude in fort worth is building:

If anyone is interested I can keep up with this, otherwise I just wanted to let you all know what I was up to

 

[Downeaster]

I'm interested!

Had one briefly in the early 80's. Didn't keep it long, my first thought was that the power band was much more suited to a dual-purpose bike than a street bike and swapped it for a Honda XL500.

Had a TON of fun in NW Florida (stationed in Pensacola at the time) on that Honda.

 

[blackbetty]

Nice!

Yes, the bike only came w ab 30hp stock; hopefully my mods will help it pull a bit more.....wheelies.

 

[alfredo]

you've got a subscriber here man. keep it up.

 

[Inevitable]

Hey Blackbetty!

So those are the bikes you got? They look fun man!

Like I said the other day, if you need any help please let me know, I'm trying to gather as much information as I can.

I might give you a shout once we finish working out all the mechanics to my build, just to pick your head on the seat and other aesthetic parts of the bike.

**Oh and I found a starter so don't worry about that.

 

[jd750ace]

That's a Kim Kardashian tail section: Something just ain't right about the proportions!

 

[ReycleBill]

Someday I'm going to get me a big thumper for short hops 'round town and such. I look forward to seeing what you do with your's.

 

[blackbetty]

Wassup inevitable!

Yea man those are it! And thanks for reminding me, I meant to tell you I wasn't able to locate that starter; I think it got left behind in my old garage when I moved, ya know, I don't need those things!

I do have the reduction gears and a load of other stuff though. Let me know if you need a part or a hand.

JD750, I'm not set on that just yet. I'm building the motor up before anything else, I'll decide on the bodywork last. I'm thinking DT400 tank though and def clip ons, unless I have a change of heart and make a tracker style bike.

Since I drummed up a few replies, here's a few shots of the motor. For those of you unfamiliar, these thumpers are similar to the XS in it's overhead, chain driven cam. It's also an OIF design which is cool. There's all sorts of cool mods you can do to these engines. They also share the same 35mm forks and brakes as the XS.

Again, the motor I pulled apart had an overbore and 88mm wiseco. In pretty good shape with only 6K miles. I did find a broken starter stopper, but everything else looked good. PO was a hobbyist kayak builder so there was a decent layer of sawdust on everything. The bikes also have a CDI and a banshee type PMA charging system. Also, the cam sprocket simply bolts on to the end of the camshaft; none of that annoying cam chain breaking w these motors! The tab on the cam sprocket spins inside a kick indicator window so you know when you're at TDC compression. Motors came stock w a decomp lever.

Look at this piston, brand new:

Clutch guts shot unfortunately:

Broken starter stopper; common in these engines w the ratchet kickstarter and violent kickbacks. There should be an ear above the top bolt. It sheared off, maybe PO found it. Hopefully PO found it. Otherwise it's in the trans somewhere, but all that stuff spun smoothly.

Finally, the sump plate. Sweet jesus. What the hell is in there, I don't know, but it stank and I almost barfed. There's dead fly in there. Dirtiest part of the motor.

 

[5twins]

My 650 replaced my SR as my local ride. The SR is one cool little bike but the key word here is little. I like the 650 much better. I did minor mods to mine over the years - K&N airbox filter, Supertrapp, shocks, fork springs, steering bearings, S.S. brake line - the usual for my bikes .....

If I ever bring it back out, it will roll on spoke wheels.

 

[blackbetty]

5Twins I saw a post you made ab your SR a longggg while back and you said some positive things, I was hoping you'd notice this.

The biggest consensus I saw when researching these bikes was "I wish I hadn't sold it!"

 

[Yamaha_chop]

Sweet! I love the thumpers, I've got an XR500 engine sitting in my shop waiting for me to do something with it.

Right on man, Can't wait to see how it turns out

 

[Royboy]

SR's are way cool. I've owned a couple and plan to be buried on the one I have now.

 

[jd750ace]

My bud had a nice little mild cafe SRX a couple years back. It was kick only, batteryless, had (worthless) bar end mirrors, and had a DG exhaust made from the right side of a set off a RD350. Sharp little bike. He got it right in a horse trade, and sold it with about 800 bones profit to a hipster from his Vespa club.

 

[Tron]

I want a sr sew bad.

Subscribed!

 

[HAPPY DAN]

Interested, these look cool!

 

[blackbetty]

Yo Dan!

That was me that called you ab the brake parts, it's going on this build.

 

[pregrid]

Yup, sub'd

 

[stuntdouble]

Subscribed!

 

[Scrambled]

Lots of us XS owners seemed to have or still have SRs. I had two of them back in '79, I kept them till around '88 ,identical black '78s. I did the scrambler treatment on one of them , and it was a fun bike. The other one I kept mostly for the street. The previous owner had it bored out and stuff . There used to be a kit for them from a company called White Brothers performance , that's what was in it. I could do wheelies in the first three gears.

There has been one for sale on kijiji in the Toronto area that the guy made into a Norton Manx clone. * Update* The '79 with the Manx type fairing is still for sale on kijiji in the Greater Toronto Area (GTA) . Check it out, it has been up for sale a bunch of times in the last few years, he is asking $4800 for it.

 

[blackbetty]

Alright, been a bit since I updated this, but seeing as this is a 650 twin forum, I'll keep this build thread kind of condensed.

I've been working at a super steady pace and knocking out jobs. I'm also glad I got two of these machines, because I've found some surprises along the way, namely one of them being wrecked to shit.

I had originally planned on making a "cafe" bike, but I got real and decided to can that euro shit....so I'm gonna go street tracker, maybe something like a bike a Bond villain's henchman would be ripping around the city on in futile pursuit. It's gonna be a muscle bike with dual sport tires and riser handlebars. All my money is going into the handling performance and engine. Paint and all the fluffy stuff takes 2nd priority. So, I'll be using a wire wheel and appliance epoxy on this nearly everywhere.

So, moving on. Here's where I am with the frame. Shaved off the center stand mounts and unnecessary tabs. I've been using chemical stripper to get this to bare metal and it's a long process. I'll be hitting it with the wire wheel on my angle grinder this weekend. (sorry for the pics. Iphone and florescent lighting aren't good together).

The swingarm pivot was also seized in the frame. It took 3 hours to finally free it. I ordered a new pivot and the swingarm will be updated with needle bearings.

There's a few more pieces I may chop off, and an XS650 rear loop will be grafted onto the rear.