Topic: CB500 cafe build- rust to ride

[tennesseebreeze]

I started posting about this project under a different thread at first. I wanted to start a new one to show my changing ideas about the bike.

I bought a 73 cb500k from a guy on craigslist for $50. I'd been looking around for a four cylinder sport bike since inhaling the fumes from my friend's '74 550k, while I rode behind on my 78 cb400A twin. They aren't even in the same class, though the 400 did keep up okay. So I went to see the bike and though it was dark out, and the bike was in pieces (the guy was trying to part it out), I knew it was pretty complete and had the original paint and side covers. In short, I knew I wouldn't lose money. After getting it home and assessing the condition, I knew I was in for a challenge.

[tennesseebreeze]

My first idea was to just clean the thing up and ride it as soon as I could. I started by cleaning all the parts with Mean Grean, PB blaster, and a lot of scotch bright and steal wool. I found a number of problems. The upper triple tree is broken and the lower TT is bent where the fork tube runs through. I haven't found an upper yet for a reasonable price, so I'lll wait on that. The rear wheel was in a lot worse shape than the front, completely rusted with the sprocket and chain basically trash. The hub itself had mismatched bolts holding the sprocket, and over time these smaller bolts had worn the holes out. I could by a whole new wheel, which would be the smart way; but I'm stubborn and cheap, so I may drill them out and add a couple helicoil to it.

[tennesseebreeze]

Here are some more photos of the wheels. The fork tubes, sleeves and boots were in bad shape. I've since ground all the rust off the tubes and applied several coats of Rustoleum to them; not the chromed travelling portion, of course. I thought of spraying them with truck bed liner for more abrasion resistance, but I haven't decided. The fork sleeves are pretty bad off, but I may just try and coat those too.

[SOHC4 Cafe Racer Fan]

Buying a used wheel in better condition will probably be cheaper in the long run than having to buy new sprocket, spokes and rim, polish the hub, and reasemble.  You can probably get one on the cheap on craigslist or ebay.

[tennesseebreeze]

I can't seem to post any images now. Having trouble.

[tennesseebreeze]

There it is. I'll try again.

[tennesseebreeze]

The big challenge was the seized motor. After mostly reassembling the bike I tried to move it and discovered the engine was stuck but good. After some advise in the pages here I took the plugs out and poured a batch of 50/50 ATF and acetone down into the cylinders. After about 2 weeks of soaking I was able to free up the engine. It turns freely and sounds decently smooth too. The motor had a visible previous head gasket leak and was caked in oil, dirt, grease, etc. It looked more like a lawnmower engine. Here's some pictures after I cleaned some of the parts and stuck it back together.

[tennesseebreeze]

The PO, in trying to take it apart to make a buck had cut all the electrical lines, yanked off the plugs, and did general mayhem to the bike.

[SOHC4 Cafe Racer Fan]

The PO, in trying to take it apart to make a buck had cut all the electrical lines, yanked off the plugs, and did general mayhem to the bike.

That's unfortunate, but still a bargain for $50.  Be resolved to going through this bike thoroughly to make sure its brakes and suspension are safe to ride, along with getting it in running condition.

[tennesseebreeze]

Ah yes. It definitely needs brake work. I'm looking into replacing that rear wheel and most likely I'll be rebuilding the master cylinder for the front. As far as the suspension I got shiny replacement shocks from sohc4 member "alacrity", along with a bunch of other parts- cables, points cover, carb boots, sprockets (although the rear doesn't fit this bike). I bought replacement spedo and tach off of ebay (the ones I had were rusted out) and used the old housing and rubber dampeners. I'm going to get new bars, either clubmans or drags, and grips. I cleaned up and painted the seat pan and may make my own cafe seat. I've done a little quick Photoshop Fu and came up with a look that I might go for.

[tennesseebreeze]

This past weekend I pulled the motor, for which getting the oil filter was the biggest pain in the ass. I ended up having to grind off the bolt which I'll replace. $10 on partnmore.com. After seeing some of the builds on this forum, I was thinking of getting a vapor blast kit and using it on the motor. But after I used about a gallon of degreaser on her, I think the finish is in pretty good shape. Hey, she was only new once right?

[tennesseebreeze]

Here's the bolt.

[tennesseebreeze]

When I got the carbs out and apart I found a ton of lacquer in them, the slides stuck, and the seals all bad. I got myself a can of Chem Dip at Autozone. And 4 rebuild kits straight from Japan for $50 off ebay. They came in less than a week. It took me longer than that to clean the crusty things. Amazing. Here are the before and after carb shots:

[tennesseebreeze]

Parts from Alacrity in CA.

[tennesseebreeze]

Here are pictures of the tank. It has this hex head lock and of course I don't have a key. So I took a small socket and ground it down to size and gave it a washer handle. Tank is rusty but not too bad. I'm thinking of going the electrolysis route for cleaning it inside. I don't know whether to paint or preserve it's vintage flavor.

[tennesseebreeze]

Last night I managed to take the cylinder head cover off of the motor. I want to break into the head and replace the rings and lap the valves and such. Now, I've never done this before, so I'm taking my sweet time doing it. I bought a Craftsman impact driver which was a huge difference in quality from the Harbor Freight and not much pricier. It took a couple of hours to remove the bolts and screws from it. I was being pretty careful, trying not to hit too hard because of the relatively scant amount of metal around those screws on the cover portion of the motor. After getting them off, I gently tapped some wooden shims into between to separate it from the cylinder head. Here're the pictures:

[tennesseebreeze]

I managed to get the cylinder head off this weekend, after careful and methodical loosening of the nuts that hold it on. There was a lot of deposit on top of the cylinders and on the valves. The lower gasket pretty much disintegrated when I pulled it off. My next decision is whether to replace the rings on the pistons. 3 out of four of the sets, when seated inside the cylinder head have almost no gap at their ends. The fourth set, though, has maybe a .5mm gap on both rings. I'll have to get a feeler gauge to be accurate. Three out of four cylinder bores are perfectly smooth, while the fourth has discoloration and deposits. I wouldn't call it rust, looks more like burned up oil or something. If anybody has some input on how I should proceed, feel free to chime in. I'm new to this type of engine work. Can I clean that one cylinder without having to hone all of them? Can I save some money just getting one set of rings, or should they all be replaced? Or should I get them bored over-sized and get new pistons?

[calj737]

Always hone all cylinders. You're not taking enough metal to change the bore diameter if done properly, so no reason to exclude. If you do hone, probably makes sense to replace the rings on all 4 cylinders anyway. But not requires. Do keep them organized and associated with their original cylinder if you don't replace them.

[tennesseebreeze]

Thanks for the advise. I did keep them with the pistons they came from. Wondering about the ones with the gaps. Do you know what the gap is supposed to be on these rings? The manual I have says to measure them, but doesn't say what the serviceable limit is.

[calj737]

0.7" or 0.27 mm

http://manuals.sohc4.net/CB500/HSM500550_10.pdf

[tennesseebreeze]

I'm posting an update on my progress on this build.

I bought a new rear wheel on ebay that turned out to have an unuseable rim on it because of deep pitted rust spots. I got a partial refund- the hub is useable, which is what I needed, but hell if I want to go through relacing the thing to a new rim. I'd love to get new rims front and back, but they do cost.

I took my cylinder head to a machinist who turned me away because he thought recutting the valve seats would take too much metal off and give me problems with the tappet adjustment. I thought about just grinding down the end of the valves to make them shorter. I have no clue if that's a possibility.

I'm about to start cutting the frame to put on a stabilizing hoop on the back. I decided to go with less stock and more racer. I'll be cutting the front fender down and getting rid of the rear fender, getting smaller indicators and brake light, etc. I was inspired by a friend who builds late model racers. He gave me this sweet custom cafe racer seat that he thought looked to big on his build. You can see the seat in this Photoshop rendering I've been working on.

[slikwilli420]

This is so great. I'm in the exact same spot with an early cb500 myself. Rotted through,  hasn't run since who knows when. I will keep my eye on this. Please share sources for parts as you move forward.

[tennesseebreeze]

I got the carb rebuild kits from Ebay member cruzinimage_co. I checked and it looks like he doesn't have any right now. That's also where I'll be getting my piston rings. I got a lot of the engine parts, gaskets, spring clips, etc. from Bike Bandit. Another place to find parts for this bike for a decent price is partsnmore.com. Good luck with your build. I hope it has more luck than mine.

[tennesseebreeze]

It's been a little bit since I posted to my project feed. I've gotten a good amount done the past couple weeks. I found a machine shop to recut my valves and valve seats. I'm very happy with how that turned out. The guy was a real old school machinist. For $40 he checked the head's flatness, cut the valve seats, cleaned and recut the valves, and even shortened the valve stem to compensate for it seating a little higher.

[tennesseebreeze]

Here's a picture of some of the engine parts that I cleaned. Look sexy don't they? Next I'll be honing the cylinder walls. I got new piston rings that I'll be carefully installing (I broke one of the old ones trying to get it on the piston).