Engine rebuild advice needed

Muckroot

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Hello all, I am new to the site and this is my first post. Please forgive any formatting errors.
I recently purchased and tore down my very own 1975 XS650B and I have some questions regarding where to go from where I am at. I currently have the engine completely apart, and have a shop that can do work on the bits before I re-assemble it. My main goal with this build is to produce a bike that is reliable and will run strong for many many years to come. I do not care so much about power output beyond stock numbers, as this will be a cruiser bike and longevity is more important to me than speed.

Firstly, if money is not a factor (money is definitely a factor lol) What work could I have done on the engine? what work is worth doing? I do not plan on having the engine rephased as that is definitely out of my budget, but at a minimum I am planing to get a PMA kit, replace the rings, hone the cylinder, lap the valve seats, and replace any bearings or seals that look worn or are out of spec. I am planning on keeping the points and mechanical advance ignition system, as it seems to offer better serviceability in the long term than an electrical unit. I also plan on keeping the electric starter for easier starting in the winter and on very rainy days. I'm also going to get TC bros Mikuni carbs and have open pipes, but I don't know if that affects any of the decisions I need to make about internal engine components. I am on the fence regarding porting and polishing the heads, replacing the cam for non-stock valve duration, and having the cylinder bored up one size for slightly better power and compression.

What other options do I have beyond these things in terms of parts to replace/modify or work to have done on the engine?

Feedback on any of the paths I've chosen is welcome.
 
Flatslide mikunis are money better spent than roundslides. I'm not sure why roundslides have proliferated a flatslide isn't that much more money and is a better, more responsive carb.

I'd do first overbore, about 11:1 compression on a rebuilt and welded crank. Basic head work. Ain't gonna use a starter with that kinda comp but it's cheap power and will still be reliable on premium. If you set the points wrong the kicker can wreck your day.

You want cheap hp just saw off all those dumb brackets Yamaha put on. Ditch turn signals, fugly seat, mega battery box. The starter is one of the most effective weight reduction mods.

Top it off with a 36 tooth rear sprocket and run light to light with much faster bikes. There is power in gearing.
 
Thanks for the info! I have a few clarifying questions; What does a welded crank mean? I am thinking about sending my crank off to Hughs to have them rebuild it because one of the needle bearings is wonky, but I'm not familiar with "welding" a crank. Also, Thanks for the info about overboring, it will give me the perfect excuse to get all new wrist pins, pistons, clips, and rings so I'm happy to do that, especially if it makes the bike start more reliably. I hadn't considered weight reduction but getting rid of both the starter motor and the heavy battery sound like a no brainer, so that's on the list. and I'm definitly planning on getting rid of as many brackets as I can.
 
Welcome to the party, Muckroot! You've landed on the greatest resource for everything Xs650 the world has to offer! You have questions? You'll be able to find answers. However, I have a few questions for you. Can you send some good pictures of your '75? (I have a soft spot for the '75. It was my first, still working on it - "The Basketcase") We love pictures here (and we're nosy! :wink2:). What kind of shape is it in? Was it complete? Was it a "barn find", or somebody's failed project you bought in boxes and bins? Was it running when you bought it? Do you have any experience with motorcycles mechanically? It's not necessary, but it helps. Do you have a manual(s)? These all go a long way to getting your motorcycle sorted out without a lot of unnecessary expense. The whole "Tech" section (see above) is a must-read and will answer a lot of questions. I hope all this blah, blah, blah helps rather than discourages you. Best of luck, keep us all updated. Cheers :cheers: and again, welcome!
 
Thanks for the welcome! I can absolutely send pictures! When I bought the bike it did not run. I found it through craigslist, the owner was selling a hardtail kit for the 650 and I emailed him wondering if he happened to have a bike to go with the kit. He said he was planning on keeping the bike for a future project, but was willing to sell it for a fair price. I think I got a wee bit skinned, but I was desperate to get my hands on an XS650 and this bike fit the bill perfectly. The guy I bought it from was a real old school chopper builder who was living in a hud house with an attached garage that had a sweet XS650 on a big lift that he was working on. He had about 14-16 semi complete bikes all over his yard, including everything from a few big twins to little vintage 2 stroke bicycles.

I have a little bit of experience with motorcycles; meaning I rebuilt a 1974 hodaka road toad over last summer and had a blast. actually made money when I sold it. it didn't run when I bought it either haha. ended up being a blown up left crank bearing. cost me the small fortune of 17 dollars to replace!

the first things I purchased for this bike was a clymer manual, an engine stand, and a mag puller tool from tc bros. there are already greasy fingerprints all throughout the manual lol. on to some pictures!

This is what the bike looked like sitting in the shop where the owner had staged it for me to have a look. the red is from a can of spray paint the old owner was heating up on his wood stove because it was winter and of course it blew up all over the bike lol.
first contact.jpg

This is a picture of the bike on my trailer after I shook hands with the guy and forked over the 800$ cash. (I know, I know). His friend 'midget' came over to help heave it onto the trailer. put the back wheel and anything that wasn't bolted on into the trunk.
first trailor.jpg

This is a picture of some progress I made on the engine in the first few days. of course I'm rebuilding it in a tent in my back yard because the garage is full to the ceiling. top end came off pretty easily, but someone had clearly been inside this engine before, and did a pretty hack job of "repairing" some components. nothing too bad overall though.
IMG_8755.jpg

these are clutch basket bolts, and were officially the first part I needed to use this forum for help with. the use of some cheap Dremel disks and a cheapo impact driver and they practically spun themselves out.
cut bolts.jpg

Woe is me! a chip in the top half of the case, above the right most crank bearing. looks like a locating pin got a little spicy and decided to throw a fit. I'm really hoping a shop can fix this up for me good as new, and as far as I can tell this appears to be the only defect in the case.
case chip.jpg

Where I am now. the only major thing left to disassemble is the drive sprocket. I tried holding the clutch basket with one hand while setting my whopping adjustable wrench on the sprocket nut and hitting the end of the wrench with a hammer to simulate a big impact driver but it showed no sign of loosening, and I really don't want to damage to tranny gears. Don't want anything getting sassy on the highway later. Any advice on this is welcome. at the time of this picture I'd had the bike for a little over a week.
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Woe is me! a chip in the top half of the case, above the right most crank bearing. looks like a locating pin got a little spicy and decided to throw a fit. I'm really hoping a shop can fix this up for me good as new, and as far as I can tell this appears to be the only defect in the case.
That locating pin is for the outer crank bearing. Looks like the doofus who put the halves together didn't have the bearing slotted in correctly. You could actually get away with just J B Weld on that. Not much outward stress in that area if the bearing is located correctly. If you have a shop weld it, make sure they re-drill the hole so the locating pin stands proud the same amount as the others.
And welcome to the madhouse!! :D
 
That locating pin is for the outer crank bearing. Looks like the doofus who put the halves together didn't have the bearing slotted in correctly. You could actually get away with just J B Weld on that. Not much outward stress in that area if the bearing is located correctly. If you have a shop weld it, make sure they re-drill the hole so the locating pin stands proud the same amount as the others.
And welcome to the madhouse!! :D

Thanks for the info! I'll make sure to locate the bearings correctly when I reassemble. Hopefully the shop won't charge more than $20-30 to fix this chip.
 
More thinking on the locating pin.... it's purpose is to locate the bearing outer race correctly so the oil holes are open to the bearing. If it was ran that way, there's a possibility that bearing was oil starved. You'd best look for heat discoloration and/or wear on the bearing.
 
More thinking on the locating pin.... it's purpose is to locate the bearing outer race correctly so the oil holes are open to the bearing. If it was ran that way, there's a possibility that bearing was oil starved. You'd best look for heat discoloration and/or wear on the bearing.
Good thinking! I'm going to send the crank to Hughes for a rebuild as one of the inner bearings has come apart in a way im pretty sure it isn't supposed to. So they'll be able to say definitively whether that bearing needs replacing or not. But I've learned something new all the same. thank you!
 
Look in the classies here. A good used crank is prolly cheaper than a rebuilt one.
 
Hadn't thought of that, I'll give them a gander!
Thank you! Silly question, is the oil breather the bit at the top rear of the valve covers that I think connects to the vacuum barbs on the carb boots? what is done with these open breather barbs after the carbs and boots are changed over to modern ones with no vacuum connections?
 
Thank you! Silly question, is the oil breather the bit at the top rear of the valve covers that I think connects to the vacuum barbs on the carb boots? what is done with these open breather barbs after the carbs and boots are changed over to modern ones with no vacuum connections?
Normally the breather goes to the air filter box. Since I'm not running the original filters, I run it down to the chain for a little automatic lubrication. Look around the site. Lots of different ways to deal with crankcase venting.
 
Thanks for the info! I have a few clarifying questions; What does a welded crank mean? I am thinking about sending my crank off to Hughs to have them rebuild it because one of the needle bearings is wonky, but I'm not familiar with "welding" a crank. Also, Thanks for the info about overboring, it will give me the perfect excuse to get all new wrist pins, pistons, clips, and rings so I'm happy to do that, especially if it makes the bike start more reliably. I hadn't considered weight reduction but getting rid of both the starter motor and the heavy battery sound like a no brainer, so that's on the list. and I'm definitly planning on getting rid of as many brackets as I can.

The pressed together pieces of crank are welded. Cheap insurance if you plan on lots of beating on it. Might as well since you are doing a full teardown. Don't forget about a new camchain. A web camshaft grind is also a power boost and somewhat affordable. I'd opt for a digital ignition but if you are savvy with points it will definitely save you money. Xs650 is inherently reliable. A lower compression bike is easier to kick but with new mikuni carbs a higher compression bike is still plenty reliable once you "know" your kick starting routine for your machine. Just make sure your points are set right or you might need a cane to get around if it kicks back on you. l watched a guy sell his xs cheap because the kicker kicked him and he was scared of the bike afterwards. A high comp kick only bike qualifies as a man's bike imo.
 
The pressed together pieces of crank are welded. Cheap insurance if you plan on lots of beating on it. Might as well since you are doing a full teardown. Don't forget about a new camchain. A web camshaft grind is also a power boost and somewhat affordable. I'd opt for a digital ignition but if you are savvy with points it will definitely save you money. Xs650 is inherently reliable. A lower compression bike is easier to kick but with new mikunis carbs a higher compression bike is still plenty reliable nice you "know" your kick starting routine for your machine. Just make sure your points are set right or you might need a cane to get around if it kicks back on you. l watched a guy sell his xs cheap because the kicker kicked him and he was scared of the bike afterwards. A high comp kick only bike qualifies as a man's bike imo.

I'm guessing pre-ignition is the culprit of the kickback issue? the engine fires too early and forces the crank to rotate backwards and spin the kick lever into your foot/ankle/calf? what mistakes should I be sure to avoid when setting the points/timing the ignition to avoid the kickback? Also, on a 1 size overbore engine how hard is it really to kick over? I figure If I use good form by starting in a knee-in-the-seat position and then hoisting up and kicking down with full body weight on the kick lever it shouldn't be that much effort to turn the motor over a dozen times or so if need be. is this assumption correct? or will 11:1 force me to never skip leg day again?
 
I'm guessing pre-ignition is the culprit of the kickback issue? the engine fires too early and forces the crank to rotate backwards and spin the kick lever into your foot/ankle/calf? what mistakes should I be sure to avoid when setting the points/timing the ignition to avoid the kickback? Also, on a 1 size overbore engine how hard is it really to kick over? I figure If I use good form by starting in a knee-in-the-seat position and then hoisting up and kicking down with full body weight on the kick lever it shouldn't be that much effort to turn the motor over a dozen times or so if need be. is this assumption correct? or will 11:1 force me to never skip leg day again?

Yeah, too much advance. Or stock advance weights sticking....

Stock compression kick was lazy man quitter style. Long day at work throw your leg over the seat, choke carb, and a lazy kick or two. High comp and no lazy man technique will do. Gotta stand on it like you would a big twin. You can skip leg day tho, lol.
 
Hot damn! I'll be sure to start with the timing firing well after TDC and work it back until it's just right. hopefully that will allow me to get the bike into the proper timing with my ankles intact. Thank you for all the info!

Edit: clarification of terms
 
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If you want a cruiser as you said in post # 1 just rebuild it stock, change the oil regularly, do basic maintenance and hand it on to your grand kids.
 
Hi Muckroot. I'm seeing the pictures now. I'd check the frame and motor numbers. I don't know if Colorado issues a "title" when you register a motorcycle, but those alloy wheels were not '75 issue. It looks like the (dreaded) PO threw a bunch of parts together to make a motorcycle. I wouldn't be surprised if that's a '75 motor in a later model frame (or "Frankenbike"). Be prepared to fasten your seat belt and return your tray table to its upright and locked position, because it's looking more like that bike is going to need all new everything before you have a safe and reliable runner. :twocents: :popcorn:
 
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