1980 CB750F for $180, modern suspension and upgrades for a cafe racer build

XS750AU said:

Hi Papinbrew
You are probably going to strip more than one thread on a project like yours! Bloody expensive to get a replacement casting every time, especially if it is an engine case. Suggest you try a Hellicoil to fix the thread. It means you need to drill out the hole, tape a new thread and screw in the thread coil (looks like a spring) and your done. The kits are a little expensive but from then you can replace many more threads. There are cheaper thread repair kits on EBay which are OK. The caliper is a good cheap place to start!
Good luck
Tim

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I'd considered it, but the piston is really siezed. I had it ultrasonic cleaned hot, the soaked with Kroil, and the piston wouldn't budge even with a C clamp. I'm considering the CB900F dual piston caliper, rotor, and brackets conversion. I might be able to get all the parts for just a little extra than a replacement CB750f single piston caliper. I had a friend stop by the boneyard earlier this week and he's got a whole cabinet shelf box full of Honda Calipers. I should be able to find one that's not stuck and give it the ol one two new rubber for you treatment. The helicoil kit is a great idea for other parts though. I've got broken exhaust studs that the PO left me to deal with, might come in handy.

Speaking of, when you get replacement studs, is it better to replace the whole darned set with Carbon steel/stainless, or just replace the ones that broke?

I have a ton of parts in very good condition from my build I'm looking to sell. If you're interested I have a full set of working brakes, along with the entire rest of the front end.

omgwtfbbq! said:

I have a ton of parts in very good condition from my build I'm looking to sell. If you're interested I have a full set of working brakes, along with the entire rest of the front end.

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AH man, where we're you two months ago LOL. I just picked up a caliper from the Boneyard that will work for me. Is your front rim in pretty good shape? I think mine has a dent on it that's unsightly but it's functional.

I'm not really sure what else I'll need. So far I'm doing aftermarket on a lot of stuff, and keeping other stuff OEM. Any recommendations will definitely be considered.

Edit. Oh I'll need a new front fender that's in good shape, mine wiggles and is not pretty. If I don't do a newer one that's solid I'll just cut the plastic off and leave the fork brace for aesthetics

Hanging out with my boys at the custom shop last night, I saw another CB750F in the lineup of work there. Asked a bit about it, and mentioned I was looking for an airbox. Turns out the guy was not needing his, offered him some cash but he said I can just have it. SCORE!

Getting a bunch of packages delivered already, gonna start treating the fuel tank and conditioning the rims with new bearings pretty soon. Still sorting out my workbench for the engine though. My boneyard guy told me that I shouldn't even touch the engine internals with my compression readings, so now I'm a little conflicted. I might as well pull the head to lap the valves and remove the carbon from the chambers, especially since I'll be pulling the valves to put the Viton seals in. Ugh.... I don't know. It's gonna be more professional to have the cases split for paint instead of leaving them. I don't know.

I'm thinking of a new exhaust system idea, instead of having the cookie cutter Mac 421 installed, I was thinking high scrambler pipes, that route into the empty space where the battery box was and exit just below the seats tip like a modern style sport bike, with a scrambler flair

Papinbrew said:

Hanging out with my boys at the custom shop last night, I saw another CB750F in the lineup of work there. Asked a bit about it, and mentioned I was looking for an airbox. Turns out the guy was not needing his, offered him some cash but he said I can just have it. SCORE!

Getting a bunch of packages delivered already, gonna start treating the fuel tank and conditioning the rims with new bearings pretty soon. Still sorting out my workbench for the engine though. My boneyard guy told me that I shouldn't even touch the engine internals with my compression readings, so now I'm a little conflicted. I might as well pull the head to lap the valves and remove the carbon from the chambers, especially since I'll be pulling the valves to put the Viton seals in. Ugh.... I don't know. It's gonna be more professional to have the cases split for paint instead of leaving them. I don't know.

I'm thinking of a new exhaust system idea, instead of having the cookie cutter Mac 421 installed, I was thinking high scrambler pipes, that route into the empty space where the battery box was and exit just below the seats tip like a modern style sport bike, with a scrambler flair

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You mentioned that you don't have experience opening a motor up, but from this entire build, it seems like you know your way around a motor. I say go for it. I'm on board for the rest of this build!

Question, would you guys pull the old bearings out of the rims, powdercoat/paint, then put new bearings in or will it matter?

I'd leave the old bearings in, get the wheels powder coated and then replace the bearings.

Parts have been raining on me, but its been too hot in the backyard to wrench. 105F!!! I also blew a fork seal on my Magna during an evasive braking manoeuvre... damn cagers. So ill be fixing that before i continue on the CB750F. Gotta have at least one good highway bike.

So far just waiting on the frame to get modded, its just sitting in the shop. Im contemplating taking the time and my angle grinder to the shop itself while theyre busy so i can say I personally did some fabrication. I want to clean up those gobby nasty factory welds, and detab the useless stuff.

I need some help finding the right headlights. I'm looking for those mini bubble projector style, do they come in LED? I want them to be pretty tough, and this new headlight I got from China is literally the epitome of get what you payed for.... somebody link me some projectors!

a grease gun is a one sure way to very easily remove a stuck caliper piston, you it the caliper cant argue with 10,000 psi
just gotta cobble together an adapter is all

xb33bsa said:

a grease gun is a one sure way to very easily remove a stuck caliper piston, you it the caliper cant argue with 10,000 psi
just gotta cobble together an adapter is all

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Yep, weld a zirc on the proper fitting and you are good. They usually don't fly out like when you use compressed air, but I wouldn't be putting my face near it either way...

Yep my piston is straight up stuck in the caliper. I'll have to try the welded zirc fitting if I can't find a MC to use and press it out.


In other news, I've been working on the fuel tank. I left vinegar in there since February, I should have packed it full of gas or rust dissolver. This is the worst tank I've ever seen, it's literally furry with rust. So, rinsed it out, added about 200 steel bbs, a bottle of CLR and shook it for two days on and off. Used my magnet extension to help get all the bbs out and rinsed. Still caked on rust so I went and bought a bottle of rust remover and it's been sitting in there about 24 hours, shaken occasionally. Going to just keep doing that until I can see some bare metal anywhere in there, then rinse and repeat again with another bottle of CLR. Once that's done I'll treat and line the tank with POR15.

Hydrochloric acid will remove ALL the rust very quickly. Minor rust will be gone instantly. 30 minutes tops if it was filled with salt water for 30 years. Not for the careless of faint of heart though. Requires complete submersion in a neutralizing bath afterward. I use a big plastic tote filled with water and a big box of baking soda. Cheap and effective. Swish with a quart of acid until bright and shiny. You can do a great deal of damage to a great many things including yourself so act accordingly. Empty acid. Rinse half dozen times with water and empty. Submerge in baking soda bath. Rinse another half dozen times and repeat baking soda bath and rinse. Empty water, add a quart of alcohol and swish. Empty again and close up all openings and add a pint of WD40 and swish. Empty and pressure test. I like POR15, but if it doesn't leak use it as is. If it has pin holes at the bottom from water sitting in the tank, the acid will expose them and you will have to seal the tank. If it does not leak after the acid, it doesn't leak and you will be better off leaving the tank bare inside.

Yeah hydrochloric acid is nasty stuff. I've got that rust reformer stuff in there now. Been a day so far, and I'm shaking it occasionally. I'd prefer to seal the tank, just one last thing for me to worry less about. I want it to be as perfect as I can get since I'm really rebuilding every part on the bike.

So I took my rims over to the shop, pulled the tires and the bearings from the rear rim, and wire wheeled the inside to get the crud out. Was gonna do the same on the front but turns out the PO had bent the fuck out of it, and then attempted to hammer it back. It's fucked. Scored a new rim from an 80 mfg date on ebay for $42 shipped, I'll have to swap the discs over. Nbd. Still in the process of moving roommates out, so my workspace is limited. Still struggling with that damned last caliper, I need to ask my guy to see if he can weld me a zirc on the bleeder, then I'll try the grease gun method. Unless the air compressor they've got can pop it out, but I'm kinda thinking that I might end up having to buy new pistons. I accidentally marred the outer edges with pliers trying to pull them. Hopefully they will buff out.

Not sure what my next step here is... I feel kinda stuck. Not only that, my fucking awesome GF just bought us a PS4 with Destiny, so I'm literally torn between binge playing destiny, and looking at my basket case wondering wtf I do next. Do you have any advice for an order of operations?

CLR is Lactic Acid and Lauramine Oxide (surfactant). It won't remove or eat rust from metal.

Not sure why you want to use hydrochloric acid when it also eats the steel. Phosphoric acid eats the rust and leaves the steel intact while also providing a protective surface from flash rusting. Because of how it reacts to rust, it has a knack for breaking surface tension that bonds the rust plates to the steel surface and make it much easier to separate in a tank. It's also much safer and is significantly less prone to contribute to hydrogen embrittlement like with HCL. Pickling of steel is done with hydrochloric acid in concentrations under 20% and it's done before processing, not after. Hydrochloric acid and steel also produces a salt mist which is extremely dangerous to breath by breaking down tissue in the lungs.

deviant said:

CLR is Lactic Acid and Lauramine Oxide (surfactant). It won't remove or eat rust from metal.

Not sure why you want to use hydrochloric acid when it also eats the steel. Phosphoric acid eats the rust and leaves the steel intact while also providing a protective surface from flash rusting. Because of how it reacts to rust, it has a knack for breaking surface tension that bonds the rust plates to the steel surface and make it much easier to separate in a tank. It's also much safer and is significantly less prone to contribute to hydrogen embrittlement like with HCL. Pickling of steel is done with hydrochloric acid in concentrations under 20% and it's done before processing, not after. Hydrochloric acid and steel also produces a salt mist which is extremely dangerous to breath by breaking down tissue in the lungs.

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TIL. What's that rust remover stuff sold at Harbor freight and walmart then? Rust reformer, or dissolver.... I remember instructions say it's good for soaking. It's been in that tank.for 2 days now, shaken occasionally. Next step is that POR15 starter kit, has 3 steps. A cleaner step, a treatment step, then the application. I think it sounds fantastic, and if it works well ill use it in my other bikes. This particular tank was just awful though.

You're probably talking about Evapo-Rust. I've heard nothing but good about it, but haven't used it myself. Their MSDS doesn't provide any chemical information except that it's a chelator and organic acid salt. Chelation is a process by which metal ions are bonded. I do an etching process which is a saline etch that essentially works off the same principals. It uses copper sulfate and table salt.

I have had wonderful results for years using phosphoric acid. You can adjust the concentrations as needed, but it's a common solution along with isopropyl alcohol to prep bare metal automobiles for paint. I've also totally cleaned out some pretty effed up tanks with it.

I've used evapo-rust and it is amazing stuff. Big fan of anything POR15... Another top notch product line.


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Evaporust is awesome. It's ready to use, non corrosive crap that you can POUR BACK IN THE BOTTLE and use again. It's pretty amazing actually. And it's biodegradable so you can pour it down your sink if you want and not have to worry about destroying the earth. It will tarnish certain metals and tools though, so be aware of that. We use it for some of my soldering tools here at work. The Flux beats up the tools and makes them susceptible to rusting with all of the water and flux we use on them. Toss them in the evaporust for a few hours and clean off, they look great. Some took a day or so...

Awesome good to hear, I'm going on day 3 now with Evaporust in the tank, now it's sitting upside down to treat the top of the tank. Which brings me to my next dilemma. Does anyone know where I can find a replacement cap and locking latch for my 80 CB750F? The cap it came with is just a nugget of furry rust, and the PO broke the lock on the latch.