Topic: My first bike rebuild. 1975 CB750 K5. **Update** Now a tall man's cafe project

[nate6]

Hello everyone!  This is my first of many post on here I am sure.  As of yesterday, I am finally a bike owner and not only that, I am also the owner of my dream bike, a 1975 CB750K.  Found this little beauty on CL after about 3 months of continuous searching for $350, haggled with the guy and ended up getting it for $300 and he wanted a 12 pack of bud light thrown in on top (never thought I'd buy my first bike with beer haha).  Its going to need a lot of work, but I hope to have it running in a few months.  Keep in mind I have never worked on a bike or any engine, but I am always willing to learn new things and luckily I have 2 friends that are willing to help me that have the knowledge I do not, both have rebuilt bikes.  When I got to it the rear tire was initially locked until we used some break release, not bad for sitting in a shed for 2 years. However, its still not rolling as nice as what it should be, but hopefully that all just needs taken apart and cleaned and lubed.  The next problem is that the kick start is not moving.  We aren't sure if this is because of the engine being seized (has had oil in it all this time and still looks good) or if its just the starter and rust.  Won't know until we can start breaking into the bike, which is being delayed while I am researching and reading up on everything I can.  The only other major things I can see is that the brake fluid is now solid so the lines will need replaced or cleaned, the  chain is very rusted and will probably need to be replaced, the carbs are so rough that it took effort to get the throttle to move, the front brake lever is not doing anything and moving freely so that will have to be addressed, and just needs a good old fashioned cleaning. 

If anyone has any tips or tricks on how to tell if the engine is seized or if its just the kick start I would appreciate it.  Read something about putting it in 5th and seeing if the rear wheel turns and something else about opening the cam shaft panel and seeing if I can turn it with a socket wrench.  Will be trying both out hopefully within the week. 

Also, if anyone has any suggestions as to what tools I will need throughout the process, the cheapest place to buy parts, and where exactly I should get started (other than just cleaning the bike up) please feel free to say. 

Please keep in mind with info that I feel that I am completely bike incompetent, despite all that I have read on this bike and just basic engine workings.  I have downloaded most of the manuals that are provided on this site and started reading. 

Thanks again guys.

[madmtnmotors]

Congrats! I am currently rebuilding my $300 special and documenting the progress here: http://forums.sohc4.net/index.php?topic=100352.0 . The engine may be easier to free up if you leave it in the frame and leave the drive chain connected to the rear wheel. Pull the spark plugs and squirt a 50/50 mix of acetone and ATF (automatic transmission fluid) into the cylinders. Put the plugs back in and let it sit for a couple days. Then, roll the bike into the driveway, shift the transmission up into 3rd or 4th gear and rock the bike back and forth using the weight of the bike and the rear wheel to try and coax the pistons free. I've had a 50/50 success rate with this method.

Good luck with the build and welcome aboard!

[Brian Barr]

Congraduations Nate6,
Welcome to the adventure. It's not uncommon in a bike that has been improperly stored, for the rings to be stuck, preventing the engine from turning over easily. I would suggest that you do not try to force things at this point as you may cause more damage. I would recommend that you remove the spark plugs and spray "SeaFoam" into each cylinder. A 3-5 second squirt should do. Loosely replace the spark plugs to keep any dirt from getting into the cylinders. Wait 24 hours and repeat the "Sea Foam" treatment.
After 48 hours the Sea Foam will have penetrated as much as it is going to and it is time to see if it has been successful. Remove the timing cover and use a 3/8 ratchet wrench and socket. CAUTION: rotate clockwise only. Otherwise you can deform the timing plate. (Yeah, I did that).  If you are lucky the rings were only slightly rusted to the cylinder walls and things will now turn over. If the engine turns over, do a compression test. This will tell you whether a top end rebuild is needed. Good to know before spending money on other things.  Best of luck. I look forward to you updates.

[madmtnmotors]

I would suggest that you do not try to force things at this point as you may cause more damage.

Remove the timing cover and use a 3/8 ratchet wrench and socket. CAUTION: rotate clockwise only. Otherwise you can deform the timing plate. (Yeah, I did that).

So you're suggesting trying to free a stuck engine by applying force to the puny 6mm stud behind the timing cover? 

 If you're going to use a wrench to try and free the engine then you need to remove the alternator cover on the opposite side of the engine (opposite from the timing cover) and use a wrench on the rotor bolt. The 6mm stud on the timing side can snap under the force of cylinder compression alone, let alone the force required to free stuck rings (yeah, I did that) then you've got a broken stud in the end of the crankshaft to replace. 

[nate6]

Okay well I will try one of these or all of these depending on the severity of the situation I guess.  It looks like either Friday or Saturday afternoon we will be finally getting underway and pulling things to start cleaning and fixing as we go.  What kind of Seafoam do you recommend? I don't really trust some of the guys at the automotive store around here as I am in a college town.  I found a deep clean one that I'm guessing will do the trick, but I figured I should ask first.  Maybe I'm just new at bikes or just new to this certain bike, but (and you can laugh all you want) I can't seem to get the gas cap to open.  I can't tell if its stuck or if its just something stupid I am doing.  Any advice on that one.

[nate6]

Alright time for a little update.  Got to start pulling some things apart this evening and checking some things out.  Pulled 2 of the 4 plugs out and couldn't get to the middle 2 with the tools we had at that moment.  Is there a special tool that I need for these or is it just a standard spark plug wrench?  Thought we might have to pull the valve covers off to get to it but we aren't 100% on that so I'm asking you guys (the experts).  I currently don't have the tool kit that these came with, but I'm thinking I'm going to order one here shortly.  Also, figured out the gas cap thing.  Felt like an idiot, but it took my friend whose been riding for years a minute or two so I didn't feel so bad.  Minimal rust inside the take, but will be coating it here in the next few days.  We pulled the master cylinder off and I have it with me to clean it up.  The small piston inside of it seems to be stuck in there.  Any recommendations as to what to use to clean it up and how to get that piston out to clean it?  Sprayed a lot of WD40 tonight and the wheels seem to be moving a little freer, but will still be pull a lot of that just to make sure.  Sprayed some WD40 into the 2 pistons I could get to and the kick starter seemed to be moving a little bit more, hopefully a good sign.  Will have some new pictures up in the morning with a little more detail. 

[nate6]

Tear down started this weekend.  I have to say, as someone who has never worked on an engine or torn one apart, I am in way over my head and have sooooo much to learn.  We did manage to drain the oil, pull the carbs, air filter, clutch plate, alternator plate, and just get a general look around some of the inner workings.  Not sure how the clutch plate and alternator plate came into the equation this weekend since I personally didn't think they needed to be pulled just yet, if at all.  But, when 3 people are standing and watching you work on the bike and throwing around opinions, its easy to get off track and confused as each one is telling you something different.  Oh well... Still haven't figured out why it won't kick (not shocking considering I was being told to tear apart the wrong side of the bike).  Anyways, still haven't managed to get the 2 center plugs out, any suggestions on that would be greatly appreciated.  Sprayed a lot of WD40 around and got a few things moving a little better than before.  Cleaning the carbs this week and probably ordering some gaskets to replace the ones we pulled this weekend.  So far the inside of this bike looks brand new, but I'm not holding my breath just yet. Here are some pictures....













Please ignore the giant oil spill on the ground. No one bothered to say "hey before you pulled the side panels, lets lay down some cardboard" or "hey, since you've never worked on an engine before, there will be a lot of excess oil stored in your side panels and you will probably spill it all over you and the floor if you start to remove it." haha.  It was cleaned up and is all good now. 

We did find something quite concerning though.  On the engine above the rear brake lever, there is this white residue that appears to have a film over it or is eating under some sort of coating on the engine.  Found something similar after we pulled the carb boots off the engine in the 3 carb port.  Thought it might be dried gas, but weren't sure.  Any thoughts?

[harisuluv]

Hmm one of the last stages of gas going bad after the lacquer phase is a white powdery appearance. I have never seen it outside of the float bowls though so it's hard to say. If that is old gas and taking into account the bike wasn't stored properly (probably never drained the bowls) it's probably not going to be pretty once you get the carbs open.

I know you are probably eager to get into the bike and make visible progress but sort out the important stuff first. You need to get your engine moving again.

[nate6]

Yeah I figured the carbs weren't drained before storage.  The guy that stored it drained the tank, put in new oil, and removed the battery, but the way those carbs were stuck on there kinda made me think that they hadn't been removed or drained before storage.  It being on the outside made me think that maybe a float bowl gasket dry rotted and leaked when it was moved from the original storage place to the next.  But I won't know until I tear down the carbs which will hopefully be this week.  Ordering carb rebuild kits just to be on the safe side today in hopes they are here before the end of the week. 

The thought process behind pulling that side of the engine first was to get to the starter motor, but I personally didn't think we needed to start there.  But like I said too many supervisors and not enough workers makes for mistakes.  I'm ordering replacement gaskets with the rebuild kits to put everything back together and see if the kick start pawl might be the issue.  Sprayed a ton of wd40 into the pistons though and hopefully that loosens them up if they are stuck.  If not this will be a much, much longer process than I originally anticipated.  Still having fun though so that's a good sign.

[JeffSTL]

#2 & #3 plugs come out the same as 1 & 4 you'll just need an extension on your socket. They are a pain if you have big hands and they come out easier than they go in.

[harisuluv]

Sorry, I'm not really following, the engine is stuck or no?  Or you don't know?

[nate6]

Well last night has been the biggest leap forward so far. Got plugs 2&3 out after quite a bit of work. Were pretty stuck in there. And the best news of all, the engine freed up. We put it in 5th and could feel the slightest movement when we rocked it. After about 3-5 mins of rocking a click and it was free. The kick still isn't moving but it looks like the clutch isn't releasing all the way when pulled. Going to read up on how to adjust/pull this and try to get it working. We figured the clutch has to be released to kick it. Is that right? If not then we are probably going to rebuild the clutch and just fix the kick while we are in there. Any thoughts?

Also pulled the Carb bowls and they look dirty but will be rebuilding them anyhow. Was right about the 4th bowls gasket being bad and that being the reason for dried gas on the outside of the engine.

Ordering stuff soon, new plugs, plug wires and caps (old not in great shape) Carb rebuild kits, master cylinder rebuild kit, and other such fun stuff.

[ffemt2466]

Ok, I am rebuilding my 75 right now and let me offer some advise...it may be "free" now but that doesn't necessarily mean the motor is unstuck. You are more than likely going to have to do a top end rebuild anyway so I would suggest pulling the motor (with two people it's not hard at all) and then taking the valve covers off (impact screwdriver from sears works amazing) pull cam, valves and then you can see how bad the pistons/cylinders are. Mine was "stuck" and it was a ring frozen to the wall. I managed to get pistons free (second the seafoam) and then honed the cylinders. I lapped the valves while I had it apart and ordered new parts. Got everything in finally to start rebuild but waiting for heat wave to end.

Anyway, that's what I'd recommend for what its worth. Take things nice and slow and mark all parts! Good luck, let me know if you have any questions. Also pick up the full manual, I have it on PDF if you want it, it helps alot!

Joe

[nate6]

Are you sure doing a full top end rebuild is necessary at this moment?  The parts that I have pulled off of this bike and had a chance to see inside of it, everything looks pretty clean.  The only part that had any kind of worrying was spark plug 2 and 3 were pretty black and there was some dry gas in the carb 3 port on the engine, but figured out that the carbs weren't drained before storage and when it was moved before me, carbs 3&4's float bowls weren't seated properly and leaked gas.  Other than that things looked pretty clean.  I'd really feel lost and in over my head pulling the cam and pistons at this point. The pistons felt like they were moving the other day and this bike has only been sitting with fresh oil in it for 3 years since it last ran (most of that time in a storage locker).  At the moment the clutch isn't releasing so it won't even kick.  I feel like making sure it will even kick is necessary before rebuilding the top end.  I am still researching clutch adjustments and such, but any suggestions on that would be welcome.  I don't like the idea of doing more than what I need to at this moment.  I'm kinda buying what I can for the bike from pay check to pay check and its already way ahead of my next 3 paychecks.  I'd just hate to pull the top end and see that I didn't need to rebuild it at all and waste even more time and money.  The plan was to get it running, learn to ride it, and then this winter pull it apart, clean it up more, paint it, and make it look all beautiful. 

[madmtnmotors]

Are you sure doing a full top end rebuild is necessary at this moment?  The parts that I have pulled off of this bike and had a chance to see inside of it, everything looks pretty clean.  The only part that had any kind of worrying was spark plug 2 and 3 were pretty black and there was some dry gas in the carb 3 port on the engine, but figured out that the carbs weren't drained before storage and when it was moved before me, carbs 3&4's float bowls weren't seated properly and leaked gas.  Other than that things looked pretty clean.  I'd really feel lost and in over my head pulling the cam and pistons at this point. The pistons felt like they were moving the other day and this bike has only been sitting with fresh oil in it for 3 years since it last ran (most of that time in a storage locker).  At the moment the clutch isn't releasing so it won't even kick.  I feel like making sure it will even kick is necessary before rebuilding the top end.  I am still researching clutch adjustments and such, but any suggestions on that would be welcome.  I don't like the idea of doing more than what I need to at this moment.  I'm kinda buying what I can for the bike from pay check to pay check and its already way ahead of my next 3 paychecks.  I'd just hate to pull the top end and see that I didn't need to rebuild it at all and waste even more time and money.  The plan was to get it running, learn to ride it, and then this winter pull it apart, clean it up more, paint it, and make it look all beautiful. 

Sounds like a sensible approach. If you get the engine tore apart before you realize you're in over your head (either mechanically or finacially) then it's too late. Let's hear it run first! Worst that can happen is it would STILL need a valve job and new rings. If you do the valve job and new rings (and pistons?) up front, you might never know that it wasn't even necessary...

[Really?]

Tagging along to see how you do with this.  Btw, how tall are you?  You look about 7' tall in this pic.

[nate6]

Tagging along to see how you do with this.  Btw, how tall are you?  You look about 7' tall in this pic.

Well welcome along Really?. The more the merrier.  I am about 6' 4" and unfortunately that is mostly in legs.  Buying the CB750 was a real coin toss, because I always wanted one, but everyone one I knew said I'd never fit and I'd be chewing on my knees.  After reading a thread on here about guys over 6' with CBs I was all for it haha. Also, after realizing that I was still too big for my friends Honda shadow 750 (without forward controls) and other friends Vulcan 800 hardtail with forward controls, the decision was easier. Will probably change back to the original style seat on this bike eventually, because the one that is on there now kinda makes me feel like I'm sliding too far forward and I also would love the extra height.

Anyway, that's what I'd recommend for what its worth. Take things nice and slow and mark all parts! Good luck, let me know if you have any questions. Also pick up the full manual, I have it on PDF if you want it, it helps alot!

Joe

ffemt2466, I appreciate any advice on this project and wanted to make sure I didn't sound rude in that last post.  Totally not doubting you, just stating my concerns.  I reread what I wrote and wanted to make sure it didn't come off in a bad way.  If it helps, my friends say that I sound like Eeyore from Winnie the Pooh so it helps to read everything I say like that lol. 

Is the manual you have for this bike just for the '75 or is it the same one that's the pdf on here?  I have just been using the one from on here for the K series bikes.  If its different I would love to see it. 



Also on a side note, I was thinking a lot about the the final paint job this week...I know, I know, get it put back together and running first.  Trust me, I know I'm a long way off from getting to paint, but I can't help it.  A little background on me, I am primarily an art student, a printmaker/painter to be precise.  And all of my friends have asked me if I was going to do something artsy with the bike and honestly it just never occurred to me to do so.  I kind of like the clean look, but then that thought got stuck in my head.  In some of my previous paintings I used to use silver leaf as an accent/ primary focus.  Now I have started thinking about including gilding into this bike somehow. Also, one of my favorite brushes to use in painting is a 20/0 liner brush, about 5-7 hairs on the actual thing and I got to thinking about pin striping and how I pretty much do something similar in paintings from time to time.  I was thinking an off-white base, custom Honda logo on both the sides that come up and around to make a stripe on each side of the top of the tank in gold or verigated gold with black pinstriping down the sides.   And then two stripes in the fenders.  What do you guys think?  And again, I know that this is a long way off and could all possibly/probably change.

[ffemt2466]

No offense taken brother, I totally get where you are coming from. I am just saying what happened with mine. Even if you do get it free you will probably end up needing to replace rings as they are probably damaged from being stuck. Just hate to see ya blowin oil by ya know. I'll keep up with this. I like the silverleaf idea actually was going to use some on mine. I am doing a bobber style with satin black and possibly some silver leaf. I am 6'4" too so I plan to lower the rear, get a custom solo seat and eventually foreward controls as well!

[nate6]

Well, hopefully for now they aren't in too bad of shape and it will at least start at some point.  I think once its started I'll know more about what I'll need to do.  I definitely appreciate the warning.  What's the worst that could happen if the piston rings are damaged and I start it? 

This summer is all about getting the bike running, maybe a little riding before the winter hits.  Then this winter I plan on pulling it apart and just giving everything a good once over and then painting it all.  That is if I can even get it running before winter lol.   That satin black bobber with silver leaf would look really cool.  I almost bought a matt black vulcan bobber, but figured for my first bike I should not get a hardtail.  Plus I have always wanted a CB and this was a much cheaper buy.  I'll post up some sketches for the final logo design and stuff when I get them done and get closer to that step.


Any clue why the clutch isn't disengaging all the way?  A lot of thing I've read have said that its probably an improper adjustment, but haven't found too much on how to properly adjust it at this point.  I am trying to avoid breaking into that side of the engine as well considering that while gaskets are cheap, a lot of them needing replaced starts to add up quickly. 

[nate6]

So it's been a while since I've posted on here or even worked on my bike.  I've had some health problems pretty much since I stopped posting from 2nd degree sunburn, having a kidney stone, car engine locking up, almost having to sell the bike, all funds going to new car, kidney stone getting stuck and causing 2 surgeries, and my new car breaking down again.  Well during this time I've gone back and forth about whether to sell or keep my bike, what to do with it, and why I have suddenly fallen in love with cafe racers.  I've got the itch to start working on the bike again.  I feel I gave up too soon and owed it to myself as well as this bike to make it awesome and running. 

So...the plan has changed yet again, and this time I'm ready to spend as much time and work as needed on this project.  No more passing up working opportunities.  And...I'm going to make a special tall man's cafe racer.  I fell in love with the style and now, like many of you, this is my kinda bike.

Right now I'm going to focus mostly on getting the bike running finally. Here is the known mechanical that I am aware of at the minute.

- Engine broken free but still a little rough (probably needing a top end rebuild, might do big bore kit if I have to do that and if I can find someone to do it professionally.)
- clutch isn't releasing, probably springs compressed planning on full rebuild
- also clutch panel has 2 stripped screws so I'm going to need an impact wrench.
- spark plugs, caps, wire being replaced now.
- Have some gaskets to replace since I pulled some wrong panels.
- Tank needs stripped and coated.
- Accidentally scratched the inside of the master cylinder while rebuilding it. The snap ring bent and scratched the entire side of the cylinder and the piston is more than seized in there.  Probably just going to be replacing it with one from cb750cafe.com
- Carbs need rebuilt.  Wanting to switch to pod air filters and 4-1 exhaust, have been researching about increasing main jet sizes, anyone have any helpful info on that?

That's all I can think of at the moment, but as usual I'm sure there are many things I'll run into along the way.

Then I'm looking into some cafe mods.  Here is what I have in mind at the moment and some advice/recommendations would be appreciated.   

- Clubman bars or clip ons - any pros and cons feel free to comment. Should I reverse the throttle with clubmans or can I leave it the same?
- rocket seat from cb750cafe.com or possibly making my own design. (does this come with a pan or does it just attach to the frame directly and does it have a seat on it or just a bare piece of plastic.)
- Switching to pod air filters
- Haven't decided on which set of pipes to put on it, but I'm thinking 4-1 to 4-2
- Some major knee indents (I'm 6'4")
- Curious about rear sets and which to get or a cheaper alternative if anyone has one.  Thought about just using the rear pegs somehow.
- 7" tri-bar headlight from cb750cafe.com
- mini 2.5 speedo and tach with mount from cb750cafe.com as well.
- Diamond mini turn signals from cb750cafe.com also

Paint options.
Roth Metal flake rattle bomb either Sublime green, Custard pie yellow, or Blue balls blue.  Anyone ever used these paints before?
Probably going to black out some of the components that are beyond cleaning up nicely. 
I'd like to do white wall tires, but that's something I can look into later.

Any suggestions on leaving the frame stock for this?  I have a professional welder at my disposal if I need to do any alteration, but I'd like to avoid that if possible. 

As always thanks for any advice.  Currently, I am still home recovering from my last surgery and won't be back around the bike for probably another week, but I'm going to order in some parts so that they hopefully get here before the time I go to do some work.  I am going to be going through the forums here and reading the posts of other cafe builds, but any links that you might know of offhand would be helpful and appreciated.

[SOHC4 Cafe Racer Fan]

Since you are definitely pulling the motor and have a welder at your disposal, I would recommend installing the Gordon's frame kit.  It may save you future hassle.  Depending on how you intend to mount your rocket seat, you can also de-tab the frame and get rid of unnecessary mounting points.  If you are going solo seat, you can get rid of the passenger peg mounts -- though you might want to keep part of the lower passenger peg mount as a mounting point for tarrozi rearsets.

[nate6]

Just curious, but what does the Gordon's frame kit do? Haven't found much info on it.  Also, any other option for rearsets?  Kinda doing this on a budget and the $400 rearsets are a little ridiculous. Probably going to have the welder help me with the knee dents and I'm thinking about making a custom seat pan and making my own fiberglass seat with storage compartment.  I've had some experience sculpting the kinds of foam that is used in the creation of the seat from previous art projects.

[srbakker]

The frame kit gives you access to the head with the engine in the frame, once you've reassembled.  Which means - no more removing your whole engine just to get access to the head.  I chose not to go with one.  I may regret that yet - heh. 

[nate6]

Oh I see.  I don't know if that's necessarily something I'm going to worry about just yet.  This is my first time doing any kind of mechanical work and I feel like that's probably a little over my head.  The only major engine adjustments/mods I want to make would be pod filters instead of the air box, and a 4-1 exhaust. Which means rejetting the carbs.  Any clue what I should rejet them to? Or how I could tell what I need to rejet them to?  I have the carbs off now and will probably start rebuilding them next week and want to go ahead and do the rejetting now rather than having to keep pulling them off and fighting those stupid boots to get them on and off.  Might start soaking the boots in xylene and wintergreen oil next week as well to give that a shot.

[SOHC4 Cafe Racer Fan]

I felt that way until I experienced a leaky valve cover gasket.  Now I get to pull the motor to fix that, when the Gordon's kit would have save me that heartache and backache.

It is a simple mod and worth it.