CB750 K5 Restoration

[motogtp]

Yes she will, especially after it's painted. She likes to ride with a fairing, so I picked up this 70s beauty at a swap meet for $8

One more thing on the list is new shocks. The old ones are on there, I want to see how close they are for her to stand flat footed on the bike. She will need shorter shocks, but I want to get some that are as tall as possible.

Looks great Grepper. If it is too tall CycleX has "shorty" shocks that are 2" shorter. I put them on mine to lower it for looks but the ride is still good.

 

[grepper]

Looks great Grepper. If it is too tall CycleX has "shorty" shocks that are 2" shorter. I put them on mine to lower it for looks but the ride is still good.

Yeah, I'm considering those, but they have been out of stock on the All Chrome ones for a while. I'm not blowing $200 - $400 on progressive, Hogans, ect...

 

[grepper]

BTW, I found out the last time this bike was registered was in 1987. So it hasn't been on the road in 27 years. Wow!

Still waiting for those All Chrome Shorty Shocks from cycleexchange to come in, I may go the eBay route for those. I got the bike off the build table yesterday! My wife sat on it and it's way too high for her, the new firm wide seat is also a factor. So it looks like I'll be shopping for 11.5" shocks.

Sorry no pictures, I dropped my phone and cracked the camera lens, so all my pictures are coming out blurry. I'll have to resort to the old digital camera for my pictures.

I'm still working on the tank, it was super rusty. Doing the electrolysis method, so far I've swapped out the water/sodium bicarbonate (washing soda) once or twice a day for a week and cleaned the steel bar every few hours. From looking inside its pretty clean. I'm going to go the rest of the way with CLR (household rust/lime remover).

So in the meantime I have an old lawnmower tank budgie'd to the frame and took it for a spin!

A few minor adjustments in the clutch and rear brake. Thought my chain would stretch, but it hasn't yet. Overall it rides real well, nice and tight and smooth. Got it up to 75mph. But it does have some bigger issues I have to address.

1. The cam chain still seems real loose. I've adjusted it a few times, but I think my cam tensioner is not moving per adjustment. I'll take it off and see if I can loosen things up.
2. This is the big one. The bike is slipping out of 2nd gear on hard acceleration. I'll take off the left side tranny cover and see if anything is loose, but I suspect a bent shifter fork or warn gear dogs. Rides fine if you go from 1st to 3rd though. Maybe I'll ride it like that for a while, and pull the engine this winter.

 

[losttravlyr]

try looking for some rebel or savage shocks. i believe they are the height you want.
l.r.t. sells some weld on adapters so that you can use harley shocks if you wish to.
i've always thought the old flh covered ones from the shovel era were cool looking,they were 12" long too.

 

[Vicman]

That second gear issue is a biggie.
My 73 has a bent fork. I've put it off for a long time shifting to third. I'm not looking forward to the rebuild.
Glad to hear you got some road time on the project.

 

[grepper]

Vicman: From what I understand it is possible to work on the transmission without totally disassembling the engine. It's a matter of removing the engine, taking off all the side covers, removing a couple of bolts on top, then flipping the motor upside down and taking out all the other bolts and splitting the case. From there you can work on the transmission. Pulling the engine is the big job. Luckily when I bought the bike I bought a second parts bike. For the most part I've either used or sold off all the extra parts, but I do have all the transmission parts. So the job will be a lot of work, but little too no costs. I even have some Gasket Cement 1104 3-Bond left over from an other project.

 

[Vicman]

I'll be staying tuned to watch your method. I haven't read it before, everything I have seen (not much) is a full tear down.

 

[dan1951]

I can not see why You would have to do a complete teardown to pull the main and layshaft with the motor inverted after the cases are split just My 2cents worth.

 

[grepper]

First Fill up!

Took a long time to get the tank cleaned out. I did electrolysis for about a week, changing/clean the sacrificial rod and water every few hours. Then filled it with CLR and water for a day before a full rinse, dry and tank liner. I also filled some dents and painted it with primer.

I got about 5 miles in before it started to rain again. Seems to be under-powered on the hi end of the rpms. I've got a list of things to check, like the clutch, carbs, timing, dragging wheels, gas cap vent, ect..

Still slipping out of 2nd gear.

Other than that, she handles great.

 

[dan1951]

Heck of a job there guy looks good even in primer, After I cleaned My tank I had to pull the fine mesh screen and bowl in the petcock 3 or 4 times for cleaning, I added twin Wix 33011 fuel filters but for some reason they would not flow when the fuel got down to a 1/3 in the tank. Combination gravity and filter construction I guess. I have a spare trans and the only gear with rounded dogs is second must be common problem, P.O. must have beat it pretty good or the gear was not completely engaged.

 

[Vicman]

Feels good to fire one up after working on it for so long doesn't it?

 

[grepper]

Vicman: Sure does. Like I said, I'm building this one for my wife. Hopefully if the weather cooperates she can ride it this weekend.
dan1951: I cleaned out the cap vent (it was clogging), checked the timing, wheels not dragging, adjusted the clutch again, and fiddle with the carbs. Between the MAC exhaust and the K&N air filter, I'm thinking I need to re-jet. I still have the stock mains in there. Upon further trouble shooting, it's exhibiting classic signs of being lean on the high end. i.e. if I'm going full on in 5th Wide Open Throttle is bogs a bit and struggles to get up to 80-90 mph, but if ease off to about half throttle I get a little bit of a surge of power. I blocked off the inlet into the air box a little to simulate a more restrictive air filter and it does a little better. I'm thinking it will be fine to ride it like this for the next month provided I don't try to do any freeway riding, till I get a jet kit.

Took some better pictures with a digital camera. The bike is a little dirty, I live on a dirt road.

Yeah the valve cover is sweating a bit.

 

[Travis]

I can't wait to see this one after paint.

 

[grepper]

Had some time off over the holiday and decided to take on the transmission problems I was having.
It always sucks taking a bike apart you just put together. Oh well, at least I'm not fighting bolts that haven't moved on 40 years.
Got the engine out.

I'm just opening up the bottom end right now. First took all the bolts out from the top, then flipped it over and took all the bolts out from the bottom. I was careful to take the 10 big ones out in reverse torque order. All the nuts and bolts are in separate labeled baggies. Then the case split! No too bad, just working around it with a rubber mallet and occasionally a block of wood and a hammer.

At a first glance the gears and dogs looked fine. But when I get my reading glasses on and look at them from all the angles with a flash light, I can see where things are worn down. The shifter forks look fine, no bends and they are well within the factory manual wear limits.
So it looks like I'll be sending the gears off to CycleX/. Might as well do it right and get their undercut gears on exchange.
I also took the time to clean up the mating surfaces. I have some TheeBond 1104 (equivalent to HondaBond/YamahaBond) for sealing up the case halves.

When that's all done, I'm going to flip it over and take the head off. I was getting some smoke at start up, so new valve seals for sure, probably lap the valves and put new rings in. If the pistons and/or the cylinders are in bad shape, then rebore and go up a size.

 

[dirtdigger]

Undercut tranny will shift a little harder then standard and you will get more of a clunk but they wont pop out of gear. You should be able to see how the bores look from the bottom side. If it was me I wouldn't put the bottom together then take the top off if you are going to do the top anyway. I would take it all apart at once, you can do a much better job of cleaning it if you just take it all apart. How many miles is on it? I would plastigage the bearings to see how they are wearing. Think about doing primary chains and for sure do a cam chain as you can get heavy duty one from Cycle X for $50. Check chain tensioners to see if they are hard and or chunking. If you take the neutral position switch out first the shift drum is easier to take out and to turn on assembly Any question ask!

 

[grepper]

You're right dirtdigger. At every turn this project is getting more involved and more expensive. I don't know how many miles are on the engine. I bought the bike with no guages. Might as well replace all the seals while i'm it. I called cycleX today, but no answer. Maybe they can give me a set w/o the clunk. So much work ahead of me....

 

[dirtdigger]

The clunk is caused by the undercutting and shifting will be harder because the dogs are cut at an angle which locks the together when under load. If you want a normal type shift only stock gears will achieve that. Undercutting will eliminate popping out of gear at the expense of harder shifting. Maybe look on ebay for a good used set or two. For me undercutting is the only way to go as the shifting doesn't bother me but is noticeable the increase in shift effort. What kind of problems did you have with the tranny? Definitely replace the seals and be sure to get new orings for everything inside. I would put the bottom on empty with a couple of bolts, flip her over and disassemble the top while waiting for the tranny to see what you are getting into as far as what needs to be done. It is probably in need of a valve job but it probably needs some guides too. No one said the 750 motor was cheap!

 

[grepper]

dirtdigger: The bike was popping out of second, and into a false neutral. This would happen under a little load. You would have to climb the rpms very slow to actually get it to where you would shift into 3rd. Sure, I could ride it by just going straight to third from a high reved 1st, but this is going to be my wife's bike, so it needs to function as intended.

I'm weary of buying used gears off of eBay. This kind of damage to the gears is hard to see in pictures and I don't always trust sellers. It wouldn't be a problem if was something easy to replace.

I did plastigage the bearings yesterday, they are within the factory manual specs.
I put in a couple of bottom bolts and flipped it over to disassemble to top. I was very careful to put everything in labeled baggies. It all came apart relatively easy. Those valve stem seals were pretty hard.
The valve guides appear to be pretty tight. I'll set them like this guy does. https://www.youtube.com/watch?v=t97lXLirOlM. Hopefully a good lapping is all they need.

As far as the shape of the cylinder walls.... I found a rough spot on cylinder 4. My guess is that a valve was open when it got parked for a long period of time, moisture got in and some rusted. So I'm shopping for a piston kit and doing a re-bore.

 

[dirtdigger]

2nd gear pop out is common. Make sure to look at the shift drum very close and make absolutely sure the shift forks are straight and the pins that go in the drum are good. The pins on the end of the shift drum have a tendency to get loose also.

That will work for checking guide clearance. Make sure you are closer to perpendicular to valve then what the video shows, you can get false reading being that far out of perpendicular but the procedure is sound. Exhausts will be the worst. You also need to make sure when you lap them that the seat sealing surface is not too wide which can cause issues down the line.

Any questions dont be afraid to ask!

 

[grepper]

I've got an extra shift drum and forks from a 74, unfortunately I sold off the transmission gears before I found out I needed them. The drum and forks off the 74 look a little bit better and I'll probably use those.

Thanks for the advice on the valves.

Here's some pics if anyone cares..
Top of case

Jugs and head

Old pistons

All in labeled baggies