Topic: CB750 K6 motor rebuild and cosmetic restore.

[markmyodb]

Hello all:

I purchased this K6 in 2007 with 18000 miles. Rode it another 17K miles over the years including two trips to Barber vintage days, 3 trips to the Tail of the Dragon, and several VJMC events.

Really happy with the results. New motor is great thanks to help from CycleX, Ken is a knowledgeable resource and a great salesman! The "new" motor is smother than I ever remember it running.  This with just a carburetor bench sync. Will sync at about 500 miles when I put it on a lift for oil change and to go over my work after the shake down.

I'll post a few other pics and stories as time allows.

Yamiya, Ikon, a local Chrome shop, and a local powder coat company all contributed to the result.

[MauiK3]

Very nice
Are those rims the Yamiya rims?

[markreimer]

Beautiful. We need more pics! What frame kit are you using?


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[markmyodb]

Thanks, Kind words are appreciated.

I came up with the frame modification myself. see pics below.  Made sawsall cuts on about 45Deg cut the vertical mid supports half way. Then made (4) 3 1/2 inch long solid bars from 1inch barstock.  Ground cordial flat to clear weld inside tube frames. Cut two 3" pieces of 3/16 x 1 "U" channel. Clamped it all together and drilled thru to bolt together with saddle washers as shown in pics.

The Rims are from Yamiya.

[newday777]

Thanks, Kind words are appreciated.

I came up with the frame modification myself. see pics below.  Made sawsall cuts on about 45Deg cut the vertical mid supports half way. Then made (4) 3 1/2 inch long solid bars from 1inch barstock.  Ground cordial flat to clear weld inside tube frames. Cut two 3" pieces of 3/16 x 1 "U" channel. Clamped it all together and drilled thru to bolt together with saddle washers as shown in pics.

The Rims are from Yamiya.

Do you have a link for those Yamiya rims?! They look like Morris Mags but Morris didn't make a rear drum rim.....
Very sharp! I'm gathering together bits and pieces to start on a K6 restoration/build(on the trailer) this winter with a sleeper motor. I have some history with this bike. My oldest brother wanted one after I bought a new K6 when I was a parts manager so I set it up from the crate for him. He had it a bit over a year and got transferred and didn't want to take it to Chicago so my dad bought it from him, dad rode it a couple years until my mom didn't want to ride anymore so dad sold it to a friend of mine. He rode it about 10 years commuting on it until it started puking oil on his dress slacks one morning. He parked it in 1988. When I got it back a few years ago, it was froze up from mice pee in a couple cylinders so a build will be necessary. I'm going to make it breath again..... With a little more grunt.

Second picture is my original K6 in @1983 not long before I sold it for needs for my growing family. I've always regretted selling it but made that choice.

I also have a K5 that is a good runner.

[markmyodb]

https://www.yamiya750.com/index.php?main_page=index&cPath=251_184

The tires are Avon Roadriders.

They are up 80,000 yen since I purchased?

[markmyodb]

Newday777

I like those rims, did you find they improved the ride quality as I feel these have?  Although some of my "improvement" may be the shocks & tires.

The original motor was putting considerable oil onto my pant leg. the gasket shown below is supposed to help this problem. On it's last long run to Barber and back it was dumping a quart of oil out every tank of gas. It has been used for short low "pressure" rides after that.

Here is a Picture of the Transmission going into frame and assembling the motor.

[newday777]

Markmyodb
Those rims were on my 75 when I bought it from a friend's estate. He put those Invaders on in the 80s or 90s so I can't say if they improved the ride or not. I hadn't seen the bike since he bought it from another friend of mine when it had spoked rims still.

[markmyodb]

A Shocking story.

Last December I decided to look seriously for new shocks. I had Classic Koni 1296's on it, wanted new. Research led me back to Ikon.  Sent email to Ikon and discussed. At little time later Roger asked if I wanted to order. I told him this months bills where pretty big, CB750gauges, Cycle X, and Yamiya where coming in, I told him I would order but would put it of while I cleared up bills. Ikon said no problem we always have some of that model in stock.

After a few months I emailed to buy the shocks. Roger informed me they were out of stock, no expected delivery!  I had sold the classic Koni's and had no shocks to fit the 750.

Roger assured me he would keep me informed. I figured I would be waiting a while so I ordered an eBay alternative for 120 bucks. They arrived and I put them on the bike, nice shocks, progressive springs, hood over top of shock, good chrome.  Two weeks later Roger told me the new Ikons would be available in June...So I bought them, they came in while we were on our National Park tour from North Carolina to Utah, Arizona, Idaho, Wyoming, South Dakota, back to North Carolina.  Roger arranged to have them arrive a few days after our return.

They look great and ride well, come with stickers for my tool box.  A long story around a simple thing like shocks, but part of the process; a good part.

[markmyodb]

Education expense.

I always pay for my education. This is an example of the cost. I had had the cases vapor blasted as part of my project. I put a seal over the cylinder mount surface to protect the threads and mounting surface. As I cleaned it and back flushed the oil ports I did not fully blast the oil from the threaded holes. (my best guess.)

When I torqued the cylinder studs in I got to the 2nd oil port stud. As I screwed it in with the ratchet I heard a pop and a clink...the casting came apart as shown in the first picture.  The second picture is a crack in the other oil ported stud.

I made a Jim Beam Black and diet ginger ale, and stopped for the day. later I looked at it and investigated operation of the oil port. Decided to continue to assemble. In fact got it nearly completely assembled, could have lit it off by just adding fuel.  I found the kick start spring was not preloaded properly...Had a Jim Beam Black and ginger ale in the back yard.

Started looking for a set of cases from the usual resources, nothing great.  Search lead me back to CycleX. A balanced crank and connecting rods, new bushings, bearing and seals through out sounded good to me. A half an hour on the phone with Ken at CycleX
and I was sold on this and included a high performance clutch, all new gaskets. (Ken is a great salesman!)

Less than two weeks after I received the case assembly from  Wisconsin had it running. The balance seems great, I can see clearly in both mirrors ad 60MPH! Something I do not ever remember being able to do with the original motor.

So I paid for another part of my education...But Like Differential Equations, properly cleaning out blind holes in a casting is not something I anticipate using much in the future.

Now the motor is all CycleX including one of their "Git" kits with performance cam, kibble springs, and 0.5mm oversized coated pistons.

Driven it about 100 miles all is good except for carburetor floats, one over flowed and I made an on bike adjustment.  Hoping to ride it about 500 miles then put it back on the lift, remove the carbs and try again to get the floats correct.

Thanks for reading.
Mark

[seanbarney41]

Hi Mark...enjoying your thread and stories.

Overflowing float bowls are a common thing on these.  Don't necessarily jump to the conclusion that your floats are mis-adjusted.  Overflows can be caused by a few different things but a too high float setting has to result in perpetual overflow right?  If it's intermittent, you have a different problem.

[markreimer]

Great update. I can feel your pain with the cracked block, I did a very similar thing to my first CB750 cases. Sickening feeling! But now your engine is super dialed in so all is well


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[markmyodb]

Hi Mark...enjoying your thread and stories.

Overflowing float bowls are a common thing on these.  Don't necessarily jump to the conclusion that your floats are mis-adjusted.  Overflows can be caused by a few different things but a too high float setting has to result in perpetual overflow right?  If it's intermittent, you have a different problem.

True, what would you think if the overflow did not stop even if the float bowl is tapped with a screw driver and after it was drained & refilled?  I took the bowl down and moved the float down a "smidgen". 

Butthoonose, it is running well.  Should make my 500 mile goal.

[Shtonecb500]

nice ride, good job.

[Stev-o]

Great looking bike and nice write-up, Mark

[markmyodb]

Shiny things.

It must be my early exposure to my Uncle Sending parts for his XLH Bagger to Chrome shops; I just like my motorcycles to be shiny.

Since I've owned this K6 I have spent significant time and cash on figuring out what works for me to make and keep it shiny. Driven many miles to drop parts off for re-chroming or nickel plating.

I have used one shop to do Chrome and plating work since 2008, even though this shop has sold twice and moved to another town.  Good guy now, just need to be assured of cost before I tell him to do the work. My last batch of 90+ parts for nickel plating had a bill of 425 dollars when I pick them up. He explained his process, I understood and the parts are shiny, was just not expecting this high a cost. I thought I had this cost controlled as the last time he did nickel plating I wound up with bright shiny parts down inside a CB550K1 airbox and a large bill. I had explained this was not necessary for this batch and had expected a more reasonable cost. As ELP sang cest'le'vie.
 
As a result of the cracked casting above I have a nice set of shiny M8 crank bolts and M6 motor bolts that are not used.

For Chrome work I can't fault his work, price seems reasonable.

Side story I used a Chrome house in western NC.  My tale is summarized by his comment " I only do perfection if you ask for it."

I tried using Browns in western Kentucky, They did a great job for me on my Friends GL1200 exhaust covers. These parts must have been among the last parts they did before the shut down. Arrived a few days after I heard they closed down. They did "prefect" work without asking.

[newday777]

I likey shinney

[markmyodb]

Shiny is also one of the things I look for in my painting. As I experimented thru the years I found the best paint for someone with my skill level was a Base/clear urethane. Very durable and possible to remove imperfections with careful sanding and polishing. I painted My 900F with this process and was pleased with the result. 

For small batches the base/clear process is a little involved; I have tried several rattle can paints, found that if I use a heat lamp to cure the paint I can get a pretty durable finish.  Only disk brake paints will hold up to the brake cleaner spray I use to clean parts and none of them will adhere to aluminum very well, often developing bare spots around fasteners.

The answer for me has been finding a good powder coating resource. For this project I had the motor mounting brackets, chain guard,  Speedo/tach mount, disk brake caliper, and instrument light/handle bar clamp. The last two I had polished because I failed to find a good method to paint the aluminum. The photos below show the result. Bought the new light label from Ricky Racer nice part.

Gatorback vapor blasted and base/clear coated these parts and they are now great looking parts that stood up well to mounting. I posted a link to them in the reviews thread.

[markmyodb]

School, I keep learning.

I wanted a perfect stock K6 paint job, decided my skills were not going to yield this result so I looked into professional help.

Eventually I went down the Yamiya path when their people contacted me that they had K6 kits available, so I bought in.  I liked that this left me a creamed tank I can paint in the future to look like my 1972 CB500 Four. Pic attached.

The schooling is the petcock side swap, and the tank emblem attachment.

First issue causes the carburetor throttle mechanism to hit the tubing connection unless the carbs are tilted rear end down significantly. Loosening the clamps and a wooden pry bar works. It also causes the airbox to move down which I panicked a little over.  Initially I left it in this position as I was concerned about the velocity stacks would lose their seal, Yamiya convinced me to just push them into place. Pleasant surprise was it seems to work just fine, but takes significant force to get the mounting screws installed.

The Petcock swap also buries the idle adjustment screw behind the petcock, turns it into a two hand adjustment. I have a set of spare carbs that I looked at and could see the screw could be swapped to LH side, problem solved...almost. After fussing around for 10 minutes I found the F0 carbs I have on the bike do not have this second tapped hole.  So The decision as to when to take the carbs back off to check the float height was pushed to NOW.  Drilled and tapped hole for adjustment screw and for a stop so it is not seated on aluminum.

Lesson one complete, I now know in detail how the Tank, Petcock, and carburetors interact, and literally how to shoehorn it all together.

Lesson two goes on. A debate between me and Yamiya is the depth of the mounting tabs on the tank emblems.  I feel the holes are not as deep as original, nor are they the correct diameter for installing the retaining clips. I had to clip 3 mm of each post to get the Lable to sit against the tank. then I used 3M glue tape to hold the emblems to the tank. I broke a nice set of replication emblems purchased from Australia. (Same seller from whom I purchased nice 550 side cover emblems.)  They were not formed to match the tank curve, in attempting to make this bend, I broke one. Lesson learned: there is a reason why the original cast emblems were much thinner. I am going to try restoring a few sets of original Emblems, have them being vapor blasted now.  Working with Powder coat company to develop a process, for now it seems I'll be painting the black & white.

Bottom line is the Yamiya parts are painted very well, as you can see in the photos. The pics below show the lesson's homework on the carbs.

Bad news is the #3 carb bowl is still overflowing, I will be taking it apart for the third time to replace this valve. Shame because it is running OK, but #3 must be running rich.

Check out my 3mm tap holder, backyard engineering at it finest.
 

[newday777]

Well that's a bummer that Yamiya doesn't have the K5/K6 left side petcock tanks..... Good that you McGuyver'd it out.
That 500 paint job is 70s to the hilt.

[markmyodb]

That 500 paint job is 70s to the hilt.

You're not the first to say my 500 paint job was very 1970,  I was into Harry Chapin and Jackson Brown so my cool judgement might have been questionable.  (Still have them in my playlist, and we traveled to Bethel NY this year to see Jackson Brown, so clearly I have not become cool yet.)

Yamiya did not like my advice to make the tanks with petcock mounting on both sides, just supply a blanking plate for the unused port.


Sub lesson; when you reach in to adjust the repositioned LH idle screw, the long cotter pin used to reassemble the choke levers mechanism will cause a small bleed and some pain. I changed it to spring clips.

[PeWe]

I changed side of the idle screw on my K6 carbs when they got a come back om my K2 where the RH petcock block the access to idle screw.
From right side to left.  1 minute job
No issues with anything on choke mechanism.

[markmyodb]

I changed side of the idle screw on my K6 carbs when they got a come back om my K2 where the RH petcock block the access to idle screw.
From right side to left.  1 minute job
No issues with anything on choke mechanism.

True, my spare set of Carbs (from K6) had the screw threads on both sides. The carbs on the K6 are from an F0 I parted out.

When I rebuilt the Carbs this time, I installed the long cotter key, it stabbed the end of my finger, I guess I did not state that clearly enough.

Just put the carbs back on this afternoon after replacing the float valves. Sometimes it is not a good idea to simply ultrasonic clean the brass parts, best to replace the valves.  Also found some eBay seller provides gasket replacement kits made from a material which absorbs petroleum. These seem to be one use bowl gaskets.

[markmyodb]

This time the carbs seem to working properly, only time to run it about 10 miles today. It did not leak after the run so maybe I got it this time. Owning these is like owning a high end stereo system in the 1970's, You spend your time listening for minor errors in the music, not the music. I need to enjoy riding this beauty, quit nit picking.

Need to get it to about 500 miles so I can go over it closely for a trip to Florida in January.

This time I set them up level, bowls down and fed gas to them 2 banks at a time.  By letting fuel out the drain I could tell the floats were operating their valves. Double checked the floats for 26mm, then on the bike. It started with a little choke and I rode it.

My 550 needs a little TLC so it is now on the stand to fix an oil leak & figure out why the tach is malfunctioning.

[markmyodb]

Up to 250 miles this week. Interesting observations:  (to me as I added this capability with the restore)

The oil reaches about 95c, at this temp the oil pressure drops from 70 to 60 above 1500rpm or so, 20psi at idle.

Slight throttle "burble" just off idle.  My fellow SOHC'er who has been playing with this model for a long time says, "no carbureted  bike I've ever built does not have a flat spot somewhere."  His way of telling me to enjoy the music.

I am pleased with the handling and ride. It carves the corners better than my 900F did.  Good tires and shocks, hoo'da'thunk?

Here are some interesting Pics:

First is bike in 2007
Second is oil temperature gauge
Third is oil pressure gauge
Fourth is fuse block from Mark Paris, I have flipped it vertically since this was taken, worked better for wire routing.

Last Pic, I thought a Picture of the pipes I was told were "solid" by the guy I bought this from would be amusing. Been seeing this "phenomena" discussed by some of the old timers on the forum