Topic: CB750K4 what did I get myself into?

[BrockCB750]

Been away from this thread for a bit but got a lot done.

Dropped the engine off at a local vintage motorcycle shop to clean the engine up and cerakote it.

Mike Rieck is doing my head work:





I laced the wheels and had a shop true and mount the tires:



Some bushing and bearing stuff:





Some painting/bluing:

[BrockCB750]

I am getting into loosely fit stuff together so I can mock up seat, tank, oil tank, etc. F

Started with the rear swingarm:


I bought some cheap shocks to get everything mounted up. Supposidly they are OEM direct replacement.

Wanted to mount the rear shocks but ran into an issue I need help with. First of all, its a huge pain getting new shocks and bushings on. Once I got the first one on I realized something was off.

I am guessing there was something here before (grab handle? turn signal? idk?) or some other crap that was mounted to shock mount or my cheap shocks are out of spec... either way I have a large gap. Its not something a single washer can fix that I have handy. In the picture those are the original nut and washer. I tossed my old beat shocks in the trash awhile ago so I can't compare them to what I am using now.

I strongly suspect this is not normal and the rubber and shock shouldn't have that much of gap/play.



Here is another thread with exactly the same issue:
http://forums.sohc4.net/index.php?topic=147409.0

Second to last post in thread mentioned about talks about putting a washer or spacer.

1) Is it acceptable solution to throw an extra thick washer/spacer between the frame?
2) I am guessing if I had just gotten the IKON direct replacements I wouldn't be having this problem? Something like these: https://www.common-motor.com/ikon-rear-shocks-honda-cb750
3) Any other advice for dealing with this problem would be appreciated.

Thanks!

[BrockCB750]

Well answered my own question. Got what I paid for or I ordered the wrong thing.

I did some quick measuring. The first black sharpie line is the upper eyelet width of the cheap shocks.

The IKON line is what IKON says their upper eyelet width is. (1.02 ")

You can see the difference exactly makes up the gap that I have.

Whoops. Need to figure out what to do next. Pretty sure I know the answer.

[BenelliSEI]

Was your bike fitted with a grab rail? Would it fill that gap?

[BenelliSEI]

When you do the final assembly, remember to fit the operating shaft for the rear brake before the swing arm. It’s a pig if you do it later……

[BrockCB750]

Thanks for the advice. This has very much been a learning process.

I sent an email to Ikon Sunday to get measurements on the top eyelet on the part I wanted just to be 100% sure. Someone in Australia got back to me within the hour and they connected me to a US Sales person who double checked it was correct and made sure to get my order out as fast as possible. Their customer service is unheard of these days.

Shocks show up today and it looks like I will actually have some time to pull more of it together. I got my seat and seat hoop. Going to be able to mock everything up for the most part probably by this weekend? Well...everything has taken about 3x as long as I expected so who knows?

Ordered a bunch of carb parts from South Sound Honda and those come in tomorrow? Might be able to throw together the carbs this weekend as well. They have been sitting after I pulled them out of the ultrasound since early on in the project. Hopefully I remember how to put them back together!

[BrockCB750]

Fits perfect.

[Floshenbarnical]

What are those rubber damper things? I didn't see any in my Comstars when I pulled the bearings. Do the Comstars get them?

[BenelliSEI]

VERY NICE!

[newday777]

I'm still running a set of the old Konis on my K5 and when they die I'll replace them with the Ikons.

[BrockCB750]

What are those rubber damper things? I didn't see any in my Comstars when I pulled the bearings. Do the Comstars get them?

I looked up a parts diagram of the comstar rear wheel and it doesn't look like you have the rubber rear wheel dampers. But not certain since I haven't had that style of wheel before.

I was wrong! They do!

[newday777]

What are those rubber damper things? I didn't see any in my Comstars when I pulled the bearings. Do the Comstars get them?

I looked up a parts diagram of the comstar rear wheel and it doesn't look like you have the rubber rear wheel dampers. But not certain since I haven't had that style of wheel before.

The comstars do have the rubber dampness. #6 (on a 78 CB750 F diagram)

[Floshenbarnical]

What are those rubber damper things? I didn't see any in my Comstars when I pulled the bearings. Do the Comstars get them?

I looked up a parts diagram of the comstar rear wheel and it doesn't look like you have the rubber rear wheel dampers. But not certain since I haven't had that style of wheel before.

The comstars do have the rubber dampness. #6 (on a 78 CB750 F diagram)

Oh, great! Another thing to do Looks like they're in the hub? Now how do I get the cap off for that hub!

[newday777]

What are those rubber damper things? I didn't see any in my Comstars when I pulled the bearings. Do the Comstars get them?

I looked up a parts diagram of the comstar rear wheel and it doesn't look like you have the rubber rear wheel dampers. But not certain since I haven't had that style of wheel before.

The comstars do have the rubber dampness. #6 (on a 78 CB750 F diagram)

Oh, great! Another thing to do Looks like they're in the hub? Now how do I get the cap off for that hub!

Pull on the sprocket while feet on the rim.

[BrockCB750]

More progress tonight. Go the rear wheel together...

[SOHC4 Cafe Racer Fan]

Unmistakable MR head work!

[BrockCB750]

Made a lot more progress.

[BrockCB750]

I should be getting the engine and head back within the next two weeks. I am not sure how much more mocking up I need to do at this point to feel comfortable with cutting, prepping and painting the frame. I am going with paint because it feels like there is 100% chance I will scratch the finish on the frame and want the ability to touch it up.

My next steps as far as I can tell:
1) Pull everything apart.
2) Cut (tabs, center kickstand, etc), sand the frame
3) Fit the seathoop and seat.
4) Cut and drill an aluminum pan for under the hook for electronics
5) Get someone to weld the seat hoop on
6) Prep the frame and swingarm for paint.
7) Paint the frame and the swingarm.
Decide if I want to paint the head and valve cover.
9) Assemble the engine.
10) Get the engine into the frame.

[Galactica]

Great thread.  I’m now starting to go through and read some more threads than the one I started. I’ve a few comments.

In the ultrasonic cleaner, I use a 4:1 solution of water:Simple Green.  You do have to be careful because it will blacken the aluminum carb bodies.

Acetone is good carb cleaner.  Aerosol carb cleaner is just acetone and propellant (probably propane).

I’ve cleaned stock jets in acetone for reuse with no issues.

Engine stumble or stalling at throttle tip in, can be caused by an initial lean-out condition.  All else being well, tiny passages in the carb bodies can still be restricted.  When gasoline has been allowed to sit in the carbs over time to evaporate, the resulting varnish can be extremely hard to remove.  Takes lots of ultrasonic cleaning, maybe immersed and soaked in acetone.  The lean-out condition typical of older carbs was addressed later by manufacturers by going to a pumper carb.  These tiny pumper passages in the carb bodies (I have experience with a ‘78CB750) can be difficult to clear of evaporated gasoline varnish.

[HondaMan]

Great thread.  I’m now starting to go through and read some more threads than the one I started. I’ve a few comments.

In the ultrasonic cleaner, I use a 4:1 solution of water:Simple Green.  You do have to be careful because it will blacken the aluminum carb bodies.

Acetone is good carb cleaner.  Aerosol carb cleaner is just acetone and propellant (probably propane).

I’ve cleaned stock jets in acetone for reuse with no issues.

Engine stumble or stalling at throttle tip in, can be caused by an initial lean-out condition.  All else being well, tiny passages in the carb bodies can still be restricted.  When gasoline has been allowed to sit in the carbs over time to evaporate, the resulting varnish can be extremely hard to remove.  Takes lots of ultrasonic cleaning, maybe immersed and soaked in acetone.  The lean-out condition typical of older carbs was addressed later by manufacturers by going to a pumper carb.  These tiny pumper passages in the carb bodies (I have experience with a ‘78CB750) can be difficult to clear of evaporated gasoline varnish.

Some good advice, here! I use acetone, too, and/or lacquer thinner.
In the carb bodies of the K0-K6 and F0 bikes with the 086a carbs, there is a long passage between the bell area at the back of the carb and the mainjet. This shows up as a little brass port in the back side of the carb. It's passages goes straight forward a few mm, then turns about 30 degrees downward, then turns striaght toward the top of the mainjet's emulsifier tube, entering that site at an angle near the little brass jet in the throat of the carb. This passage often plugs up with a white powder (zinc corrosion) if the carbs were exposed to the years of MTBE gasolines, then parked and left to dry out. When this passage plugs up fully or partly, the cylinder will foul plugs in less than 10 miles (usually in 4 or 5 miles). Clean it manually by removing the needle jet from the carb's body (I use an old screwdriver that I ground the tip to fit nicely into the needle jet to press or tap it out) and then run a soft wire thru from the little brass hole in the bell area of the carb, all the way to the mainjet emulsifier's passage. It will come into the passage at about a 40 degree angle. Go gently, feel your way around the 'corners' at the back as it starts in, and push it back-and-forth to push out any of the white powder you might find.

This didn't accumulate in the bikes that were run thru the MTBE years and then kept running, nor those that were parked before that nightmare was imposed on us all: it occurs in those that were parked with gas in them during those years.

[newday777]

Great thread.  I’m now starting to go through and read some more threads than the one I started. I’ve a few comments.

In the ultrasonic cleaner, I use a 4:1 solution of water:Simple Green.  You do have to be careful because it will blacken the aluminum carb bodies.

Acetone is good carb cleaner.  Aerosol carb cleaner is just acetone and propellant (probably propane).

I’ve cleaned stock jets in acetone for reuse with no issues.

Engine stumble or stalling at throttle tip in, can be caused by an initial lean-out condition.  All else being well, tiny passages in the carb bodies can still be restricted.  When gasoline has been allowed to sit in the carbs over time to evaporate, the resulting varnish can be extremely hard to remove.  Takes lots of ultrasonic cleaning, maybe immersed and soaked in acetone.  The lean-out condition typical of older carbs was addressed later by manufacturers by going to a pumper carb.  These tiny pumper passages in the carb bodies (I have experience with a ‘78CB750) can be difficult to clear of evaporated gasoline varnish.

Some good advice, here! I use acetone, too, and/or lacquer thinner.
In the carb bodies of the K0-K6 and F0 bikes with the 086a carbs, there is a long passage between the bell area at the back of the carb and the mainjet. This shows up as a little brass port in the back side of the carb. It's passages goes straight forward a few mm, then turns about 30 degrees downward, then turns striaght toward the top of the mainjet's emulsifier tube, entering that site at an angle near the little brass jet in the throat of the carb. This passage often plugs up with a white powder (zinc corrosion) if the carbs were exposed to the years of MTBE gasolines, then parked and left to dry out. When this passage plugs up fully or partly, the cylinder will foul plugs in less than 10 miles (usually in 4 or 5 miles). Clean it manually by removing the needle jet from the carb's body (I use an old screwdriver that I ground the tip to fit nicely into the needle jet to press or tap it out) and then run a soft wire thru from the little brass hole in the bell area of the carb, all the way to the mainjet emulsifier's passage. It will come into the passage at about a 40 degree angle. Go gently, feel your way around the 'corners' at the back as it starts in, and push it back-and-forth to push out any of the white powder you might find.

This didn't accumulate in the bikes that were run thru the MTBE years and then kept running, nor those that were parked before that nightmare was imposed on us all: it occurs in those that were parked with gas in them during those years.

This is where pictures sure would come in handy to show the spots pointed at in the carb and the screwdriver ground to fit and going in. Do you have pictures of this? Did you put them in the 750 book?

Edit: I did some net searching for the time-line of MTBE use, found it started in 1979 in many big air polluted cities especially in the winter months as late as May known as winter blend gasoline and mostly stopped by 2006 when ethanol replaced it. MTBE still is being made and exported to other countries especially to Mexico.
More disturbing than even the damage it did to our carbs is the health effects it is still producing from the ground water pollution it caused through leaking in ground fuel storage tanks as also airborne particles of it while being pumped, inhaled and and airborne spread to the ground into the ground water after dropping to the ground........
I have a friend who tests wells and municipal water that says it will be with us a long long time to come, it's not even close to being fully disclosed as to the damage it is doing to people and animals.

Some reading of it's exposed results from the National Library of Medicine
It says that MTBE in water is absorbed through skin pores and breathing taking showers.....

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6957274/

[MauiK3]

MTBE is one of the forever pollutants I think

[newday777]

MTBE is one of the forever pollutants I think

Yes that is what I've learned in this past year. It is hydoscopic so it mixes with the ground water and travels polluting more and more as it goes.
Thankfully there are filtration systems available, with state aid to clean well water at the house and off of municipality water supplies (yes they have high levels also) not much is said about it unfortunately because of the vast areas that have been contaminated by leaking gas and huge international companies that go in to an area and do their thing with the chemicals that they use and then run out of country when caught to avoid prosecution. There was a French company local @ 15 miles from me that did just that. Left the employees hanging out of jobs and the cities and towns surrounding areas from airborne particles polluting the ground water.

[BrockCB750]

Two quick questions. Having a hell of a time figuring out what these two mounting points are for.

1) Underside of the swingarm:


2) These on the frame:


Going to keep digging but hit a wall with these two.

Thanks!

[newday777]

Rear brake stay mounts to the front under the swingarm.