Topic: Ugly CB750K4 Rat Resto

[Kelly E]

A file will work. File from different directions trying to keep it flat. Some 220g wrapped around a chunk of steel will work as well. Make sure to clean out the grit when you are done.

[Jake88]

I ended up using a random orbital sander with 120 grit paper to thin down the face of the bushings. I would say the collar is sticking out about 1/32 ish on either side, maybe not even.  Put it back together, tighten it up, pumped grease into it and not much improvement. I think the collar is just too tight in the bushings. I believe even with the bolt tightened, the collar is just turning against the inside of the metal caps.  I think I'll pull the collar out and apply some Emory cloth until it fits a little easier.. I did have to slightly coax it into place with a dead blow.  From what I've read, I can picture Hondaman shaking his head about everything I have done with this situation!

One thing I don't get that I was reading in another thread about how tight to torque the swing arm bolt- I saw multiple people saying that you should tighten the nut and bolt until the swing arm falls slowly under its own weight. Say about 40 ft/lbs or so. But, if all the tightening is doing is pinching and immobilizing the collar, why would tightening it more create more resistance in swing arm movement? Once the collar is pinched, it's pretty much just The bushings rotating on the collar which I wouldn't think would be affected by more tightening. 

[Kelly E]

Fit the bushings to the collar, don't sand the collar. You need to lightly sand the bore of the bushings so they barely slide over the collar by hand. Then in the future a new set of bushings won't have the bore already too big.

[Jake88]

Fit the bushings to the collar, don't sand the collar. You need to lightly sand the bore of the bushings so they barely slide over the collar by hand. Then in the future a new set of bushings won't have the bore already too big.

That's an excellent point! Thanks. Any recommendations on how to sand the inside of the bushings uniformly? I don't have a little hone or anything.

[Kelly E]

I used to use small flap sanding drums for the 1/4" die grinder but I can't find them anywhere. Whatever you use check it after every pass, if you don't all of a sudden it's too big.

[Jake88]

Ok. I got the bushings fitted to the collar.  Ended up having a wire bore brush that fit into the bushings with just enough room to wrap a piece of emery cloth around. I used it like a hone, making a couple passes then checking. Worked real slick. 

Swing arm is in place. Front forks, triple tree and tapered roller bearings are installed up front. Still need to add oil. 10w30?

I did a light spit shine on the wheels. I'm going to put them on with the old rubber until I know the engine is viable and the transmission works after the rebuild.  Then I'll put new rubber on it and shine up the rims and spokes. Will also have to rebuild the front brakes.   

[Kelly E]

Nice job improvising a hone and fitting the bushings.

[BenelliSEI]

I sometimes tape/wrap a piece of plumber’s sanding cloth (the stuff that comes in a 1” wide roll) to an appropriately sized drill bit, as a make shift hone. Works very well......

[Jake88]

I've been making some progress. Got the wheels, handlebars and a few accessories installed. Took me a hot minute to figure out how that damn spring on the rear brake pedal fit into the equation! I shined up the fenders and cleaned and painted the underneath with rustoleum.  I also realized that my ignition location is probably not stuck. It's on a bracket up by the handlebar mounts and I think it should be down to the left of the tank.  Was this a common mod back in the day?

I believe I'm going to install the oil tank, carburetors and air filter next.  I've got to make a run for some o-rings for where the oil hoses attached to the motor.

I also started fiddling with the master cylinder. I got the attention ring and circlip out but the innards seem to be stuck in place. Any suggestions on how to remove?

[seanbarney41]

Yeah, that key switch relocation kit is very common.  The frame bracket for the stock location under the left front of the tank is nla from honda.  I think Yamiya and other resto sources sell reproductions.

[BenelliSEI]

Master Cylinder: drop it in a pot of boiling water for 5-10 minutes. That will soften the crud. Don’t be afraid to stick a small rod in from the outlet end and give it a solid hit. Assuming you have a rebuild kit, you are replacing all the piston, rod and seals inside? Don’t use a sharp poker and careful not to score the walls of the bore.

[Jake88]

Thanks for the advice. I gave it 10 minutes at a good hard boil. A great excuse to use my little swedish white gas stove!
Still would not budge using a small punch from the backside. Then realized there was still a cruddy washer on the plunger side. Tapped around on that a bit and then picked it out. Went back with the punch and was able to drive it out fairly easily. It must have been getting hung up on that washer The innards were extremely corroded.

[newday777]

Yes those innards are nasty looking. I have a few masters that need to come apart too. I'll try the boil up.

[Jake88]

Hello!

Making a little progress on the K4. Getting the wiring harness all back into position. Carburetors are on. Just made one of my last orders for parts online.

I have a question on where a wire goes- see in the picture. The one in question is the one I'm holding that has the braided cover on it and the brass eye end.  Where does this attach?

In the same picture, under the sprocket cover, there is a tab held in place by a bolt. I assume it holds a wire or wires in place. Which ones is this tab supposed to keep in check?

There is a similar tab on the bottom of the motor held in place by an oil pan bolt. Remind me again what this tab holds in place? 

I really appreciate the wisdom and help.   

[Jake88]

Update time!

I got the air box on, wiring harness in place, drive chain and new front sprocket installed, oil pump primed and installed. 

Drive chain goes tight loose tight loose as the rear wheel spins. I tracked it down to the rear sprocket not being exactly centered. I adjusted the tension in the chains tightest position and will roll with this for initial testing of the bike. I'm going to try to get that sprocket better aligned for the long run. 

I turned the key and neutral light and high beam worked. Oil pressure light not coming on. Disconnected the wire at the pressure switch and grounded, still not coming on.  Switched bulbs with neutral light and did the same and bingo It lit up.  Got a new pressure switch in the mail And it works.

I put two quarts of oil in the tank. Rotella 15 w 40. Poured another 8 oz up top through the tappet holes. I'm missing my starter button, but I'm able to stick a little pick in there to actuate the starter.  Gave it four 5 second bursts with the starter. Checked the dipstick and the oil level no longer registered which I took as a good sign. Still no oil in the main galley. Tilted the bike towards its left side about 45° and did the same four 5 second bursts.  Took the plug out of the galley on the right side of the bike and oil spilled out. Hooray! Added another quart of oil into the tank. Hit the starter a few more times watching with a flashlight through the tappet holes And finally could see oil moving in there. Victory!

Also checked for spark on all four wires coming out of my accel coils.  All seem to be working.

I rigged up a temporary fuel delivery system. Used an old gas tank that I got from my grandpa. On off valve, inline filter and a y splitter.

Got the new button and right hand controls all buttoned up. Gas hooked up. Ready for the big moment of truth. Turned it on and hit the starter button. She fired right up but then everything went black. Blew the 15 amp fuse. Replaced, try it again and ended up with the same result. I thought maybe it was something in the right hand controls since I was fiddling around in there so I took that back apart, but at the same time also turned the headlight off. This time the fuse did not blow and the bike started! And idled! I'll have to dig into that fuse blowing a bit more. It seemed to be idling well, but when crouching down behind the bike, The sounds from the left tailpipe told me something was a miss in one or both of cylinders one and two. It was not firing consistently. Cylinders 3 and 4 seem to be working just fine. 

With the plugs out and grounded to the motor, I have spark at the plugs. Unless somehow when the plugs are in the motor spark is somehow arcing elsewhere I think spark is not my problem.  I seemed to have fueled delivery to both carbs one and two up on unscrewing the drain.  Bike would start and run on cylinders three and four when the other two plug wires were disconnected. It would not run on cylinders one and two alone.  I got a compression tester coming in the mail. By putting my finger over the spark plug hole, there seems to be good compression though I know this is not a great test.  I took the air box off and sprayed some carb cleaner in carbs one and two while The bike was running and there was no change in RPMs or anything. I put my hand over the intake boot and It would suck my hand tight and then flood The intake with gasoline.  Spark plugs and cylinder one and two were clean and wet  when removed. That's about as far as I got before I had to call it quits.

Next plan is to switch the plug wires around a bit and see if that changes anything, then test compression when the tester arrives. If those both check out, then it's got to be something in the carburetors or fuel delivery.  Any ideas, please share. Much appreciated!

[Jake88]

Pics

[Jake88]

Pics

[RAFster122s]

There have been reports of some plugs not firing correctly under compression, leading to misfires or dead cylinder... So, possible to have a bad spark plug.
Glad you have it running again. Congrats.

[newday777]

Pics

Nice tank you got from your grandpa. Is it rust free inside? If not, it needs to be derusted.

I noticed the plug caps and wires against the head fins, that can be the problem of it not running correctly if they are touching the fins(grounding out).
Have you put a meter on the coils, plug wires and the caps to test the resistance on them to be sure they are within specification?

[Jake88]

There have been reports of some plugs not firing correctly under compression, leading to misfires or dead cylinder... So, possible to have a bad spark plug.
Glad you have it running again. Congrats.

Interesting. I never would have thought of that. Anyway I can check to see if this is the case? Well, I suppose I could switch spark plugs around.

Pics

Nice tank you got from your grandpa. Is it rust free inside? If not, it needs to be derusted.

I noticed the plug caps and wires against the head fins, that can be the problem of it not running correctly if they are touching the fins(grounding out).
Have you put a meter on the coils, plug wires and the caps to test the resistance on them to be sure they are within specification?

The tank is pretty clean inside. I do have the inline fuel filter also just in case and there's a screen on the inside of the tank.

Apologies, the bike doesn't have spark plugs in it in that picture. The wires are kind of just hanging out.  These are accel coils that came on the bike and the wires are resistor wires. Graphite I think. The longer of the wires measured about 4-5 ohms resistance and the shorter of the wires measured about 2.5 to 3.  It was a while back when I checked the coils but I believe they both were right around 5 ohms.   

Don't know if it's relevant, but I was turning the engine over one time with the kill switch on still and plugs out and wires and caps laying on top of the motor. There were sparks arcing from inside of the plug caps out the bottom of the cap to the motor. Got to be like almost an inch of arc. Is it possible that with the plugs in, the spark is arcing someplace else other than the tip of the plug?

[scottly]

The number 1 spark plug wire should come from the same coil as number 4, and the number 2 spark plug wire should come from the same coil as number 3.

[Jake88]

The number 1 spark plug wire should come from the same coil as number 4, and the number 2 spark plug wire should come from the same coil as number 3.

Yep, that's how I've got it set up.  I have not attempted flip-flopping wires one and four and two and three yet. I'm going to try just on the off chance that that gives me different results on which cylinders are firing. 

Even cylinders one and two, the ones I'm having trouble with, are hitting occasionally. When I measure temperatures right where the headers connect to the motor, after a minute or two of running, cylinders one and two we're at like 150 and three and four we're at around 210

[scottly]

The pipes will get warm from compression, even if the cylinders aren't actually firing. What do those 2 spark plugs look like?

[Jake88]

The pipes will get warm from compression, even if the cylinders aren't actually firing. What do those 2 spark plugs look like?

I hope they are getting warm because of compression! Spark and fuel I can fix, low compression might mean another tear down. Compression tester coming in the mail tomorrow. Plugs look Clean. Gassy. 

[Jake88]

Had a little bit of time to screw around with the bike this evening. I'll tell you what I did and please let me know your thoughts.
I started by doing a cold dry compression test with the air box off and throttle wide open.  Started with the cylinders that seemed to be running well, which both tested 148 or 150 PSI. Then moved to cylinder 1. I nervously hit the start button and it lept up to just under 150.  Same with cylinder 2. So I've got good compression!

Next I flip-flopped the wires between 1 and 4 and 2 and 3.  No change. Then I switched a few spark plugs around. No change. 

I took the cylinder one carb bowl off and checked the slow and main jets and they were open like I figured they would be.  Float height is 26 mm. 

Then I pulled the exhaust headers and muffler off of cylinders one and two and confirmed that it was not plugged up in any way. It did not seem to be when I blew compressed air through it. There is some baffling or something in there that kind of looks like two pipes right next to each other and it is loose And kind of floats around but I can't get it out.  The baffling out of the tip is missing.  I started the motor with the exhaust off of cylinders one and two and when I blipped the throttle there were some flames coming out of the exhaust ports.  Put the exhaust back on. Started it up and let it run for 5 minutes or so varying the RPMs with the throttle.  Put my hand over the end of the mufflers and blipped the throttle up to 4k.  There's definitely pressure coming out of each one, maybe even similar pressure, but the exhaust coming out of the one and two muffler just feels cooler to me.   Temperature where the headers go into the motor got up to about 270 on cylinders 3 and 4 and around 220 on cylinders 1 and 2.

Thoughts: carbs one and two are connected and share a vent tube.  If this pressure vent is plugged could that affect both of those carbs?

Could it just be that the carbs need synched? Maybe my bench sync wasn't that great. 

I think the issue seems to be most prevalent at idle. 

There's definitely a little bit of whitish smoke coming out of the exhaust. Is this normal after a rebuild? 

I wish I could take it for a spin but it is not ready to ride yet.