Topic: 1975 CB750 K5 "Rhonda the Honda"

[evanphi]

Winter has arrived... so no more riding.

Plans for this winter/spring:

Cut frame and install Frank's kit
Set carb float levels to 2mm below seal using clear tube method
New kick stand (Carpy)
Top-end gasket set (CycleX)
Tach plug (CycleX)
Fuse Holder (Hondaman)
Headlight relays (hondaman)
Black pipe wrap (maybe)
Fork oil flush and change

What should I use for fork oil? I weigh 160lbs, if that makes any difference.

[evanphi]

Had the day off yesterday, so I did some prep for the frame cut/head gasket change and winter storage...

Removed:

Battery (and put on tender in basement)
Exhaust (will re-paint headers and allow them to cure over winter)
Carbs (coming inside for storage and thorough cleaning, and new rubber fuel lines)
Airbox (box is getting peanut oil treatment)
Breather tube from valve cover
Spark plugs

Recommendations for what to do with my gas tank? Should I top it off with fuel and Seafoam?

[evanphi]

Disassembled carbs somewhat to be able to give them a good scrub and get rid of some road grime. Diluted simple green should take care of all that oil that's been leaking! Here comes the toothbrush, carbies!



Also, new 1/4" rubber fuel line and worm clamps just behind the bins.


I want to have the float levels more in check (2-3mm below the seal) before the spring. Would it be a terrible idea to use say... water... to get my floats right? Or is that a silly idea? Should I just suck it up and be prepared to drip a bit of gas?

[evanphi]

Carbs and airbox have been degreased and reassembled.

Also did the HondaMan suggested rerouting of the bowl breather tubes to the airbox. We'll see how that changes things come springtime.

[evanphi]

Bit of puttering today...

Made some tubes for the clear tube method of checking float height. I have some new bowl drain screws coming in the mail (along with some other things!), so the two slot-most-hacked-up ones got re-purposed! Cut the heads off, then spread the end of a 1/8" ID vinyl tube to fit over the end with the holes in it using a pair of needle-nose pliers. Then added a bit of shrink tubing over it all just to be safe and have something for the threads to seal against when they get screwed into the bowls. Made two.





Exhaust needs a touch-up coat of VHT flat black exhaust paint... and I'm actually going to let it cure this time before heat-cycling it!

So I degreased it all, and rinsed with cold water.



Now it hangs in front of the heating vent for the night.



Tomorrow I will attack it (lightly) with a wire brush to remove any flaking black paint, and possibly do the touch-ups.


I've gathered my tools for doing the frame cut to dig in to the top-end... too bad we still have buttloads of snow!

[evanphi]

Sorted out what gaskets and and O-rings I need to dig in to my top-end. I ordered a whole engine gasket kit, so I had to measure the orings and see which ones I needed... Hondaman's book was helpful in figuring out what I needed: two on top of the cylinders, along with the stud rubbers (holes in gasket are big enough!), and four little orings for the metering jets on top of the head. I got 6 pucks in the gasket set, and I also ordered four more. So I will measure their pocket's depth when I have the towers off, and see which pucks are closest to 0.030" more than that value (according to Hondaman here. Also going to change out the orings for the tappet covers and breather cover. Set aside the head gasket and valve cover gasket too, as well as four new exhaust gaskets.

Getting organized for this job is half the fun!

I'm going to get everything taken apart, and bring the head and valve cover inside to be cleaned. Going to clean the rest of the engine once everything is put back together and the weather warms up. No sense in everything getting wet when it is always below freezing!

One other thing I plan to do... remove the tach drive gear from underneath the valve cover. I am not running the stock tach on this bike (electronic tach weeee). I have a plug all made up and ready to go in, and hopefully removing the driver will reduce any tendency for that spot to leak oil. I have an Oring on the plug anyway, but just want to be sure!

[evanphi]

Stage 1 of frame cut/top end work...

Marked the spots


Cut them with a tube cutter to give a guide for the hacksaw. Covered the engine after threading the saw... and decided it was too cold to start getting in to this now. Bringing the space heater to the garage tomorrow.

[evanphi]

I cut just above the carb linkage, and all the way forward allowing for the ignition bracket.



Also got my valve cover off... turns out it is K head, just painted black by PO.




What is the consensus on the 5mm bolts in the cam towers? Keep them in? I see one was "replaced" by PO...

According to Hondaman, leave them out!

if i read that right mark, i should leave the little bolts out that keep the shaft from roatating?

I always do: I have a little box full of them, now! 

[evanphi]

Picked up some slick stuff from the post office...

[evanphi]

So I started taking my top end apart last night... and found a few surprises...



See that big bolt there? It is A) too large, B ) not necessary, C) Imperial.

Turns out the PO/whoever built the bike last time DRILLED AND TAPPED to put a 1/4" bolt into the rocker shaft. FOR FORKS SAKE!!!

All the other shafts came out no problemo... this one, on the other hand, scratched my rocker shaft bearing surfaces all to #$%*. The shaft has burrs on it from the drill/tap hack job, so there are gouges in all of them now...



You can see gouges already...





And here's the shaft... leftovers from the drill/tap on both sides of the hole.



PO had to ram the shaft in, and I had to tap it out.


AND! (more surprises)

NO 6x35 flanged bolts under the pucks?!?!?!?!




So obviously I need to get 4 flanged bolts. Easy.

BUT what do I do about the scratched bearing surfaces on my 3/4 cam tower? Get a new one? As for the shaft, I can get rid of the boogers at the edge of the holes using some emery paper. I'm not putting the bolts back in anyway... going to be like the K0-K2.

Can I salvage my cam tower? Can I use it as-is? There are no high spots in those bearings, just the gouges.

I'm going to also start a separate thread so others can see/chime in/gain info from it.

[evanphi]

Got the head off last night... Following the diagram:



I went around to check if all the nuts were at least 15 ft-lbs... turns out the #2 and #4 nuts were loose, which was probably causing my head gasket leak around #3 piston, and the blowout which you can see in the pics. I notice 1 and 4 are much more carbon-heavy than 2-3. When I was checking everything before teardown, I noticed that all the tappets were very tight, no matter their position on the cam lobes. I'll be sure to set them all right when I reassemble.

Lots of carbon to clean off... I soaked the combustion chambers in engine cleaner last night, and it took away all the flaking. Need to get rid of all that stuff though... any tips? I was thinking of a stiff plastic bristle brush and some brake cleaner, or just straight up acetone. So now the cleaning process begins, as well as waiting on some cam towers...

 
CYLINDERS
1:


2:


3:


4:


HEAD
1:


2:


3 (Notice the blow-out to the front!):


4:

[evanphi]

Did some cleaning prep today...

Cleaned most of the carbon off the pistons. Cleaned most of the old oil off the cylinders and head. Also removed the dowel pins and rubbers on the studs.




Also found out just why the PO had to ram the rocker shaft into the tower... IT WAS BENT!!! It was out about 0.020" at one end from the center. Maybe from when it was drilled/tapped? Who knows. The whole thing needs replacing, regardless. I have a lead on a set... just waiting now...

Here's the combustion chambers all cleaned up (1-4):






Put some spark plugs in last night and filled the chambers with WD-40. No leakage!

[evanphi]

Got my head torqued down... PO didn't install the M6x35mm under the pucks, so I replaced all 6 of them: 5 M6x35 and 1 M6x90 10.9 grade socket heads with washers. Torqued those all down to 90 in-lbs. On to the head nuts... added a dab of oil on the threads and washers, then torqued in sequence to 8 ft-lbs first, then 15 ft-lbs. Checked them all again afterwards, and the M6s needed a bit of snugging. Tonight I will loosen everything and do it again!



Now I just need to wait on new cam towers to come from a generous forum member, and then I can proceed! I'll check all my torque again before sealing the pucks and putting on the towers.

Also took off the cam chain tensioner and lubed it.

[evanphi]

Nice haul from Canadian Tire...

Mothers Back to Black
STP High Mileage oil treatment (for the ZDDP)
Permatex Ultra Grey (AKA Hondabond)
Permatex thread sealant
Permatex dielectric grease



Mothers Back to Black really works! Holy smokes! My airbox is all scratched, but at least it's shiny now!


Also did the second round of torques on the head.. loosened 1/2 turn in sequence, tightened to 8ft/lbs then 15ft/lbs.

Installed a new gasket for the cam chain tensioner, which is held back until I get the cam/sprocket on.

Drained all my oil. I'm letting everything drain overnight, and then I'll be dropping the pan tomorrow, too. Just to see what might be lurking inside... we shall see! Probably will give the oil pump screen a scrub, too.

[evanphi]

Knocked a few things off my list this weekend...

Dropped the oil pan. Found little flakes of what looks like aluminum (probably from PO's drill and tap), and a bigger piece of something ferrous... Piece of piston ring (Not enough radius to be piston ring). Anyone have an idea? Cleaned everything out, sprayed with engine degreaser  and scrubbed. Torqued the bolts down like a drum head (opposite sides, clockwise) to 75 in/lbs with a bit of Permatex Ultra Grey (AKA Hondabond) around the flanges to seal them off. Topped it all off with 3L of oil.







Also replaced fork oil. HOLY HELL that old stuff stinks. Opened the drain screws, bounced the forks till the holes were just farting, but not sharting. HAHA. Then added 160cc of 10W fork oil. I was able to keep my bars in place and use my adjustable wrench to get the caps out, using a 3/8 ratchet extension to keep pressure so the cap didn't fly off. (don't mind the white on the disk, just reflection of the flash)




Cut some channels into the brake pads, and rounded off the edges of the pads. Added some anti-sieze behind the pads to give a bit of lubrication, too. Lifted the front end and hit the disk with some 600 grit wet-dry to take some of the glaze off. Wiped it all down with brake cleaner, and called it a night.



Just got word last night that my cam towers and rocker shafts are going in the mail today! Looking forward to getting it all back together. Going to be doing touch-ups on the engine paint by hand. Using Duplicolor Engine Enamel in low gloss black, I will spray into a little bucket and paint with a brush... don't want any overspray on the valve cover.

[SOHC4 Cafe Racer Fan]

Old fork oil has a bouquet unto itself.

[evanphi]

SO I have the same issues as described in this thread: http://forums.sohc4.net/index.php?topic=70403.0

Especially the last post:

I've seen a few torque arms where the holes have stretched out to oval and even with the correct bolt there's slack. The slack does just what you describe - after braking in reverse you have a problem next time you use it going forward. The braking suddenly gets a lot stronger with a loudish CLUNK.

I have noticed the holes in my torque arm are possibly stretched, but more importantly, the bolt holding the torque arm onto the brake is NOT what should be there. So my question: What size is the threading on that bolt? Has anyone successfully made a replacement part? Anywhere in north america that carries it? Anyone want to sell the bits to me?

I know Yamiya750 has the part I want, but it would cost me close to 50$ by the time exchange rates were applied (Canada) for ONE bolt...

[Restoration Fan]

Old fork oil has a bouquet unto itself.

That it does.  Eau de arse!

[Restoration Fan]

SO I have the same issues as described in this thread: http://forums.sohc4.net/index.php?topic=70403.0

Especially the last post:

I've seen a few torque arms where the holes have stretched out to oval and even with the correct bolt there's slack. The slack does just what you describe - after braking in reverse you have a problem next time you use it going forward. The braking suddenly gets a lot stronger with a loudish CLUNK.

I have noticed the holes in my torque arm are possibly stretched, but more importantly, the bolt holding the torque arm onto the brake is NOT what should be there. So my question: What size is the threading on that bolt? Has anyone successfully made a replacement part? Anywhere in north america that carries it? Anyone want to sell the bits to me?

I know Yamiya750 has the part I want, but it would cost me close to 50$ by the time exchange rates were applied (Canada) for ONE bolt...

The threading on the arm is 6 mm with a 1.0 pitch.  I just purchased a tap and die set from Northern Tools last week and repaired the threading on my 78K successfully.  I had to get my rear hub and little drum nut thingey from Bill Benton because the PO of my bike had "redneck engineered" a solution out of two common bolts.

[evanphi]

I might roll my own out of an appropriately sized stainless bolt, then just turn down the smaller end on the lathe, then thread the end... Hmmm fun long weekend project...

[evanphi]

Got some more things ticked off "the list"...

I made some shims out of gasket material to get adequate compression of my stud pucks. Gasket material is 0.75mm, cut in 1" circles.

with the crop of too-thin head seals we keep seeing, here is a way you can check the ones you got in your gasket kit (or elsewhere, like PartsNmore or CB750Supply, etc.).

First, check the step depth of the head hole. Then, check the thickness of your seal. You need at LEAST .030" compression, .040" is better. The too-thin ones are only about .005" thicker, which won't seal when the head heats up and the hole becomes deeper.

The pics tell the story!




This would have resulted in only 0.010" of compression. Not enough!






Boom! 0.040" thicker than the recess!


Also checked my float heights with clear tube method. I used water indoors. No gas.



Checked them all to the line on the left, which is 3mm below the lip of the bowl.



They all had to come up about 1-2mm, as I had replaced the needle valves with aftermarket parts, and the little spring in the needle is very stiff!


Also did end up making a custom bolt for the rear brake torque arm, as described in my previous post. I used a 1/2" stainless bolt that was 2" long. Went over to have my Father use his fancy-dancy lathe to turn the shaft down to 10mm diameter. Then cut 1.25" worth of M10 threads. PO had enlarged the hole at the end of the torque arm to 10mm. Then I filed down the bolt head to 15mm wide on the skinny sides. Slid it in perfectly! Using a nylon lock nut as well as a lock washer, this bolt won't be going anywhere!

Good start to a 4-day birthday weekend!

[evanphi]

Re-re-routed the fuel lines.


Airbox mod.



Also built myself a new fuse panel for ATC fuses. No pics, though... all tucked away now!

Got some final touchups done on my headers. All black again now! Going to properly bake on the paint this time.

[evanphi]

Something came in the mail today! Thanks Rafi! (aka edwardmorris)



Shop night on Friday!

[Tetter]

Airbox mod.

Just curious what would this Airbox mod solve / help ?

BTW super bike !     Just read the whole thread !

[evanphi]

Airbox mod.

Just curious what would this Airbox mod solve / help ?

BTW super bike !     Just read the whole thread !

Thanks!

Adding the little holes here allows the airbox to pull air more efficiently. Putting holes here, rather than taking out that whole wall, improves airflow without increasing noise. The tuning characteristics are not changed because the filter is not changed, though! Read HondaMan's book to find out more!