Topic: Cb750F 1978, and hello

[Thousandson]

Hi all, this is my intro and i have questions. I've been reading about taking my engine apart http://forums.sohc4.net/index.php?topic=29364.0

Thank you all for posting it will make job easy, and fun. Information so far, we have a Honda Cb750F 78'. I have been dreaming about getting a 750 for about a year. This past summer I traded my Honda cm200t(I still miss her) for the current project. Carb.s cleaned, but I still need all new gaskets. The engine turned over, and is running. It can only idle with the throttle at a quarter turn.(and when I mean Idle, I mean 2k revs) I fear the pilot jets might be clogged, the idle adjustment screw is all the way in. What should I do with the carb.s, will new gaskets fix everything?

The last picture is the diagram of breather hoses. The second to last picture is the part the is bolted to the bottom of my battery box. Can someone give me the end all be all, to where all breather hoses go. From exact part to exact location. If the hose goes to open air, I will run those hoses correctly away from hot moving parts. Thanks, wish me luck.
















The Part in question, what is it and where do all of the hose connections go?



This diagram is under the seat right behind the battery compartment.

[toytuff]

Greetings!

Always liked that year F. Most will tell you to completly rebuild the carburetors but the first thing to do is download the service manual.

From there it is straight forward.

tt

[madmtnmotors]

Using your picture as a guide:



Connection one goes to the connection at the top of the air cleaner, connection two goes to the connection at the back of the valve cover, and connection three (drain) is typically routed around the front of the swingarm then back to the muffler bracket, either open to atmosphere or plugged and drained at oil change intervals. It looks like you've got an early model (75/76 750F) seperator there, the later (77/78) air seperator looks a little different, but the basic function and connections are the same (or similar).

[bjbuchanan]

Welcome and good luck with the build

In the faq section there are the manuals. chase down the good links and familiarize yourself with them, it will help a lot to be able to just spot recognize stuff.

Your carbs will need to be cleaned well and I would say use the search bar on the left and type in the model bike you have because your carbs need a little bit better cleaning than say my 72's

Hopefully you just need gaskets and not accel pumps

Have fun

[bollingball]

Look at page 291 or close to that in the Honda service manual that you can download from this site. It shows where all the hoses go.
Toytuff is correct you need the manual and it is free

http://forums.sohc4.net/index.php?topic=17788.0

Ken

[Thousandson]

I have the clymer cb750 manual, I've look through it, some times it doesn't give you enough detail. Or i might of missed it, or not even printed. I do have one tube that does have a hard end plug in the end, now it makes sense.

#1 Goes to the Air cleaner/ Air box
#2 Goes to Top of the valve cover
#3 Is my drain

Excellent thank you.

Please confirm the next few hoses
Fuel tank over flow ---> Open Air?
Carb breather port --->open air?
Rear of crank case --->oil tank over flow?

The bike is a 78', on the plaque on the neck, this could be just the frame, but parts always get traded around.

Lastly, I want to find a new wireing harness, i saw a post that that cb750k (76-78?) is the same harness. I just wanted to confirm, if i'm going to have to pay for the $150 for cb750F 78' harness. Or $90ish for the cb750k.

PS. The clymer cb750 manual just says to remove fork tube seal. HOW?! I Don't Have Hulk Strength. I had to go out and buy an 18" flat blade to get the dang thing out. But it worked, thank you SOHC 4.

[lucky]

Using you picture as a guide:



Connection one goes to the connection at the top of the air cleaner, connection two goes to the connection at the back of the valve cover, and connection three (drain) is typically routed around the front of the swingarm then back to the muffler bracket, either open to atmosphere or plugged and drained at oil change intervals. It looks like you've got an early model (75/76 750F) seperator there, the later (77/78) air seperator looks a little different, but the basic function and connections are the same (or similar).

If you cannot read and follow that diagram, which is excellent ,then I do not know how you will fix your carbs.
What really scares me is when you said," Wish me luck"

You need to get a workshop manual.

BTW You asked, "What IS IT?"  It says right on the sticker... Separator. (air/oil separator.)

[bollingball]

I have the clymer cb750 manual, I've look through it, some times it doesn't give you enough detail.

This is one reason to download the factory service manual.

 PS. The clymer cb750 manual just says to remove fork tube seal. HOW?

Download the Honda manual
Ken

[Thousandson]

Progress, Its been about two months of tear down.

Beginning of October
Engine freshly painted and a clean work bench...


Cover removed, its looking clean.



This was a camera phone photo, but it came out pretty well


Man its a lot of parts to take the heads off.


Ok getting these cylinders/jugs off was a #$%*. I found water and a ton of corrosion in one studs, it wasn't a oil passage, but I had to pour a little soda into the passage eat away at the corrosion to get the jugs off. Cylinders are measuring great, still got some wear in them.


#2 is looking a little wet...::clearing throat::...spark plug is new. Newer then I would of expected. More electrical issues, never a problem.


Upper half


End of November
Lower half, I've gone this far because the kick starter wasn't engaging.


What is the center double sprocket between the clutch, and transmission? Does it help dampen shock to the crank shaft?


The kick starter has been repaired, I need some more polishing, but its already better then before. I had a burr that was holding back the engaging tooth.  A few more stripped phillips heads nothing an extractor didn't fix.

[nitsua93]

I love this bike. Wish I had a 750F. Just so you know. The oil/seperator thing isn't a necessary part. All it's for is emissions. I was talking to an old timer who built these from the 70s to the late 90s he said they're completely unimportant and pointless, unless you're a "green" kind of guy.

Sent from my HTC One X using Tapatalk 2

[Rigid]

Ok, you painted the engine and then tore it completely down.  Did i miss something here or are you just doing a complete teardown and inspection for "fun" ?  Love that model F btw.

[madmtnmotors]

Ok getting these cylinders/jugs off was a #$%*. I found water and a ton of corrosion in one studs, it wasn't a oil passage, but I had to pour a little soda into the passage eat away at the corrosion to get the jugs off.

Okay, a little tip here... you see those acorn nuts? Those acorn nuts also have copper washers associated with them (the other head nut washers are steel), THIS IS IMPORTANT! I am currently correcting a P.O.'s comedy(?) of errors on a 78 750F motor right now. Those acorn nuts and copper washers seal the threads to prevent oil leeching out where these studs are exposed to the atmosphere. THIS MUST ALSO BE ADDRESSED AT THE BASE OF THE CYLINDERS WHERE IT MEETS THE TOP OF THE CRANKCASE. THESE FOUR CYLINDER STUDS EACH REQUIRE AN O-RING THAT IS NO LONGER DISTRIBUTED BY HONDA FOR THE CB750. Good news is that they still distribute this o-ring for their lawn mowers and outboard engines. Have to pull the head and cylinders just to install these four stupid o-rings. Of course this also requires a new head gasket and cylinder base gasket.









































Damn P.O.'s....

[KRONUS0100]

madmountain.........do you have a part number available for those 4 orings?  they appear to be somewhat conical shaped on mine (78F)........i cleanes up mine as best as i could an put the tiniest amount of black rtv on them to make sure they sealed.  would rather replace them if they are easy to get ahold of.

[madmtnmotors]

madmountain.........do you have a part number available for those 4 orings?  they appear to be somewhat conical shaped on mine (78F)........i cleanes up mine as best as i could an put the tiniest amount of black rtv on them to make sure they sealed.  would rather replace them if they are easy to get ahold of.

The original CB750 part number is: 91301-410-000

The identical 5.5x3mm o-ring from http://www.boats.net/parts/detail/honda/H-91353-921-310.html is: 91353-921-310


These fat little o-rings get compressed into a conical shape by the base of the cylinders when they are torqued into place. DO NOT USE SILICONE! EXCESS SILICONE THAT FINDS ITS WAY INTO THE OIL SYSTEM TURNS INTO LITTLE OIL PASSAGE CLOGGING BB'S THAT CAN STARVE YOUR VALVE TRAIN OF OIL! I have documented a similar condition in this post: http://forums.sohc4.net/index.php?topic=115375.msg1300128#msg1300128

[Thousandson]

Thanks Madmtnmotors, I know i needed to replace all of my seals. I didn't know about a missing/discontinued o ring, sweet. Those four stud towers all had water in them at one point in time or another. I had corrosion from the stud to the wall, it took a bunch of pulls to get the studs past the thick corrosion to get the jugs off.

@ Rigid, I needed to repair the kick starter, so I decided to replace the piston rings to. I'm also looking through and sizing up the project for later. My cylinders are in speck, but the pistons are a few thousands small. I don't have the money now, but in a year or two this engine is getting an over bore. With a few other things like new front end, rear hoop, new lighting, new front and rear wheel and tries.

She's going to be road worthy enjoyable, the cb450 "Sixty Five" bobber project is next.

[madmtnmotors]

Those four stud towers all had water in them at one point in time or another. I had corrosion from the stud to the wall, it took a bunch of pulls to get the studs past the thick corrosion to get the jugs off.

Yeah, the head casting was changed on the 77/78 F model that exposes these four studs to the atmosphere where they pass through the head. I had considered greasing up these studs to help prevent the corrosion associated with this exposure. Makes their bores through the cylinders tall skinny holding tanks! Of course when run regularly and garage kept then the only water intrusion would be from riding in the rain which would burn off before having time to collect.

[MRieck]

Those four stud towers all had water in them at one point in time or another. I had corrosion from the stud to the wall, it took a bunch of pulls to get the studs past the thick corrosion to get the jugs off.

Yeah, the head casting was changed on the 77/78 F model that exposes these four studs to the atmosphere where they pass through the head. I had considered greasing up these studs to help prevent the corrosion associated with this exposure. Makes their bores through the cylinders tall skinny holding tanks! Of course when run regularly and garage kept then the only water intrusion would be from riding in the rain which would burn off before having time to collect.

How about electrical shrink tubing over those studs? That's what they did for the old FJ1200's Wilbur. I don't know if clearance is a problem.

[Bankerdanny]

My favorite F. I think the Comstars really work with the F and I also like the triple disk, which was a '78 only thing.

The downside is that the 77-78 F carbs are different from prior years F bikes and all 750k's. And the lower sales volume of the F model means that 77-78 carb gaskets can be a real #$%* to find. If you find carb gasket sets, even if the seller only has a set for one carb I highly recommend buying them.

[Thousandson]

Plastigauge says we be good on my crank shaft, all the way across the shaft, of course.
The before


The results, we good.


I got the oil pump apart, and dam. She is so close I couldn't even try to get a feeler gauge in to check it. One piece of the puzzle, I don't have to touch at all. ::reinstall::

Who knows about shocks? I don't want the stock, or retro progressive shocks. I like the look of them, but I'm going modern Cafe Racer here. I'll spend the money, more money better ride. I need a part number.

I know I've seen something like these on other Cb750's. I want the backpacks, but they don't have to be adjustable.

[Jerry Rxman Griffin aka MuthaF'er]

Looking back through your thread just a little. Great project. Take your time and pay attention to details. And yes, a Clymer is not perfect NOR is the Honda shop manual. I use 4 manuals  and each has some 'issues' whether it's model specific, translation issues or just incorrect.

That separator is NOT one from an early F. The early F has the bottom drain (3) coming off at a 90 degree angle. The EXACT drain hose is no longer available for the early one but I found a 650 worked and it just needed a little length cut off. Perhaps you can find a 'replacement' for yours. That looks like the one in the online parts fiche for your bike. The drain tube is actually 3 pieces with an elbow that attaches to the outlet. No longer available.

http://www.motogrid.com/pages/OemParts?aribrand=HOM#/Honda/CB750F_A_(78)_MOTORCYCLE%2c_JPN%2c_VIN%23_CB750F-2200001/AIR_FILTER/CB750F-78-JPN-A/2Y134102F13410216A

[UK Pete]

Great looking F2, listen to all the advise about rebuilding this engine , as you might have gathered there are a few extra things you have to make sure are correct , as mentioned in other posts , the 4 dome nuts and copper washers, those cylinder base 5.5 o rings, oval fire ringed head gasket, and definetly no silicon anywhere, be sure to check the valve guides, espesially the exhaust side, check the valve spring retainers they fracture and then brake, i was lucky i checked mine with a magnify glass and found  1 was fractured, also the valve tips get indented on these which makes setting the valve clearence awkward and unreliable, there are probably a few other things that i can't remember, i built my f2 engine two years ago and it still runs real sweet with no oil leaks, so its all possible just take on board all advise
Pete

[Thousandson]

After a little thought and beer. This bike needs to run, and work well when spring arrives. I have been drooling over from pictures online, in magazines, and beautiful show/expensive bikes. This is the first bike in the long list that's posted my my wall of project bikes I want to work on. Money has been extremely tight. I haven't even had enough money to buy gaskets to reassemble my engine. After thinking about simple parts, cam chain guide, cam chain roller, cam chain, primary chains and primary chain tensioner. I am going to inspect all three chains, replace just the guides and tensioners, and button it all back up(with new gaskets of course). I don't have all of the money in the world to make this the show bike that I want, but I want to ride again. The thought of my one and only bike sitting in parts in my basement just depresses me more, and more. The first few months, turning wrenches, taking parts off. I will remember and cherish those thoughts for the rest of my life. It will sadden me even farther if I don't keep moving forward with this awesome machine 30 feet from me.

To inspection, buy the parts that need to be replaced, to grease, blood, sweat, and beer. To get this bike back on the road.

[tweakin]

To inspection, buy the parts that need to be replaced, to grease, blood, sweat, and beer. To get this bike back on the road.

Well put!  Good luck with the build.

[madmtnmotors]

To inspection, buy the parts that need to be replaced, to grease, blood, sweat, and beer. To get this bike back on the road.

Well put!  Good luck with the build.

Riding is the ultimate goal, bling is just a bonus. You can ride the heck out of it without bling, I sure do!


Chrome won't get you home...

[Thousandson]

What companies have people been using for online parts stores? Cycle X, Cb750 supply, Vintage CB, Z1 Enterprises? I need parts but I want companies I can trust. I want a good price, I can find it for a few bucks cheaper, but who do you trust?

Out of all of my worrying, and concern. I find cheap chirstmas presents. I'm recharged and ready to rock on this project. Bead Box Air Filter

I bought this yesterday, $45 thats a deal. I won't even polish it right now, new filter slap it on and get this thing running

[UK Pete]

I like that filter, never seen one like that
Pete

[Thousandson]

Pete, the air box is from what I've called it a "bread box" filter. Chopper guys in the 80's, would put them on their bikes. I saw one, and fell in love. Don't like the stock box, never really liked the pods.

Progress! I am a theatre carpenter/welder, I have also done some machine work. My uncle was in the shop working on his own projects, so I had some time in front of a drill press to work on my disks. With a bench grinder at the shop it made quick work of the crud on my valves.

I have 18 days until the end of January, I should have my motor put back together. Waiting on a few parts, but it should be buttoned up soon. Need to get to the rest of the bike, brakes, bearings, and a few electrics to deal with.

Home made spring compression tool, a little notch in a pipe, and some double sided tape.



Cleaning some valves, so much better.






Valves cleaned and lapped, took two goes on a few but much cleaner.



My disk sanding station, wile still wearing a resperator. I have no idea what kind of nasty stuff they used as pads, not taking any chances.



A little Auto Cad and help from my roommate using a large format printer, easy lay out.



A can on super spray 77. Spray just the paper, low tack easy to pull of sticker



So many holes.



After 3-4 hours of drilling, I'm still not done. Looking at maybe another 2 hours in front of a drill press.

Just a  rough idea what it should look like when I'm done.

[Retro Rocket]

The bread box is slightly better than pods but the stock airbox is far better...

[Bru-tom]

thanks for the rotor tip mate. they look really good!

Sweet build too! 

[Thousandson]

Real quick update...

New rubber, Avon road raiders, and they are freaking pretty. Engine is back together, ready to rock. Final assembly, mounting, and more parts are bought already in process to arrive. New smaller gauges, more fuel line, new rear shocks(not the best but better then 30 year old tech.). New rectifier, ditching the old top of crank case breather hose for new tiny filter. Carbs are rebuilt and ready, replacing the float needle should help that fuel leak from last time.  That's what I have so far, more photos coming soon, build should be over the course of the next two weeks. I still need to get new brake hoses, I have a lead just a little more money, and sent my master cylinder out to be rebuilt(its just not working for me, I'll get the next one).

I hope to take a firday off and tune the crap out of it for a day. With hope to ride it all weekend. Final stretch, beautiful weather here in Boston, more beer is needed. Get riding my friends.

[Vinhead1957]

Gonna rain Friday ! Sorry I won't ride til Sunday  North shore

[Thousandson]

Picture update, begin.

Jan:

Heads cleaned ready for gasket, a little high speed wire brush, flat file, and flat sanding block. Looking pretty.


Pretty new painted steel and new rear sprocket.


PO put the wrong chain on like 1.5 extra links. I measured...



I had to buy a new rear, and front sprocket, with a new chain. I wasn't screwing around to make sure this thing ran with no problems. The front and rear showed signs of wear, I was not planning on screwing around with a new chain, with old (stupid PO) sprockets.


Engine has been split, repaired the kick start(works freaking great, I'll get to that) All greased up, and ready to go.





This was the first attempt to put the halves together. I it went together as smooth as it could. Also, their is no gasket between engine halves, I used Gasgacinch(from amazon). Apply both sides, using a respirator(do not breath in fumes in enclosed spaces), let dry, then assemble.


If you look closely at the bottom case half I forgot to reinstall the main drive tension-er. (CRAP) Tear apart and re do. One thing that did help, I put the case halves together and apart a few times. On the last tear down I put it in first gear, wile it was together, I spun the crank shaft by hand and changed gears with a screw driver, stopped(in first gear, and don't move a single gear), disassemble, paint gasket, lastly reassemble. I spun the crank again, changed gears, dropped bolts, tightened it all down. 


First round more to come in the next hour.

[Thousandson]

Alright, my time line is all screwed up, I think we are now in Feb-early April.
I had money issues, paying bills, and getting some awesome work for great pay...that payed 30 days later. My bike sat on hold for a  few weeks. No progress.


Pistons back on, I broke one ring, I got a used replacement(I'm going to over bore this bike, the bore measurement is so close to the wear limit). I need to ride, next tear down, she will be very pretty when I'm done.



Cam chain, cam shaft in, all greased, time for those tappets.



Ooooooo, refurbished rotors pretty.






I tired boiling my master cylinders, no luck. I'm using a used front master, i tried to find the correct rebuild kit. My cylinders are now at a pro. My front was giving me all hell, didn't work right, tried different parts. My rear, I have the correct rebuild kit, I couldn't get the old piston out.

[Thousandson]

This is where I stand today, I'll let the pictures speak for them selves.


New tires, with the help of my roomates, I got the engine in the frame, and tires on.









Holy Crap, its almost starting to look professional.

[hiljak]

I just wanted to let you know that I am watching this thread. Thanks for posting.
I recently bought a non-running 1978 CB750 F. I haven't had a lot of time to tear into it yet but I dig your thread and look forward to you getting her running.

[Thousandson]

More and more stuff added, problems. Also new home made parts are good fun, and now awesome. I bought two new gauges, some tiny 2.5" chrome gauges with black face. Pretty freaking sweet. I need to make a bracket, took some measurements, sat at my computer for an hour, and drew up something I was really happy with.



Take some super spray 77, spray paper, attach to steel, cut and grind.



A little filing and sanding ready for a trial assembly, and fitting.



Looking pretty sweet, fits on the bike great. I had access to a large cnc mill (I could of prototyped it better), so the gauges are a little farther away from the handle bars, but I still like the look.



I panted the bracket gloss black, and I need to get some hardware. Easy bolt on part.

[brandEn]

Bracket looks great!

[Thousandson]

So the sad news about the spedo bracket, I had to cut it down, but I as able to salvage and make it work. The bike sits as you see. More parts, and more wiring. Its really coming along, I wish it was much faster. Having a real job it getting in the way. I might be really late into this season, I'm still going to tweak it, and put a thousand miles on it before winter. That's just something I have to do.

I ran into a wiring problem with my new indicator light for my turn signals. I put two diodes in and it fixed the problem. I also found a slick way to ground out my front turn signals. I just put my bread box air filter in, it looks really good. I was hoping for it to look a little better, but I need to make more parts to make it look real slick.

The brakes is the last little bit. I got brakes seals from http://www.hondapartshouse.com. Freaking amazing, I wanted to replace all of the rubber, but finding brake rebuild kits was killing me. I also got a new Front master cylinder from http://www.davidsilverspares.com. The new MC is from a CB750FA 1980, I won't complain, I had to cut down the output bolt from the MC. I finally got all of my calipers apart and painted.