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[RR-CB750]

Hello everyone.

New to the forum. Just thought I’d say hi and give a little story to what brought me here. Bear with me as this is a somewhat long story. But it’s a special one, and worth the read.

In 2018 my Wife lost her grandfather to undiagnosed brain cancer, no signs or symptoms, happy and the usual Pop one day, and gone the next. Her grandmother, not being able to deal with the pain of living in the house they build together in WV in the 1980s, decided to sell and move to PA this past spring to be closer to family.


As she was moving, none of her children cared to take the bike and she was going to send it to a salvage yard.

Now this 1977 CB750 Four was Pops life, he bought it new in 77 and he rode it everywhere while healthy.

In 2017, I remember us going up to their house before we moved across country. He asked if I could come up and help him get the bike running after 8 years sitting. Which after a weekend, we got it going.

He bought a full engine gasket and seal kit, new cables and brakes for it. With the intention of getting it rebuild and restored to a daily rider condition.

6 months later he laid it down on the WV gravel and pothole ridden roads. It got towed to their garage where it sat since. And now it’s in my possession. To be restore to something that he’d be proud to have. He always loved my 79 GS550 hard tail, and 82 GS850 brat, that’s what his intentions were in style.

So I plan to aim for either a tracker, cafe or beat style with this bike.

Anyways, here’s some picture of the bike, how I had to get it in my truck by myself in WV, and it’s current state after a week of digging into it.

Also, a couple ideas of the finished bike, as wells as a paint color to keep the original burgundy color, maybe add some gold flake to tie in the gold stripes.

If anyone wants to follow the Facebook page I created for more current updates, here the link.

https://www.facebook.com/profile.php?id=100086589786145

 

[dirtdigger]

Keep us posted on the build. Dont be afraid to ask any questions. Any upgrades being done to the engine?

 

[RR-CB750]

Keep us posted on the build. Dont be afraid to ask any questions. Any upgrades being done to the engine?

I was debating maybe an 836 kit. But it doesn’t need to be fast. So most likely not.

Probably try and find an old kirker 4-1 and some pods, that’s it.

As for questions, what would be the best way to get 45 years of oil and dirt out of the head fins?

 

[RR-CB750]

And a small update, the whole motor was covered in oil and dirt from gravel roads.

The oil pan itself turned out nice. But so did most of the other covers I’ve done so far.

Some before-during-and done shots of what just the oil pan, as well as the other parts looked like.

 

[RR-CB750]

If anyone has any pointer on stuff that these bikes are known for and to look out for I’ll take it. Like the cam tower bolts, I’m already planning and have the m6x1 Heliopolis to just redo them now.

But a little more information on the build.

First, the RR isn’t meant to be like the race RR, it’s her pops initials, that will get ghosted in gold on the rear section of the tank. But if I did big bore it it would also fit the RR race aspect too.

Second, I’m getting all new lash covers in polished, all new stainless hex or P3 hardware for the case covers, and stainless bolts that will be showing on the motor, i.e. engine mount bolts, cam tensioner bolts, and the like.

Once the engine is painted I will sand back the fins and polish them to have an overall semi-gloss black and polished motor.

Hubs and spokes will be black with polished rims, black fork housing with the polished/chrome tubes, black rear shock with chrome springs, a triple tree top mount for clip ons, and a full re-wire with updated electronics like that dash and all. I may keep the points system as it was all replaced by pop with oem Honda stuff.

 

[dirtdigger]

I would say keep doing what your doing as far as cleanup. Parts wash tank with parts washer would cut the oily grime well but have use oven cleaner on bad stuff to get it down to the aluminum.

I do work on the 750 motors so I have a lot of tips etc but it would take me all day to type. There are different suggestions for different power levels and engine sizes. Kind of depends on the build and how you are going to use it. I like to build stronger than needed so dont have to worry if I add more power later. Stock motors I would upgrade cylinder studs, cam and primary chains and new tensioners, if engine is apart and doing machine work have top of cylinder and head machined for MLS head gasket......no leaks....., Have cylinder head rebuilt by a bike shop not automotive...I suggest cycle x or APE. Stock valve sizes are fine for stock bore but a ported head makes a huge difference in power in the cb750 because the head really isnt designed that well to flow. Even a stock rebuilt head(so it is tight and seals well) and a little bigger cam from cycle x will help wake it up on stock bore. Undercut transmission so it doesnt pop out of gear. Rebuilt oil pumps from cycle x because they are terrible for valve in them leaking oil out of tank into the engine. Upgrade to dyna ignition so no messing with points. Thats just a couple things to consider. Much more info if you want to dig deeper into the motor.

 

[RR-CB750]

I would say keep doing what your doing as far as cleanup. Parts wash tank with parts washer would cut the oily grime well but have use oven cleaner on bad stuff to get it down to the aluminum.

I do work on the 750 motors so I have a lot of tips etc but it would take me all day to type. There are different suggestions for different power levels and engine sizes. Kind of depends on the build and how you are going to use it. I like to build stronger than needed so dont have to worry if I add more power later. Stock motors I would upgrade cylinder studs, cam and primary chains and new tensioners, if engine is apart and doing machine work have top of cylinder and head machined for MLS head gasket......no leaks....., Have cylinder head rebuilt by a bike shop not automotive...I suggest cycle x or APE. Stock valve sizes are fine for stock bore but a ported head makes a huge difference in power in the cb750 because the head really isnt designed that well to flow. Even a stock rebuilt head(so it is tight and seals well) and a little bigger cam from cycle x will help wake it up on stock bore. Undercut transmission so it doesnt pop out of gear. Rebuilt oil pumps from cycle x because they are terrible for valve in them leaking oil out of tank into the engine. Upgrade to dyna ignition so no messing with points. Thats just a couple things to consider. Much more info if you want to dig deeper into the

 

[RR-CB750]

I’ve never ridden a cb750, so idk how they perform. Will I be disappointed with it if I just threw it back together stock?

If so I guess it’s time to dig into it and get some performance out of it.

I’ll try and do some digging on here to find a good build, unless you don’t mind throwing a quick list together. On top of what you already stated.

 

[dirtdigger]

They were good for the day and for new riders they still make good power. A modern 600 sport bike blows them away, but they they make almost twice the horse power. Gotta remember your bike is 45 years old and has 45 year old technology, its low on horsepower for the displacement, the brakes suck, the handling is twitchy and its heavy. But they are nice bikes and I wish I had more of them. These engines are money pits. But they are the best looking engine built if you ask me and they sound great too.

A good basic little build with a little more power would be to start with a 10 1/2 to 1 836cc bore kit. If your going to run it hard put cycle x super rods in it, if you will ride it for fun and not beat on it at redline you could use stock rods and put new rod bolts in them. Have the crank lighted and balanced. Lightened alternator rotor as well....just wont charge at idle but then the stock 750 wont charge at idle either if headlight is on. New heavy duty cam chain and primary chains along with new tensioners on both. Heavy duty cylinder studs a must. I always suggest undercut transmission, keeps from popping out of gear. Cylinders are just bored for 836 pistons only so dont need to deal with new sleeves. Have cylinder and head machined for MLS head gasket=no leaks. Now cylinder head is where you gain all the power in the 750 but its also where you spend most of the money. 750 heads suck at flow, they need a lot of porting work to make power. You can run a stock head on 836 but you will gain very little. If you spend a little and have the head ported and large intake valves installed you will have a little runner of an engine. Even ported with stock size valves will run very well if you want to go a little cheaper. Camshaft selection will depend on how you want to run it and how you want it to sound. You can make these things idle like a timex or can sound like a racecar depending on the camshaft, but there are trade offs in both cases on how it will run. cycle x cx 3 or cx 4 depending on desired characteristics. New valve springs and refurbished rocker arms are a must with a new camshaft. To top it off dyna ignition so no more point setting and a good set of carbs...either Keihin CR carbs or Mikuni RS carbs and you will have a good runner. Stock carbs will run pretty good if you spend a little time on the jetting. All of this is from and done by cycle x and highly recommend them.

Sorry just reread you wanted quick list

10.5 to1 836cc kit
bore cylinder and surface for MLS
MLS head gasket
balance and lighten crank and alternator rotor
stock rods and new upgraded bolts or cycle x super rods
heavy duty cam chain and primary chains
new OEM timing tensioner and primary tensioner
Undercut transmission
stock clutch but new disks will work, maybe heavy duty clutch springs
heavy duty cylinder studs
rebuilt and ported head with or without oversize intake valves and surfaced for MLS head gasket
cx3 or cx4 camshaft
refurbished rocker arms
heavy duty valve springs
dyna ignition
Keihin CR29 carbs or stock if needed

 

[RR-CB750]

So what would a build like that be similar to in performance? And the two cam options, what would be the characteristics of them?

Sounding like a race bike and being an outright street machine would be cool. Probably only going to ride this thing to shows anyways. Maybe cruise around a couple times in the summer. So having a nasty machine would be cool.

So it sounds like doing any paint work on this motor will have to wait until it’s built. Just gotta put some dough aside for this. Sounds pricey.

In the end, what would be a list to be an outright race machine but not unwieldy around town? Don’t want something that’s straight line 1/4 mile only.

 

[dirtdigger]

The cx3 would have a better idle and more bottom end power, the cx4 would be rougher idle and mid range to top end power. Either one is still good for street riding.

Yes paint after machine work is done, it would be damaged during machining process and final cleaning and assembly.

You can easily make a 1000cc motor drivable around town but you will double your cost going that big with all the extra parts and machine work needed to make good power and make it live. I have around $7000 into my drag race motor not including carburetors and ignition system which will also need upgrades at big power levels. For a streetable version look around $5000

 

[RR-CB750]

Yeah, just looked all their services up. And seeing the prices of all that, I think this bike will be fine in stock format. As will I.

Yeah a racey bike would be cool, but not at $2400 for a shortblock. Let alone a BB kit, cylinder and head work. We’re talking $4000+ in the motor alone.

I’ll throw this stocker back together and just ride it like that. If it weeps oil, oh well. I’ll just clean it up after every ride and make sure I keep an eye on the levels.

 

[Scootch]

You will have a blast riding it. Its like driving a classic car around. You will get many looks and thumbs up Even people who are not motorcycle people look, stare, and want to talk to you. The bikes are beautiful and pleasing to the eye. I had always wanted one. It took me 50+ years to get one. Every time I ride mine it takes me back 50 years. I know I could get an up to date bike with many features and better handling and rideability. But those bikes aren't these bikes.

 

[RR-CB750]

So here’s where I’m at as of now.

Decided to not do any performance modifications to the motor and move forward with restoration.

I have yet to split the cases to check the bottom end. I will be putting in new bearings for the whole bottom end, seals and orings, and new chains, tensioners and guides.

But the head and jugs checked out, so new seals and a paint job and they will be good to go. Have to let the paint on the head cure for a couple days then I’ll sand the fins back like the jug. Those poor fins took a beating from the gravel roads in WV, a bunch of chips and dents from rocks. But no cracks or pieces missing bigger than a BB.

 

[RR-CB750]

Update:

The top end is done. Everything’s painted, lapped the valves, all new seals and waiting for the bottom end.

I got that opened up. All the bearing in the transmission are nice and smooth and quiet. Gears all look good, primary chains look great, tensioner is still supple rubber and it’s spec before dis-assembly was 66.3mm from case to plate. So I think I’m going to reuse all that.

Case markings are BBBBC, crank looks fine, but the mains, anyone have an input on these? Can’t see a color on them. Will have to check the book on what to use if they need replaced.

Main reason for DA was to clean it and paint it. When I drained the oil a bunch of sludge was in the filter housing and in the pan. And as suspected, it’s in the bottom of the case too. I think the filter bolt or housing prong was bad and the gravel/dirt roads were kicking mud and dirt up and it was getting in the case. As you can see, the bottom is covered in mud and oil. Really, nothing higher than the filter housing is this bad.

But I also want to replace anything bad while in there. Bunch of photos to show what I’ve found and why I took it apart to clean it.

 

[RR-CB750]

Oh, pics of the top end stuff, and the valves.

 

[RR-CB750]

So case markings are BBBBC and crank markings are ACACA,

Rods are 1111/4444

So if I’m understanding this correct, these should’ve been

Green brown green brown brown bearings for the crank and all yellows for the rods.

Should I just order all greens and be ok with a little more clearance? We’re talking a max of .005-.010 of difference in clearance on the crank.

Rods I’m going to leave alone. I think the scratch was from me when trying to wipe the bearing to check for wear.

 

[RR-CB750]

Been a couple weeks. Stayed busy with progress just didn’t post anything up.

Here’s what was accomplished.

 

[Biebs]

WOW amazing progress.

Thank you for saving / restoring this family heirloom!!!

 

[RR-CB750]

WOW amazing progress.

Thank you for saving / restoring this family heirloom!!!

Thanks! I was thinking of getting a new points and clutch adjustment cover as they were pretty pitted, chrome flaked and rusty.

But after I cleaned them and polished them the best I could, I kinda like they way they look. Letting some of the original patina show through.

I don’t want it to be 100% showroom new. Then I’d never want to ride it.

Next on the list is the wheels and forks. I have all new bearings and seals for them ready to go for a rebuild and repaint.