Topic: '74 CB750 Cafe - new guy, new project (old bike)

[schmolze]

Howdie everybody. I recently sold my beloved '85 Nighthawk 450 after riding her across the country, and decided to find a CB750 to refurbish and maybe make into a cafe racer.

Here's the bike I found. I was able to negotiate the price down from $800 to $300. Bought it from the original owner, a guy in his 80's. Hard to get it started, and it won't idle properly, requiring constant choke adjustment. Once it's moving though, it seems to run pretty dang well. It's got some pull for a 36 year-old bike! Exhaust has some holes, otherwise nothing obviously wrong on the outside.

I know this forum wants pictures, so here you are. Feast your eyes (and help me answer some questions).



























Alright, here's some weirdness (non-matching frame and engine numbers):





And:



I take it that's not the stock airbox?

Tread looks good, but the rubber is all checked. The wheels themselves look pretty good.



So, I've got Zimmerman's book and have read it. I have the Honda manual from this site, and a Clymer en route. I also have HondaMan's book on order. This will be my first real foray into serious motorcycle work.

The goal is to get it running well within the next two weeks, and then ride it until November or so. Towards that end, I will be pulling the carbs and the engine and working on them first. Over the winter, I plan on completely tearing it apart, and either restoring it or turning it into a cafe racer.

I have some questions for you guys:

1) What engine do I have here?

I want to get a few things right away. Does anyone have a good source for:

2) A tool kit for this bike.
3) A 4-1 exhaust that doesn't break the bank.
4) A stainless steel Allen head bolt set (I've seen widely varying prices online).
5) A vacuum gauge carb kit (again, don't want to spend too much).

Thanks! I'm pretty excited about this bike, and think I got a damn good deal (do you guys agree...?)

P.S. - I met a forum member at Burning Man recently (wearing a SOHC t-shirt). If you see this thread, then "hi" and hope you had a great time.

[rickmoore24]

Great find. I beleive that is the stock airbox, my late K2 had the same one. Also, that engine case number looks sketchy.

Rick

[schmolze]

...Also, that engine case number looks sketchy.

Rick

Right? Like someone scratched the digits into the case or something. Real odd.

[Stev-o]

First off, welcome and nice find! Great deal!!

Answers:

#2 - I've heard you can still buy the tools individually from Honda, about $25 for the set.

#4 - Bolt set       http://www.z1enterprises.com/detail.aspx?ID=1184

Engine & frame #'s don't match exactly. Your engine may have been a warranty replacement and the dealer added the digits?

PS. That bike is in too good of cond to chop up!  

[schmolze]

Thanks for the info meriggi. I may just end up restoring the bike, we'll see.

[Stev-o]

PS. That Fugly seat has got to go!

[fergie]

Wow you stole that thing. If it were mine I would clean the bike up,new bars and seat, 4 into 1 mac pipe ,change all the fluids, new battery and tires, go through the brakes,check the points, plugs, valves, and timing,  and clean the carbs and air filter. Then go ride.

[schmolze]

PS. That Fugly seat has got to go!

Haha, yep! It is super comfy, though.

[Old75_ratafe]

Nice bike I would bet the carbs are a little gummed up definitly a steal I paid 250 for mine (5 years ago) and it was in A LOT worse condition..... Yea that seat needs to go... could be worse though my uncles 550 had a full vetter fairing bags and trunk in a pearl white and that same seat only in WHITE... Just ewww.

[schmolze]

So today I yanked the carbs and airbox. The rubber liner that mates the two halves of the airbox was half gone, any chance I can find just that part somewhere?

On to the carbs:



One of the pilot jets broke off as I was trying to unscrew it. Bugger! I think I can drill it out easily enough though.


This broken bit on one of the float assemblies had been sloppily repaired at one point with something that had turned to goop. Any ideas on fixing it? JB weld maybe?








Here's the extracted half of the pilot jet that broke off.






So aside from the two obvious issues, do you guys see anything that needs attention? They're pretty clean, right? I'm sorta flying by the seat of my pants as my various manuals have yet to arrive. Do I replace jets and needles as a matter of course?

Where can I buy individual jets, needles etc. without buying one of these rebuild kits?

I've got everything sitting in a bucket of Pine-Sol at the moment. My current plan is to get a new pilot jet after drilling out the old one, then clea neverything thoroughly and put it all back together. I have a vacuum gauge sync kit on the way, so I'll do that too.

Any and all comments, advice, warnings, etc. are more than welcome.

[fergie]

You need some good carb cleaner to get those carbs really clean (pinesol will not work). let all the metal carb bits soak at least 24hrs. Also you will need compressed air and an air chuck that has a rubber tip. Use this to blow out all the passages and jets in the carbs. You will never get the bike to run correctly without doing this. When you have cleaned the carbs so they are spotless, the next step is to clean them again! then replace all the o rings ,rubber bits and gaskets and reassemble. once installed back on the bike you will need to set them up and vacuum sync them. good luck.

[Old75_ratafe]

Simple green worked pretty good for me to get the really big grime off then I let them soak a few hours each in the carb cleaner.  I agree pinesole will not cut it..... Although it may make your exhaust smell like a deep pine forest for awhile    I used carb cleaner and compressed air to chase the passages personally.

[schmolze]

Alright, carb cleaner and compressed air it is! I also went ahead and got 4 rebuild kits, even though I only want to replace the rubber parts (and the one pilot jet). I guess it can't hurt to get all new jets and needles.

More work/pictures to come on Friday, probably.

[Old75_ratafe]

Alright, carb cleaner and compressed air it is! I also went ahead and got 4 rebuild kits, even though I only want to replace the rubber parts (and the one pilot jet). I guess it can't hurt to get all new jets and needles.

More work/pictures to come on Friday, probably.

Trust me... Do it your there anyway.  I didn't my first go round and spent the time I could have used to do something cool rebuilding them.  But was rewarded with first crank starts even when cold without so much as dialing them in at all.

[rickmoore24]

A solid carb cleaning is like magic to these bikes. A carb dip, some scrubbing and compressed air through ALL the orifices, coupled with a good rebuild kit will get most of these bikes running pretty well. Even without a carb synch.

[Old75_ratafe]

A solid carb cleaning is like magic to these bikes. A carb dip, some scrubbing and compressed air through ALL the orifices, coupled with a good rebuild kit will get most of these bikes running pretty well. Even without a carb synch.

Couldn't agree more I still haven't dialed in my timing or synced them and it runs great

[schmolze]

Well, after a good carb build and synch, she's running well! Well enough that I think I'd feel bad tearing her apart. But, I've still got the hankering for a racer build...


...so I bought another one! It's a K1, obviously much more of a basketcase:



My brother volunteered to pick the thing up in his completely f'ed up, illegal truck that's on the verge of tearing itself apart. Remarkably, it was up to the challenge.













That honkin' bolt on the oil filter housing was stuck, and it was an epic saga trying to drill it out to free the engine. Eventually I prevailed, at the cost of a trashed housing.





I badgered my Mom and sister into huffing the motor into a wheelbarrow, then down into the basement. The whole thing was a hilarious ordeal, but we finally managed.





Let the teardown commence!

[schmolze]

I followed along with HondaMan's book for the teardown.

Breather cover removed:


Valve cover off:



Loosening the cam chain sprocket bolts. One was completely stuck and had to be drilled:


At this point, the rockers are supposed to lift off. #2 and 3 were holding a valve open and wouldn't budge (does this mean I have a non-stock cam?). I futzed with trying to compress the springs for ages, then had the bright idea to slap on the kickstarter and turn the engine by hand. Bingo.


Rockers off:


Towers off:


Head removed, view from the top:


View from the bottom. Heavy carbon buildup:


Cylinder block and pistons:


Pistons out:


Alternator off:


Alternator and pistons:


Shifter cover removed:


Had to drill out 2/4 of the bolts from the countershaft bearing cover:


What's under there:

[schmolze]

I cracked the cases with some help from my Step-dad. I felt like HondaMan's book coulda used a few more pictures at this stage (it was awesome up until then though!). We spent lots of time hunting down bolts. When it finally started coming apart, we realized the points plate had to be removed first.









So, I guess the next step is taking everything out of the cases and inspecting.

I have a couple questions:

1) What tools exactly do I need for inspection? All I have is a pair of digital calipers. Would a micrometer and some inside calipers be enough?

2) Tool to remove the clutch nut. Where's the $8 one mentioned in HondaMan's book? The one I found at Z1 Enterprises is $42.84 (http://www.z1enterprises.com/detail.aspx?ID=2161).

I'm gonna soak the head and cylinder block in lacquer thinner for a day or so. I figure that should get rid of the carbon (probably the remaining paint too).

Any thoughts, suggestions on how to proceed, etc. would be very welcome. This is my first time on the inside of any engine!

[Old75_ratafe]

Mind you I haven't done it yet but I would expect a feeler gauge would be good (any auto store).  I know you need it to set the valves, I believe for those the angle ended ones work best.

[schmolze]

Did some work on the frame today.

Started by removing the swingarm, center stand and kick stand:


I ran out of degreaser, so I grabbed some oven cleaner from the kitchen. Worked like a charm!


Swingarm was coated in this thick layer of gunk. A wire brush + degreaser worked well:


Center stand off, never to be used again (going for maximum power:weight ratio with this project):


Next up was stripping the paint. I got some stuff from the hardware store and sprayed it on. Pretty much on contact, the paint looked like this:


After letting the stuff sit a few minutes, I just hit it with the hose, and most of the paint came off:


Next up, chopping off all unneeded bits:




View of chopped rear. Will have to grind these guys flush:


Goodbye little pieces of frame...


I've been thinking about what to do for an oil tank on this project. I want it to be invisible or as close as possible. Has anyone used the frame as an oil tank? Is there some obvious reason why this wouldn't work?

[KB02]

I would think that the frame would not have enough capacity to act as an oil tank. I'm certainly not against the theory (look at the Buell's - it worked for them!).

I like the thought pattern you have going, though - Bike too nice to chop up, so get one that isn't.     You should put the carbs from the second bike on the first and get it running.

[MoMo]

You stole the first bike, 300 is what I would have expected to be paid for the second. good luck with the project, Larry

[schmolze]

I would think that the frame would not have enough capacity to act as an oil tank. I'm certainly not against the theory (look at the Buell's - it worked for them!).

Yeah, I'm thinking that might be a problem. I think I'll test the capacity by drilling a small hole somewhere and pouring in some oil. If the frame idea doesn't fly, I might try to do an integrated gas/oil tank.

[schmolze]

I like the thought pattern you have going, though - Bike too nice to chop up, so get one that isn't.     You should put the carbs from the second bike on the first and get it running.

The first is running! Needs a little ignition system tweaking methinks, but it's on the road.

[Stev-o]

Note to self - oven cleaner to clean frame in a pinch!

[schmolze]

Not a ton of progress to report. I decided to do an 836cc kit, and went with one from this eBay seller: http://stores.ebay.com/cruzinimage-co1484/Pistons-/_i.html?_fsub=1783269011&_sid=526414511&_trksid=p4634.c0.m322. 'Twas pretty cheap, but appears well-made. I'm waiting now for the cylinders to be bored out.

My step-dad gave me a hand gutting the beast. Such a sorry hovel of a workshop in the basement =[


Now, I know you guys aren't gonna like this, but I've decided to use the good parts from the runner for my project. I'll be using the K1 motor (which is in GREAT shape) and frame, but most everything else will be from the K4 (former) runner.

So, here's the K4 stripped down, with clubman bars and the new shocks I'll be using (14.5", so less rake in front - note the wheels are on the ground despite the center stand).


I'm gonna use that pic to design my tank and and seat, which I'm gonna attempt to make myself out of fiberglass. If anyone wants to offer me some Photoshopped possibilities, I'd love to see 'em....

While waiting for the bore job, I've been working on the head. Did some major valve de-shrouding, kind of a "semi hemi" job. Also did some mild porting (the ports were pretty good untouched).


"Yeah, it's got a hemi" - no, not quite  Um, I didn't majorly screw anything up here, right? Never done this before...


Topside 'o the head, with valve guides removed.


Also painted the cases with Duplicolor Engine Enamel. Came out awesome, real happy with that stuff.


I've also thoroughly cleaned and inspected everything. Based on the wear, I think this engine had like 10k or less on it 


Here's a question: how the hell do I clean up my exhaust valves? All of 'em look like this, and soaking in carb cleaner and lacquer thinner hasn't done the trick. The intakes are fine. Maybe I can just leave them alone and lap them in as is?


Still thinking about oil tank locations. I want it invisible. Does the swingarm have enough volume? Maybe with some hacked enlargement?

[Stev-o]

The painted cases look great!

[BrianAdair]

For cleaning the exhaust valves, I used a razor blade to scrape the carbon buildup off, then used a brass wire wheel on a bench grinder. Try not to get on the seat part of the valve, I don't think it would hurt it much anyway but I stayed away from the seats.

[schmolze]

The painted cases look great!

Thanks Stev-O, I was pretty pleased!

For cleaning the exhaust valves, I used a razor blade to scrape the carbon buildup off, then used a brass wire wheel on a bench grinder. Try not to get on the seat part of the valve, I don't think it would hurt it much anyway but I stayed away from the seats.

That sounds like a good technique, I'll give it a shot tomorrow.

[schmolze]

I got my bored cylinder block back today:




Looks good so far, right? Unfortunately, there was a little problem with one of the sleeves: it cracked, and the guy had to grind it down.



Now, he thought I might still be OK, and that the piston travel is short enough that it won't just fall out of the sleeve. Is he right? The alternative would be to re-sleeve and bore just that cylinder. Anyone know what that would run me?

In other news, I decided to just replace my entire valve train. So, stainless valves, bronze retainers, HD springs and camchain, Webcam 61a cam. Just hope my home porting job is up to snuff...

[MoMo]

That cylinder does not look like it will work.  I think the piston comes down too far.  Mock it up back together  and check it out.  I also use a very soft wire wheel on a bench grinder-does a great job cleaning valves,  Larry

[lucky]

Not a ton of progress to report. I decided to do an 836cc kit, and went with one from this eBay seller: http://stores.ebay.com/cruzinimage-co1484/Pistons-/_i.html?_fsub=1783269011&_sid=526414511&_trksid=p4634.c0.m322. 'Twas pretty cheap, but appears well-made. I'm waiting now for the cylinders to be bored out.

My step-dad gave me a hand gutting the beast. Such a sorry hovel of a workshop in the basement =[


Now, I know you guys aren't gonna like this, but I've decided to use the good parts from the runner for my project. I'll be using the K1 motor (which is in GREAT shape) and frame, but most everything else will be from the K4 (former) runner.

So, here's the K4 stripped down, with clubman bars and the new shocks I'll be using (14.5", so less rake in front - note the wheels are on the ground despite the center stand).


I'm gonna use that pic to design my tank and and seat, which I'm gonna attempt to make myself out of fiberglass. If anyone wants to offer me some Photoshopped possibilities, I'd love to see 'em....

While waiting for the bore job, I've been working on the head. Did some major valve de-shrouding, kind of a "semi hemi" job. Also did some mild porting (the ports were pretty good untouched).


"Yeah, it's got a hemi" - no, not quite  Um, I didn't majorly screw anything up here, right? Never done this before...


Topside 'o the head, with valve guides removed.


Also painted the cases with Duplicolor Engine Enamel. Came out awesome, real happy with that stuff.


I've also thoroughly cleaned and inspected everything. Based on the wear, I think this engine had like 10k or less on it 


Here's a question: how the hell do I clean up my exhaust valves? All of 'em look like this, and soaking in carb cleaner and lacquer thinner hasn't done the trick. The intakes are fine. Maybe I can just leave them alone and lap them in as is?


Still thinking about oil tank locations. I want it invisible. Does the swingarm have enough volume? Maybe with some hacked enlargement?

You can use a wire brush on valves. they are very hard steel.
DO NOT use a wire brush on the top of a piston. It will ruin it!
The best place to put the oil tank is the stock location or under the
battery.
Oil in the swing arm has been done but presents many problems with air getting into the lines from the swing arm bouncing up and down. Hoses and fittings bouncing up and down etc., filling problems.
The angle of the swing arm would make the oil want to drain towards the rear. Just lots of problems.

The easiest way would be to add the oil tank as part of the gas tank with a small space between the two so heat will not transfer. also you would want the oil in the front of the tank so it will not be next to your body.
That oil tank gets hot very quickly.

I think the stock location makes the most sense.
Back then when the bike was made the design people were motorcycle people and were very smart about things.

Now they have car people designing motorcycle things.
The water pump UNDER the intake manifold on the Honda sport bikes
is one of the worst designs I have ever seen. Cannot see it ,cannot get to it.
The VF 1000R /F  water pump was very easy to see and work on.

[lucky]

I have seen that clutch nut tool on the internet for $20 something dollars.
Just use your hand impact driver with that tool to remove the nut.

Make sure you use GASKACINCH engine sealer between the two case halves.
Do NOT use silicone!

GASKACINCH has been around forever and is proven.

[pat english]

cool projects...and thats awesome that you made youre mom and sister carry that engine..classic.