Topic: First bike, first project. '76 750 Four S with pics

[Gungosa]

Hey everyone. Here's my situation. I'm completely new to motorcycles. I'm also completely new to engine repair. I have almost no money to spend and limited tools.  To the best of my knowledge it's a 1976 Honda 750 Four Supersport. I've put a battery in it and it cranks right up and runs. The carbs have been cleaned since the bike was removed from storage a couple years ago. The bike has only 8000 miles on it but it has surface pitting/rust in some places and will leak oil after it is cranked but not really while it sits (more on this shortly). I understand that I need a book on my bike, but right now I'm attempting what i hope will be a good beginner's project and i'd like to get it done without paying/waiting for a book. Any help will be greatly (stupendously, gargantuanly, amazingly hugenormously) appreciated.

First, me and the bike


see how happy i look? don't we all want to keep me happy? yes, i think so.



Now, the problem. The bike leaks oil. This was a mystery, but in my infinite wisdom i took off what i believe to be a sprocket cover and found the source of the oil that was being slung around by my chain during my one joy ride around the neighborhood whilst i tried to not stall/fall/crash/destroy someone's lawn. The source: a crack beneath/behind the front sprocket that appears to have been knocked in the case by a broken chain or somesuch. It looks pretty bad but right now i'm trying to remain positive. In light of my optimisim, I've bought a cool little package of JB Weld and some socket wrenches. (see how much i've learned in 2 days?)
Here's where the hole is. See that dark spot to the left of the sprocket?





First I need to get a better look at what i'm up against. I've got to get that sprocket off. I've removed the two bolts (go go gadget socket wrench!) and got the retaining ring thingy off (go go gadget hammer and screwdriver!). Now i need to know what to do next. The sprocket has that star shaped nub sticking out of the center of it. As far as i can see there is no "central bolt" that is mentioned in other threads (see? i even searched before i posted). I think it's the drive shaft and therefore separate from the sprocket, but if it's not attached, someone needs to tell it that. I've tugged and pulled and pried with a pry bar (gently, but still...). it was when i realized that i was wielding a pry bar in the midst of all sorts of things i didn't want to beak that i came here for help.

So, my questions:
1. How do i get that sprocket off?
2. If you're about to tell me all about loosening the chain, then how do i loosen the chain?
3. How crazy am I to have this bike as a beginner bike?

I'd like to get this project knocked out (or off, as it were) so i'll check back often. Once i get the sprocket out of the way and the well cleaned off i'll post pics and then we can debate the wisdom of jb welding a crack that seams to go right to the seal. Thanks for reading! Thanks for responding!

[kslrr]

Welcome, and nice find.  To loosen the chain, unlock and back out the chain tighten bolts at the end of the swing arm.

Also, go the the FAQ section and download a manual for FREE.

Have fun and Good luke.

[6adan]

Welcome good looking bike but you have a K model not a F. To get the sprocket off there are two bolts on the sprocket that looks like you have already removed, under that is a plate that you turn slightly and pull off and then the sprocket should pull off

[CBGhia]

As he said above.  you need to loosen the nuts at the back of the swing arm, but you also need to loosen the bug nut that is on your rear axle.  Just loosen it, don't remove it.  The rear wheel should be able to move forward a little bit now.  The chain should be loos enough to allow you to remove the sprocket.  

I have used JB weld to fix so many things (notably, a thermostat housing for an old Buick) and it has held up well under almost all circumstances.  It should be fine to repair your case.  

The only problem I see is... what happened to the chunk that is missing?  It is probably in the case.  Hopefully it is not getting lodged into everything.  I have no idea if you can remove the oil pan from a 750 while it is in the frame, but you need to get that off and look for those pieces.  

That's my opinion, others may not agree.

[Johnie]

Well, you sure picked the best board for 750 restoration!!!  A wealth of knowledge here and a lot of "ribbing" goes on...so be prepared.  But very nice find and free...when will someone give me a 750 - you lucky guy. 
One thing...we like pics so you got off to a very good start.  I would dump those bags, just my personal opinion (PO).  But I like to get these 750's back to original.  You may have something else in mind.
Yes, you will need to take the chain off the front sprocket to get it off.  Once the bolts are off it should slide off with a little persuasion.  As far as the hole in the case, that is a bummer.  You can try JB, but you will need to be sure there is no oil in that hole for it to hold.  Let it set up for 24 hours at least.  The other problem I found with JB is it will run during cure.  So you may have to apply it a few times.  I really hope it works for you.  If not, you will need a used lower case.  The hole appears small, but it does get hot there and maybe someone here knows of a better epoxy for the higher temps.
I know on most 750's if you have the OEM exhaust you can get the pan off without any problem in case you want to clean out the pan from pieces of the case.  The gasket is still available from Honda.  Just remember, when you put those little bolts back on do not use all the force in those arms or you will break them off and have another problem.
Welcome to the board and have fun with your restoration.

[Gungosa]

Thanks for the help so far! As far as the accessories go, at least i got rid of the huge windshield that used to be on it... while it was nice (matched the red paint even across the bottom), it was old, yellowed, and made me flash back to old CHPS! episodes (all seen as reruns... i'm only 25).

As he said above.  you need to loosen the nuts at the back of the swing arm, but you also need to loosen the bug nut that is on your rear axle.  Just loosen it, don't remove it.  The rear wheel should be able to move forward a little bit now.  The chain should be loos enough to allow you to remove the sprocket.   

ok, on the left side of the back "axle" there is a chromed piece with a hole through it diagonally. on the right there is a huge nut with a pin through it... i removed this pin (i bent it to remove it because it doubled back on itself... not sure if i was supposed to but i decided it was just a pin). i then dug out an adjustable wrench and gave it my all to no avail. any tips? is this the correct nut to loosen? is it threaded in reverse?

[Johnie]

Don't know how big your wrench is, but that is torqued pretty good.  Plus, it has not been moved for a while.  You may have to put some muscle into it. 

[333]

And the opposite end of the axle has that hole in it to put something in it so the axle won't spin.  I use a long #2 phillips screwdriver.

[trprbill]

Hi, I'm a newbie to the site and I haven't learned my way around yet. Anyway my drive chain broke last year and knocked a hole through the case similar to yours but measured about 1" x 3". I searched up and down the road when it happened but I didn't find the piece. Even if the piece was inside it would just lay flat in the bottom and not cause any problems, right?. I sealed the hole with a piece of aluminum and JB Weld and rode it the rest of the summer. After a couple thousand miles I started hearing some grinding. To make a long story short, the motor was wasted, full of chuncks and metalflake oil. You can't see that part of the transmission when you take the oil pan off either. Don't start it again until the piece of case is out or you're sure it's not in there. It would be worth it to pop the cases open and have a look. Good Luck, Bill

[Gungosa]

FOR SALE! 1976 HONDA 750 FOUR. INNOVATIVE CHAIN LUBRICATION SYSTEM!
Ok, just kidding.

Thanks for all the help so far! I gave up on the nut on the back... my wrench was too small i think so I couldn't get good leverage (note to self, put that pin back in!). I popped the little clip off the chain and took it off. After the effort involved in getting the sprocket off i'm pretty sure this was a good idea. it took about 15 minutes of me spinning the sprocket and using a pry bar (the wide flat kind) to "move" the sprocket off it's mount. the thing moved so little each time i pulled that I thought I wasn't doing anything at all for the first 10-15 tries. is that normal? there was a rust color around the mount but it was so oily that rust seams unlikely. I could have been rust from before the crack formed I suppose. So, here, as promised, is the crack.



the problem that I see is the way the seal is separated. If I use jb weld on this will I ever be able to crack the bike open if I need to? It looks like a crack to me, not a punched out piece, but I'm open to opinions on this. Also, the gouges from the chain look new... like they happened yesterday. Could they be from last summer when the chain broke? If those gouges are new how do i keep that from happening?

[CBGhia]

If the bike runs well, I say JB weld it up.  If you need to split the case later, you can crack the JB weld.  Hell , if you need to split the case later you will probably want to replace the lower half anyway.  I don't see a hole, but there could be slivers in the oil.  I would change the oil right away!  Filter too!

Then drive the heck out of it. 

You will probably need to loosen the rear wheel a little to get that chain back together.    Get a bigger set of tools, your gonna need it.  Having an old bike can be fun like that.   

[Johnie]

Geez...the first pic you sent was a small hole.  Now I see a big crack too.  Man oh man, I think I will be surprised if JB will fix it and that it will hold forever.  I would sure hate to be somewhere and have it let go on me.  Do what you want, but I would start looking for a case.  Man, that is sad looking.    But the price was right...

[hopterfixer]

I would stop drill those cracks before you fill anything.  Personally I am of the "where will you be when it gives up" mentality.  Good luck.

[chopstar500]

Yes - unless you're equipped to do a major overhaul (which it sounds like your not), I'd try the JB Weld (or a better equivalent) and see how it holds. There's some stuff out there called ThermoSteel that is pretty wicked - has a high temp capacity of 2400 F (no joke - 2400 degrees F) - plus its about the same price as JB if you can find it locally. I'd try the stop drilling method and do some excellent prep work - clean, clean, clean!!! The ThermoSteel and JB can both be sanded and painted (maybe the JB as more of a finish/seal   coat and the ThermoSteel as the structural repair) - do a good job, and if it holds you'll never know it was there. If it doesn't hold, you'll only be out $20-$30.

The SOHC engines/bikes aren't so overly complicated that a mechanically inclined novice can't handle restorations and repairs, but it takes a fair amount of work, tools, paitence, and money to accomplish what you need to make your bike "right" - why not tune her up a bit, go through some of the basics, and see how you take to bike ownership before jumping in face first with a total engine teardown/rebuild?

Whatever transpires, good luck - you've already found the most powerful source of information right here on the SOHC4 forums!

[andy750]

Here is a different opinion from my esteemed colleagues, Johnie and Hopterfixer, both have extremely nice bikes and solid mechanical skills......
I would try the JB weld as well and ride it and "take the chance". I understand the "where will you be when it gives up" mentality and respect that but if you thought like this about everything then no one would install a Dyna S ignition unit - what if it fails and Im stranded?! It might and you could but in my experience there is always a way out of being stranded  Afterall you are riding in the USA not in Outer mongolia.....Basically the CB750 is almost bullet-proof in what it will endure a lot - runs to get you home on 3-cylinders, kickstart and electric start etc etc. If it dosent hold then you have a small oil leak. Once you get accustomed to doing basic maintenance on your CB750 at some point you can decide whether to pull the engine or not and replace the case (not so hard really). But for now Id JB Weld it up and ride it and keeo an eye on it.

Enjoy the summer!
cheers
Andy

[hopterfixer]

Here is a different opinion from my esteemed colleagues, Johnie and Hopterfixer, both have extremely nice bikes and solid mechanical skills......
I would try the JB weld as well and ride it and "take the chance". I understand the "where will you be when it gives up" mentality and respect that but if you thought like this about everything then no one would install a Dyna S ignition unit - what if it fails and Im stranded?! It might and you could but in my experience there is always a way out of being stranded  Afterall you are riding in the USA not in Outer mongolia.....Basically the CB750 is almost bullet-proof in what it will endure a lot - runs to get you home on 3-cylinders, kickstart and electric start etc etc. If it dosent hold then you have a small oil leak. Once you get accustomed to doing basic maintenance on your CB750 at some point you can decide whether to pull the engine or not and replace the case (not so hard really). But for now Id JB Weld it up and ride it and keeo an eye on it.

Enjoy the summer!
cheers
Andy

That is another reason I don't have a Dyna 

[andy750]

Here is a different opinion from my esteemed colleagues, Johnie and Hopterfixer, both have extremely nice bikes and solid mechanical skills......
I would try the JB weld as well and ride it and "take the chance". I understand the "where will you be when it gives up" mentality and respect that but if you thought like this about everything then no one would install a Dyna S ignition unit - what if it fails and Im stranded?! It might and you could but in my experience there is always a way out of being stranded  Afterall you are riding in the USA not in Outer mongolia.....Basically the CB750 is almost bullet-proof in what it will endure a lot - runs to get you home on 3-cylinders, kickstart and electric start etc etc. If it dosent hold then you have a small oil leak. Once you get accustomed to doing basic maintenance on your CB750 at some point you can decide whether to pull the engine or not and replace the case (not so hard really). But for now Id JB Weld it up and ride it and keeo an eye on it.

Enjoy the summer!
cheers
Andy

That is another reason I don't have a Dyna 

  40,000 miles on the current Dyna S since 2001 cant be too bad.

I have been left stranded several times, some in the US and other times in other countries - always by a puncture. You cant cover everything 

[goon 1492]

76 k alrighty, just like mine; good luck on the jb weld. Make sure you clean the crap out of it before you apply jb weld on there too.

[Gungosa]

Where can i find a rundown on why my bike is not a supersport (which i now know is the F model). I see that the back cowl piece is not there but I also have the four into 2 exhaust, not the 4 into 4 like most seem to have. My rear turn signals are mounted on the saddle bags, so is it possible that the rear cowl was removed/replaced when the accessories were put on?

In other news, i've got some degreaser, wire and nylon brushes, a toothbrush, and a dish scrubber on deck for tonight. I'm gonna clean like mad. Hopefully I'll get some before/after shots with the entire area cleaned and then 'welded'. then i'll change the oil.

[trprbill]

You can JB Weld it and it will hold forever. If the JB Weld falls out it's no big deal since there's no real oil pressure in there. You can take your chances on the piece of case not being in there. If it's in there and you ride it no big deal just rebuild it later. The only difference is that you won't need the new everything like I do for the one I rode like that.

[my78k]

I am not as learned as most on this site about the subtlties of the various models but if memory serves the biggest cosmetic difference with the F is that it had a black motor and the seat cowl. If the Cowl was just removed the seat would be different...

As for the Fix...yeah JB weld it...as for getting starnded get AAA+ (CAA+ for those of us north of the border) as they will cover bikes in addition to cars!

A little trick for your small adjustable wrench is a tool that I use most in my garage...a hunk of metal fence post. It slips right over the handle of most wrenches and with the additional length I have enough leverage to break damn near anything loose.

Dennis

[Gungosa]

A little trick for your small adjustable wrench is a tool that I use most in my garage...a hunk of metal fence post. It slips right over the handle of most wrenches and with the additional length I have enough leverage to break damn near anything loose.

Dennis

I actually looked all over my house for a piece of pipe/fence post to do just this, but had no luck... i even asked a neighbor. It just proves that I need more junk in my garage. I'll check out the serial number and see what i can find out about the bike's model that way.

[trprbill]

The front forks, lights, gauges, gas tank, side covers, frame, or anything else on your bike is not specifically from a Super Sport. The engine might be, and your bike is a nice "K" model. I have 8 CB 750"s, three of them are Super Sports. And if you start using leverage such as fence posts to break bolts loose, you should invest in a good set of drill bits, easy-outs, and taps, because you'll end up breaking them off too. Get yourself some PB Blaster, and an impact tool for the stuborn bolts, and you'll be glad you did.

[my78k]

Did I forget to mention that I have 3 sets of easy outs and a full tap and Die set? Can't imagine why I needed to buy those?!?! 

Yeah you are right, patience is definitely a virtue....that I don't have!

Dennis

[Gungosa]

Ok, an update as promised. The crack is repaired to the best of my ability and knowledge (and we all know what that's worth). The sprocket is back on, the chain is on and adjusted and i did my very first oil change! I've gotten to the bottom of what caused the problem... apparently the rear wheel nut was either not tightened (yikes!) or at least the chain was not properly tensioned when the bike was ridden last summer. My dad suddenly remembered that those 'two screws sticking out the back' were 'pointing down' instead of 'pointing out straight' (he never rode the bike and he's never owned one).  Yesterday i would not have know wh hat he meant but today i know that someone didn't have a clue and rode the bike with at best only the tension on the rear wheel nut holding the chain in tension and the wheel in alignment. I hope i have remedied this problem and i also hope i'm not creating any new problems because, like the last guy, i really don't have a clue either. But I'm learning fast!  During the repair i found a second hairline crack just out of site in my pics. You can see where i patched it to the left of the big blob in the following pics. This second crack was not as clean so it might need a repair in the not to distant future. Hopefully the JB Weld will hold and i can have fun. I rumbled down the street and back without stalling but i almost got a mailbox in the culdesac when i first got going. Here's the repair job:

Cleaned up but blurry


This stuff was hard to control. Try not to be impatient like me. Let it set for about 10 minutes if you want to be even remotely precise. I also used my gloved finger to spread it which might not have been the best tool.


This is how it set up. You can barely see the material covering the crack on the left. There was some oil there that might cause a problem in the future but it's doing fine for now.

[andy750]

Looks like it might work..keep us updated on oil leaks or lack thereof.

And you were right that the two bolts at the back of the swingarm should NOT have been pointing down!!  Glad to hear you are figuring it out.

Good luck
Andy

[goon 1492]

You should also buy an impact screw driver set, home depot has em for about 25 bucks, you'll need it when you have to take the altenator cover or cam cover off etc. good to see the "weld" took like you planned.


Oh yeah since no one else said it yet you should tie that left side cover down so it doesn't fall off on you most of them do or have; I'm sure others can comment on this 

[Roach Carver]

if I were you, or if alternately you were me.... Maybe I (or you) could look for a good motor. quite often I see them here and on ebay for a little to nothing if they are close enough to go pick up. then you could just do an engine swap.

[trprbill]

I swear the one pic looked like a hole. The JB Weld should work fine, and I think that certain years the bikes came with steel case protectors to gaurd against the chain breaking the case. It might be a good thing to look into or if anybody knows about them? I think if your chain comes off again it might be a bigger problem.

[MrZxp]

You definitely have a "K". Follow this link to confirm for yourself - http://www.sohc4.net/index.php?title=CB750K.
Here is the link for the "F" model guide - http://www.sohc4.net/index.php?title=CB750F.

Good luck with your repairs!

Cheers, Phil

[Johnie]

I sure hope it works for you.  Have you downloaded a manual yet?  You will get a lot of info from that manual.  Nice pics...

[Gamma]

I did the same type of repair to my cases on a CB750 F1 in 1980.  The hole was bigger, in both cases, due to a chain break.  I used a product called Doublebond (2 part epoxy putty) and oversealed it all with Araldite 24 hour epoxy.  I remember using M.E.K. to degrease the area, and dropping the sump plate and changing the oil in an attempt to get the bits out.
I ran that bike hard on a daily basis, for another year, with no engine problems before it was stolen in Germany.  Then I bought an F2

[mystic_1]

OK, so I have had damage just like this on a 750 motor.  The biggest concern in that area is whether the crankcase has been pushed in enough to come into contact with the transmission gears, the clearance at that point is not very big and it only takes 1/2 inch or so before the case is in contact with the gears.  At this point your gears will begin to machine a nice arc into the inside of the case.  After a while of driving like that your oil will be a nice bright silver from all the aluminum shavings   Ask me how I know this

So, I can confirm that sealing this crack with JB Weld WILL in fact work.  I cut a piece of sheet steel into a patch and JB welded it in place.  It held up through a full riding season and then some, couple of thousand miles I figure.  Once I changed my oil and saw the aluminum particles I decided it was time to give it up and just rebuild the engine, and that's where I am now.  When I pulled the engine apart I had to chisel out the JB weld, it was still sealing the area just fine. 

Now, having said all that, I'd recommend trying to source a replacement motor if that's within your budget, it probably would be cheaper than trying to repair the existing one, and safer than the JB Weld routine.

cheers
mystic_1