78 CB750F- Putting her back together!

[Buff CB]

I bought this 1978 CB750F 4 years ago and have been using it pretty stock with just clubman bars and repainted tank as modifications. The bike always ran alright with minor hiccups like dead batteries and prematurely running out of gas (wrong o-ring on the pepcock) but after riding some friends motorcycles it seemed like my bike never ran as well.

So with the colder months upon me I decided the bike needed to be restored to it's former glory while also modifying it to true Cafe Racer standards.


So let it begin...I'm sure I have no idea what I'm in for.


I decided an adequate workbench was needed first.

Tank off easy going so far

Stock engine

Seat off and battery removed

Tool box and inner fairing gone

 

[sxecafe]

Re: Simple teardown goes south. 78 CB750f

Should be interesting. One of my fav bikes. I'm amazed you were able to hold off restoring it as long as you were. I admire your patience haha.

 

[Buff CB]

Re: Simple teardown goes south. 78 CB750f

Removed the air box and carbs. Notice the stuff starting to pile up in boxes under the work bench. I'm labeling all nuts and bolts and small parts in ziploc bags. I'm hoping this system works in the end.

The carbs look to be in good shape but still will get a good cleaning

Handlebars removed

Next the rear wheel comes off mainly because both sprockets and chain are in dire need of replacement

Brakes removed

Foot pegs and sets detached

 

[Buff CB]

Re: Simple teardown goes south. 78 CB750f

Should be interesting. One of my fav bikes. I'm amazed you were able to hold off restoring it as long as you were. I admire your patience haha.

I've been lurking here for a while and taken a lot of inspiration from other readers rides and decided it was time. Plus having money to pay for helps too

 

[sxecafe]

Re: Simple teardown goes south. 78 CB750f

Understood but being on here never leads me to go to the ride and say... "yes I am indeed satisfied". More like "fuck this... I have to do something!" Again, admirable patience hahahaha.

 

[overdraft]

Re: Simple teardown goes south. 78 CB750f

wikked bench man! if your wrenching is up to your wood butchery this'll be a great build!

 

[Buff CB]

Re: Simple teardown goes south. 78 CB750f

Rear wheel gone & draining the oil

It looks like the battery was leaking acid pretty bad, could be why the chain fell to shit so quickly.

Also found a short in the wiring harness...shit
The bottom couplers are melted together. Not good but could have been worse. I'm glad I caught it.

Wiring harness removed along with the instrument cluster

Engine ready to be pulled with all mounts removed

Engine removed with the help of my brother.


Helpful tip! If you have the engine in just the frame, lay the engine on its right side (on cardboard) and pull the lighter frame upwards off the engine. It works so much better than fighting gravity and a tight frame.

Empty frame ready for cleaning, modification and painting...eventually

Put the engine on the workbench and it didn't break! It seems I know just enough about being a carpenter and mechanic to do this project.

I did this all in 2 days time but I imagine that just the engine rebuild will take considerably longer. Fingers crossed it goes smoothly. This is ongoing so I'll try to post as I go.


Cheers!

 

[IndieSol]

Re: Simple teardown goes south. 78 CB750f

Cool bike. I'm looking forward to seeing the finished product.

 

[Juggernaut]

Re: Simple teardown goes south. 78 CB750f

This looks similar to to build I'm doing. We seem to be in the same knowledge range. You can be my lab rat I can learn from.

 

[Buff CB]

Re: Simple teardown goes south. 78 CB750f

This looks similar to to build I'm doing. We seem to be in the same knowledge range. You can be my lab rat I can learn from.

What's your bike and how's the build going?

You're welcome to learn from my mistakes because I'm sure there will be plenty.

 

[Juggernaut]

Re: Simple teardown goes south. 78 CB750f

The build is going way too slow. Too many speeding tickets, and bills from a broken ankle haven't helped. So far I've painted the headlight shell, triples, engine. I have also detabbed the frame, stripped the gas tank. I need a few things welded then it's just purchasing a ton of stuff and painting and powdering the frame and swing arm. I'll update my thread when I get the time.

 

[Buff CB]

Re: Simple teardown goes south. 78 CB750f

This might be the point of no return. I've started tearing the engine apart


Valve cover off. Everything looks good.

Taking note of the exhaust and intake rockers and on which side they came from. Could be important

Rockers off, cam shaft off and also the cam bearings.

Here is the head taken off. Looks like there is quite a bit of carbon built up. I kind of expected this.

 

[Buff CB]

Re: Simple teardown goes south. 78 CB750f

So here is the biggest obstacle I've faced so far. I've pulled the cylinder walls and find this orange rod. I have to say I'm quite baffled how this happened. Here is what I don't understand.
-It's an air cooled engine so no coolant running in the block
-The gaskets on either side of the bolt are in good shape with no breaks near the bolt.
-The bolt exists in it's own chamber running in the block. So once any oxidation that occurs would use up all the oxygen in the hole and the process would stop. But this rod is severely rusted with orange dust everywhere.


WTF

Does anyone have any ideas how this could happen? And the next question is what do I do to fix it?


Do I try to remove the bolt with out shearing it and where do I find a replacement?


Do I leave it in and clean it up and so some rust prevention?


I am truly baffled.

 

[VonYinzer]

Re: Simple teardown goes south. 78 CB750f

Justgot some water in there at some point would be my guess. As long as the integrity of the stud is ok, clean it and re-use.

 

[Buff CB]

Re: Simple teardown goes south. 78 CB750f

Update:

So I've managed to pull off the pistons and started taking off the cylinder bolts only to find that four of them just won't come off. I've been using the double nut technique and it worked great for the others but I just cant seem to break the other four loose.

I've been soaking them in WD-40 to help ease them out and I've also tried heating the bolts with a blowtorch and letting it cool to see if the expanding and contracting would shake any rust off but no luck.

Does anyone else have any ideas as that might get these four free. I'm hoping for a better chemical agent that might work better than WD-40 because rusted ones feel like they are going to snap from the torque I've been putting on them.

Thanks a bunch

 

[bikeboy]

Re: Frame off restoration 78 CB750f

make sure you check all your oil galleries. That overflowing blue silicon around that rocker seal would be enough to send shivers down my spine. I'll bet you oil pick-up is covered in the stuff

cheers
ian

 

[Buff CB]

Re: Frame off restoration 78 CB750f

make sure you check all your oil galleries. That overflowing blue silicon around that rocker seal would be enough to send shivers down my spine. I'll bet you oil pick-up is covered in the stuff

I too am a little worried about that stuff. I guess we'll see when I get it all apart.

 

[Buff CB]

Re: Frame off restoration 78 CB750f

Now it's down to just three

This one snapped like a candy cane

The two lower ones came out eventually but the two rusted one just could not handle the torque. Off to the machinist they will go.

Moved on to removing the valve springs

Does any one know what I need to do to remove the valve guides without screwing them up? I can't figure how to take them out.

Cylinder walls look alright

I am worried about the wall on #3. This looks like burnt oil but may be just discoloration rather than corrosion.

Now you see it...

...and now you don't.

 

[bikeboy]

Re: Frame off restoration 78 CB750f

I'm really surprised those studs snapped like that ???

Are you sure those bores are OK it looks like some fine scratches running down there? There's a special punch (tool) to remove the valve guides, but why do you want to remove them without screwing them up? If you're replacing them it won't matter. Usually just the valve guide seals go off, and that's an easy fix.


cheers
ian

 

[BWJ]

Re: Frame off restoration 78 CB750f

Teardown is looking good. I am smack dab in the middle of rebuilding my 78 CB750 F. Those 4 studs are a bitch. I snapped 3 of mine. This is a common problem on these older SOHC's. I am not sure if you are aware or not but the 77-78 F models are prone to top end valve guide wear and spring retainer failure. I am betting you will need to replace the valves and guides as a miniumum. Since your in there you should replace the stamped steel retainers with titanium or the alloy ones offered from Cycle X. To remove the guides you need a drift punch that is just a tad smaller and just pound them out.

Here is a link to a shop manuals
http://www.mediafire.com/file/nzkmzodmgin