Topic: Modern Classic CB750K5 Restomod **noob**

[haredondo]

     A couple years ago I bought a pristine CB550K5 which I absolutely loved and regretted selling right after it was out of my garage. I rode a BMW R1100R for a bit after that, but still had the longing for a CB. I finally found a 6/10 condition 750K5 at a decent price (people are insane about their prices, at least around here in TX). It was running a little rough (would only run on half choke until after a couple miles) and I rode it like that for a while. I stopped riding for a couple of weeks over this past winter, and then the bike just gave up. It had a terrible time starting, and would only run with full choke or half.. after it warmed up smoke came out of all exhaust pipes, and giving it some gas resulted in very loud backfiring from the exhaust. Putting it in gear and trying to take off killed it instantly. I also saw some smoke coming from the cylinder head gasket / cylinder 1 exhaust flange area when revving it. So I started lurking the forums, got the manual and Hondaman's book, and took a deep breath. This would be a first for me, so I was a bit apprehensive.
     I thought the problem might be an ignition issue, so I replaced the points. When I tried starting the bike to check the timing, I noticed the carbs were leaking badly. I closed the petcock, and waited a couple of days. I took another deep breath and removed them. At this point everything I'd done seemed straightforward and I was more comfortable working on the bike. That's when I got the idea of doing a full restoration / modification.
    I researched this subforum quite a bit and got some ideas of what I wanted to do. In essence, I want to upgrade the bike as much as I can to improve handling, braking, power and reliability. On the aesthetic side I want it to look close to stock, but with a couple modern details.
    Here's the bike:
   

[haredondo]

I started removing the panels and de-greasing the engine:



It looks decent on the pictures, but it is pretty bad in person. All the fins look pitted / corroded. I hope soda blasting can help with this.





One last look before tearing down:

[haredondo]

I went with the "pray, tip the bike on its side, grunt, curse, sweat and remove engine" technique. It took me about 4 hours to remove everything, gather courage to tip the bike, and remove more things with the bike on its side (wheels  ). I definitely recommend getting help, did it alone and my back was sore for a couple of days. Also, removing the exhaust flanges (spigots) helps quite a bit. Here's something to note: they came out super easy. No binding or stuck screws. And the gaskets seemed crushed and stuck to the head. Is this normal?

Before:



After:

[haredondo]

A quick warning: this might be the messiest rebuild ever. I don't have much space in my garage so i've been relegated to pretty much working on the floor. I'll definitely enjoy some extra space when I send the frame out for powdercoating.

Took the head apart and was shocked. According to Hondaman's book this should be the hardest part to remove. As soon as i removed the last of the nuts and pulled on the head, it came off instantly. The gasket was separated, and intact. The cylinder cutouts looked oval. Was it not torqued down properly before? Did some PO delve into the engine and did something wrong?

You can see the gasket on the right side of the picture next to the cam towers. You can see an odd thing on piston #1, there is a part of it that has absolutely no soot. It is shiny metal. Is it weird?



The head looked very sooty, I sprayed some WD40 to see if the valves were leaking. After an hour or so I couldn't find much. I ran my finger inside the ports and I could smell the WD40 so maybe they're leaking a bit. I'll get a spring compressor and remove them. I also noticed that PO had tried to match the ports. There are some very deliberate grinding marks. I'll post some images soon.

[haredondo]

Pulled the cylinders, there is some definite oval look on the sealing surface and the edges of the bores, but I don't know about the bores themselves. They look very shiny (glazed?) and smooth, no nicks or damage there. I'll get them measured for taper / out of round.



Here's the odd thing on piston #1.



There's some weird yellow residue around the wrist pin hole. I'm also worried about the rusty stud. I'm replacing them with APE studs though.



The rest of the pistons look like this:



Another rusty stud. WTF?



All of the pistons had a slight scratch on the skirt / thrust face of the exhaust side (if it makes sense?) of the bore. I can barely feel it with my fingernail. It is the darkest one in the picture. Are they junk? Usable?

[haredondo]

Another look at the head. I guess there's not much to look at here. Cylinder #1 exhaust valve looks a little different than the others



P.D. ignore the polar bear, it's not dangerous

[Vinhead1957]

Looks like 1 and 4 were burning a tad leaner than 2&3 but over all not bad.  Was it using some oil?

[Bankerdanny]

The slightly out of round gasket is not unusual.

[haredondo]

Vinhead:
I didn't ride it enough to notice oil consumption on it. When I drained the oil before teardown, it was dark and (fortunately) free of particles

Bankerdanny:
I read around and saw that. Still, I guess the head wasn't torqued down properly since the gasket was completely loose and apparently leaking (I saw smoke come from the front of the engine a couple times while revving it).

I'm taking the cylinder block to a shop tomorrow to get it checked for out of round and taper. As well as piston to bore gap. I'm tempted to see how expensive it would be to get the head ported and getting something like the 915cc stage 2 kit from dynoman.com. I might be able to stretch my budget a bit.

Thanks for your replies! I'll hopefully be posting more stuff this week, I'm having a bit of trouble finding time to work on the bike since I'm looking for a new place to live in