Topic: Nebraska CB750 K8 Resto/Mod

[zeffcat]

Retimed - I had cylinders 2/3 off a bit. Started right up and idled better this time. Still had to run on choke the whole time. Heres a video, I'm pretty sure I was running on all 4 cylinders this time.

Started the strip down process. Left the wheels & engine on for now so I can scrub everything down. I did a leak-down test and was losing 40-50% w/ audible leakage through intake & exhaust valves. This verifies the need for a top end rebuild in my book. Need to go get an engine stand from harbor freight to start the engine rebuild.

[zeffcat]

Really like how clean the rear section and seat is on this XS 650. Might try to work something like that into this build because I really don't care for the bulky, disjointed look.

[zeffcat]

Scored an engine stand for $25 yesterday and made up some adapters quick. Got the engine out by laying the bike on its side and pulling the frame up and off with the help of a couple friends. Engine is now mounted and ready to be degreased before I start the rebuild.



I also found this crack in the lower right frame rail. It appears as though some water got in the tube and froze because the section is buldged out a bit. Hoping this is a simple fix for a welding shop.

[SOHC4 Cafe Racer Fan]

That frame rail is repairable.

[zeffcat]

That frame rail is repairable.

Good to hear. I'm planning on using simple green to clean the engine. I've ordered plugs for the breathers and intake/exhause holes from Widgetco.com. Do I need to seal up the points cover with some kind of gasket before i start washing?

[Stev-o]

I dont use water when cleaning my motors.  Gunk Foamy Engine Cleaner works great.  I'll be doing this on my next project soon...

[zeffcat]

Simple Green sells a "Blue" formula that is especially kind to aluminum if you care... The pH of the standard stuff, while probably not going to hurt noticeably, is a bit caustic to raw ally.

The points cover does use a gasket and should be installed if you're planning to bathe the motor. Along with every other orifice.

Thanks for the info and advice Cal, taking note of that.

I dont use water when cleaning my motors.  Gunk Foamy Engine Cleaner works great.  I'll be doing this on my next project soon...

Don't you have to rinse that stuff off somehow?

[Stev-o]

I dont use water when cleaning my motors.  Gunk Foamy Engine Cleaner works great.  I'll be doing this on my next project soon...

Don't you have to rinse that stuff off somehow?

Not necessarily, just depends on the amount of crud on your motor. It can be wiped off.

[zeffcat]

I dont use water when cleaning my motors.  Gunk Foamy Engine Cleaner works great.  I'll be doing this on my next project soon...

Don't you have to rinse that stuff off somehow?

Not necessarily, just depends on the amount of crud on your motor. It can be wiped off.

Great, I'll keep that in mind. This engine is pretty nasty. Had a number of oil leaks over the years coupled with road grime I'm guessing.

[zeffcat]

No progress to report, spent yesterday afternooning putting together a metal parts shelf and cleaning/arranging the garage in preperation for the engine rebuild. I've got a couple non-engine related questions. Concerning the swingarm - I've read up that Hondaman's swingarm rebuild seems to be the way to go but at $200 (I think thats the price I saw) I'm a little aprehensive. I'm sure its great but thats a lot of money to fork over on one small portion of the rebuild. So my questions are -- how do I tell new bushings are in order before I remove the swingarm from the frame and could I save money by ordering bronze bushings from ebay and doing this myself?

[Stev-o]

If you dont know when your bushings were changed last, it is prolly time to replace them.  Put the bike on the centerstand [or jack up the back end], then move the rear tire side to side to check for lateral play, there should be very little.

Earlier this year, I changed em on my K3, it is a very basic job.  I bought mine from "the kid"...

https://www.ebay.com/itm/Honda-CB-250-360-400-500-550-750-Four-swingarm-bronze-bushing-set-bearing-new/282075118558?epid=625903160&hash=item41acfcbbde:m:mG0QhF_iJosILFRIK_jobWw&vxp=mtr

[zeffcat]

If you dont know when your bushings were changed last, it is prolly time to replace them.  Put the bike on the centerstand [or jack up the back end], then move the rear tire side to side to check for lateral play, there should be very little.

Earlier this year, I changed em on my K3, it is a very basic job.  I bought mine from "the kid"...

https://www.ebay.com/itm/Honda-CB-250-360-400-500-550-750-Four-swingarm-bronze-bushing-set-bearing-new/282075118558?epid=625903160&hash=item41acfcbbde:m:mG0QhF_iJosILFRIK_jobWw&vxp=mtr

Thanks stev-o, you've been a huge help.

Looks like the weather is going to be favorable for painting this Friday so although I wasn't planning on doing this later I'm going to go ahead and blast the frame and repaint. So another question to throw out on paint. My local paint shop supplies spraymax 2k and that's what they suggested to me. Im wondering if I should spray the 2k color and clear or if VHT color and then clear over with the spraymax 2k would be sufficient.

[Stev-o]

Why would you use VHT on the frame?  [VHT = very high temp] I use it on my motors...

[zeffcat]

Why would you use VHT on the frame?  [VHT = very high temp] I use it on my motors...

Sorry, I meant VHT brand paint. They make a line of automotive paints including a "roll bar and chassis" paint that I've used before and had good results with on small pieces.

[zeffcat]

Over the weekend I silica blasted the frame, swingarm and other small pieces.


Had my cousin weld up the crack in the frame rail, not perfect but about as good as he could get with his MIG.


I attempted to paint using spraymax 2k primer, black base color mixed up by the shop and spraymax 2k clear to paint the frame. It ended up being too cold and the color coverage was awful so I took back the extra paint I had left to to save a little bit of face and I will powdercoat at a later date.

Started degreasing the engine and will continue this over the next few weeks until I'm done with class for the semester and have time to start tearing into it.

[zeffcat]

That makes sense. He went to welding school in Tulsa so he knows what he was doing and had the MIG turned down as far as possible and just did spot welds to prevent burning through. Now I just need to get him to teach me a thing or two about welding.

[gwallis]

Zeffcat...

The rear rim on the green CB750 is off a Harley-Davidson.  Similar to the one that I have on my 1973 CB750.  See pic.

[zeffcat]

 

Zeffcat...

The rear rim on the green CB750 is off a Harley-Davidson.  Similar to the one that I have on my 1973 CB750.  See pic.

Thats a  16" rim, correct? The stock rim on the K8 was a 17", at least I thought thats what the manual said. Mine happens to be an 18" on the rear. Good looking bike you've got.

[gwallis]

Yes...16 inch rim.

[zeffcat]

Got started on the engine. Valve cover, cam & holders removed. So far everything is looking pretty good. Should be able to get the head and cylinders off when I have time next.

[zeffcat]

Got the head & cylinders removed last night. Cylinders look to be in good shape. Going to soak in degreaser and clean things up while I wait for my valve spring compressor to show up in the mail. Then I'll take the head and cylinders into the shop to have things looked over.









I need some help on determining if I need to take the cases apart. I'd like to avoid it if I can but if the consensus is that I should just go ahead and do it while everything is apart I will.

As far as parts that I need - is the Cycle X standard gasket kit good quality?
Where should I order the cam chain guide and wheel from?
Do I have to replace the cam chain, how do I know?

[Stev-o]

Most likely will not need to split the cases, the trans in these bikes are nearly bulletproof.

Bring the pistons to the machine shop as well.  The machinist should measure the bores and determine if they can just be honed and re-ringed or if you need to bore and buy a new piston kit.

[zeffcat]

I'm going to be taking in the things to be powdercoated this week or next. For the swingarm, do I need to remove the bearings before I take it in? I'm planning on replacing them eventually anyways, just didn't know what would be best.

[SOHC4 Cafe Racer Fan]

I'm going to be taking in the things to be powdercoated this week or next. For the swingarm, do I need to remove the bearings before I take it in? I'm planning on replacing them eventually anyways, just didn't know what would be best.

Have you dug yourself out from yesterday's snowfall?

[HondaMan]

Now if I do the 18" rim, do I have to get a special spoke kit from buchanan or will a regular cb750 18" spoke kit for the 69-76 cb750k work?

The 8" rim from any other K0-K6 bike will fit, you'll just need new spokes. Or, Buchanon makes fancy ones, like I am lacing up now for someone.