Topic: Nebraska CB750 K8 Resto/Mod

[zeffcat]

Finally had some time for the garage today, unfortunately I've been super busy with school lately. But I did get the carbs thrown on the bike and got it started up.

This first video I was struggling to keep it idling, likely due to the fact that the PO put pod filters on and did not rejet for it.
https://www.youtube.com/embed/FaZIBAVFOjY

And this second video is a very brief segment where it was idling on its own, sorry for the snapchat caption.
https://www.youtube.com/embed/466ojvYpGYw

This was really all I wanted to accomplish beforing tearing it down to either repaint the frame or have it powder coated. So next step is strip down and media blast. I think I'll also go ahead and order a gordon's frame kit as soon as I save up the funds since I'm planning on a top end rebuild to address a leaking head gasket.

[seanbarney41]

It's only running on 3 or less cylinders.

[zeffcat]

Not sure why but I didn't think of that. I'll make sure I'm getting spark to all 4 cylinders and try to figure out what's going on. Thanks.

[zeffcat]

I was able to verify that all plugs (except #2 because my socket doesn't fit that hole for some reason) were getting a nice fat blue spark. Plug 1 looked new still though so I think I didn't have that coil boot on all the way, hence only running on 3 cylinders. She still didn't want to fire up tonight but it was only 20 degrees out. All 4 carb bowls are getting fuel and float levels are spot on (verified with tube method). Clearances are checked and double checked. I static timed but I think I need to revisit this to verify I did it correctly. I think the pod filters are really screwing me.

[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?

[calj737]

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.

[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.

[calj737]

The reason your cousin struggled with his MIG is due to rust on the inside of the frame rail. The more heat, the more impurities it pulls out. Plus, that’s really thin tubing, so blow outs are very easy. It will hold up though, and that’s the important thing.plus, I suspect you’ll be a great deal kinder to this bike than the PO was.

[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.