Topic: Nebraska CB750 K8 Resto/Mod

[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.

[SOHC4 Cafe Racer Fan]

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.

I think we all know Mark meant 18" but an 8" wheel would need new spokes! 

[zeffcat]

Have you dug yourself out from yesterday's snowfall?

I have indeed! We didn't get it nearly as bad here in eastern NE as the western part did. Only about 3 inches here but the 30mph wind iced everything over real good. Into the 40s & 50s for the rest of the week though. My folks in western NE got over 12".

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.

I think we all know Mark meant 18" but an 8" wheel would need new spokes! 

I ended up finding out that someone had switched the rear to an 18" at some point! So less work for me. I've got the wheels all dissembled at the moment, spokes removed and such. Water had gotten beneath the tubes so there was some rust happening. I'm going to have rims blasted and powdercoated rather than buying new rims. New spokes are in order and hubs will be polished.



Still have not heard back from the shop about the engine, getting a little impatient with them as it has been over a month. I guess it doesn't matter so much as I've still got a lot of cleaning to do on the rest of the engine and need warmer weather for painting.

[zeffcat]

Finally heard back from the machinist today, missed the phonecall but from the voicemail I gathered the following: Need to go first oversize on the bores, so I'm in the market for 61.25 pistons. Valves were good, intake valve guides also good, exhaust valve guides need replaced. He suggested cast iron valve guides.

Currently looking at cycleX for these parts. Pistons, rings, pins & retainers can be had for just shy of $200. 8 cast iron valve guides just under $100, going to see if I can just get the 4 exhaust ones. Haven't gotten pricing for the bore yet.

[zeffcat]

Got my engine back from the shop finally. Cylinders bored out one size over, 4 new exhuast valves, ports blasted, valves recut and base of head resurfaced. Going to be ordering a gasket set, cam chain and cam chain guide and tensioner wheel soon. Also got the frame, swingarm, triples and rims powdercoated in gloss black and they turned out fantastic. I'll get some pics up of those eventually. In the mean time I've finally had some free time to get to work on polishing. Here's a little before and after on the rear hub.

[MauiK3]

Will you be taking the Cush drive apart to check the rubbers? They are easy to change and not too pricey. They protect your transmission and drive chain. Mine were pretty hard.
Also, I think the cam chain tensioner is a must. I also can't stress enough how important it is to get Hondaman's rebuild "bible". It will save you a lot of time and grief, most of the answers you need are in there. Best Benjamin I ever spent.
One more thing, inside the case is a primary chain tensioner, it has a roller like the cam chain, I would worry myself to tears if I had not changed it.
Nice project. Keep going.

[zeffcat]

Will you be taking the Cush drive apart to check the rubbers? They are easy to change and not too pricey. They protect your transmission and drive chain. Mine were pretty hard.
Also, I think the cam chain tensioner is a must. I also can't stress enough how important it is to get Hondaman's rebuild "bible". It will save you a lot of time and grief, most of the answers you need are in there. Best Benjamin I ever spent.
One more thing, inside the case is a primary chain tensioner, it has a roller like the cam chain, I would worry myself to tears if I had not changed it.
Nice project. Keep going.

Yep I've taken the cush drive apart and already pulled the rubbers out. Just put it back together for the picture, I'll plan on replacing them. Is replacing the cam chain tensioner wheel not sufficient? And yes, I'd like to get hondaman's book. Just still convincing myself to spend $100 on it when that could go towards parts haha. I'm assuming the cases have to be split to accomplish that last task? I'm desperately trying to avoid that. Although maybe it would be worth it since I've come this far.

[MauiK3]

I too was nervous about splitting cases. The interior of the lower end comes apart very easily, no "shower of parts" will result. When doing the cam chain tensioner you do the wheels and the slipper, they usually come as a kit.
Hondaman's book is a big help with case splitting, he has all the tips and tricks in there. Also, watch Dean Segovia's you tube video on Hackaweek about his K3 rebuild. It's not always helpful but the part where he puts the cases together is a pretty good visual. It's really simple in there. You can measure the main bearing clearances with plastigauge very easily.
Would hate to see you go through all the trouble and have to go back in later.

[Restoration Fan]

zeff,
If you haven't downloaded the specific service manuals for the 77 and 78 bikes yet, I have them on a shared Google Drive that you're welcome to use.  Here's the link and it has some other 78 stuff in there as well (parts list, etc)

https://drive.google.com/drive/folders/0B4nqeBb662mZZjZjTWdGRk9Qd0E?usp=sharing

[zeffcat]

I too was nervous about splitting cases. The interior of the lower end comes apart very easily, no "shower of parts" will result. When doing the cam chain tensioner you do the wheels and the slipper, they usually come as a kit.
Hondaman's book is a big help with case splitting, he has all the tips and tricks in there. Also, watch Dean Segovia's you tube video on Hackaweek about his K3 rebuild. It's not always helpful but the part where he puts the cases together is a pretty good visual. It's really simple in there. You can measure the main bearing clearances with plastigauge very easily.
Would hate to see you go through all the trouble and have to go back in later.

Yeah I am pretty nervous to get in there but I suppose it would be worth checking while I'm going through everything. And it would make the process of cleaning, stripping and repainting the cases WAY easier. I'll consider just doing that I suppose. I've watched all of hackaweeks's rebuild along with his whole other series on the other bike. As far as the cam chain tensioner, you can buy just the wheel on cyclex and for cost efficiency I was just going to do that since I figured the metal "slipper" as you called it would still be just fine.

zeff,
If you haven't downloaded the specific service manuals for the 77 and 78 bikes yet, I have them on a shared Google Drive that you're welcome to use.  Here's the link and it has some other 78 stuff in there as well (parts list, etc)

https://drive.google.com/drive/folders/0B4nqeBb662mZZjZjTWdGRk9Qd0E?usp=sharing

Thanks restoration fan, I've got one downloaded on my computer and referencing it as I go.

[zeffcat]

Checked the primary chain tensioner today. I'm guessing the general consensus would be too split the case and replace this? The tensioner to deck height was 67.8mm.


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[zeffcat]

Haven't had time to work on the bike in while but got a slew of parts from Honda: cam chain tensioner, wheel, rear wheel dampers,etc. Plus a 4-1 exhaust from Bill Benton! Also got some alumiprep and bonderite to prep the engine for painting. As soon as the weather is favorable I'll be spraying the engine and getting it back together.


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[Stev-o]

Why do you need alumiprep and bondoite??!

[zeffcat]

Why do you need alumiprep and bondoite??!

Well I like to be thorough and I suppose too much so sometimes but I'd found this engine painting prep guide a few months back and wanted to follow through with it! Alumprep is an etching compound that cleans and removes oxidation from the bare aluminum, then the bonderite forms a chromic acid coating which helps stabilize the aluminum to prevent any future corrossion and ensure the paint sticks for good.

[MoMo]

^^interesting info,thanks....Larry

[SOHC4 Cafe Racer Fan]

Interesting post from the CBX forum.  Thanks.

[Stev-o]

Why do you need alumiprep and bondoite??!

Well I like to be thorough and I suppose too much so sometimes but I'd found this engine painting prep guide a few months back and wanted to follow through with it! Alumprep is an etching compound that cleans and removes oxidation from the bare aluminum, then the bonderite forms a chromic acid coating which helps stabilize the aluminum to prevent any future corrossion and ensure the paint sticks for good.

Hope your motor doesn't turn gold!

[zeffcat]

Hope your motor doesn't turn gold!

You and me both! I actually contacted the manufacturer of the product with concerns that it was the engine running temp that caused the discoloration mentioned on the CBX forum. They told me that it is commonly used for pre-powdercoating treatment though so engine temps shouldn't be an issue. The OP of that CBX forum said he thinks it was due to the curing process. The chromic acid product requires that the surface being treated be kept wet the entire time during the cure by reapplying product and then rinsing off with water. I imagine thats the step that was missed.

[zeffcat]

Painted the head today. Pretreated with alumiprep 33 followed by bonderite1201 (super easy process). 1 layer of VHT engine primer followed by 2 light, 1 medium coat of VHT engine gloss black. Very happy with the result. Will do the jugs the same and the crank in VHT aluminum. Finish off with polished covers when I get to that point.



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[markreimer]

Wow that looks really really good! I’m painting an engine black soon, was going to use PJ1 satin, might do the same prep process as you did.


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