Topic: CB750 K1 project

[Dunk]

I figured I'd start a project thread to help keep me motivated. I'm restoring a '71 CB750 K1. Not a true 100% correct restoration I'm sure, but I want to have a nice and presentable bike when I'm done. Some things will be upgraded, I'm sure all colors and such aren't a perfect match for factory, but my goal is to have a safe and presentable bike.

This started because I needed a new front tire, so ended up getting a matching set of period correct tires. Next thigns I know I have the bike totally stripped down because... "While I've got this apart, I may as well ..." I went down a few years ago on my last K1 in a nasty tank slapper on the highway, I suspect mainly due to worn steering head bearings that I was going to replace but who knows what else may have been loose and contributing to it. It sucked and I'd rather not do it again, so here I am.

This is what I started with, a CB750 K1 I got the next summer after I went down. I rode it a little over the course of two years but never rode a lot. I started riding more this year, ordered the tires, and now it's a restoration.

[Dunk]

So I started tearing it down, at first just to get the wheels off to change the tires. Then I figured I ought to do the wheel bearings and at that point the swingarm bushings were easily accessible.... Than got carried away.





I stripped the frame and painted it. Rattle can with VHT Roll Bar and Chassis paint, which is epoxy based and supposedly one of the more durable rattle can paints. I like that I'll be able to touch up any scratches easily.

I also installed roller swingarm bearings. I was going to do bushings but the places I looked did not have any in stock and I didn't know about HondaMan's bushings and swingarm rebuild service. I will save all the original parts so I can convert back to bushings if the bearings don't last.

The steering head got tapered roller bearings as well, one of my primary reasons for doing this.

[Tews19]

Subscribed! I have a K1. Love it. The K0 I currently have has the same 4-1 exhaust. It hugs the frame very nice... How does it sound?

[Dunk]

Excuse the mess, as I'm sure you can see I have too many projects going on at once! I'm trying to focus on the bike for now since this should be the quickest, cheapest, and easiest to get done. At which point hopefully I can get cleaned up and reorganized to tackle another project.

I don't really have any plans for the engine. It runs well so I'm just planning to go over the basics like clutch, clean what's easy to get to, and fix two minor oil leaks I've noticed (neutral switch and valve cover). I've toyed with the idea of getting the engine from my wrecked K1 running and pending no issues using that one. It was a real screamer, no idea what was done to it but it comes on strong at 8k and pulls hard well over 10k. The engine will be last so I'll deal with that when I get everything else together.

So the forks were pitted, particularly around the lower clamp. I understand this is common on the early bikes which were not chromed the full length of the tubes. They are fairly thick, and as per advice of people here I have simple cleaned up all the rust and painted them to hopefully avoid further rusting. I completely disassembled and cleaned all parts and reassembled with new seals. The snap rings were quite rusty, but I could not find replacements locally. I just cleaned up the rusty ones and put them in for now to prevent the seals from popping out. I think I found a suitable size from Grainger so I will order that and see. I also ordered new caps for the top. When these parts come in I'll put the new progressive springs in along with the clips. Maybe I got ahead of myself reassembling them with the lowers not exactly pristine, but I'll polish them before putting them on the bike.

[Dunk]

Subscribed! I have a K1. Love it. The K0 I currently have has the same 4-1 exhaust. It hugs the frame very nice... How does it sound?

It sounds nice, though I don't recall the sound exactly as it's been about two months since i took it apart (and I haven't worked on it a lot in that time). I believe it's fairly mellow and deeper at lower RPM/higher load cruising around easy but really screams when opening it up. If I keep the stock engine that came in it I'll sand blast and paint this pipe. If I end up using the engine from my other bike I'll use the pipe that came on that which is supposedly a fairly rare equal length pipe from back in the day. AAA was the brand or model I believe.

Miraculously it survived the tank slapper with only one minor dent.

[Dunk]

I believe I'm jumping around a bunch, forgive me. I haven't taken a lot of pictures along the way so am mostly focusing on the pictures I have so far and filling in the blanks.

My work space... Nothing like many here have but I make it work. Could be cleaner I suppose....



Since the forks are almost ready I need to figure out what I'm going to do for paint. I'll need to headlight ears soon to reassemble the rest of the front. The current paint is presentable, a good 20 footer, but it has flaws and was done with all the parts on the bike and various things taped off. Most people think it looks great but it drives me nuts that it was not done right. I'd also like the correct K1 tank stripes on it as well. My buddy knows a guy who paints bikes and supposedly is pretty good so I'll talk to him this week and see if he can do it or point me to someone who can. I want to stay with an original K1 color but not sure which color just yet. Also, I see the stripe decal kits for sale from various vendors. Were the original stripes decals or painted? I can't help but think painted stripes would be nicer.

Anyhow, along the way I attempted rear wheel bearings. To my dismay I found the aluminum threaded insert in the rear hub was cracked in two places. This had been apart previously, when the PO had a new rim laced on the rear and tire put on. Apparently someone thought it was okay to run like this. I was able to remove the retainer but it didn't come easily as it was hanging up on the damaged part. On the cracked part the threads got pretty messed up and apparently this part is unavailable.... My understanding is the hub is basically trash since the cracked piece is unavailable. Anyone think different? I can pull the rear wheel from my wrecked K1 if I need to and hopefully that one is not damaged. That is my next step.

I was disappointed with this so haven't got around to bearings on the front wheel yet and instead did some minor reassembly of the parts I have ready, and have been cleaning up and painting other small parts. I try to keep things together with all the fasteners and laid out on the floor oriented as they go on the bike, so as soon as something is ready to go on the frame I put it on or reassemble what I have so I don't lose track of things. This is the first bike I'm completely going through so I don't want to lose pieces or forget how they go together.

[Tews19]

I'm partial to the gold K1. Don't mind the flat rear tire. I was stranded on a Friday night

Sent from my SAMSUNG-SGH-I337 using Tapatalk 2

[edhaeuser]

I'll be following this one asI have a K1 project also.  It looks like you are going to do it right.  And yes, starting a build thread tends to keep one motivated and honest. :-)

[Terry in Australia]

Great project thread mate, hey if that ol' Mustang is taking up too much space in your garage, you can always send it to me? Don't use that cracked hub, and if you replace the wheel bearings on your other hub, first remember to drill out the punch marks, that's probably what caused the other one to crack. Cheers, Terry.

[Dunk]

Stayed at work fairly late tonight but managed to get a little work done. Nothing exciting, but progress. I'll be happy when this part is done.

[Dunk]

Had a little time tonight to work on the bike.

Battery box in with rubber pieces. Should I paint the bolts and washers on top or leave them as is? Not sure what's correct but was thinking I should hit them with paint to match the frame.


Put this motor mount where it goes so I'll know when the time comes. Where does that little clip go and what orientation? I kind of think it goes there, can't really tell for sure fomr the pics I took while tearing down. I believe it is the clip that holds the rear brake light switch.





Got some polish and started on the forks. About 10 minutes worth with a power buffer on slow speed. Don't think they came extremely shiny and polished from the factory so just going to get some shine in them so they're presentable but not wet sanding and going through different compounds for mirror finish. I'll do some more and then get the real tight spots by hand and see how it comes out. Perfection is not my goal, but a nice looking and very presentable rider.

[edhaeuser]

I'd leave the bolts.  I am pretty sure they were plated from the factory.

[Dunk]

Also, does anyone know a source for K1 shocks with the correct chrome cover and springs and black inside and such? Doesn't have to be a perfect match for originals but should be close and I wouldn't mind something that performs better. I'd still like it to look like a K1 though.

[Terry in Australia]

Looking good mate. As has been said, the bolts should be shiny, they were either zinc or cad plated from the factory. The clip is where it should be, you're correct, it's the bracket for the stop light switch.

Your forks were polished then clear laquered from the factory, so you need to strip the old clearcoat off (sandpaper or acetone) then polish the alloy, and recoat them, unless you enjoy polishing. (I don't) Cheers, Terry.

[Tews19]

Hagons for rear shocks... They make repop look alikes but better I've been told.

[iron_worker]

All the hardware is either chrome plated or zinc plated ... The exposed ones on fenders and such are usually chromed and the more hidden ones like battery trays etc are usually zinc. If you have sandblasted the plating off then the hardware will rust quickly.

IW

[Terry in Australia]

And if you want it factory original, you can buy OEM K1 shocks on eBay.

[Dunk]

Hagons for rear shocks... They make repop look alikes but better I've been told.

Which model Hagon would fit my bike and be the closest match for stock K1 shocks? I see they offer several models. I'd like to get shocks soon and have the rear of the bike buttoned up.

All the hardware is either chrome plated or zinc plated ... The exposed ones on fenders and such are usually chromed and the more hidden ones like battery trays etc are usually zinc. If you have sandblasted the plating off then the hardware will rust quickly.

IW

I have sand blasted some of the more crusty fasteners. To prevent rust I'll paint either black, chrome, or zinc so they look presentable or similar to original. Won't be 100% correct but should meet my goals. Thanks for the heads up on the plating though. I think it would be beyond what I want to do to document each fastener and location in order to have them all plated.

[Dunk]

I have manged to get some more work done. Finding time can be difficult.

Forks polished. Not perfect, but plenty presentable for a rider. I ended up going back over the first one with 3m heavy duty rubbing compound on a wool pad, then finishing with Meguiars metal polish on a foam pad. There are some vise marks on one fork from previous owner that would require sanding to get completely out, irritating.





So now that the forks are ready I need the headlight ears painted and ready to go to start getting the front end back together. I could not get the reflectors off after a week or so of heating and soaking in PB every day. One spun freely in the reflector housing so impossible to remove and the other the nut was basically part of the fork ear. I ended up cutting them off with a hack saw. Interesting to learn the bike was originally the gold color that I liked so much. I think I'll end up doing valley metallic green though



Then some aircraft stripper and started sand blasting.

I was very disappointed to find they are rotted out and were shoddily repaired by previous owner prior to repaint. Some weld boogers inside and bondo over the holes in and out. The patches fell apart very easily. I'm not sure if I should try to have a body man repair these or if I should try to find a set that isn't rotted out. I stopped cleaning them up until I decide which way to go. Thoughts?

[Dunk]

Since I'm debating whether to clean these fork ears up the rest of the way and repair or find a better set to work with I decided to start on the front wheel.

To remove the bearing retainer I should use a drill bit the size of the existing holes and drill about 1/4" or until the retainer will come out nicely? I was screwed with the rear retainer outer ring being cracked, but since this is good I want to be sure I don't mess it up.



This piece under the speedometer drive... How does it come off? I assume I need to remove this to get the bearing on this side out?




Also, I got a Solberg silencer and filter/silencer for my compressor. I got sick of all the noise while blasting and thought this might quiet it down some. I'm a bit disappointed as it doesn't seem to have reduced the noise as much as I had hoped, though it has greatly lowered the pitch and it does not carry as far. I may plumb the intake outside and put the filter housing on the other side of the wall. Still, even as is it is better than it was previously. I was pleasantly surprised that my compressor is putting out more CFM now. Long sustained blasting the pressure in the tank doesn't seem to drop below 120 psi whereas with the old tiny filter it would only hold about 90 psi in the tank while blasting. It still runs nearly continuously, but a big improvement. I'm considering making an aftercooler for it to keep moisture down during sustained operation.

[Tews19]

http://www.ebay.com/itm/707-CB750-K-Sandcast-Fork-Ears-Headlight-Brackets-Head-Light-Bracket-K0-K1-K2-/161089438516?pt=Motorcycles_Parts_Accessories&fits=Make%3AHonda%7CModel%3ACB750&hash=item2581adc334&vxp=mtr

Not a bad price..

[Terry in Australia]

Those headlight ears look excellent Tews. Thanks for posting, I've saved that in case I need a set!

Cadunkle, the speedo drive mech should just come right off your hub now mate, it's probably just old grease and muck holding it on. Give it a tap with a mallet and it'll come right off.

Drill out those punch marks as you've described, and you shouldn't do any damage to the threads, although it wouldn't hurt to go up one drill size larger than the punch hole size, as the threads will be mashed at those points.

If you don't want to spring for new fork ears, you could probably solder up the holes, the metal's really too thin for welding, even brazing might be too much for that rusty old tin, don't forget that they rust from the inside out, so it doesn't matter what they look like on the outside, it's what's inside that counts. Even some metal putty like JB Weld would work, I reckon. Have fun! Cheers, Terry.

[Dunk]

Thanks, just some grease and the o-ring holding it on. Got the retainer and bearings out easily enough. Cleaned up the front hub a bit and now ready to install new bearings. One curiosity was the All Balls bearing kit included a second larger seal which I did not notice when disassembling. Where does this go? I don't see it in the parts fiche either. Perhaps it's for another model bike that this kit fits? Unless someone says otherwise I'll just reassemble as it came apart of keep this seal in the box with spare/old parts.



Those fork ears were sold by the time I saw this, so figuring something else for that. Since the guy who I thought was going to do the paint can't do it I'm trying to find someone else, I'd really like to start getting the front end together. More parts on the way too, all the random pieces and "while I'm at it" parts sure add up.

[Tews19]

Those ears are listed all the time.

[Terry in Australia]

No mate, you don't need that larger seal for your front wheel. Cheers, Terry.