Topic: Late CB750 K0 Mold to Gold, the nugget.

[Terry in Australia]

I've got to replace the 40+ year old Dunlop K70's on the Suzuki T500 with new Dunlop K70's. I was gonna do it myself, but the guy at the tyre shop who fitted the new Stinko's on my CB750A said to just bring them over and he'll do them. I need new tubes anyway, so I may as well.

[BenelliSEI]

“I have a junk shop vac base that works great to lay the rim over to wrestle tires”

Don..... I have the usual plastic, “green garbage can” that’s just right for laying a wheel over (perfect for a 19” front. 18” can fall in until I get the tire started). I’ve often though about carving (jigsaw) two round discs of scrap plywood (front and rear dia), mount them on a pipe, then create a “wall socket” they fit into. Mmmmmm.

Probably just stick with the garbage can!

[Don R]

 I keep my plastic tire mounting can under the wood chop saw table with a spare gas can in it.
       The short chain case on the nugget is for an older model, it appears to want a different bolt than the long slightly hacked chain case. I made an offer on a set of sandcast type repop shocks from Z1 parts. I offered what I paid last January.

 Late breaking news, they sold me the shocks for the last Jan. price. $149.00 I shoulda low balled them a little. They are nice, black top and shock tube cover, 7 coils of the smaller spring showing like stock, except they have 5 adjustment settings on the spring like a newer shock. I have not tried to swap on an oem 3 position adjuster yet but might if I have a nice enough pair. 

[Don R]

 I'm going out to work on the nugget, it looks like it's getting the 341 cmsnl exhaust since I don't see the 300 no number pipes being available for quite a while. I need to pick up from other work and set up a work table.
  Edit, I've ben half a day cleaning up my mess from working on the tire and wheel, and changing out the front sprocket. I thought I should get a pic of the chain area of the engine for when I sell it later. The sprocket and it's area was caked with chain grease so I took it apart and cleaned everything. 

 Edit, I may finish the tune-up and check one more time. If there aren't any no number pipes for sale by then I'll bolt on the cmsnl 341's. I have shortcuts to DSS, Webike, and Yamiya on my computer. DSS had some a while back but I snoozed and loozed.
 

[Don R]

 The pipes, they coated around all of the welds with the silver coating and the head pipes looked coated inside too. The mufflers were not coated inside for sure. I had paint running out of the drains when I lifted the tape so I'm pretty sure they got an even coat. I'll hang them tomorrow in case there's any liquid paint left in there.

[Don R]

 Coated and soaking before I dry them out.

[Don R]

 I hung the pipes and a little paint drained out, I'll bake them internally with my hot air gun before putting them on a bike.

[Don R]

 My Z1 sandcast repro shocks arrived. They are gorgeous but seem pretty stiff. Hopefully they will break in a bit. The only visual flaw is the 5 setting spring adjusters rather than 3. I bought off ebay and made a $149 offer which I paid a year ago. They took it.
https://z1parts.net/sandcast-shocks-1969-honda-cb750/

[Prospect]

Incredible what is available repro these days. I remember hunting down a used set 8 years or so ago for a similar price. Let us know how they fit and feel.

My Z1 sandcast repro shocks arrived. They are gorgeous but seem pretty stiff. Hopefully they will break in a bit. The only visual flaw is the 5 setting spring adjusters rather than 3. I bought off ebay and made a $149 offer which I paid a year ago. They took it.
https://z1parts.net/sandcast-shocks-1969-honda-cb750/

[Don R]

 Not a good close-up and not the nugget but same shocks taken today. They ride pretty stiff on the soft setting. I'm not sure if it's the spring or shock.

[Terry in Australia]

They're probably out of the same factory as the Ebay cheapies I put on my K0 Don, stiff as fcuk, but the bike is nice and stable around corners, so I can live with the pounding muh poor old back gets on our "patchwork quilt" backroads.

K0 Monday 1 Nov 2021 i by Terry Prendergast, on Flickr

[Don R]

 That looks a lot like my sandcast Terry, she's a beauty.

[Terry in Australia]

Thanks Don, I'm really happy with it, it was my 2 month lightning build from last year, and by sheer luck I pretty much got it right the first time, and the engine is an absolute gem, which isn't bad considering I built it from a bare pair of cases and whatever junk I had lying around in my garage! The CB72 pistons really make it, I think Cruizinimage sell good repros, and I reckon with those high comp 61mm pistons it makes just as much power as my 836 with Andrews cam in my K2.  

[PeWe]

CB750 has room for more compression.
My K2 also got cheap Cruzinimage pistons giving more compression. K7/K8 pistons (392 type) so not very much into the higher area, but good enough for a peppier throttle behavior.
61.5 mm makes 748cc so closer to the side cover badges.

[Don R]

 My 836 Cruisin image kit in the blue green bike had an odd deck height, the cyl block was low or something. Anyway, I assume it made some compression over stock.
   That bike came with a K3 812 high compression engine but the pistons were installed backwards, they even clearanced the pistons but didn't figure it out, the exhaust was plugged by fiberglass over the end of the 4-1 baffle, the PO must have ridden it a long time like that, it was loaded with carbon. It had a stuck exhaust valve and I've never seen the inside of an engine that black before.  I swapped in a K4 motor to get a bike running to ride that fall.

[Don R]

 DSS just missed their last chance to sell me a Yamiya exhaust set before I use the cmsnl pipes on the nugget.

[Don R]

 The K0 is rejecting the 341 pipes, the inlet of the 1 or 2 header pipes won't insert into the engine nipple even after running a rotary wire brush through it. I was tempted to get the rubber mallet but went in the house instead.

[PeWe]

You need to lower down the rear part of the exhaust to get it properly onto the head spigot. Then raise the rear to fit the fotpeg bolt  thru the pipes and frame.

If holes do not line up, redo the procedure lower rear of pipe to adjust how deep pipe must enter the spigot.

No hammering on pipes needed.

[Terry in Australia]

The K0 is rejecting the 341 pipes, the inlet of the 1 or 2 header pipes won't insert into the engine nipple even after running a rotary wire brush through it. I was tempted to get the rubber mallet but went in the house instead.

If I was a K0 I'd reject HM341 pipes too Don, I don't blame it.

[Don R]

 I wonder how it would feel about an RC 4 into 1. Bwahahaha

[Terry in Australia]

I wonder how it would feel about an RC 4 into 1. Bwahahaha

I'll bet my poor old prune shaped testicles that it'll run waaaaaay better with an RC pipe Don, not all choked up with a poxy set of 341's.....

[PeWe]

Carb jets say it all about the restrictive  341. With stock airbox:
Needles  middle (3)
Main jets 105

No numbers 300 style
Needles 4
Main jets 115

I understand HM341 for pure stock restorations and maybe cruising around in legal  speeds only.

No numbers 300 style for fun rides and nice sound, modified engines, bigger bore.

[Don R]

 I really want the 341's on my brothers K4 where they seem natural but I can't get any no no's for the nugget. Especially since I drug home two more bikes. 

[Don R]

 I could not get the 4-4's to start into the exhaust flanges so I took them off and ground, sanded, wire wheeled, scotchbrited etc all of the rust and carbon out of the insides of them. The #3 snap on bit on my little battery impact popped the crosspoint screws right out.  The last effort at removing a set of these resulted in me breaking two bits that snap on happily replaced.
 I've been doing 8 to 10 hours a day in the shop so I have a lot to post. I hope it doesn't get annoying.
 The nugget is amazingly close to being finished. I even got two oem rear footpeg/exhaust mounting bolts with the drag bikes I bought. 

[Don R]

 I got two of the 4-4's on the nugget, the fight was epic, I pried, beat, twisted, and M'F'ed them something awful until I realized the footpeg hole no longer fits the proper footpeg bolt. I drilled out the footpeg hole and it went together in short order but now of course now the balance tube doesn't line up and the rubber connector fell out. The obvious pry point is the footpeg bolt holes but then you start over.
 Yamiya's no no.s are much easier. I wish DSS had some to sell me. 
   I think I'll make a metal tube to fit into the balance tubes to help keep them lined up while I put the peg bolt back in.