Topic: 1971 CB750 K1 Restoration Project- Restoring Still...

[Oly]

Haven't post in quite some time and it looks like I'll need to start a new project post.
Here's a link to my original posting
(http://forums.sohc4.net/index.php/topic,185745.msg2151564.html#msg2151564).

   Last post I was cleaning up wheel assemblies (bearings, spokes rims, etc.)  I manufactured an Evaporust soaking tub like "Alan F " did for his Red CB160 project.  placed the rims and spokes to soak and soak and soak.  They came out looking good so I performed my first wheel lacing and truing on the Harbor Freight balancing stand.  I'm awaiting the Battlax BT46 tires I ordered.

[BenelliSEI]

Turned out very nicely!

[Oly]

Thx John>

[Oly]

Moving onto my first engine rebuild.... disassembly and inspection.
The combustion chamber had lots of carbon buildup, as did the valves and pistons. 
I inverted the head and filled each cylinder with Marvel Mystery oil and let it sit for 30 minutes... No leaks at all.
Cleaning the carbon became a task requiring lots of patience, but eventually I got the majority removed.  The gasket on the bottom of the jugs was like like trying to scrap porcelain off a metal surface.  I used multiple cans of gasket remover with overnight soaks and shaving it little by little till gone.  Removing the heads two oil jets also was a multiple day soak before removal.

[Oly]

More disassembly pictures...

[denward17]

Looking good Oly.....

Do the valve guides go bad in these early heads?

[Oly]

Denward17...

  The measurements that I got for the valve stem diameter (O/D) to valve guide diameter (I/D) were all within specification.
I'm sure all heads live a different life but I've heard pretty good things about these early heads.  The measurements tell the story.

[PeWe]

The ex guides without oil seal is a known reason for smoking at start-up.
Common to replace them to the later version.
Yamiya sell a complete kit of 8.

[Mark1976]

Denward17...

  The measurements that I got for the valve stem diameter (O/D) to valve guide diameter (I/D) were all within specification.
I'm sure all heads live a different life but I've heard pretty good things about these early heads.  The measurements tell the story.

Really great documentation, best thing you can do...

[Oly]

The ex guides without oil seal is a known reason for smoking at start-up.
Common to replace them to the later version.
Yamiya sell a complete kit of 8.

With the clearances between the valve stem/valve guide coming in within specs,  have you typically replaced these components (valves & guides) while you have the engine opened up because they are old or the newer parts are just that much better?

[Oly]

More upper valve train measurements and disassembly pictures:

[PeWe]

The ex guides without oil seal is a known reason for smoking at start-up.
Common to replace them to the later version.
Yamiya sell a complete kit of 8.

With the clearances between the valve stem/valve guide coming in within specs,  have you typically replaced these components (valves & guides) while you have the engine opened up because they are old or the newer parts are just that much better?

I have a smoking K1 head without  guide seals on ex guides.
I have read other posts about it. I used the head anyway on my K2.

I replaced it with another later head, refurbished with new guides with seals, lightly used valves and new springs.

The K1 head is to be fixed later on.

There are several posts about smoking heads with those guides with no seals.

[Mark1976]

The ex guides without oil seal is a known reason for smoking at start-up.
Common to replace them to the later version.
Yamiya sell a complete kit of 8.

With the clearances between the valve stem/valve guide coming in within specs,  have you typically replaced these components (valves & guides) while you have the engine opened up because they are old or the newer parts are just that much better?

   The best money spent will be in reconditioning the head. Those valves look a bit rough.

[Oly]

More disassembly:
  *End gaps of existing rings.
  *Wrist pin to Piston/Crank clearances. (Updated dimensional data after reviewing my bad math and learning how to use new measuring tools)

[Oly]

Clutch disassembly and specs:

[Oly]

This is the first time I've had the clutch out and during my inspection, I see that the clutch lifter plate (#22360-300-010) has a hairline fracture on one of the tabs. 

Has anyone purchased one of these lately?  Source?

[newday777]

South Sound Honda has them available
https://www.southsoundhonda.com/--xpartsstream#/s/HOM//22360-300-010//1/y

[newday777]

Or on feebay you can get a billet aluminum lifter plate that is stronger

[Oly]

Or on feebay you can get a billet aluminum lifter plate that is stronger

Thanks Stu.   Do you have any experience using the billet aluminum piece?

[newday777]

I haven't but there are posts stating they are good and much stronger than the stock lifter.

[Oly]

The ex guides without oil seal is a known reason for smoking at start-up.
Common to replace them to the later version.
Yamiya sell a complete kit of 8.

The ex guides without oil seal is a known reason for smoking at start-up.
Common to replace them to the later version.
Yamiya sell a complete kit of 8.

With the clearances between the valve stem/valve guide coming in within specs,  have you typically replaced these components (valves & guides) while you have the engine opened up because they are old or the newer parts are just that much better?

   The best money spent will be in reconditioning the head. Those valves look a bit rough.

PeWe and Mark1976... Thanks for your input.  I agree that the money spent on reconditioning the head is well worth it.
Although most of my inspection dimensions are within serviceable limits, I also see issues related to storing my bike for the past 35 plus years with heavy carbon build up on the cylinder/head components that I was not aware of till disassembly.  Bike has 30,000 miles on it and as I read Hondamans book, he talks about how the cylinders become out of round after 10,000 miles and that you can capture 10% on horsepower if a rebore is done.  His book also talks about how great the original valve guides are, but I am thinking I don't want to take a chance on them not smoking while I'm already planning on having a full valve job done.  I'm not getting any younger and this will probably be the only time I have the engine dismantled prior to sending it to another home.  I'm thinking I'd like to just go 0.25mm oversize bore, so the next owner has an open slate for their future wishes.   Right now my wish list for this build would be .25mm oversized bore/piston set, new piston pins, new valves, new valve guides, and some mild porting to support a stock setup.  This is the only bike I own and this is the first time I've ever done this, so any and all input from this wonderful forum would be greatly appreciated.

[PeWe]

Cruzinimage has cheap and functional pistons kits
+0.50 mm. The smallest bore after stock size.
They need tight total clearance below 0.025mm.
Last cylinder I left to shop got the message max 0.02.
My K2 got the K7/K8 variant for extra compression. Work fine

https://www.cruzinimage.net/page/2/?s=Cb750+piston

Their clutch is OK too.
My K6 had them with 836 and 80whp without slip. (Stiffer springs + washers)

[Kevin D]

Hi Oly, I have a similar story as yours and a similar K1, mine is an
11/70 and 18000 s/n higher than yours. That’s 6000 CB750K1s per month! And that is a lot of motorcycles.
I rode mine for several years (5000miles?) after a 15 year park, before I pulled the engine last time in 2007
 
 I have had my engine out a couple times: nuisance oil leaks at the point seal and pucks/head gasket drove the decision to pull the engine. Also replaced the internal chains, cam chain and primary chains, tensioners “while I’m in there”. Also hone and rings “while I’m in there” but end gaps were good. At 70000 miles there was some carbon in the exhaust ports but still at 100000 miles no smoke. At least, I don’t see any smoke in the mirror, and no smoke reports from following riders.
 Torque/retorque the head gasket was good advice.

My clutch was slipping badly even though the fiber plates measured good. I roughed the surface of the old plates and got temporary improvement. Finally new (supple) fiber plates have done the trick and the clutch now grabs like it should. I still have my original lifter plate and always loosen/tighten the four bolts slowly and evenly. Maybe I should have a heavy lifter plate on hand for my heirs, or the next guy that goes in there.

I’m not an engine builder, I have just the experience of one CB, this one.
My bike still goes from zero to illegal mighty fast without performance mods, not VRod fast, not CBR gixxer or Ninja fast, not even Z1 fast, but fast enough for this guy.

You’re doing a nice job Oly. Make sure you keep your measurements for the future.
 

[Oly]

Cruzinimage has cheap and functional pistons kits
+0.50 mm. The smallest bore after stock size.
They need tight total clearance below 0.025mm.
Last cylinder I left to shop got the message max 0.02.
My K2 got the K7/K8 variant for extra compression. Work fine

https://www.cruzinimage.net/page/2/?s=Cb750+piston

Their clutch is OK too.
My K6 had them with 836 and 80whp without slip. (Stiffer springs + washers)

Thanks PeWe.  I haven't used cruzinimage before.  Do they have long lead-times for delivery of parts?

[Kelly E]

I just got a set of 550 pistons from Cruizin Image. It took 7 days because the post office gave them a free ride to the east coast before coming back to the west coast. I ordered something else the next day and it took 4 days.