Topic: Reviving a '73 750

[MauiK3]

Did I mention Hondaman's book?
Very helpful.
By the time the K3's rolled out the head work was getting a bit "mass produced" so they were not that clean
The head will benefit from some careful casting flash removal and a fresh grind by someone like Mark Paris who knows what he's doing.
It's all in the book

[gpzkat]

Will check into it, thanks.

I am now considering my pipes, which have some dents.  I've read that freezing works on thin wall 2 stroke but not so much on thick.  Makes sense.  Maybe a muffler shop could repair them?   The pipes are the bugaboo of these bikes IMO, what a pain.  Here's a pic, both are the outside.  They actually will look OK from normal angles if these are fixed somehow.  They were coated with grime and rust but cleaned up quite a bit.

Did I mention Hondaman's book?
Very helpful.
By the time the K3's rolled out the head work was getting a bit "mass produced" so they were not that clean
The head will benefit from some careful casting flash removal and a fresh grind by someone like Mark Paris who knows what he's doing.
It's all in the book

[Stev-o]

I am now considering my pipes, which have some dents. 

Those appear to be aftermarket pipes, I'd consider buying some others.  Nor sure what your budget is but these are very good...

https://www.ebay.com/itm/Honda-CB750-CB750K-69-76-Full-4-1-Exhaust-Stainless-Steel-Header-and-Muffler/173429014778?fits=Model%3ACB750&hash=item28612cc0fa:g:oJQAAOSwofFbmYdg

[gpzkat]

These are stock for sure, maybe cut to fit the Mac 4/2 slip ons, and banged up a bit.  You can see the full pipe set in post 2 above and the correct collars (?) for the attachment at the head. I  already have a brand new replacement set of Mac slip ons (same as it had on it before, which was totally shot), just need to get some of the dents out of these down pipes.

I am now considering my pipes, which have some dents. 

Those appear to be aftermarket pipes, I'd consider buying some others.  Nor sure what your budget is but these are very good...

https://www.ebay.com/itm/Honda-CB750-CB750K-69-76-Full-4-1-Exhaust-Stainless-Steel-Header-and-Muffler/173429014778?fits=Model%3ACB750&hash=item28612cc0fa:g:oJQAAOSwofFbmYdg

[750K5]

The Suzuki looks incredible! I can't wait to watch the 73' take shape.. Subscribed

[gpzkat]

That 77/78 front hub bit me, tried to lace up wheel and no luck, very frustrating after several tries the light bulb came on. I checked Partzilla, which lists the lengths.  Turns out they are .5 mm too big.  Not an expensive mistake, especially if someone needs a new spoke set for the front (I'd take $20). 

[gpzkat]

I was searching eBay for pipes and saw one with the exact same indentation on the lower one in the pic in post 23 (which actually does look less like a dent than being formed). Interesting.  Anyway there's a set of 3 (dang!) for a good price, one outer is missing.  Don't bid against me!

[754]

That 77/78 front hub bit me, tried to lace up wheel and no luck, very frustrating after several tries the light bulb came on. I checked Partzilla, which lists the lengths.  Turns out they are .5 mm too big.  Not an expensive mistake, especially if someone needs a new spoke set for the front (I'd take $20).

Do you mean diameter is bigger  ? Just drill out the holes.... spokes should be same length far as I know..  just measure diameter of hole pattern.

[gpzkat]

They are too long. I checked Partzilla and off by .5 mm, seems like it shouldn't matter but it does.

[/quote]
 Do you mean diameter is bigger  ? Just drill out the holes.... spokes should be same length far as I know..  just measure diameter of hole pattern.
[/quote]

[754]

.5 mm is 20 thou 5 mm is 200 thou.. just over 3/16 of an inch.. you any still get them in, I would try.

[gpzkat]

Yes x2 it seems under half an inch would make a difference but it sure seemed to. 

It's not expensive at $25 and sell mine ($15?).  It was frustrating, I had the spokes on right, watched two tutorials, did my rear no problem. There was no way they could be on wrong, I just didn't seem to have enough thread to cinch it up, and looked at Partzilla - same rim, different spokes.   Plus cb750supply lists them differently so I've ordered them.

As always, thanks - Tom

.5 mm is 20 thou 5 mm is 200 thou.. just over 3/16 of an inch.. you any still get them in, I would try.

[754]

I wil, try to measure the two hubs, and spokes.

[754]

Hubs are identical , except late has bigger holes for spokes. . Approx  .233 vs .200. Some length on early US approx  7 7/8 long.
 They only way there us a length difference is the rim, might be drop center on the front, meaning a slightly  shorter spoke. . For sure 77 and 78 used a drop center 17  rear.. so might have on front with 19 inch rim.

[gpzkat]

Thanks, I trust you more than the sites I visit. Depending on what I see with the new ones I will decide. Either way I just eat the $25 or recoup some with a sale to a member or eBay, no big deal.

I've got lots of irons in the fire, stripping the tank to fill some minor dents, researching paint options for the sunrise orange (looking toward house of kolor), rebuilding forks with new stanchions, seals and gaitors, etc.  Got my new Avon AM26s ready for the wheels but waiting on rim strips and tubes.

I got Koyama stanchions from Z1 and I think they are a deal for $130 delivered.  Like my pal says: Here's $130 - make me a set! 

 I have no idea what happened to the fork that was on the bike, only one of them was corroded like this.  The other was clean but pitted. 

[754]

2 different  forks , 73 up to 76 they used the right side one. 77 and 78, the early F and the auto used fork on left.. hard chrome top to bottom. The left fork will fit all K bikesfrom 73 to78, and you can run without the boots or gaiters if so desired .

[gpzkat]

It is great to have someone so knowledgeable following my build.... I'll take CB750K year by year differences for 1000 Alex!  What threw me was the other is chrome all the way, maybe a replacement.  I'll run the gaitors, I like 'standard' and they serve a purpose.

2 different  forks , 73 up to 76 they used the right side one. 77 and 78, yhecearly F had the auto used fork on left.. hard chrome top to bottom. The left fork will fit all K bikesfrom 73 to78, and you can rum without the boots or gaiters if so desired

[gpzkat]

Stripping the tank, used spray stuff, works pretty good. Interesting effect!  Found some bondo spots from previous repairs, but nothing too bad.

[mrbreeze]

It is great to have someone so knowledgeable following my build.... I'll take CB750K year by year differences for 1000 Alex!  What threw me was the other is chrome all the way, maybe a replacement.  I'll run the gaitors, I like 'standard' and they serve a purpose.

2 different  forks , 73 up to 76 they used the right side one. 77 and 78, yhecearly F had the auto used fork on left.. hard chrome top to bottom. The left fork will fit all K bikesfrom 73 to78, and you can rum without the boots or gaiters if so desired

If you run the gaitors you have to have stock headlight ears which hold the gaitors up. The only purpose I see with the stock headlight ears is a place for rust to form. Plus the gaitors hide when your fork seals start leaking. I got some used forks off an automatic that had good chrome all the way up. I mated them to my stock K5 lowers and went to the dust seals instead of gaitors.

[754]

Stripping the tank, used spray stuff, works pretty good. Interesting effect!  Found some bondo spots from previous repairs, but nothing too bad.

If the whole tank looked like that and you could harden it up again, I would run a tank like that on certain bikes.

[gpzkat]

It's a wrinkle tank....
 
Figured out my spoke problem.  Me. Oh well live and learn.  Truing and balancing will be a challenge given my skill putting it together.

[/quote]
 If the whole tank looked like that and you could harden it up again, I would run a tank like that on certain bikes.
[/quote]

[gpzkat]

Now that wheels are together and true, I am mounting a new Avon AM26 on the front, it's a 3.25 19 and it is really tough.  I have mounted M/C tires before but not with tubes so I'm being extra careful.  I'm using proper levers with rim strips and Windex for lube, but by the time I get it mostly on there is no room to get a lever under - it is really tight.  Weather warm, tire pliable, everything is new.  Got one side on (with effort), inserted the tube, and the 2nd side won't go....yet anyway. Anybody mount these and had issues?

Update: Put on mountain bike knee pads, grabbed a couple of large rubber faced woodworking clamps, and wrestled it on.  Tube holding air, no damage to the rim.  Well, maybe a light scratch, damn.

[seanbarney41]

Sure, tube type tires suck to mount.  So much so that I pay pros to do it.

[gpzkat]

I went and bought a valve stem puller for $8, that was a key. The tire is very rigid to open up. I have a new 'Duro' POS rear that came with the bike and that I'll give away, it is so flimsy.  It reeks of cheap.  I put the AM26's on my '82 GS1100E, but tubeless (on EPM magnesium 18" wheels) with much less bother.  I haven't even ridden that bike yet as it's getting jetted (going on 5 weeks wait now, sheesh) so I'm heavily invested in these AM26s, with 4 new ones.

[gpzkat]

Attacked the base gasket today, original one. I looked for the Permatex remover, but think the old stuff is banned in CA now.  Not sure I trust the new 'foaming' formula to the tune of $10, so I tried some good quality paint stripper I had (still the old formula, strong stuff), laid it on and had a 2 hour beer break/nap.  Back at it with a small woodworker's carving chisel and it softened up really well.  Most just peeled off clean in large chunks. For the small areas that are stuck I shaved down and re-applied the gel for another try tomorrow.   

I also got 3 exhaust pipes (#s 1, 2 and 3) that are in really great shape for only $22 plus 25 shipping off eBay.  The 4th I have is the non mangled and pretty good chrome one so I'm very happy about that.  I was worried they would either be worse than the picture or cut too short for my 2>1 Mac slip ons, but they are fine, longer than the ones that were on it, in fact. 

Last progress update, I meticulously cleaned the cylinder block and head and sprayed with VHT Nu Cast.  They look great.  The bottom end will get the treatment soon, after the gasket surface is done.

[gpzkat]

I got the engine paint done, came out good, a couple nits I may address.  I usually take the bolts off and hit them with brass bristle to get the paint off, doing one at a time.  Never had any issues doing this way so I will again.  The engine was grimy due to top end leak, and I had to really work hard to get it surgically clean. 

So now it's on to reassembly, cylinder bores honed, new rings, oil seals etc.  But stupidly, perhaps, I bought a no-name full gasket kit, and after reading the 'no leak' posts about heavy duty studs,  MLS and Viton from Cycle-x, quality pucks etc, I'm wondering how much of my bank account to deplete. 

I checked the surfaces for warping as best I can, and the surfaces seem OK (me? I'm warped!).   It had a bad leak so there is something fundamentally wrong or it just aged. I read the early bikes leaked - my '76 was tight.   So I wonder: has anyone just very carefully rebuilt the top end on an Early CB750 with a no-name gasket set and it was OK?  Or is that just a fool's errand and me succumbing to my inner cheapskate?  Copper spray, any good?  There are a million posts on this, I know.  Valve guides, 3 angle grind, and so on just get me into hock more than I really want.  I am tempted to just roll the dice, clean well, seal it up and pray a little.  It took me about 2 hours to pull the motor out and apart, and another hour to scrape gaskets, that's not gonna kill me if I have to do again but there will be some cursing.

Anyway you can't offend me more than I offend myself, so let me have it!