Topic: CB750K Basketcase

[dthohler]

Well, its not much of a basketcase to be honest. I am a habitual, though nowadays seldom, lurking on the forum. So seldom that I forgot my past username!

In any case, the recent selling of a 72 750K forced me out, but the purchase of a 78 750K has brought me right back!

The problem with the bike was often discussed (more discouraged) use of the oil delivery system to the cams of the 77-78 K's. SO my motor was blown and when looking at the bike I thought it would be easy enough to replace the holders/cams/rockers etc. and get a perfectly fine running engine for cheap. Not the case.

I deciuded it would be easier to buy a running earlier style engine to get away from the problem in the first place. From the serial numbers, mine is a mid 76. Compression over 150 in each cylinder.

These are the problems I am in the middle of now- please advise as you see fit-

1. 78s run 630 chain, my 76 motor has a 17 tooth 530 sprocket, easy enough fix. Switched rear to 48t 530 from a 76. Done. My problem now is chain line. As the motor was put back in I am wondering if I missed a washer here and there leading my chain to hit the chain guard. Maybe Ill just adjust the chain guard and call it a day, I still need to address the chain line so it is not a main concern as of yet.

2. Carbs- I have the set of 78's and have the carb boots from the 76 (which will be treated with wintergreen oil, the jury is still out on that). My main question- Can I use the later style carbs on the earlier motor provided I have the 76 boots with the 76 motor?

I couldnt seem to find direct answers to these questions in the past forum entries. Thanks for reading! Hope Turkey Day went great for all of us in the West!

[754]

 You have to use an earlier spocket carier on a 78 wheel..or offset sprocket on the front, or cut down the rear sprocket carrier.
 Carbs will work, enjoy the accel pump,, You will have more clearance for gas tank, good thing if you feel like running a difff tank..

[dthohler]

Thanks for the reply. What is the difference between the earlier and later sprocket carriers?

[MCRider]

Thanks for the reply. What is the difference between the earlier and later sprocket carriers?

The difference is the problem you are experiencing. The earlier carrier carries the sprocket nearer the centerline. The later ones are thicker/taller/ whatever you want to say; carries the sprocket further away from the centerline.

[dthohler]

Yea I should have guess that, tenfour, Ill get an older one. Thanks guys. Anyone got one to sell?

[MCRider]

Yea I should have guess that, tenfour, Ill get an older one. Thanks guys. Anyone got one to sell?

I might, I'll check tomorrow. Anyone else steps forward, go ahead.

[dthohler]

Thanks, I look forward to hearing if you have one.

What do you guys know about putting the stock K8 mufflers on the K6 motor? I just looked at the parts fiche, and they have different mounting hardware, though I thought I just needed to get bolts on the K6 as opposed to studs on the K8...

[GammaFlat]

The head where it connects to the exhaust (tapped holes) is the same but there may be a difference in the hardware used to attach the exhaust.  You may have studs, then again, you may have screws holding a spigot.  Either way, you can switch as long as you have the hardware you need. 

In terms of the chain type and alignment with a K7/K8 bike using an earlier motor... There's a 3/8ths inch difference.  As mentioned, the later bikes have a more outboard sprocket on the engine.  The swing arm, sprockets, chain, wheel and carrier are different on the later bikes.  If you change to an earlier (narrow) carrier, I think you may also need different spacers on that side of the wheel to fit correctly into the K7/K8 swing arm which is wider than an earlier one.   

[dthohler]

Thanks for the info Gamma, makes more sense now. I suppose if I decided to change the carrier, changing the spacers would not be too much more hassle. What are my options in terms of adding a spacer to the front sprocket?

[dthohler]

In terms of the exhaust, these flanges should mount my K8 pipes to K6 motor?

http://www.ebay.com/itm/1974-HONDA-CB750-EXHAUST-FLANGES-/220901642028?pt=Motorcycles_Parts_Accessories&vxp=mtr&hash=item336ec38f2c

[ekpent]

In terms of the exhaust, these flanges should mount my K8 pipes to K6 motor?

http://www.ebay.com/itm/1974-HONDA-CB750-EXHAUST-FLANGES-/220901642028?pt=Motorcycles_Parts_Accessories&vxp=mtr&hash=item336ec38f2c

Those are called spigots and are used as the mounting points on the 69-76 K model 750's. Think the K7-8 are a different setup.

[Roach Carver]

"2. Carbs- I have the set of 78's and have the carb boots from the 76 (which will be treated with wintergreen oil, the jury is still out on that). My main question- Can I use the later style carbs on the earlier motor provided I have the 76 boots with the 76 motor?"
No. you will need the boots that go with the carbs. the boots are not engine specific, they are carb type specific. Hope that makes sence.

I am a habitual, though nowadays seldom, lurking on the forum. So seldom that I forgot my past username!

I feel used.

[Retro Rocket]

Thanks for the reply. What is the difference between the earlier and later sprocket carriers?

The difference is 10mm, the later engines had a 10mm longer out put shaft on the gearbox and the sprocket carrier had to be 10mm wider to keep the chain aligned ....

[buffaloejon]

Either way you go with the exhaust, early style spigots or later style studs, I have spares. Spare stud exhaust retainer-things, and spare spigots with the clamps. New studs or screws would be needed though.

Let me know which one you're needing if you do need them, I'd be glad to give em to you on the cheap.

[mrbreeze]

Thanks for the info Gamma, makes more sense now. I suppose if I decided to change the carrier, changing the spacers would not be too much more hassle. What are my options in terms of adding a spacer to the front sprocket?

Cycle X sells offset front sprockets. Never heard of a spacer up front.

[dthohler]

"2. Carbs- I have the set of 78's and have the carb boots from the 76 (which will be treated with wintergreen oil, the jury is still out on that). My main question- Can I use the later style carbs on the earlier motor provided I have the 76 boots with the 76 motor?"
No. you will need the boots that go with the carbs. the boots are not engine specific, they are carb type specific. Hope that makes sence.

I am a habitual, though nowadays seldom, lurking on the forum. So seldom that I forgot my past username!

I feel used.

No need to feel used, we are all family here. Using family is practically what family is for, right? Eh?
Thanks for the info on the boots, I have both sets, I guess I'll switch back to the K8 carbs/boots on the K6 engine. Thanks, I think those boots are more pliable anyway.

In terms of the exhaust, these flanges should mount my K8 pipes to K6 motor?

http://www.ebay.com/itm/1974-HONDA-CB750-EXHAUST-FLANGES-/220901642028?pt=Motorcycles_Parts_Accessories&vxp=mtr&hash=item336ec38f2c

Those are called spigots and are used as the mounting points on the 69-76 K model 750's. Think the K7-8 are a different setup.

Thanks for the info, I was just wondering if the K8 pipes and hardware can be used on the K6 motor, and in hearing that they can, I will try to mount those tomorrow.

[MCRider]

The K6 has the spigots. They will need to come off. Held on by 2 flat head screws each, that have corroded themselves into the head by now.  You'll need a clean path to use a hammer impact driver n them. Don't know about that with the engine in.

Once you get them out, and drill out the broken headed screws, pick out the old crushed exhaust gaskets you'll need new exhaust gaskets to put the K8 pipes on.   

[dthohler]

Thanks for the info Gamma, makes more sense now. I suppose if I decided to change the carrier, changing the spacers would not be too much more hassle. What are my options in terms of adding a spacer to the front sprocket?

Cycle X sells offset front sprockets. Never heard of a spacer up front.

That makes more sense, though I just bought a new 17t from Z1, so I would hate to have to buy another one, especially at 69.95, but perhaps thats what happens when we buy 40+ year old bikes. Seems like a simpler approach than buying another carrier and sourcing the proper size spacer.

[mrbreeze]

Sell the one you just bought,save it for another project, or get a carrier and spacer. Lots of options and believe me.......lots of parts out there. Anytime you're not sure what will fit between the years.....ask here before buying to save yourself from grief!!! The first thing I bought wrong was around 5-6 years ago. I bought a grab bar from a 77-78 to use on my 75............thats one part that changed among many others. I did end up selling it though and finally found the right one. They're out there.

[MCRider]

Thanks, I look forward to hearing if you have one.

What do you guys know about putting the stock K8 mufflers on the K6 motor? I just looked at the parts fiche, and they have different mounting hardware, though I thought I just needed to get bolts on the K6 as opposed to studs on the K8...

Check your PMs