Topic: CB750K 'Sport Tourer'

[knottedknickers]

I'm tearing down the engine these days. My intent was to replace the cam chain tensioner parts: rollers and sliders (I read someone's opinion here that after nearly four decades they're going to begin to get brittle and ought to be replaced; made sense to me). I got the head off, and the valves and pistons look OK (to my eye). I was trying to leave the cylinders in place so I didn't have to replace the lower gasket, not to mention mess with rings, etc. But it's looking like I'm going to have to lift the cylinders in order to remove the slider and rollers. Is that true? Advice?

[MCRider]

I'm tearing down the engine these days. My intent was to replace the cam chain tensioner parts: rollers and sliders (I read someone's opinion here that after nearly four decades they're going to begin to get brittle and ought to be replaced; made sense to me). I got the head off, and the valves and pistons look OK (to my eye). I was trying to leave the cylinders in place so I didn't have to replace the lower gasket, not to mention mess with rings, etc. But it's looking like I'm going to have to lift the cylinders in order to remove the slider and rollers. Is that true? Advice?

YEs the cyls have to come up at least an inch or two, enough to break the gasket, to get the removable pin out that anchors the bottom of the tensioner slide. IF you're lucky you can get it up without breaking the gasket, and leaving the pistons in the cyls. So, do you feel lucky?   

[ekpent]

Hmmm... I just came here to ask a question and noticed that my first post is gone. Anyone know what could have happened? Any way a moderator could retrieve it from the ether?

Anyway, I'm putting together a list of things to order (carb kits, gas cap rubber seal, etc.) and wonder if anyone knows what those rubber boots that cover the carb sync nuts are called? And if they're still available anywhere? Mine are a bit tired...

I would save my money and pass on the carb kits and try to re-use all the stock bits. Kehin brass is the best and some aftermarket bits are real dodgy spec wise. I have done a ton of 750 carbs and never have even had to replace a good stock bowl gasket yet.  Depending on what your intake and exhaust ends up at you may be needing to fine tune at the end anyways.

[knottedknickers]

YEs the cyls have to come up at least an inch or two, enough to break the gasket, to get the removable pin out that anchors the bottom of the tensioner slide. IF you're lucky you can get it up without breaking the gasket, and leaving the pistons in the cyls. So, do you feel lucky?   

Depends on the day! The head came off with a steady pressure pull from intake and then exhaust sides (just to break it free). But then the head gasket did have a few minor leaks, so it obviously wasn't tight... The bottom gasket is tight, i.e., no leaks (which is kind of why I wanted to leave it alone). But I think replacing the tensioner bits is worth breaking the bottom gasket. Right? I'm overseas for the next four weeks, so I guess I'll have time to come to a decision...

By the way, is there any way to replace the small wheel in the tensioner, without replacing the whole assembly? That thing is silly expensive (for what it is)!

[knottedknickers]

I would save my money and pass on the carb kits and try to re-use all the stock bits. Kehin brass is the best and some aftermarket bits are real dodgy spec wise. I have done a ton of 750 carbs and never have even had to replace a good stock bowl gasket yet.  Depending on what your intake and exhaust ends up at you may be needing to fine tune at the end anyways.

I've come to the same conclusion myself, after reading things like this article by Mike Nixon. After six years of not being ridden, the gas had congealed in the carbs, but they cleaned up quite nicely.

I was going to replace the bowl gaskets, but maybe I'll give mine a try and see how they seal... Is there a way to clean them? It was as if mine were glued in and they feel quite gummy.

[754]

Use a strong light and examine the cam chain slider....then decide..

[knottedknickers]

Use a strong light and examine the cam chain slider....then decide..

Good call. I'll do that. You don't think age is necessarily a deciding factor? But rather what shape it's in? I have no idea... And from what I've read, you've run some of these engines for a long time--longer than most.

[MCRider]

Use a strong light and examine the cam chain slider....then decide..

Good call. I'll do that. You don't think age is necessarily a deciding factor? But rather what shape it's in? I have no idea... And from what I've read, you've run some of these engines for a long time--longer than most.

Age is a factor. So is circumstance. IF the engine has been run continuously, with oil getting splashed onto the blade that would slow the aging process. IF the engine has set unrun in a garage in Tucson for 20 years, I'd say its more likely to be dried out.

IF its a budget get her rollling deal. Check it with a flashlight, see if there are any crumbs flaking off, it will be obvious. If not, all's nice and smooth, with crisp edges, go ahead and run it. Check your oil pump screen once in a while for evidence of failure.

[ekpent]

I would save my money and pass on the carb kits and try to re-use all the stock bits. Kehin brass is the best and some aftermarket bits are real dodgy spec wise. I have done a ton of 750 carbs and never have even had to replace a good stock bowl gasket yet.  Depending on what your intake and exhaust ends up at you may be needing to fine tune at the end anyways.

I've come to the same conclusion myself, after reading things like this article by Mike Nixon. After six years of not being ridden, the gas had congealed in the carbs, but they cleaned up quite nicely.

I was going to replace the bowl gaskets, but maybe I'll give mine a try and see how they seal... Is there a way to clean them? It was as if mine were glued in and they feel quite gummy.

I find some of the replacement gaskets are made of some crap rubber. Easy to put the carbs together and fill them from a slave tank on a simple jig to test for leaks before mounting.

[Garage_guy_chris]

If you still havent found a suitable tail light and have a good 4 hole k4 fender consider what im doing.  I had a 71 cb450 tail light and bracket off a previous bike, the tail light is a hm-11rc which is the same as the smaller K0 750 tail light. But the  71 450 bracket bolts the early tail light to the 4 hole fender without any modification. Just be careful because just like the 750 around 72 73 the 450's tail light and bracket also grew to the bigger uglier  light.

[knottedknickers]

If you still havent found a suitable tail light and have a good 4 hole k4 fender consider what im doing.  I had a 71 cb450 tail light and bracket off a previous bike, the tail light is a hm-11rc which is the same as the smaller K0 750 tail light. But the  71 450 bracket bolts the early tail light to the 4 hole fender without any modification. Just be careful because just like the 750 around 72 73 the 450's tail light and bracket also grew to the bigger uglier  light.

Thanks for the great tip, Garage_guy! It's always good to know what fits (and what doesn't...)

[knottedknickers]

Just a brief update before I head overseas for four weeks...

Head removal, before cleaning:


after:


How best to clean the head domes?


Cam chain slider:

Looks in fairly good nick. It was nice and wet with oil when I pulled the head.

Oil screen and pan:


Again, looks fairly clean? A few bits on the screen and some sludge in the pan by the drain hole, but mostly soft. No serial numbers.

Like I said, I've got a few weeks to stew on the next steps. From what I've been reading, basically every oil passage O-ring ought to be replaced: in the head, oil pump, countershaft oiler. Any others? The drilled clutch basket makes good sense too. I sure appreciate your helpful tips.

I'm going to miss my therapy sessions in the garage!

[knottedknickers]

I'm back...

I just pulled my starter apart to have a look at the brushes (they're good!). Putting it back together I'm wondering about the fibre washer and two metal shims--does the fibre go to the armature? or the case? or does it matter?

[knottedknickers]

"Cap side." Thanks, goldarrow!

[knottedknickers]

I posted in the Oil Pressure + Easier Shifting HOW TO / WALKTHROUGH thread about my intentions to drill some more holes in the clutch hub. Wonder if anyone would be willing to give feedback on where I propose to drill the extra holes? See the PDF for details.

[knottedknickers]

I feel like a dweeb, bumping my own thread and all, but anyone willing to comment on drilling the clutch hub? Basically, I'm thinking the new holes should line up with the clutch plates rather than the clutch disks, which would see the oil distributed to two clutch disks rather than just one (if the holes lined up with a clutch disk). Does that make sense?

[knottedknickers]

I bit the bullet and pulled a couple of valves, just to have a look. I'm glad I did!

Things look a bit cruddy in there. I'm really not excited with how the exhaust valve looks... In fact, all four look the same.

Looks like it wasn't even seating... Adjusted too tight? Will a simple hand lap fix this? Or am I looking at something more involved?

[MCRider]

I feel like a dweeb, bumping my own thread and all, but anyone willing to comment on drilling the clutch hub? Basically, I'm thinking the new holes should line up with the clutch plates rather than the clutch disks, which would see the oil distributed to two clutch disks rather than just one (if the holes lined up with a clutch disk). Does that make sense?

My 2c, don't overthink it. Whatever Hman said in his hints is adequate. Just the fact that you are doing it is 90% or ore of the result.

You asked.   

[MCRider]

Yeah the exhaust valves were likely leaking a bit. A hand lap dould take care. Try it first, no good, do something more.

[knottedknickers]

My 2c, don't overthink it. Whatever Hman said in his hints is adequate. Just the fact that you are doing it is 90% or more of the result.

You asked.   

I did--thanks for replying! And I'm guilty as charged... I tend to overthink things (note the slow progress on this project!) Time to get out the drill.

[MCRider]

I think I get the prize for slow progress. Though it is done now. So keep at it.

[knottedknickers]

I've got a line on a 1997 GSX-R750 front end. It has me quite excited, but I need to ask: Has anyone done a front-end conversion with this model year? Any tips? Cautions? I've had a look at "Sam's Fork Chart" but there are a number of blanks in the GSX-R750 SRAD 96-99 column... Can anyone help me fill them in? Especially, 'fork length' and 'stock rake/trail'? I'm tempted to guess that Suzuki used the same fork on the Hayabusa (99-07), since most of the numbers are the same (one exception: Triple Clamp Bottom Fork Dia -- 55 vs. 54 mm). I do note that CognitoMoto makes a hub for this series of GSX-R750, so someone must have done it before.

While I'm asking, anyone know what the stock numbers are for the CB750K6? Fork length, rake/trail, offset, etc.?

[knottedknickers]

Cognito not only makes a hub for that series, but they also offer an adjustable triple tree to allow you to change the offset to achieve the riding geometry you desire.

Roger that. It is pretty, but the hub will put a big enough dent in my budget...

Lacing the Cognito front hub requires an inside-inside spoke pattern, so be aware of that.

I've seen that noted elsewhere. Can you enlighten me? Will I still be able to use my stock rim and spokes?

[SOHC4 Cafe Racer Fan]

Yes on rim, no on spokes (probably). Stock pattern is spokes laced from outside and inside, in an overlapping pattern. Due the width of the hub, the "outside" spokes are added to the inside to avoid conflict on the backside of the caliper.

Buchanan's knows this hub, and can provide spokes for it.

Good to know!

[knottedknickers]

While I'm asking, anyone know what the stock numbers are for the CB750K6? Fork length, rake/trail, offset, etc.?

I found some of this info in the 'dimensional drawing' on p. 3 of the CB750K service manual (a reasonable place to look... ):
   Rake: 27º (90º - 63º [caster angle] = 27º)
   Trail: 95 mm / 3.74 in
And some I worked out on my own:
   Fork length: 754 mm (from centre of axle to top of tube; *off the bike, uncompressed*)
   Offset: ~ 60 mm
Getting there... But for accuracy, I'm thinking the fork length measurement should be taken with the forks on the bike. Could someone with a stock 750K6 (or similar) measure that? I'd appreciate it!

By way of comparison, the '97 GSXR 750 dimensions (again, from the '96-99 GSXR 750 service manual, p. 1-9):
   Rake: 24º (90º - 66º [caster] = 24º)
   Trail: 96 mm / 3.8 in
   Fork length: 729 mm
   Offset: 30 mm

Of course, the big things are fork length and offset, since it will be going on the CB750 frame with its 27º rake...