Topic: Senior project for high school - 78 CB750K

[madmtnmotors]

My money is on the kickstarter "ratchet" mechanism.

[grcamna2]

Nice work Restoration Fan and Welcome to the forum

[Stoli]

My money is on the kickstarter "ratchet" mechanism.

It is certainly starting to look that way. I am wondering if a worn shaft is compounding the problem though. It looks bad in a couple of the pics but it might be an illusion. If in doubt, need to clean the shaft up, remove the oil seal from the hole in the cover, put the cover back on (just temporary with the two collars and a few of the screws) and see if the shaft can wiggle around in the hole.

[Restoration Fan]

My money is on the kickstarter "ratchet" mechanism.

It is certainly starting to look that way. I am wondering if a worn shaft is compounding the problem though. It looks bad in a couple of the pics but it might be an illusion. If in doubt, need to clean the shaft up, remove the oil seal from the hole in the cover, put the cover back on (just temporary with the two collars and a few of the screws) and see if the shaft can wiggle around in the hole.

I don't see any really visible issues on the shaft itself and the hole in the clutch cover looks to be fine as well.  With the clutch cover off, how much play should there be in the shaft itself?  This thing will move a good centimeter or more without the cover on.

I'll try testing it with the cover on in a little while to see how much/if any play there is.  My wife has been gone for 2 weeks opening a hotel and just arrived back home very late last night.  Because I'm an idiot, we set up the workshop in a large unfinished part of the basement directly beneath the master bedroom and my wife is still asleep.  I've been trying to get this worthless hunting dog of mine to start barking at squirrels so that it'll awaken her, but no luck so far.  Normally, he barks when he sees the shadow of one.

If it's not the clutch cover allowing too much play, I'm assuming that means we're going to need to take the rest of the bottom apart so that we can get to the other side of that gear...back on the transmission side of the housing?

[Stoli]

It is normal for that shaft to be able to flop around quite a bit with the cover off. Back and forth and in and out as well.

If the kickstart lever goes all the way down without turning the crank shaft, then the only way to fix it will be to split the cases. Might be getting a little ahead, but a few things pop to mind regarding that -

- Make sure you remove ALL the bolts (top and bottom) that are holding the cases together. The cases won't just fall apart after you do that (the liquid gasket is holding them together like glue) so you need to persuade them with some light tapping and or prying in some strategic areas being very careful not to damage the case.

- The kickstart mechanism (shaft, gear, etc) is kind of a bugger to remove and replace. It is held in place by a roll pin which in my experience doesn't like to come out very easily. The best way to do that is to use a large pair of wire cutters to grasp the pin at its base, then pry it out a little at a time by rocking the pliers. Use just enough squeeze on the wire cutters to hold the pin (you don't want to break it or damage it too badly). Put a small piece of wood or something between the case and the wire cutters so as to not mar the surface of the case during removal. You will be able to reuse the pin if you don't damage it too badly.

- Getting the kickstart mechanism back in always gives me some trouble because of the spring. I usually scratch my head for about 30 minutes and try different things then all of a sudden I figure it out and it clicks into place. The manual is not much help in that regard. You'll see what I mean. I am actually reassembling a K8 engine in the coming week so things will be fresh in my mind.

- I use ThreeBond Liquid Gasket 1184 to seal the cases back together. There is other stuff out there but I have had good luck with it. A very thin coat is all you need. .

[flybox1]

Great project thread. subscribed, and good information so far from these guys.
I'll just add that getting the kick spring back in is a lot easier with the lever (or a pair of vicegrips) carefully clamped on the end of the kick starter shaft to leverage the spring in place.  I must have fought this for an hour until the dim light started shining bright 

[Stoli]

Thanks Fly. Excellent timing on that one. I just assembled the cases on my 3rd engine rebuild and that never dawned on me before. There was still some head scratching but it only took me 5 to 10 minutes instead of an hour to get the kick start assembly back in.

A couple more things about the cases-

You will need to remove the countershaft bearing holder. That is held in with 4 countersunk Phillips head screws that are staked in position. In my experience, you will most likely strip 2 or more of them trying to get them out. So if you wind up drilling them out, that is the norm.

You don't need to remove the rotor to split the cases if you don't want or don't have the right tools.

On page 9-5 of the manual there is a misleading picture of the cases just prior to reassembly. In that pic, the final drive is shown in the bottom case. In actuality you will have that installed in the top case. Otherwise it will fall out of the bottom case when you are putting them together. The text of the procedure is correct. It is just a bad picture.

[Restoration Fan]

Just an update for everyone.  I now have the 78 K8/F3 Manual (it's missing Chapter 11), the 78 Parts List, and now the missing Chapter 11 PDF manuals hosted on a Google Drive that I'll leave up indefinitely.

For anyone wanting to download them, feel free:

https://drive.google.com/folderview?id=0B4nqeBb662mZZjZjTWdGRk9Qd0E&usp=sharing

[Davidov]

Just an update for everyone.  I now have the 78 K8/F3 Manual (it's missing Chapter 11), the 78 Parts List, and now the missing Chapter 11 PDF manuals hosted on a Google Drive that I'll leave up indefinitely.

For anyone wanting to download them, feel free:

https://drive.google.com/folderview?id=0B4nqeBb662mZZjZjTWdGRk9Qd0E&usp=sharing

Nice work! Free knowledge is the best.

[Restoration Fan]

Today was a good day.  My son and I are having an absolute blast! 
Got a few things accomplished:
Got a little more sanding done on the frame (had hoped to have this done by now but wife came home and we had to let her sleep to get back on east coast time.  She's gone to Bali now for the week, so no conflicts on getting in the workshop)


Also, got the first coat of Aircraft Stripper on the first tank (we have 2...not exactly sure which we're going to use yet but we're going to strip and at least prime both of them before we decide).

Finally, began the teardown of the engine by removing the cylinder head cover as well as points cover and all the other side covers. 

But the absolute best was taking the ratchet and turning the engine slowly over and over and letting him watch the rocker arms and hear the exhaust "pffft" as the exhaust valve opened.  He stood there grinning and said, "Man...this is the sexiest, coolest thing ever!"

Good times. 

[Davidov]

With the frame stripped, now is a good time to install a set of tapered steering head bearings (All Balls, Timken).

[Restoration Fan]

With the frame stripped, now is a good time to install a set of tapered steering head bearings (All Balls, Timken).

I've seen a lot of posts about this.  Do they really make that much of a difference over the stock bearings?

Also, when I go to www.allballsracing.com and try to select my bike, the CB750K's only go up to the "CB 750K1-K5 750 Four" in the "Select Vehicle" options.  There isn't a K8 in there.

[Stoli]

I'm sure there are varying opinions about that, but personally I don't think it is necessary if the stock races are in good shape. I know you didn't ride the bike before teardown, so take a really close look at the races top and bottom and see if there are any noticeable dimples. If so, then the decision is easy - get an All Balls kit. If they look good, then not a bad investment but certainly not required.

I wish my wife would go to Bali for a week.

There is a specific thread with links to all the manuals, I am going to post your link there so more guys find it if it is OK with you.

[Restoration Fan]

There is a specific thread with links to all the manuals, I am going to post your link there so more guys find it if it is OK with you.

Please do.  I was looking for that specific thread last night and didn't find it.  Albeit, it was late and I was tired so I didn't look for it very long.

I plan to leave the link up indefinitely, so as long as Google Drive is around (& free), the manuals will be there.

[knottedknickers]

With the frame stripped, now is a good time to install a set of tapered steering head bearings (All Balls, Timken).

I've seen a lot of posts about this.  Do they really make that much of a difference over the stock bearings?

Put your triple tree and bearings back in the frame and turn it from side to side. You'll know if you need new bearings. ;-) What you want is smooth, fluid motion from lock to lock. Mine had a 'snap-to-centre' effect, probably caused by someone overtightening with the steering straight... Definitely NOT what you want!

[Restoration Fan]

There's 2 big advantages to tapered bearings over stock ball bearings:
1. Sealed grease bearings. No more servicing (as if people ever did this frequently enough)  This yields superior performance for much longer and won't allow dirt, grime and contamination to collect.

2. Installation. Both have races, but tapping in the bearing and not having to chase 37, 38 or 39 steel balls around the shop is a pretty nice luxury. Fitment is very easy, and it's such a low expense item, it's worth doing over "not doing".

So how would I order from All Balls then for a K8 if they only list 750's up thru the K5?

[SOHC4 Cafe Racer Fan]

They are universal K0-K8 F1-F3

[Restoration Fan]

Excellent.  Thank you.

OK, another question though.  We have made the decision to at the very least, lap the valves.  So we have removed cam shaft.  We also removed the 22 nuts holding the head on, but how do you get the head to separate from the jugs?

Conscious of not breaking the fins, we were tapping gently on the various places on the head.  But it looks like the jugs are starting to separate slightly from the bottom...but the jugs aren't separating from the head.  How do you guys get those to separate?

[Stev-o]

+1, why not upgrade to tapered head bearings while the bike is apart?

I get em at Amazon, only $29 w/free shipping...


http://www.amazon.com/gp/offer-listing/B000GZQ3XW/ref=dp_olp_new?ie=UTF8&condition=new

[Restoration Fan]

+1, why not upgrade to tapered head bearings while the bike is apart?

I get em at Amazon, only $29 w/free shipping...


http://www.amazon.com/gp/offer-listing/B000GZQ3XW/ref=dp_olp_new?ie=UTF8&condition=new

Thank you.  Got my All Balls on order.

Now just have to figure out how to get the cylinders and the head separated without breaking fins.

[Stev-o]

Here is a pretty good thread about head removal....


http://forums.sohc4.net/index.php?topic=78392.0

[Stoli]

Keep at it. Don't rush it or you will start breaking fins. Persistence. Find the solid pry points and give equal attention to all sides. Eventually it will give way. 

Hate to mention this but now that you have the top end apart, might want to consider HD studs. Min cost is around $80 for the APE studs. Z1 is the lowest price I have found. In my opinion, a key ingredient to prevent head leaks. If you decide to go there, ask me about stud removal before you start in. There is the easy way and the hard way and I can tell you the easy way. Namely a $15 stud removal tool on Amazon that is worth every penny and then some.

[seanbarney41]

Excellent.  Thank you.

OK, another question though.  We have made the decision to at the very least, lap the valves.  So we have removed cam shaft.  We also removed the 22 nuts holding the head on, but how do you get the head to separate from the jugs?

Conscious of not breaking the fins, we were tapping gently on the various places on the head.  But it looks like the jugs are starting to separate slightly from the bottom...but the jugs aren't separating from the head.  How do you guys get those to separate?

in addition to the 22 nuts there is a couple regular 6mm/10 mm hex head bolts, you did not forget them?

[Restoration Fan]

Excellent.  Thank you.

OK, another question though.  We have made the decision to at the very least, lap the valves.  So we have removed cam shaft.  We also removed the 22 nuts holding the head on, but how do you get the head to separate from the jugs?

Conscious of not breaking the fins, we were tapping gently on the various places on the head.  But it looks like the jugs are starting to separate slightly from the bottom...but the jugs aren't separating from the head.  How do you guys get those to separate?

in addition to the 22 nuts there is a couple regular 6mm/10 mm hex head bolts, you did not forget them?

We didn't forget them.  There are actually 16 regular nuts and 4 of the 6mm under the rubber diaphragms and the 2 10mm hex head bolts.  We got them all off.  But thanks for the suggestion; I really do appreciate it.

[Restoration Fan]

SUCCESS!!!!  We got the head off pretty easily after reading that thread, Steve-O.  Thanks for posting it.

Cal, I wish we had seen your idea before we started; that sounds like a great idea.

I first tried Hondaman's idea of using a sharp knife to cut the head gasket.  I went all the way around to make a small cut with the knife, but when I got the side just over the points plate, my son noticed a small gap there.  We inserted a very thin flathead screwdriver and lightly tapped it in about a half inch and the seal was broken.
So then we were able to pull the head off easily.

Below are photos of the pistons and valves right after coming off the engine, and then after a very light cleaning with carb/parts cleaner. 

The pistons and cylinders look incredibly good.  As a matter of fact, they look good enough and the camshaft was in such good shape that we are now thinking that we will only lap the valves and then button the top of the engine back up after cleaning up surfaces, etc.

Regardless, there's a LOT of cleaning to do but overall, very encouraged with how the inside of the engine is looking.  Thanks to all of you guys once again for your willingness to offer advice & encouragement.