Topic: 1978 CB750F rebuild: The Long and Slow Road: And now, on to the pistons!

[brandEn]

You need a shop manual. Do you know about the free online copies?
http://forums.sohc4.net/index.php?topic=17788.0

[filipo]

 

You know, I have one. Several, actually -- official Honda shop manual, Clymer, a series of exploded diagrams, and Hondaman's book. But sometimes when I'm in the flow, man, I don't think to check them. To wit: I asked that question, then couple hours later was leafing through the Clymer where I saw the official name and diagram of the "valve spring seat". My life is complete now.

Guess I should make a habit of checking the manuals first, eh?

[brandEn]

Haha, you work like me. I had my motor town down without having read any manuals. Once I finally started reading I discovered I did just about everything the wrong or hardest way possible.

[filipo]

Ha -- yeah, a useful combination of overconfidence and ignorance!

Anyway. After pulling the head apart and discovering what the valve spring seats were called ( ), I figured what the hey, time to pull the cylinders. Removed the roller and slider, took a bunch of pics to remind myself where all the gaskets, O-rings and knock pins go, and… well… not much else to do, so I decided to pull the pistons off as well.

Now, I know to all you dudes on these forums this is akin to, I don't know, deciding to use Angel Soft instead of Charmin Ultra, but to me it was a little scary. I don't know why, maybe because I'm getting closer to the deep dark insides of the machine, but I was a little hesitant to go messing with the pistons. No more.


(Note that those rust-looking spots aren't really rust, just a bad camera-phone flash...)

For those of you that have read Hondaman's manual, you know that part where he's talking about removing the pistons, and he says to make sure to "stuff rags into the holes under the pistons, so you don't drop the circlips down into the engine"? Yeah. LISTEN TO HONDAMAN.



That little ring in there, looks like a hoop earring? Yep, that's the circlip, way down in the hole. The crap thing about this situation is, a magnetic grabber won't help you much, since it wants to grab everything else on the way down. I'm lucky that the circlip was just sitting there, ripe for the picking.

Got all four of them pulled, and -- going by my limited sense of these sorts of things -- they all look pretty good to me. Clean, not kinked or cracked or whatever.



Plus, lots of clean(ish) oil under them in the cases, even though I drained the oil in 2002 and haven't ridden the bike since 1998 or so.



All the oiling holes were clear and clean, too.





Crowns weren't too bad -- nothing a few minutes with the soda blaster can't fix.




The good/bad news is that I got called to work next week, so I won't be able to touch anything for 10 days or so. Bummer for the bike, better for the bank account. So it goes.

[wedoo2]

Good thread you have going here filipo and one to watch.  I am about to take my motor off the frame and look at things and since I would also be an amateur at breaking down the thing I am interested in your progress.  One thing I would ask, or for anyone else following this, is what do you think you will need to buy?  Valves and pistons seemed to be okay.  And you didn't snap off any of the long bolts or complain about the valve springs.

Do you still need to hone the cylinders or reseat the valves?  Buy rings?  Gaskets?  What else would I need to know if I did similar things?  Cost?

[filipo]

Well, for me, I haven't really started measuring things and checking clearances and whatnot yet. That's probably bad practice; I imagine I should be checking things as I go, but for now I'm having a lot of fun just tearing it all down.

That said, I already bought a set of Vesrah gaskets and O-rings. (Bought these from Dennis Kirk in 2002 or 2003; good thing about 70s motos is that it's not like the original technology has changed in the ensuing 10 years...) I had originally fitted them all on the bike when I first started messing with the motor, but all of them are coming off now that I've decided to go ahead and open the cases. As for the pistons, they look good to me, but that's not worth much. I'm going to check the rings hopefully today. If they're within spec, I don't know -- should I hone and buy new rings? Or just call it good? Or is it worth just doing all I can while I have the engine out of the frame?

At any rate, the list of stuff I'm planning to buy/do isn't that long. Still deciding whether to repaint the frame and/or cases (I kind of like the "used" look); and there is nothing electrical on this list -- still have to tackle that bear.

Clean valves
Lap valves
Clean pistons
Check clearance on pistons/cylinders
Check bearings
Cylinder base o-ring set
Hone cylinders?
New rings?

Replace all gaskets and o rings
New oil seals and disks
New valve guide seals
New valve guides?
New headset bearings (mine are fried)
New headlight (cracked)
New grips: Oury?
New brake lines?
New oil lines?
New air filter
New cam chain
New cam chain tensioner
New cam chain roller assembly

Obviously this list gets longer as I go deeper...

[filipo]

On that note, I can't remember where I copied these notes from (I believe they are both from Terry in Australia in response to a similar question), but here are a couple of low-stakes guidelines I picked up while browsing the forum...

ON WHAT TO BUY

Full gasket set (CycleX, $59.00)
Set of Piston Rings (Rusty Riders $30.00)
Cylinder Hone (buy the tool to fit your cordless drill, around $10.00)
Heavy Duty Tsubaki Cam Chain (Z1 Enterprises $28.00)
OEM cam chain tensioner, wheel, and guide (Z1 Enterprises $61.00)
Engine seal set ($20.00 from Rusty Riders)
New OEM Primary Chains (Terry Quail, $70.00 per set)
New NGK Spark Plugs ($10.00 from your nearest auto parts store)
New points ($10.00 from Rusty Riders)
Engine Enamel ($10.00 from your nearest auto parts store)

ON WHAT TO DO

I'd strip the top end, clean it (glass bead, etc as needed), lap the valves, replace all gaskets and seals, dingleberry hone the cylinders, re ring it stock and go on your merry way. Cheap and effective.

Let me know what you decide! Do you have a build thread yet?

[Jerry Rxman Griffin aka MuthaF'er]

New cylinder studs from Big Jay at APE if you plan on putting some high performance miles on it. If you won't be doing serious/semi-serious miles and in the 10,000 rpm range and you'll just be putting around Boulder then the stock original studs would probably be fine. I had a Yoshi 812 kit in mine and I cranked it up when I got on it for each ride. It developed the dreaded oil leak around the head. I thought it was more than likely the pucks under the cam towers until I started taking the top end apart. There were some slightly loose head bolts and some that would turn by hand. They don't just come loose, the studs stretch. And unless you put a frame rail kit in it then you don't get to re-torque until you take the engine out again.

[filipo]

Good point, Jerry. I had thought about doing a frame kit, but I want to keep things as "natural" as I can before I start hacking and boring and whatnot. What can I say, I'm a classicist. (Or just really, really cheap...)

No big plans for super high revs. Midway through this project my wife has informed me of her distaste for the idea of me riding a motorcycle at high speeds. (As I told her, why didn't you tell me this before I got started?!) So yeah: putt-putt-putt, all around Boulder town. 

[filipo]

Oh la la! It's been a while. But for the moment I hope to have a few solid weeks of work on this. I posted the following in the main forum, but I thought I'd post here as well. I will post any replies here as well.

===

I've looked through the forums and seen a lot of pictures, but I still can't understand *where* the wear on my cylinders ends/begins. In Hondaman's book, he writes that you should be able to see where the top ring of a piston stopped its travel within each cylinder. But I see a couple of types of wear in mine. See this photo:



There is a very clear delineation between the darker brown/rust area at the top of the cylinder, about 1/4" thick, and the lighter gray/black area below it. There are also a couple of fainter, whitish lines in a doubled pattern, well within the gray/black area.

Should I be looking at the red/brown area as the line where the top ring stopped its travel?
Or is this where the crown of the piston itself stopped its travel? and the fainter, whitish lines are where the rings stopped their travel?

Or should I not worry about it, and hone the whole cylinder so it's all one sheen? 

Thanks for any and all answers.

[Sdsbassist]

Any updates?

[filipo]

Updates? Moved to the East Coast last fall for work --> Sandy --> moved back to Colorado --> wife is pregnant --> scramble like hell to find enough work here --> "complicated" pregnancy --> healthy awesome son is born --> holy hell has more than a year elapsed??

 

Just starting to get back to the bike. Last I left it, I had honed the above cylinder and discovered it's out of spec and needs an overbore, and now deciding how to proceed with that. (Like the title says: this is the long and slow road.) But I'm going to put those on the back burner for now while I get the bike up to a roller. So:

- painting or at least touching up the frame, swingarm, etc.
- new headset
- suspension
- wheels and tires

Also looking around to find a cheap-ish Four that I can use as my "learner" bike. I have a lot of nostalgia tied up in the 78 F, and I want a bike I'm not so worried about screwing up. Know what I mean?

[SOHC4 Cafe Racer Fan]

Updates? Moved to the East Coast last fall for work --> Sandy --> moved back to Colorado --> wife is pregnant --> scramble like hell to find enough work here --> "complicated" pregnancy --> healthy awesome son is born --> holy hell has more than a year elapsed??

 

Just starting to get back to the bike. Last I left it, I had honed the above cylinder and discovered it's out of spec and needs an overbore, and now deciding how to proceed with that. (Like the title says: this is the long and slow road.) But I'm going to put those on the back burner for now while I get the bike up to a roller. So:

- painting or at least touching up the frame, swingarm, etc.
- new headset
- suspension
- wheels and tires

Also looking around to find a cheap-ish Four that I can use as my "learner" bike. I have a lot of nostalgia tied up in the 78 F, and I want a bike I'm not so worried about screwing up. Know what I mean?

If you are looking for a starter bike and still want something vintage, think about a CB350. It's much lighter, cheaper and more plentiful. Plus there are aftermarket parts to improve engine performance when you outgrow it in stock form. The make for good little racers.

[filipo]

Good call. I've been looking at CL360, which was my first bike, but they're all super expensive now thanks to the cool factor.