Topic: Another CB750 Engine Rebuild...I hope...

[thomellis]

My time has come.  Although there are quite a few of these threads out there already, and I've read as many as I could (until I was inspired enough to try it for myself), I figured I learned something from just about everyone, so I figured I might as well chronicle my adventures as well in the hope that it might help someone, someday.  I doubt I'd be brave enough to crack into this if it weren't for the brave souls who did it before me.

I got my bike last summer, 72 cb750, and mainly based off of information in this forum got it to a good enough working condition that I could drive it around town a bit.  I should state, going into this I knew next to nothing about bikes.  I did know 2 things though:

1) I've always really wanted to ride
2) I really wanted to learn about the bike

There's only a few good "dry" months of riding available here in the Pacific Northwest, so I decided this winter I'd strip everything down, and put it all back together.  Again mainly I just wanted to use it as an excuse to learn more about the bike.  The engine leaks a little oil in a few spots, so I'll fix that, and anything else I run across along the way.

The bike itself isn't in terrible condition, only about 14k original miles and nothing glaringly wrong.  Found a few slightly odd things along the way, but overall nothing shocking.  I got everything stripped off, down to the engine and frame in a couple evenings, documenting everything along the way.  Then tipped her over, and slid the frame off (it really was as easy as everyone says to my surprise).  Then, took a few deep breaths and got to work on the engine.

3 days later, a can of penetrating oil and probably a hernia, I had 2 screws out of the cylinder head cover, and gave up for a while I knew my dad had an old impact screwdriver lying around from back when he had his bike, and I was waiting to get that from him (too cheap to buy my own, I know I'm pathetic), once I got a hold of that, my life would never be the same:



In no time at all, the rest of the screws were out, and the cover was off:





Pretty oily in there, but it seems to look alright, as far as I can tell.  Should it be this wet up there?  I got the rocker arms off next.  I didn't have the "tool" to remove the rocker arm shafts, so I just used a dowel I had lying around which I'd previously used on my carbs.  Worked like a charm.  All but one shaft came out without too much extra effort.  And finally I got the cam shaft out.

I've been using the cardboard cutout method that I heard about from these forums, to store all the screws/bolts/etc. and so far it's worked really nicely.  My goal for tomorrow is to get the cylinder head off.  Just from looking at it now, it looks like it leaks a bit of oil between the upper and lower sections.

There was a list posted in a few other threads by Terry, which I've been looking at to determine what kind of $$damage this could end up costing me.  I figure while I'm in there I might do a couple easier things:

Full gasket set (CycleX, $59.00) -- Got it
Set of Piston Rings (Rusty Riders $30.00) -- Do I have to get new rings?
Cylinder Hone (buy the tool to fit your cordless drill, around $10.00)  -- Need to look into this a bit more
Heavy Duty Tsubaki Cam Chain (Z1 Enterprises $28.00) -- Got it
OEM cam chain tensioner, wheel, and guide (Z1 Enterprises $61.00) -- How do I tell if I should get a new tensioner?
Engine seal set ($20.00 from Rusty Riders) -- Got it
New OEM Primary Chains (Terry Quail, $70.00 per set) -- Chain was said to be replaced by PO, so not sure here yet either
New NGK Spark Plugs ($10.00 from your nearest auto parts store) -- Got it
New points ($10.00 from Rusty Riders) -- Just replaced
Engine Enamel ($10.00 from your nearest auto parts store) -- On the list

Did I miss anything?

Well, so far so good.  I haven't ran into anything that's completely baffled me yet, so hopefully I haven't screwed anything up   If I have please feel free to let me know.  Any and all comments, advice welcome for sure. 

Sorry for the long post, I'd imagine the posts will be shorter, and more pic heavy from here on out

[wrenchmuch]

If the internal rubber pieces (primary tensioner , cam tensioner , front cam chain guide ) are old they are likely hard . If they haven't already they will eventually shed rubber bits into the sump . I'd replace them since you have the engine out . You should determine how worn the pistons / bores are before deciding on rings . Rings are usually replaced when you remove pistons from the bores . Others have gotten away with just putting what they had back in and not had bad smoke or compression issues . If the pistons / bores are close to the wear limit , honing and putting back the rings and pistons you have will likely take those parts beyond the wear limit once they bed in causing smoke and compression issues . Try to measure the pistons / bores or have them measured for you before deciding on a course of action . If the PO replaced the primary chains he might have also ( should have ) replaced the tensioner as well . When you get the cases open check the tensioner . When you push on the rubber does it give ?
If it feels more like a piece of plastic it needs to be replaced . If it needs to be replaced I'd question that the chains were replaced as well . Don't rely too much on what a PO tells you "was done to the bike" .

[ekpent]

Be sure to borrow Dad's good torque wrench also.When you remove the head take out the 4 small bots hidden down in the center first before you loosen the nuts. Have fun Grasshopper 

[bollingball]

I was going to say get HondaMans book then I read about the impact driver . However it would be a good tool to invest in the book that is.


                                           Ken

[Cain74]

Do you have a link for those primary chains from Terry Quail?

[thomellis]

Thanks for the replies guys.  I'll have to take a look at the tensioners, but as you pointed out wrench, makes sense to just change them out while I'm in there.  Sounds like I can't pass much judgement on the pistons until I get them out and measured.

I'm not putting too much stock in the "new" primary chain either for now. 

ekpent: funny you might say that, he did lend me his torque wrench as well at the same time

bolling:  I probably should get HondaMan's book at some point...

Cain: I think I've seen mention of Terry's chains at some point in a different thread, but I'll have to dig it up.

[thomellis]

Back at it tonight, made some more progress.  Got the cam out tonight.  Honestly the biggest pain was getting the camshaft holder out.  The shop manual just says "remove the camshaft holder" as the instruction.  Well that would be fine and dandy if it were that easy.  I wasn't entirely sure if there was anything to be wary of on the underside, so I took it real slow, and eventually got them to pop up and off.



Then lots of bolts, including those tricky ones hiding under the rubber pucks.  Luckily they were pointed out, or it might have taken me a bit to figure out just where they were.  I just used a razor blade and carefully slid it in there to pop them out.  Once all the bolts were off, the top of the cylinder head came right off, and I got my first look at the valves.





Definitely dirty here.  I guess the next step for these is to pull them and inspect a bit more.  I'll leave that till a bit later.  You can see here where the oil was leaking out.  Is this where possibly putting in some new cylinder studs would come into play, or do I just need a new gasket here?




The bottom portion of the cylinder case didn't want to budge for awhile.  Some careful coercing and I was finally able to get it up and off.  It got hung up on cylinder 1 & 4 a tiny bit, and i wanted to be extra careful not to bugger anything up slipping it off.  Got that set aside, the cylinders don't look too bad, I'll still have to measure, and they could use a good honing I'm sure.




The pistons seem to be in decent shape as well.  All the sides look pretty smooth, no extensive wear visible anywhere at least.  Although, I'm not really a piston expert so maybe they're in terrible shape





Well that does it for tonight.  Anyone see any issues I missed, or things I should be worrying about at this point?  I think I'll probably end up cracking the case.  If I'm gonna go this far it seems a shame not to go the whole way, but I haven't quite convinced myself 100% to do it.  I've got plenty to work on with the top end, and various other areas of the bike for the time being, but I don't want to be too far removed from this, so I can have it fairly fresh in my mind when I reassemble it.

Any comments/advice welcome!

[Harsh]

I am at the same stage in my engie rebuild as you.  I want to take it apart, but am hesitant since I have never had an engine apart further than the stage I am currently at. 

[ekpent]

At 14,000 miles if the bike was shifting good and the tranny felt right and there was no knocking or other sounds coming from the bottom end I would not crack the cases.Don't think it would serve any purpose but possibly make for more problems. The top end def needed the attention. Go forward for sure on replacing those rubber bits in the cam chain area as the 'wheel' in your picture looks a little chewed up. Dropping the oil pan if not done yet could hold some clues as to what may be going on overall in the engine also.
  Looks like your rolling along in good shape.

[thomellis]

Well, finally back at it today.  Try to keep it short and sweet, I know most people just want pics

So here is the camchain tensioner, definitely looks like it needs to be replaced, pretty chewed up.  You have some amazing eyes to spot that earlier ekpent



Put that on the list of items to order.

Next I worked on pulling all the valves.  I got a pretty cheap valve spring compressor from sears for $15, and for the most part it worked really well.  There was a little finesse involved in getting it lined up just right, but it wasn't bad.  Took me a little while to get a good method of popping the cotters out though.  But, eventually they were all out.





One part I was baffled on was the shop manual says to "remove and disassemble: cotter, retainer, valve spring (both), valve steam seal, spring seat, in that order".  Ok I got the first few pieces no problem, but how the heck do you get the stem seal and spring seat out?  I don't just want to dive in there and start digging, any tips?



All of the valves look about the same (sorry, fuzzy pic).  I don't see any real pitting or anything, but didn't examine them all that closely.



They look pretty good, is there any reason I shouldn't lap them?  I kinda figured since I was this far it might not be a bad idea?  Should I clean the rest of the valve up too?

And here's a question.  The fins on the cylinder case have these tiny rubber pucks between them.  It looks like from what I've found, they were there just to help with vibration, so it sounds like I can pop them out and survive without?



One of them has kind of melted out like a marshmallow now   They look darn expensive to replace, so unless the vibration is ear piercing, I'll probably try to skip them, unless convinced otherwise.

Anyone see anything to be worried about?  Is there really any point to removing the valve guide?  All the valves seem to be moving pretty smoothly, and the guides themselves don't show any issues.

Until next time.

[thomellis]

Been busy and haven't had much time to work on things lately.  I did finally get the pistons out though.  I was sooo careful not to drop the piston pin clips into the case, and magically didn't lose one.  I did however manage to drop an entire pin down.  Luckily my little extendo pen magnent picked it right up.  So I started pulling the rings.  I used the old thumb method, and it worked great up until the oil rings.  I just cant spread them far enough to slide em off without feeling like my thumbs are going to get scewered.



The one on the right was my one mistake.  All was going well, but one end got caught up just enough, that when i tried to slide up, i just snapped it.  Guess I'll be replacing that one.  On the right you can see another brokent one, that one however was broken on the piston though.  It also is really thin comparitively, so I'm guessing it wasn't wearing well?  Should I be more concerned about this?  It was in a few pieces.



If I replace these top 2 rings, do I need to replace all the sets?  Or rather, should I? 

I spent some time just cleaning up some things in the garage, bagging and tagging bits that were lying around so I wouldn't lose them.  Finally got almost everything else off the frame, need to de-tag and a few minor things still.  Now I just need to decide if I want to send it out to get media blasted, or if I should just put in the time to do it myself. 



It seems like people have has success with both, it's more of a time vs. money trade-off.  Decsions, decsions...

[ekpent]

You should clean and hone your cylinder bores and check them over carefully and if all check and specs out Ok then get a complete set of new rings at this point.  You did say 'rebuild' in your thread title.

[VTCBike750]

Subscribed! I always like these threads

Good work on figuring things out.  I got into bikes for the same reasons, l wanted to ride and learn how these bike work.  I have a 72 750 that I'm about to do the same thing to. http://forums.sohc4.net/index.php?topic=87951.0

Definitely get Hondaman's book.  The best way I can describe the book, it is the textbook on your bike

[Stev-o]

subscibed, I have an engine I should be doing this to.

[Really?]

Subscribed

[JamesH]

Subscribed

[ekpent]

Looks like Thomellis should be charging for subscriptions   

[Really?]

There are two discount codes from Lulu that you can use for HondaMans book that are good through the end of this month.  They are sizable discounts.  So if you are going to do it, do it soon.  I got mine the other day and am glad I did.  The codes are in his thread.

[thomellis]

Glad to see the interest pick up   Like I say, it's a learning experience for me, and hopefully helps someone else at some point too...

Got to spend some time yesterday working on the bike (a bit pic heavy).  A lot of time was just spent cleaning, scraping gaskets etc.  I also finally got the strength to pull the oil rings off of the pistons.  As I was working on one of them, I noticed a chip I hadn't before:



What should I do for this?  Can it just be filed down, or do I need to look into getting a new piston?

Cylinder head is almost clean:



Still a few small spots here and there that need to be cleaned up.  I eventually resorted to using Permatex gasket remover.  Put it on and let it sit for awhile, it would soften up the gasket that was left so I could scrape it off, then repeat until it was all gone.  Is it safe to clean up the left over little bits with some steel wool?

The top of the case isn't quite as far along, but it'll get there:



I was trying to get this last post out of the cylinder head.  The rest pulled out super easy, but this one seems to be fused in almost.  I've buggered it up pretty good trying to get it out, I was more focused on making sure not to gouge the aluminum.  Looks like I'll have to resort to using some heat or something to get it out.



Starting pulling the rest of the guts out under the points cover, and started working on the clutch:



One thing I noticed, is all the bolts that were holding the clutch spring plate down came out with this oxidized powdery white substance on all the threads.  Is this normal, or anything I should be concerned about?



Also, to get to the clutch plates, the shop manual recommends a special socket to get this bolt off, which I definitely don't have.  Where can I pick one up? 



Or any other recommended methods to get it off?

On the other side started to pull off all the shifting bits.  I made it this far, but then got a little worried as it looks like a few of these screws are already kinda buggered up.  Is there anything special about these, or can I just hit them with my impact screwdriver and get them out?



The one bottom left looks like it might even be chiseled in?

Also haven't gotten around to pulling the rotor off yet.  I know I've read a lot of suggestions on the forums about the best way to get this off since I don't have the tool, so I'll have to go back and do some more research to refresh my memory on that one as it's a bit foggy.  Open to any suggestions you guys have as well.



After all of this, I went to take the chain gear off, and it looks like I left it in neutral, so if I try to pop these bolts off, the sucker just spins on me.  Anyone have any tips on how I can pop this off now?



Lastly I pulled out the starter.  Another one of those times the shop manual just says something like "and lift it out", when really it takes a lot of wiggling and such to get it out.  I used the handle of my dead blow hammer to push a bit from the outside of the engine as I wiggled it up.  Took a little time, but I was trying to be careful.



Eventually it did come out.  Upon inspecting the wire, I noticed the old plastic wire wrap had cracked, and there was a good chunk of wire exposed.  The copper itself looks to be in fine condition (so I don't think it was cut or anything like that).  Will need to be sure to get some shrink tube around it before she goes back in though.



Lots of scraping and cleaning in between, but nothing too exciting to report there.  Getting close to having everything off the case so starting to look for someone to media blast everything for me so I can get some fresh paint on there.  Apart from that, starting to get my list of things to order together (this is just engine-wise).  Still need:

• Piston rings (4) http://forums.sohc4.net/index.php?topic=101889.0
• Cam chain tensioner, wheel, guide
• cylinder hone
• engine paint

I plan on lapping the valves, so I picked up the necessary tools for that.  February is a really busy month for me work wise, so I'm hoping to get things close to wrapped up soon, that way I can ship things out/have blasting done/order parts/etc. soon when I won't have much time to work on things myself.

Thanks for all the comments, help and advice everyone.  Until next time.

[ekpent]

Lotsa questions there. I'll input on a couple. That metal item you kind of mutilated is called a knock pin. You will need to find another. A screwdriver and a hammer can be used to remove the clutch nut if no other tool is available. As for getting the sprocket off wedge a piece of wood in there to keep it from spinning. The rotor does not really need to be removed per say may be best to not mess with it. Are you splitting the cases to check things out in there ?   Be careful when putting back together you do not break that clutch plate that was held on by the 4 bolts,they can be fragile.

[UK Pete]

Really enjoying this thread keep up the good work
pete

[mrrch]

If I remember correctly you can maybe use a wheel axle as the puller bolt for the rotor.

[Pecantree]

Carb soak will clean up those pistons real purty!

[thomellis]

Well, I suppose it was inevitable, but hit the first big bump in the road today.

http://forums.sohc4.net/index.php?topic=102093.0

Looks like the PO at one point or another busted a chain, which in turn cracked the case (that's my best guess at least).  So whereas before the plan was to not crack the case, it's looking like I might have to now in order to get the case properly welded.  Looks like I've got a lot more work ahead of me now unfortunately.

ekpent:  thanks for the tips and advice, looks like I'm splitting the case now, so there's really no need to mess with the rotor, since it sounds like I can just pop it out once she's open.

mmrch:  thansk

Pecan:  hmm...I'll have to give that a shot, their definitely pretty carboned up right now.  I'm still not sure if the chipped one is going to cause me problems either.

Anyways, looks like I'll be cracking her open this weekend, so if anyone has any advice about that task, I'd be happy to hear it.  Looks like I've got to add a few extra gaskets to my shopping list now too

Until next time...

[Stev-o]

I may have some engine parts for you if welding is not an option.