Topic: 1977 CB750 K7 /// Rebuild 2.0, Project Anna

[mkoski]

Yeah, I'm really bummed about it. It's completely nonsensical. How can the top end tick after I literally just verified that everything is good in there?!

[robvangulik]

Have you paid any attention to the lower end of the engine?
Big end and crankshaft bearings are very susceptible to damage by lack of oil.....

[RAFster122s]

It didn't sound like you did anything mechanical in terms of replacement other than seals. Unless it was a tuning issue previously I think you merely made it leak free and fixed any smoke issues from seals.
I just don't buy that a loud tick grts fixed by disassemble and seal replacement.  The problem wasn't uncovered.
Dropping thd pan do you have access to the bottom end on the 750?
I would want to inspect the bottom end to see is the ticking is from a rod or crank bearing.
Got any video of the ticking noise?

[mkoski]

I am almost certain it's not bottom end from where the sound is coming from. The video is on the previous page.

[knottedknickers]

I am almost certain it's not bottom end from where the sound is coming from. The video is on the previous page.

Just watched the video. Yikes. What a drag... Alternator rotor? Clutch? Something in the points? Oil pump? It does seem to be louder on the front / exhaust side of the engine (where you end the video). It'd be nice to find something with your screwdriver stethoscope that wouldn't necessitate splitting the case... But your earlier description of being sure you tightened the cam chain tensioner and then finding it "really loose" sure sounds suspicious. Is your tensioner OK? Cam chain guide?

[seanbarney41]

ok...first of all, the very last rocker arm in YOUR pics is shot, period.   ...and a few of the others look very suspicious.  Where are your pictures of the cam lobes?  My guess is oil is not getting to the cam towers.  I already told you this the first time.  Before you tear it down again, do yourself a diagnostic favor....pull 1 and 4 exhaust valve tappet covers with the engine running.  If oil does not literally splash out, oil is not getting to the cam towers in proper quantities for some reason.

[Don R]

If the lash is set and it still sounds like the rockers, I'd check the rocker shafts for wear, they should be the bolted down style, you could flip them over to see if the lash changes.

[Desert-SOHC]

That sounds EXACTLY like the wore out rocker shafts that were in my sandcast

[mkoski]

Alright guys, I really do appreciate your thoughts on this matter.

I would be lying if I said this didn't discourage me so I left it for the last few days to mentally regroup on this.

Here is what my plan is looking like:
1. Note if oil is coming from front tappets at 1 and 4.
2. Install a frame kit so I don't have to pull the damned engine again.
3. Turn her over with the valve cover off, hopefully exposing the source of the problem/noise. This will also allow for inspection of oil making its way to the top-end.
4. I should also check out my oil pump. Can this all be rebuilt in the frame?
5. Solve problem and wheelie into sunset.
6. Full engine overhaul/rebuild/big-bore over the winter months.

So I need to source a frame kit this week, I think, to get something going!

Side-note-thoughts: I am mostly thinking that this has to do with oil getting to the top-end. My only counter-argument to this idea is why does the bike run so poorly because of this? I cant think of how a lack of oil causes SUCH a dramatic influence on the engines ability to rev higher / make power. Can someone explain how this is possible or if it is possible?

[mkoski]

Alllllrighhhhhttt.

I can see why everyone raves about frame kits. If I wouldnt have been such a stubborn POS I could have saved myself a lot of effort. Regardless, its done now. 

Here is my second video:

https://www.youtube.com/watch?v=GgEil9GAgs4

And third:

https://www.youtube.com/watch?v=B_lzgQ9m5Lc

So I think I might have found the source of the ticking from this evidence I found with a mechanics stethoscope. Tonight I will pull off the rocker and see if the ticking ceases... If it does then I know its either the rocker, rocker shaft or the valve/spring assembly. If not, I continue the hunt.

I am very happy that everything is well lubricated up there. That was far and away my largest concern for my engine.

[mkoski]

OK,

New video:

https://www.youtube.com/watch?v=jAt-pq1CGM4

After this video I talked to my neighbor and we were discussing more possibilities for this issue. Together we came across the idea that it might be the connecting rod or wrist pin. I really think this is a reasonable explanation as the sound is just below/around the 3rd cylinder and is intermittent and dependent on RPM. Thoughts? Or has everyone given up on me? 

So after realizing I need to go deeper I spent some time looking at motorcycles so I could ride something for the rest of the season and decided to pull the trigger on this little beauty:





2004 GS500F with only 9000 km on her. I really like her and got an unreal deal!

  Good day today, just not for my CB750.

[knottedknickers]

There were some really good results from that little mod, I had to pull the little straw bundles out though as a bit of gas was getting on them which was loosening the electrical tape. I just need to attached them together in a stronger fashion before I can give a good result of the mod.

My mind is going on this one! How long do the straws need to be to create laminar flow? Yours look about 3 cm long--is that about right?

bump...

I've been looking into this (with some tips at another forum) and think some MAF airflow straightener would be useful. Thoughts?

[knottedknickers]

I've been researching this too, and hoping he'd pipe back in with some more data. I'm planning to 3d print a few as a test and install them on my 550 before venturing on with some other engines.

That's an idea, calj. I'd appreciate if you'd keep us posted on your findings with 3D printing (or anything else).

I just saw a plastic honeycomb at my local grocery store--it's a decorator strip at the back of the freezer bins. It's about 5 cm high and looks about 3 cm deep. The holes seem a bit big, though... Especially in light of, "the length of the straw must be a 'significant' multiple of the wave length of the frequency of interest. The diameter of the straw is generally considered close to ideal at 1/10 the length of the straw or less" (TonyR). I'll try to remember to snap a picture next time I'm there. Better yet, ask the manager for a broken piece he'd be willing to part with.

I'm still a ways from starting my bike (still waiting for a hub from Cognito Moto, which means I don't have my front end together, which means my electrical isn't done, which means I haven't tried to start it yet...) I'm sure I'll get more serious about this when it's running!

[mkoski]

Hey guys,

Been really busy with work, events and whatnot and haven't really been involved with my CB lately, thus the lack of replies.

What kinda data are you looking for for this laminar-flow device? I'm a 3D CAD modeler so I might be able to make up a design here in the next week or two..

[knottedknickers]

Hey guys,

Been really busy with work, events and whatnot and haven't really been involved with my CB lately, thus the lack of replies.

What kinda data are you looking for for this laminar-flow device? I'm a 3D CAD modeler so I might be able to make up a design here in the next week or two..

Here's a crude drawing of my pods:

Questions:
1. Do I want to butt my 'straw sausage' up against the inner lip of the carb throat rubber (44 mm from end of the pod filter body), or to extend farther by squeezing (tightly!) through the 29 mm carb throat opening?
2. Obviously, there needs to be an air gap between the 'straw sausage' and the end of the pod filter body; how much? I guess this question could be asked another way: how long should the 'straw sausage' be?
3. The answer to 2. will help to answer: what diameter straw to use (if diameter.straw=1/10*length.straw)?

I leave it there for now. No need for 3D models (I hope!) I appreciate you taking the time out from your other activities to respond.

[mkoski]

1. You will want to squish it into that 29mm opening. THis will allow the flow to come in through the filter, enter into the "pipes" and go cleanly and directly through the rest of the filter, into the carbs mouth.

2. The longer your tubes, the better (or more laminar) the flow. Too long will butt up against the end and restrict flow, though. I kept them a cm or two from the end.

3. The diameter of the straw depends. As it gets to be smaller and smaller you increase surface friction (as there is more area to rub the air against while the engine pulls it through) this induces a bit of turbulence. (Note that this can be calculated as a head loss from the friction factor, determined by this chart: https://en.wikipedia.org/wiki/File:Moody_diagram.jpg) Due to the fact that extruded plastic has a roughness of .0025 mm, this is essentially negligible.  On the other hand, larger straws don't straighten the flow effectively enough to note a difference. There is no simple ratio to use, you must use a Reynolds number calculation. Interestingly enough, length has nothing to do with calc. This is because after a certain point, it doesnt change any more and the flow pattern remains the same. Here's a visual: http://img.bhs4.com/a7/4/a747bcaa3997a49eb84ea8b30328019ad7ce8c70_large.jpg. This distance that is required for flow to "fully develop" is called the "entrance length".

This is calculated as: L = 0.05*Re*D (Source: https://en.wikipedia.org/wiki/Entrance_length) This gives us L=.05*998*0.004 m ---> ~=.02m = 2cm.

After 2 cm (using my previous volumetric flow calculation to determine the reynolds number of the flow for my straws and motorcycle) the flow is as laminar as it will get!

So hopefully that gets you going (probably way too much info but I enjoy the full explaination)! If you are curious about anything else, let me know!


Two final thoughts:
1. A 3D print will be a terrible way of creating this as it has a very high roughness (as its extruded in layers). An acid wash should cure this. THis is the perfect solution, right here: http://hackaday.com/2013/02/26/giving-3d-printed-parts-a-shiny-smooth-finish/ (Also illustrates the roughness.)

2. Make sure you secure those straws together and they dont go into your engine!  My glue got some gas on it and made it a bit loose. Next set I do they will be bound together in a better (but undetermined, as of yet) way.

[knottedknickers]

VERY helpful. Thank you. And, no, not too much information--I enjoyed the 'full' explanation (though I suspect it's still the 'laminar flow for dummies' version ).

[mkoski]

Well, we're back! I'm ready to start getting into my CB's again because I missed this community quite a bit over the last year, you are a good bunch that make me feel like I'm not taking this on alone!

The last time I was here you guys were helping me out with my "top-end engine sound". After my futile top-end job, I'm now down to split cases, just this week.

In the time since I was here on the project (just to fill you in) I have been up to a few different motorcycle-related ventures. I have bought, modified to naked, and sold a GS500 (which was a cute little A-B bike that treated me pretty well).




I also purchased a Ninja 650R with my funds from the GS500, which I think is a bit more suitable for me! With that bike I have put over 6000 km's on, including a 3000 km solo road trip across a couple provinces and a few states. I also crashed it at 80 km/hr, which required me to do a decent bit of work on it and repaint it to black! Almost all of the time I have been not working on my 750 I have had it on my mind. A combination of guilt about leaving the project unfinished and desire to have my baby back rolling on the road.

Pre-crash:

Post-Crash:



But we aren't here about silly Kawasaki's or Suzuki's, are we? So, what was that knocking sound in my engine!? Well, when I pulled the oil pan I saw what looked to be a couple of pounds of glitter in my oil! So I split the case and found the culprit. Rod bearing number 3 has been spun! Here's how she looks...




Fortunately, the inside of my engine otherwise is looking really great. All the gears look brand-new, the shifting bits look un-worn and my bearings look (what I would call) serviceable.




My crank bearings look mostly like the following, any opinions on these?


A slight concern I have is the way this bearing (and one other) sits... It's a bit mis-aligned. Is this indicative of a problem? They look fairly decent still...


So now I'm here with my engine opened and I come to you for advice. While I'm in here I need to figure out everything I should be replacing. I have done a lot of research up to this point and kinda just want to have a second opinion for a lot of this.

New oil seals for everything, new orings for everything, new gaskets for everything. Other than that, I want to replace the bearings that I need to, but not all of them. What do you guys thing about that?

Thanks, good to be back!

-Matt

[mkoski]

I pulled the trigger on a bunch of parts. Thus far I have ordered all the engine seals (including the odd-sized '77 specific one) and a full set of gaskets including rubber pucks and exhaust copper-crush gaskets. Throttle cables (push and pull) were thrown in because mine were a bit sticky (and from '77). Honda seems to have all the bearings in stock so I have my mission set up for tonight... Inspect all bearings, determine what color bearings I need, and order them, alongside a new cam-chain tensioner, which is surprisingly in stock as well.

I'm going to be re-using the tension-bolts on the con rods, as I can't justify the tag for a new set of 8 of them, and I will also be trying to minimize the number of bearings I buy, as those suckers come out to be 32$ per pair of shells. If you multiply that across all the bearings it turns out that it's $$$. Either way though, I think my bottom-end will be a happy place for a long time anyways, as it's already been pretty bullet-proof for me up until late. This weekend I want to clean out the cases, clean all the parts and prep everything for re-assembly. Lot's of parts cleaner and degreasing in my future, I think. Anyone know a decent place to source 3-Bond / hondabond here in Alberta, Canada?

[knottedknickers]

I haven't lived in Alberta for a while, but would Blackfoot Cycle have it (even though they don't carry Honda)? I don't much enjoy darkening the doors of the 'big box' bike stores--the parts guys looks down their noses at me when I say "1976"--but it might be worth a try.

[mkoski]

I'm not sure about blackfoot! Maybe I'll check them out if I get the chance. I typically avoid the 'big box' stores like you mentioned, they have not been kind or helpful in my experience and don't like to spend money there for that reason.

I popped open my rod bearings for inspection and it looks like I'll have to spend a few bucks on those, as I see they are all in pretty bad shape, which is pretty realistic considering I spun one of them due to lack of lubrication... Here they are with/without flash:

Cyl 4



Cyl 3 (no bearing)



Cyl 2



Cyl 1



I cleaned out the top case and have been adding in parts as they are cleaned and ready to be installed. Right now I'm waiting on oil seals for the shafts, gaskets and rod bearings. Looking pretty good to me thus far though!

[mkoski]

She lost oil pressure (and all volume) due to a failed oil filter leaking heavily out of the front. No blockage was the cause of this but I also took the care to ensure everything is open with thorough pressure wash, degrease and clean. So that shouldn't be a concern but thanks for the advice!

[firebane]

I pulled the trigger on a bunch of parts. Thus far I have ordered all the engine seals (including the odd-sized '77 specific one) and a full set of gaskets including rubber pucks and exhaust copper-crush gaskets. Throttle cables (push and pull) were thrown in because mine were a bit sticky (and from '77). Honda seems to have all the bearings in stock so I have my mission set up for tonight... Inspect all bearings, determine what color bearings I need, and order them, alongside a new cam-chain tensioner, which is surprisingly in stock as well.

I'm going to be re-using the tension-bolts on the con rods, as I can't justify the tag for a new set of 8 of them, and I will also be trying to minimize the number of bearings I buy, as those suckers come out to be 32$ per pair of shells. If you multiply that across all the bearings it turns out that it's $$$. Either way though, I think my bottom-end will be a happy place for a long time anyways, as it's already been pretty bullet-proof for me up until late. This weekend I want to clean out the cases, clean all the parts and prep everything for re-assembly. Lot's of parts cleaner and degreasing in my future, I think. Anyone know a decent place to source 3-Bond / hondabond here in Alberta, Canada?

Fellow Alberta from Calgary here... and I honestly find that getting stuff from online is far better. VintageCB750 and 4into1 have been my go to places. Locally for me things are just silly expensive or difficult to find. I couldn't even get 5.5mm fuel line locally from Honda.

[EvLoutonian]

Did you get this all sorted in the end?

Following along on your thread and enjoyed the details (as my K7 project nears completion also)..
(on the other side, in Melbourne, Australia)

[mkoski]

So at least two years have passed since I last updated. When I last updated I had a grenadified engine (thanks chinese oil filter!) and a serious case of denial to myself on how viable the engine was to re-use. Since then I bought a "new" engine, threw it in and rode my CB750 for a couple thousand km's. Things were great! Except the "new" engine liked to pop outta first gear when any throttle whatsoever was applied! So that was no good!

Eventually I got a new project, then another one, then my CB was forgotten again and went all summer this year without being ridden. My two projects since my CB have been an XL600R and a KTM 450 EXC that is my most ridden bike now! I feel like I have matured a lot as a motorcycle restorer/fabricator/customizer and my work is of significantly better quality. It's work that I'm actually proud of now!

XL600R Before
https://imgur.com/VTLjvlT

XL600R After:
https://imgur.com/RFgzV13


KTM Before:
https://imgur.com/ZfZmFvL

After:
https://imgur.com/9xUsfIn


Having winter rolling in now, I decided my CB750 needed to have 1st gear fixed. And then I got carried away and decided to rebuild the whole bike, but this time do it right, make it perfect both functionally and aesthetically.

So I'm re-kindling my thread here to carry this thing through the finish line!

If you are just joining me, this is what the bike looked like in 2014, when I bought her!

https://imgur.com/YL2R0CB

And just this week before tear-down:
https://imgur.com/wHxubJm