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

[mkoski]

What VERY little consolation there is, your bike is still up for BOTM. 

When my CB750 motor was initially rebuilt by a pro, I was told not to bother with a frame kit.  It leaked like a sieve when it was first fired.  The motor was pulled 2 more times to correct leaks.  Even though it was "rebuilt" all of the original OLD seals were used and a few o-rings were missing, too.  My 750 now has a frame kit!  I learned the hard way.  I began to think that my bike was cursed.  She now runs great -- and yours will too.

The good thing is that you've taken down this motor and your problems are almost certainly limited to the valve train.  This should not take all summer, but maybe a week to three, provided you have the help to pull and re-install the motor.

Hahaha, its a pretty big consolation. I'm very stoked that I built exactly what I like and everyone thinks its pretty cool. =)

Thanks for the encouragement. You are correct, I should have a diagnosis on the problems this weekend, parts on order Monday and then problem solved and back in within a week or two.

[Davez134]

When you do figure it out and fix it, (which you will) don't use words like "complete, done, finished, fixed" I have found them to be bad luck If you must, then modify with "hopefully, or for now."  seems to have worked for me!

[SOHC4 Cafe Racer Fan]

When you do figure it out and fix it, (which you will) don't use words like "complete, done, finished, fixed" I have found them to be bad luck If you must, then modify with "hopefully, or for now."  seems to have worked for me!

Too true . . . .

[mkoski]

When you do figure it out and fix it, (which you will) don't use words like "complete, done, finished, fixed" I have found them to be bad luck If you must, then modify with "hopefully, or for now."  seems to have worked for me!

Too true . . . .

No kidding! It's like she knew and immediately reacted.

[SOHC4 Cafe Racer Fan]

Worse is if they know you are planning to sell them!

[SOHC4 Cafe Racer Fan]

FYI - the Gordon's kits are available (no wait).  Email member RRRToolSolutions:  rrrtoolsolutions@gmail.com

Member 754 aka Frank also sells weldless frame kits

[mkoski]

Alright, so I have taken the head off of the engine here is what I have found thus far:



Here are the rocker surfaces that slide on the cam:







They all seem to be okay-ish to me. There is a little bit of uneven wear but everything is very smooth, definitly nothing with the rockers causing that tick.

The camshaft has a similar wear pattern, a little bit uneven in spots but pretty good.

I'm no expert but I think I can confirm that the camshaft/rocker is not the problem here.

Now, when I was removing the camshaft, I noticed that my cam chain was really, really loose. I was sure I had tensioned it correctly at 15° past TDC of Piston 1 in compression stroke (as this is the proper method, I recall). I set the chain tensioner and it was a lot tighter. Could this simply be the reason I was getting a tick and lack of high-rpm power?

Next I did a leak-down test with the valves. The result was 1 and 3 were leaking:



I think that I will have to do a valve job, at least a lapping. I'll lap em and if they seal up, I'll call it good. If not I'll get new faces cut I suppose.

Pistons look perfect. There are zero scratches on the cylinder walls, everything moves butter-smooth.

So in conclusion I found two leaky valves and a very loose cam-chain. Would this be the cause of the issues I had? I'm scared that if I missed something, buttoned it up and then reinstalled the engine I will have to do it all again. Please let me know what else I should look at while I'm in here to solve this problem if you dont think its was the previous two problems!

[Desert-SOHC]

I had a 69 sandcast that made noises like that, but without the power loss. I ended up finding 2 bad tappet shafts when I did the top end.

[mkoski]

I had a 69 sandcast that made noises like that, but without the power loss. I ended up finding 2 bad tappet shafts when I did the top end.

How can a tappet shaft go bad?

Also, anyone else have some insight? I plan on getting this thing back together ASAP.

[Desert-SOHC]

I had a 69 sandcast that made noises like that, but without the power loss. I ended up finding 2 bad tappet shafts when I did the top end.

How can a tappet shaft go bad?

Also, anyone else have some insight? I plan on getting this thing back together ASAP.

Sorry....the rocker shafts or pins. Check for ANY movement.

[mkoski]

Things are looking pretty good. Head gasket, valve seals are ordered.

I was floored by how hard the valve seals were! I had to chip them out, almost. No wonder I was blowing smoke. As much as I hated pulling my engine, I can see some serious positives in the work I can do here.

Alongside the valve stem seals being complete #$%* I also got to look at my valve seats and its amazing the thing even runs. Lots of carbon buildup and the seal surfaces are pretty rough looking. My guides are in great shape though, very tight tolerances still, zero wobble. After she is back together I shouldn't be throwing smoke-screens up anymore.

Right now I'm just cleaning, lapping valves and then waiting for parts to re-assemble the top end.

I'm just bummed that all this nice weather is passing me by...

[SOHC4 Cafe Racer Fan]

Things are looking pretty good. Head gasket, valve seals are ordered.

I was floored by how hard the valve seals were! I had to chip them out, almost. No wonder I was blowing smoke. As much as I hated pulling my engine, I can see some serious positives in the work I can do here.

Alongside the valve stem seals being complete #$%* I also got to look at my valve seats and its amazing the thing even runs. Lots of carbon buildup and the seal surfaces are pretty rough looking. My guides are in great shape though, very tight tolerances still, zero wobble. After she is back together I shouldn't be throwing smoke-screens up anymore.

Right now I'm just cleaning, lapping valves and then waiting for parts to re-assemble the top end.

I'm just bummed that all this nice weather is passing me by...

You're making great progress.  You should be back on the road pretty soon after receiving your seals and gasket.

[mkoski]

Thanks.    The plan is to have everything sitting, waiting for those parts. When they come in the seals go in, head goes on, engine get mounted, all the parts go back on the bike and I ride that day to test everything out.

I'm actually debating a 3rd motorcycle right now for long distance trips (as this one is definitely not meant for it, ergonomically, and my second bike isnt even started yet, done for next summer) but I really think that three is unreasonable at my age and the climate around my parts.

So you think those rockers and the cam all look pretty good? No one has given me an opinion on em yet.

[SOHC4 Cafe Racer Fan]

At your age?? If you have the money for it, age doesn't really play a part in the equation.  The trickier thing is finding time to ride them and keep them all in running condition.

[knottedknickers]

At your age?? If you have the money for it, age doesn't really play a part in the equation.

Like his signature says: "There are some things nobody needs in this world, and a bright-red, hunch-back, warp-speed 900cc cafe racer is one of them — but I want one anyway, and on some days I actually believe I need one...."

[seanbarney41]

rockers look "well on their way to Davey Jones locker" to me...especially that last one.  I am not finding pics of the cam lobes?  Better find the cause or they will soon look like this (pics are of cb750)
DSCN0554 by Sean Barney, on Flickr
DSCN0556 by Sean Barney, on Flickr
DSCN0559 by Sean Barney, on Flickr

My guess is the wear is caused by an oil supply problem.

[Restoration Fan]

That first picture looks like there's a nick in the top of the rocker arm.  I'm not sure what would cause such but you would think it's hitting on something to do that.  But I don't know that I've ever heard of having clearance issues with the rocker arms.  There's nothing "extra" up there for it to hit on and cause a nick in the edge like that.

But, yeah...those rockers look a little rough.

[martin_uk]

When rebuilding top end I always lub cams and rockers with some EP80 oil to help during initial running.

Dont know if it works but seems a good idea.

[mkoski]

That first picture looks like there's a nick in the top of the rocker arm.  I'm not sure what would cause such but you would think it's hitting on something to do that.  But I don't know that I've ever heard of having clearance issues with the rocker arms.  There's nothing "extra" up there for it to hit on and cause a nick in the edge like that.

But, yeah...those rockers look a little rough.

Those rockers (with the one with the nick in it) are not mine. Mine are in the post above and look quite a bit better than those, just some uneven wear.

And SeanBarney, I think I agree with you, I will have to take a look at my oil passages up there to be sure.

I'll definitely lube everything really well so it's not oil-starved when I fire it back up, thanks Martin.

[mkoski]

Well, she's buttoned back up for now and the engine is back into the frame. Going to get the rest of the bike assembled today or tomorrow before I can test it.

I have to say, I'm pretty proud she all went back together with no pieces missing at the end... I was at a point during the top-end rebuild that I was scared I would never see it through when I had all the parts separated and everything was on the table.

So now I pray that everything works as intended for when I start her back up... Wish me luck!  I'll follow up with the results as soon as possible!

[SOHC4 Cafe Racer Fan]

Good luck!  Looking forward to an update after you fire it.

[mkoski]

The report is in! What we have is complete and utter failure! 

After rebuilding the top end (complete inspection of everything down to the cylinders, lapped valves, new stem seals, ect.) I have reassembled and reinstalled the engine. She does the exact same thing as she did before the rebuild.

First, here's the video I made:

That gives a good idea of the sound that I have going on here. I also have a bit more information to go along with this...

When I was first starting her up I didn't realize I had a missing connection for coils 2+3 so I was only getting spark on 1-4. Regardless of that she fired up and sounded quite good running only on those two cylinders. No ticking at all! At this point I was excited because I thought once I got power to the coils for 2-3 she would be a dream!

Alas, that was not the case. After getting 2-3 to fire she ran pretty well at idle/low rpm. Anything above lower rpms she hesitates, lacks power and sounds like #$%*.

So, my much appreciated friends of the SOHC forums, what the heck do I do now? It has gotta be top-end, right? How could I have missed something that could be making a sound like this!?

ALSO: Please note to anyone new in this thread that the rocker arms pictured directly above ARE NOT my rocker arms, those were posted from another bike. Mine are above, and look much more serviceable.

[flybox1]

you mentioned nothing about tuning your bike after the engine went back in 
Cam Chain set properly?
did you perfectly time your engine?  advance, too?
are your carbs right?  vacuum sync done?

just throwing in a rebuilt engine will not make everything right in the world.
you have some fine tuning to do

[RAFster122s]

The photos you showed of your rockers look like the harden surface is wearing thin ss evidenced by the edges showing a different color.  If you're rocker shafts have wear they could have some play causing the edges to wear. But you are claiming that the shafts have no play in any direction. A ticking noise can be caused by play or adjustment.
I think you might be having some play and are not feeling it or measuring it.

[calj737]

could it be something so simple as an exhaust leak? Have you tried the "Mechanics Stethoscope" method of holding a screwdriver to your ear, and placing the tip at different locations around the engine to locate the origin of the sound? This works extremely well, actually.

Touch each tappet cover, the breather cover, the cam ends, the intake and exhaust manifolds (flanges) for each pipe. You will locate the source pretty quickly.