Topic: Tappet lock nut

[jwurbel]

Well I did it.  After adjusting valves for over 50 years I didn’t lock one down when I adjusted the valves.  Luckily I caught it during idle right afterwards.  I pulled the oil screen but not there.  Assume it’s hiding under the valve cover.  Am I facing having to remove the engine to access the valve cover?

[88BuckMeister]

Lets start with what bike do you have?

You do not have to pull the engine luckily. Which valve specifically because of it was 1 or 4 it may have gotten knocked into a crevice. 2 and 3 may have dropped down the cam chain hole then you may have to pull the sump but again all doable. You'll need to pull the cam cover anyways to check your springs/rockers/cam for damage did the whole tappet work out with the nut, or just the nut? You'll want to pull the breather cover and the side caps and then the cam cover. Have your tank off to allow a thorough inspection of all components without visual impairment. You've really got 2 issues, one that you've got something missing, two that it went rogue with the engine running. Not you should take a Gander at the valve train. Feel free to PM me with any queations I literally just finished a build so it's all fresh in my mind. Everyone on this forum has been so incredibly helpful to me since I joined, happy to return the favor whenever I can.

[HondaMan]

Which valve?

[jwurbel]

Cb k2

#3 is the valve

[jwurbel]

Not sure I understand “pull the sump”

[88BuckMeister]

Cb k2

#3 is the valve

I'm half tempted to help and half tempted to let HondaMan take it because this man knows EVERYTHING about these bikes. No you don't have to remove the motor. Remove the tank to get a full unobstructed view, and you should be able to pull the breather and cam cover off with the motor in the bike. A tiny mirror may help as well if you want to try that in the tappet plugs before pulling the cam cover. I dropped a keeper past my spring while assembling my head, and there are deep crevices in there that go deeper than you'd thing around the spring seats. But with everything moving as fast as it was the bike being running, I'd want a look at everything in the process. Not more than a few hours work

[88BuckMeister]

Not sure I understand “pull the sump”

Sorry I'm an aircraft mechanic. A sump is an oil pan. We call it a sump, but this is a Honda not an IO-360L2A

[bryanj]

If its a 750(k2 does not help) you will need to pull the engine to remove rocker cover and find nut then new rocker gasket.
Living in hope is not a good idea as the nut may eventualy drop down, jam the cranl wrecking any or all of
Crank
Cam chain
Camchian tensioner
Cam
Rockers
Valves
Piston
Head

[88BuckMeister]

If its a 750(k2 does not help) you will need to pull the engine to remove rocker cover and find nut then new rocker gasket.
Living in hope is not a good idea as the nut may eventualy drop down, jam the cranl wrecking any or all of
Crank
Cam chain
Camchian tensioner
Cam
Rockers
Valves
Piston
Head

100% agreed without a doubt. You'll want to check for damage as it went rogue while running, but you can't walk away without that nut in your hands. Period.

[HondaMan]

I've had to chase down those nuts before.
I last found one in the bottom of an engine, next to the oil pump, when I pulled out the pump to rebuild it.

But - if it is #3, I can take my (newly-constructed) convertible-top valve cover and install it on the engine on the floor of my garage at the moment, and make a picture of what you're fighting with. The drain holes for the oil from the exhaust valves are not big enough for the nut to fall down inside, so if it is the exhaust side the nut will be sitting next to the bottom of the spring. If on the intake side it usually also falls next to the spring, but might also be sitting toward the front side of the spring instead (pretty rare). I'll go make some pix, back in a bit...

[88BuckMeister]

I've had to chase down those nuts before.
I last found one in the bottom of an engine, next to the oil pump, when I pulled out the pump to rebuild it.

But - if it is #3, I can take my (newly-constructed) convertible-top valve cover and install it on the engine on the floor of my garage at the moment, and make a picture of what you're fighting with. The drain holes for the oil from the exhaust valves are not big enough for the nut to fall down inside, so if it is the exhaust side the nut will be sitting next to the bottom of the spring. If on the intake side it usually also falls next to the spring, but might also be sitting toward the front side of the spring instead (pretty rare). I'll go make some pix, back in a bit...

Yup its those crevices by the spring seats they are sure lil nooks aren't they. Even with the head off the bike I had to flip the head over and shake it to get my keeper out 🤣

The other thing is Jwurbel please specify whether it's a 550k2 or 750k2 different heads

[HondaMan]

(Note: I'm assuming a 750, sorry if yours isn't?).
Here's some pix: the first one is the top view of #3=#4 side (I left the cover off), followed by the #3 exhaust and then the #3 intake side.

[88BuckMeister]

(Note: I'm assuming a 750, sorry it yours isn't?).
Here's some pix: the first one is the top view of #3=#4 side (I left the cover off), followed by the #3 exhaust and then the #3 intake side.

Hondaman how many of them motors you got laying around 🤣 you are so my hero

[HondaMan]

(Note: I'm assuming a 750, sorry it yours isn't?).
Here's some pix: the first one is the top view of #3=#4 side (I left the cover off), followed by the #3 exhaust and then the #3 intake side.

Hondaman how many of them motors you got laying around 🤣 you are so my hero

At the moment....6, I think?
I rebuilt 7 of them since last March, been a busy year.

[newday777]

Cb k2

#3 is the valve

CB() K2

CB by itself doesn't answer the question.

[jwurbel]

It’s on the exhaust side

[newday777]

Cb k2

#3 is the valve

CB() K2

CB by itself doesn't answer the question.

This is also a CB

[jwurbel]

And it’s a CB 750 K2

[88BuckMeister]

And it’s a CB 750 K2

My friend, 750 makes it trickier. What I would do is peak in there with a flashlight and a dentist's mirror, and maybe fish tightly around the valve springs with a flexible magnet. Your nut is probably literally right there in that crevice by the spring seat. At least do that and listen for the SNAP of the nut hitting the magnet as you're fishing for it. Hondaman is correct those oil return bosses aren't big enough for the nut to enter.

[88BuckMeister]

HondaMan that is so cool I'm jealous. My wife would crucify me. But these bikes are really the coolest thing ever developed. I'd kill to rebuild 6. Please do keep us all updated on that 550 book 📖 🙏

[Floshenbarnical]

I did this in June. It was so much fun!

These guys are right. Check around all the crevices, check on top of the cam area etc. If you don't find it upstairs, then it will either be in the oil pan or sitting balanced on top of the cam chain tensioner (this is where I found mine). Very important not to run the motor until you've found it, obviously.

[jwurbel]

Floschenbarnical

Did you remove the engine?

[Floshenbarnical]

Floschenbarnical

Did you remove the engine?

I did not. I removed the valve cover fasteners, which enabled me to lift the cover up like 1/2" and sneak in a snake cam with some rare earth magnets attached to the tip. Nothing. Checked the oil pan, and whole bottom end with same camera. Assumed the nut must have fallen down the cam chain tunnel, so I went fishing with magnets on a wire. Total ball ache.

Was about to roll the bike into the river when I remembered someone had suggested checking the CC tensioner, so I did that and immediately found it.

I didn't pull the motor because 1) effort 2) I was nervous that it might jostle the nut somewhere unreachable.

It's in there. You can find it.

[jwurbel]

Started looking with a magnet tool in the 3 & 4 tappet areas.  Tough to get it fished down.  So far no luck.  Excuse my ignorance on the valve cover design, but could the nut travel across the head to the breather area and then to valves 2 and 1?  And lifting the cover, valve and or breather, help prior to going all out with engine removal? 

[Floshenbarnical]

Those things move like nobody's business so it could have been thrown off with a lot of force and pinged all over the place under the cover. It could be on the opposite side of the motor. Equally it could have flown off down the cam chain tunnel and landed on your cam chain tensioner (easy to remove, probably will need a new paper gasket) or is sitting in the oil pan. If it's in neither place, as Hondaman pointed out there are a couple of ledges above and around the pan and oil pump that it could be sat on top of. You wont be able to see it from below but you can get your fingers up in there.