Topic: Cam chain tensioner shaft

[74750k4]

Anyone know if the tiny hole in the end of the tensioner shaft serves any purpose???

The manual just says loosen the lock not and bolt at idle, and it self adjusts.

[74750k4]

It appears that it is threaded. Maybe to hold it open with a screw and big washer during factory installation? Doesn't makes sense though when you could do that with the bolt. Unless...  it's for pulling the shaft back out...  no other way to do that if  the tensioner is installed.

[74750k4]

No one !!!

[MCRider]

It serves no purpose that we know of. Except.

If you cheat on your tensioning protocol you can stick something in there like a allen wrench or screwdriver and push to make sure the plunger isn't hanging up. However once pushed you should remove the pusher and let the spring set the tension.

In off road usage like a hill climber that hole will collect debris like a belly button. 

It is sealed off from the inside of the engine by a ORing in the housing.

[crazypj]

It appears that it is threaded. Maybe to hold it open with a screw and big washer during factory installation? Doesn't makes sense though when you could do that with the bolt. Unless...  it's for pulling the shaft back out...  no other way to do that if  the tensioner is installed.

!00%, give the man a cee-garr
Check the manual, it's there to pull the bolt out WITHOUT DAMAGING THINGS
 There used to be a nylon/rubber plug to keep crap out

[MCRider]

It appears that it is threaded. Maybe to hold it open with a screw and big washer during factory installation? Doesn't makes sense though when you could do that with the bolt. Unless...  it's for pulling the shaft back out...  no other way to do that if  the tensioner is installed.

!00%, give the man a cee-garr
Check the manual, it's there to pull the bolt out WITHOUT DAMAGING THINGS
 There used to be a nylon/rubber plug to keep crap out

Huh? What bike? I assumed CB750.

[crazypj]

Honda use the same method on various models

[MCRider]

Honda use the same method on various models

Granted I may not know what the OP is asking. Rereading it he asks about the hole in the end of the shaft. There is no hole in the shaft but in the end of the housing, on the CB750.

But the CB750 tensioner is nothing like the CB500/550 tensioner, for example.

[74750k4]

Let's see if I can clarify a bit...

CB750K1 bike complete  but I can feel the threaded hole
CB750K4 engine out, tensioner assy removed
CB750k1 engine out can see end of shaft, tiny threaded hole is there.
CB750K8 engine out, tensioner assy removed

ALL of these tensioners have a shaft. If you remove the shaft out of the assy., there is a small threaded hole in the end of the shaft. It is threaded and short. Less than a 1/2 inch in depth I think.

The only explanation is to be able to pull back on the shaft releasing chain tension, or to check to see if the shaft is free to move with the lock nut, and bolt loose.

I will check the factory manual as the poster said.

Any clearer?

[74750k4]

Not seeing anything about the small threaded hole in the end of the tensioner push rod.

Here's K8, and K0 manual pages.

So where do you see that?

[MCRider]

SON of a GUN! I just coincidentally have mine off my engine chasing down an oil leak. Pulled the plunger shaft out and sure enough there's a tiny about 3mm hole, actually offset from center a little. All these years and all the times I've seen that part out of an engine I've never noticed that hole!  Live and learn.

So we can spec on its purpose but I venture no one knows for sure. You can use it as you've mentioned to manipulate the plunger. Generally you just push it in all the way, lock it with the lock bolt, install the housing then loosen the lock bolt.

While its the same plunger on all CB750s, I'm willing to bet not another single Honda has a tensioner even remotely similar.

[74750k4]

Yep, it's there. If you didn't want to remove the assembly, but wanted to release the tension, you could do it by threading in a screw, or whatever. It's tiny, like 1, or 2mm or so.

[MCRider]

Yep, it's there. If you didn't want to remove the assembly, but wanted to release the tension, you could do it by threading in a screw, or whatever. It's tiny, like 1, or 2mm or so.

Interesting.

For removing the tension, we would loosen the lock bolt, turn the engine backwards. That would tighten the backside run of the chaiin putting all the slack on the front, and forcing the plunger out. THen lock it down. Roll the engine forward a skosh and all the slack is now on the rear with no tensioning. Then you can remove the tensioner with no resistance.

Think I'll practice with a screw while I've got it off though.

[crazypj]

Honda use the same method on various models

Granted I may not know what the OP is asking. Rereading it he asks about the hole in the end of the shaft. There is no hole in the shaft but in the end of the housing, on the CB750.

But the CB750 tensioner is nothing like the CB500/550 tensioner, for example.

There is a Honda special tool to screw into it.
Your supposed to relieve tension before stripping top end (pretty doubtful anyone does, I never have)
 On the 100~125~200 CB/XL/XR motors you can use it to tension chain by pulling up on tensioner plunger (they stick, frequently)
There is a difference between a profesional and an amateur

[MCRider]

Honda use the same method on various models

Granted I may not know what the OP is asking. Rereading it he asks about the hole in the end of the shaft. There is no hole in the shaft but in the end of the housing, on the CB750.

But the CB750 tensioner is nothing like the CB500/550 tensioner, for example.

There is a Honda special tool to screw into it.
Your supposed to relieve tension before stripping top end (pretty doubtful anyone does, I never have)
 On the 100~125~200 CB/XL/XR motors you can use it to tension chain by pulling up on tensioner plunger (they stick, frequently)
There is a difference between a profesional and an amateur

As I mentioned we removed the tension another way, and yes it was done quite regularly. Otherwise the tensioner would shoot off the back of the cyl.    Or it would be very difficult to get the chain off the sprocket.

Never worked on the smaller bores, mea culpa.

But I accept that is what the threaded hole is for.

[74750k4]

Great, well now we just need to know the thread size/pitch. Maybe the Honda tool number with photo???

[crazypj]

I know I have the number, saw it recently when I was skimming through a service manual
 I've given several away, used to make them on a regular basis