• Don't overlook our Welcome Package, it contains many links to important and helpful information about functions at VHT like posting pictures and sending PMs (private messages), as well as finding the parts you need.

    AD

Rocker adjuster nut falls off!

Windmill John

Veteran Member
Joined
Jun 4, 2022
Total Posts
446
Total likes
64
Location
East Sussex, England
Exhaust rocker adjuster nut falls off!

CB250K0 1968

As it says…

Okay, a bit of background, as obviously I’ve created this issue.
Points case had a leak. I removed it, fitted new home made gasket and new o rings to rocker arms.
The o rings were the new version according to CMSL, David Silver etc.


The nut didn’t just undo, it came off; inlet one not tight either.


Okay, so let’s look at history.


I made a gasket. Could be a little thicker than the one that came off.
I fitted new revision o rings. As I ordered the originals and the ‘new’ version, nothing wrong with spares… I thought (imagined) that the new ones were the tadiest of tads thicker than the originals.


So, even with a ‘thicker’ gasket and a ‘fatter’ o ring, the adjuster still went through the nut fully. Still fell off after two rides.


Any thoughts?


I’m at the point now of locktighting, nylocking, serrated washering the damn thing in place.


Answers on a post card please.


Thanks.
 
My first thought would be the gasket you made, being thicker, is crushing down and allowing the tightness of the nut to be affected, but then why doesn't it affect the intake adjustment lock nut?
 
The intake has loosened a little, but not coming off.

But even if the gasket is slightly thicker, surely when squashed down the nut should tighten.

Or are you thinking that there is still just enough give in the gasket to stop the final tightening?
Whilst flying in the face of standard, do you see any downside of me either using a serrated washer, or thread locker?

Of course I could remove it all again and make a thinner gasket; rather not.
 
I don't suppose a serrated washer (what I envision as an internal star washer) would hurt, though it shouldn't be necessary.

star washer.jpg

These kinds of little things that happen when you go off the beaten path are the reasons I stick with the factory design and parts in most cases.
 
The problem with threadlocker is it works too well at times. Since this is a regular service item and not something that's a "one and done" I would avoid it.
I would be inclined to use a Nylock nut more than a serrated lock washer.
 
Thanks both.
I’d got two nylocs ready when the rain came, so carrying on tomorrow.
I was going to use blue thread locker, so hopefully not an issue.
I’ve degreased the threads on the adjuster and the nuts and I’m going belts and braces by applying a little thread locker with the nylocs.

If I need to get in the engine in the future, then I may make a thinner gasket at the time. Or order an asbestos gasket from America…….
 
Gasket thickness SHOULD have nothing to do with tightening the adjustment eccentrics as they do not bear on the gasket at all IF gasket is properly cut and installed.....
The gasket thickness MAY come to bear when considering shimming the camshaft for axial clearance......

Early versions of these (250 and 350) engines had a smaller/shallower chamfered depth at the adjuster holes, and thus a "fatter" o-ring might be problematic.....
Some early bikes had sealing washers exterior to the head cover, just under the jam-nuts...
This was recently discussed....I'll add a link as soon as I can locate it....
 
Last edited:
Okay, I’ll try the nyloc without thread locker. ( Not even blue thread locker? Loctite 242, 243 for example?)

I was wondering if it was the O rings. The washers I have are plain, but then again I do not know the bike’s history. Definitely not sealing washers.
 
You can lightly peen the crimped part of the nut to tighten the nylon a bit. Before you put the nut on, of course.
 
Okay, I’ll try the nyloc without thread locker. ( Not even blue thread locker? Loctite 242, 243 for example?)

I was wondering if it was the O rings. The washers I have are plain, but then again I do not know the bike’s history. Definitely not sealing washers.

They did not come with sealing washers when they had o-rings on the shafts, though I can't speak to the prior version when there were no o-rings.
 
Right you secretive buggers ;) you kept that quiet that the adjusters are a thread pitch of 1!!!

I’ve got loads of nyloc and plain M8 nuts, all with 1.25 pitch.
Looked online and only one place in the UK had nylocs with a thread pitch of 1.
£30 plus carriage for 25!!
Well, as I’ve never needed these in forty years of fiddling, I’ll give them a miss.
Went down the thread locker route with internal star washers. Giving it the full cure time of 24 hours and riding tomorrow.
 
Back
Top Bottom