Snapped a rocker adjuster!?

[999 ORX]

Hello, has anybody ever had this happen to them? I took my car for a mot and was driving it back then it started to miss.. luckily it was right outside my old mans gaff so I pulled it in and took my plugs out to find that No.1 was wet through.. I had my suspicions that it had backed off due to possibly touching my rocker cover and closed a valve.. to my horror it had actually snapped!
They are the longer ones as used on a 8port (which my head is) because the deck Height is thicker. I had some longer push rods made a while back but I found that they would possibly bind in the tube through the head, so I decided to use longer adjusters.. Now I'm not one to pick faulty but I have noticed it's snapped just above where the hardening process had been applied to ball on the end.. Has anybody else had this? Or is it just coincidence or bad luck.. I'l upload a photo later too

[mk1]

Using longer screws will always put more loading on a rocker & it's adjuster than using longer rods. I'm not saying this is the reason, but it will be a contributory factor.

M

[999 ORX]

Hi Mark,

yeh that was my first assumption. I did think because of the extra length, more of a angle more fulcrum and leverage etc.. but when i actually looked at the broken one and compaired it to the new onese (as you cant buy them in the singular) is it me or dose this look like fault in the material or just one of those things!?

[Pandora]

Not had an adjuster snap, but I had a pressed steel rocker snap once at full chat in the outside lane of the M9.

It ran a bit rough! Luckily didn't do any damage as it rattled round in the rocker cover as it was a Downton head.

[Astro]

Hi

I had a similar problem. I needed some new adjuster screws and when trying to screw them in with my fingers, there was some damage. The reason is faulty manufacturing. When hardening those screws, you have to cover the thread. I just made this gadget, heated the thread until becoming grey and cooled down the ball that it would not loose the hardening. It seems to work.

[InimiaD]

I too managed to snap a rocker screw whilst hooning around Oulton Park (stages).
Had a misfire and when checked in the service area, found the broken off ball end on top of the head.
Changed the broken item for a thin nut and bolt, adjusted it for clearance, carried on for the rest of the event, then drove 100 miles or so home.
Ahh, those were the days.

[999 ORX]

Cheers, it's interesting to see similar problems... I don't mind the fact it's broken if it's just a one off fault, it's just now I'm not very confident in them now!

[mk1]

That is a classic fatigue fracture caused by poor rocker geometry.

Rocker failure is particularly common in Mini engines because many people don't set the geometry as it should be, this includes a lot of "experienced" engine builders as well as "amateurs" like me. Fannying around with the length of the screws & using rockers that are outside their design limit angle will not only reduce the effective life of the adjuster, but can cause premature breakage of the rocker (even when using roller tipped ones) and in some extreme cases can cause the rocker to fall off the tip of the valve at high lift, get stuck & either flick the collet out or break the tip off the valve causing catastrophic failure.

If I was you I would take this as a very cheap warning that all is not well & spend a bit of time sorting the underlying problem rather than hoping that its a material fault.

[999 ORX]

Cheers Mark, i'l have a study..

[1071 S]

I have one just like that.... I blamed it on a trip to 10K (that's as far as the tacho goes) when a throttle cable snapped.

Is there a tutorial somewhere on properly setting up rocker geometry???

Cheers, Ian

[1071bob]

To get the maximum lift from the rocker geometry check when the valve is 50% open that the line from the rocker pad, pivot centre and the centre of the ball end on the adjuster should be horizontal, this puts the adjuster screw almost vertical giving maximum stiffness. when the valve is fully open or closed the angle change of the adjuster screw is minimal. You can adjust this by altering the rocker post height or changing the lengths of the pushrods.

[mk1]

I am sure this can be made far more technical than I can make it.

However, if when you set up the rockers you make sure that they are a level as possible when the rocker is tapping i.e. The follower is sitting on the cam base circle.

Depending on what you have changed you can see the rocker either tilted back towards the rear of the engine. This is the condition when over long adjusters can end up breaking.

The other possibility is that when the rockers are "at rest" they are tilted forward. This can cause valve / rocker breakage.

the situation can be solved by either lengthening or shortening the push robs or spacing the rocker posts off the head or grinding some material off the bottom of them. The best method should be determined on a case by case basis.

[999 ORX]

Well,
The problem I have is my head is unique and a bit of a unknown. I have discovered with some help that the valves are higher in the head than standard. Ie the protrude higher in the top of the head causing the rocker to slightly sit upwards to the valve and that the adjusters are now on an angle which probably caused it to break.

I'm going to over come this by lifting the rockers up with a specially made plinth which will be machined fully flat and will sit between my head and rockers to correct this position problem. My head is also about 10mm thinker than a standard stock A series head so my push rods need to be longer. I already have a set made which are longer and I hope I can use them. This will then hopefully correct the problem caused by using longer adjusters to compensate for the original push rods being in effect 10mm shorted because of the head thickness being 10mm thicker so I can hopefully resort to using standard adjusters at the correct resting position with the longer push rods

To be honest though I now dont understand why these longer adjusters are actually available because the reason I bought them was to take up this extra length I have (ooo er mrs) and because I used them "extended" for the purpose i thought they were available/designed for they break because they are under side loading it's probably my fitment like.. But In my opinion now they are pointless and your just trying to quickly fix a problem that cant be cured by them. But I must not grumble as I've learnt a lot because of this! Anyone want to buy a mini!? Haha

[999 ORX]

Depending on what you have changed you can see the rocker either tilted back towards the rear of the engine. This is the condition when over long adjusters can end up breaking.

The other possibility is that when the rockers are "at rest" they are tilted forward. This can cause valve / rocker breakage.

the situation can be solved by either lengthening or shortening the push robs or spacing the rocker posts off the head or grinding some material off the bottom of them. The best method should be determined on a case by case basis.

Mark, So I'm I right in thinking the rocker top should really be parallel to the deck where the post bolt too?

[mk1]

Yup, that's correct. Assuming all is correct the rocker should be parallel to the head face at rest.

The reason the longer screws were made originally was that the 649 cam had a slightly smaller base circle than most other BMC cams making the standard adjusters just a bit too short to work properly. To solve this problem BMC made the longer adjusters they were designed to accommodate changes of around 80 thou (2mm) not 10mm +.

[1071 S]

Thanks Mark.

Cheers, Ian