Rockers/Pedestals (pillars) Etc

[svenedin]

I thought it might be useful to start a thread on rockers, pedestals, rockers shafts etc. Questions about the various types of rockers arise quite often and information is spread in bits and pieces all over the place.

BMC and then BL produced variants of rockers including pressed steel (in small bore and large bore variants), forged steel (Mini Cooper S type) and sintered steel. These rockers differ in various ways including the rocker lift ratio, strength of the material, cost, availability, whether they have a bush that can be replaced, how fussy they are about being perfectly aligned with the valve stem etc.

There are also variants of the rocker pedestals (or pillars) with some being forged steel, sintered steel or even alloy. Some are more suited to good alignment of the rockers than others. Some are stronger.

Then there are exotic rockers like roller tipped but there is enough to discuss of the standard types without mentioning those as well.......

I will dig out some different types of rockers from the garage and post photographs but there is some good information here:

https://www.calverst.com/technical-info ... %20minimum.

Until I started looking into this I did not know that there were small bore and large bore variants of the pressed steel rockers and that they have different lift ratios.

Stephen

[philthehill]

Without trying to steel Stephens thunder -----
Stay clear of the alloy rocker pedestals - the alloy is soft and compresses easily. This makes keeping the head torque at the correct setting very hard to achieve. I have seen them advertised as race pedestals which could not be further from the truth.
The best pedestals are Pt No 12A210 & 12A211 and are steel. They can be machined as per photo below to allow the rocker to be placed central over the valve stem. Sintered steel pillars are near impossible to machine to get the rocker of what ever material central over the valve stem.

Rocker pillar machine 1.jpg (77.8 KiB) Viewed 5044 times

There is also a complete back history on the tappet adjusting screws and rocker shafts.

[svenedin]

Not at all Phil,

I was hoping lots of people would contribute to the thread over time.



Here is a set of small bore pressed steel rockers. These have a circular contact pad and when combined with steel pillars they make a very tidy registration with the valve stem. Everything is nicely in line. 12G202 head.

IMG_2459 2.jpeg (2.7 MiB) Viewed 5033 times

On the other hand, here is a set of pressed steel rockers and steel pillars on a small bore head (1098 engine, standard 12G202 head). These are not making nearly so neat an alignment. They may actually be large bore (oval contact pad) pressed steel rockers. I am not sure. At the time I did not know there were different types of pressed steel rocker. The observant may notice the locking plate is missing on pedestal 2. It is now in place.

IMG_1768.jpeg (1.23 MiB) Viewed 5033 times

Pictures to follow of sintered rockers and forged (Mini S type original) rockers and of the early adjusting screws with oil hole (prone to snapping).

[Pete Bags]

Thanks for this thread Stephen. This is my set up - it's a 1098 with a 12G202 head. It has the sintered rocker arms. The engine was rebuilt around ten years ago with a Kent cam, with a 16 thou tappet gap. Any idea why the locking nuts for adjusting the tappets are different sizes depending which type of rockers are used? Mine are 1/2inch, but other (pressed steel/forged?) seem to be 5/16inch? And why would the valve springs have red paint on them?

sintered.jpeg (618.11 KiB) Viewed 5028 times

[philthehill]

As regards the rocker locking nuts - the early small dia adjusters were prone to failing at the waisting which allowed oil from the rocker shaft to get to the push rods. BMC then decided the delete the waisting of the adjuster screw as there was sufficient oil getting to the pushrods. Later on to give more reliability the dia of the adjuster was increased.
If you have waisted and centre drilled adjusting screws they should be replaced with non waisted and non centre drilled adjusting screws.
As regards the paint on the valve springs - The colour indicate the manufactures poundage of the spring.

[svenedin]

Thanks for this thread Stephen. This is my set up - it's a 1098 with a 12G202 head. It has the sintered rocker arms. The engine was rebuilt around ten years ago with a Kent cam, with a 16 thou tappet gap. Any idea why the locking nuts for adjusting the tappets are different sizes depending which type of rockers are used? Mine are 1/2inch, but other (pressed steel/forged?) seem to be 5/16inch? And why would the valve springs have red paint on them?



sintered.jpeg

Hello Pete,

Phil is the engine expert and I see he answered whilst I was typing

I think the red paint on the springs denotes how strong the spring is in the same way that carburettor piston springs are marked but I am not aware that there is a consistent colour code across manufacturers.

The pressed steel rockers have a 7/16" adjuster locking nut. All the others use 1/2" locking nuts.

Sintered rocker arms were introduced in 1974 by BL. They are robust and they have a large valve contact area so they do not have to aligned perfectly. They have no bronze bush so if they wear where the shaft goes through they have to be thrown away. However, the shaft is the bit that wears. Mini people don't seem to like the sintered rockers because they have the lowest ratio of all of the variants of 1.21:1 although this is very similar to the original Mini Cooper S forged type which are 1.23:1

Stephen

[Pete Bags]

If you have waisted and centre drilled adjusting screws they should be replaced with non waisted and non centre drilled adjusting screws.
As regards the paint on the valve springs - The colour indicate the manufactures poundage of the spring.

Thanks Phil - can you tell from the photo if the adjusting screws are the waisted/centre drilled ones? And if so, where would you get the replacement ones from?

As for the poundage rating of the springs, is a greater or lesser figure better and are different springs used for different reasons?

[philthehill]

I am not aware of a consistent colour coding of the valve spring poundage. Some of the NOS valve springs I have are painted and some are not. All you can do is refer to the suppliers/manufactures data sheet or measure the deflection (compressed length) at a specific loading. Vizard has load/deflection listings for the 'A' Series valve springs in his book 'Tuning the 'A' Series but not all current information is included.
Tuning valve springs for max performance is an art in its self.

[philthehill]

You cannot tell if the screws are waisted as the waisting will be inside the body of the rocker. You can remove a rocker screw without disturbing the head by slackening the adjusting screw right off. Slide the rocker sideways off the valve stem and push rod. Rotating the rocker will allow you to remove the screw for examination. As you have the sintered rockers you will not have the waisted adjusting screws. Only the small early adjustment screws had the waisting.
When replacing the waisted adjusting screws I just use good S/H non waisted adjusting screws.

[Andmurph]

These are the rockers on the pickup. I was adjusting them earlier.

[philthehill]

Andmurph
Unless you remove a adjustment screw you cannot tell if the adjusting screw is waisted or not.

[svenedin]

These are the rockers on the pickup. I was adjusting them earlier.

Those are the pressed steel type. They were the standard type until 1974. The pressed steel type have a bush for the rocker shaft but it is generally said that the bush cannot be replaced as it would distort the rocker to do so. In any cause the rocker shaft wears before the bush does. Folk on Mini forums maintain the bush CAN be re-bushed.....

I notice you have high-tensile head studs, conical ends. Sometimes high-tensile studs have a dimple instead or are marked with a Y. Mine are marked with a dimple and a chamfered end.


Stephen

[philthehill]

You can re-bush the pressed steel rockers but the risk of distortion is so high that in my honest opinion not worth the risk.
I would also suggest that if the rocker bush needs replacing then the hardening of the rocker anvil tip will be worn through and the rocker will be scrap.
The new rocker bushes would have to be accurately reamed and honed. Replacing the bushes in the forged rockers is a much easier job.
Regarding the valve spring poundage - generally you need stronger valve springs if you increase the rev range of the engine so as to keep the valve under control and eliminate valve bounce. The stronger valve spring requirement can be partially offset by fitting double valve springs. The use of good quality valve springs is a must.
As I said above tuning valve springs is a fine art and there is much more to it than just fitting new valve springs.

[philthehill]

Photo of waisted rocker adjustment screw.
You can just make out the oil entry hole in the side (between the threads) and the oil exit hole in the bottom of the ball.

Waisted adjustment screw.JPG (67.89 KiB) Viewed 4933 times

Waisted adjustment screw 2.JPG (57.37 KiB) Viewed 4933 times

To clean the threads in the pressed steel rockers, adjustment screws and nuts I use a BSCY (bicycle thread) tap and die nut. I have been unable to identify the thread used but it is so close to BSCY as to make no difference.

[svenedin]

And here are the waisted type fitted to pressed steel rockers

IMG_9338.jpeg (699.57 KiB) Viewed 4928 times

[philthehill]

The reason for the waisting of the adjustment screw is to allow oil to flow from the rocker shaft through a gallery located inside the pressed steel rocker to the waisted adjustment screw. There is a transfer hole in the rocker bush to allow this. Oil then passed through the horizontal and vertical drilling in the adjustment screw to the cup of the push rod. The excess oil ran down the push rod to the cam follower so lubricating the ball on the bottom of the push rod. The oil then passed out through the small drilling in the side of the cam follower to lubricate the cam follower in the block. The oil then ran down onto the cam lobe to lubricate the cam follower on the lobe. The oil then drained down into the the sump and the process started all over again.
BMC discovered that there was sufficient oil circulating around the engine to provide good lubrication without the waisted adjusting screws. Which added to the sometime failure of the waisted adjusting screw all was deleted including the small hole in the cam follower (from which radial cracks sometimes appeared) without any lubrication problems.
Over the years there were several items deleted from the 'A' Series most which did not have a detrimental effect on the operation of the 'A' Series.
One thing that was a detrimental move was the removal of the drain pipe from the rear main bearing cap. The drain pipe made sure that any excess oil did not get anywhere near the rear sump seal.

[les]

Is this literally a pipe Phil, or perhaps a hole ?

[svenedin]

It's interesting that they went to so much trouble to consider oil flow with the pressed steel rockers and the waisted adjuster screws with oil holes. The forged type rocker also has oil holes to allow oil out from the rocker shaft but not waisted adjuster screws. The later sintered rocker doesn't have a bush or any oil holes at all and they used it for decades......I like the fact that the sintered type have a large contact area so they don't need fiddling around t0 get the rocker pad exactly aligned with the valve stem. Also, if the contact area has worn a bit they can be moved around on the rocker shaft to new positions where a fresh area of the contact pad contacts the valve stem. Incidentally, the sintered rockers are very cheap second hand. I got a complete rocker assembly with sintered rockers for £5. Assuming replacing the rocker shaft as a matter of routine, that's very cheap for 8 rockers.

Stephen

[philthehill]

Les
The transfer passage between the rocker shaft and waisted adjuster screw is just a formed passage in between the wrap around body of the rocker.
If you remove the waisted adjuster the passage can be seen.

The forged rocker has a discharge hole and nothing else. It is intended to spray oil around inside the rocker cover and which it does very well.
Phil

[svenedin]

Photo of waisted rocker adjustment screw.
You can just make out the oil entry hole in the side (between the threads) and the oil exit hole in the bottom of the ball.
Waisted adjustment screw.JPG
Waisted adjustment screw 2.JPG
To clean the threads in the pressed steel rockers, adjustment screws and nuts I use a BSCY (bicycle thread) tap and die nut. I have been unable to identify the thread used but it is so close to BSCY as to make no difference.

I thought it was UNS (Unified National Special) like the thread for the bypass stub in the cylinder head?

Stephen