Rockers

[Mark Wilson]

I'm installing an NOS Mini Mpi head on my Midget 1275 block, and was intending to use the pressed steel rockers off my 12G940 head, which I don't know the history of. I need to do some grinding and shimming to align the rockers and valves, but I'm not completely happy with the rocker pads which appear to have been "stoned" previously. Although no serious dents there are definite ridges and the face isn't quite horizontal where it meets the valve tip. Darker metal is starting to show through the chrome hardening, so it looks like it's time for new rockers.

These are a bit expensive and some guidance would be much appreciated. I can buy new forged Cooper S style rockers from Minispares, at nearly £70 the set. ESM do a reconditioned rocker assembly at around £50. Their photo shows pressed steel rockers, but I didn't know these could be reconditioned and haven't found anyone supplying new. ESM can only tell me that the photo is of what they have on the shelf.

I already have a new shaft, and the pillars seem OK, so the rockers would be really all I need from the ESM assembly.

Has anyone had one of these reconditioned shafts - are the rockers really pressed steel, and are the pads new? Or even better, does anyone know anywhere cheaper for either type of rocker?

Mark

[philthehill]

Mark
Depends what is meant by reconditioning.
Pressed steel rockers should not have the bushes replaced as the arm can distort when removing and pressing in the bush. Pressed steel rocker are a once only use as regards the bushes.
As regards the servicing of the tips of the rockers - both pressed steel and forged rockers need to be placed on a jig for grinding as the original profile needs to be retained otherwise excessive and quick wear of the rocker gear and valve guide/valves will occur. Whilst it can be done with a stone I personally would not recommend it as the profile has to be kept square and at the right radius.
New pressed steel rockers are not available only the forged type and the sintered steel are available as per the BMC/BL spec.
New bushes in used forged rockers have to be reamed to size.
I would go for the forged Cooper S rockers or a new set of sintered rockers or do as I did and buy a very good set of S/H pressed steel rockers off 'e' bay. They do exist.
As an aside early pressed steel rockers had hollow adjuster screws which can fail if used spiritedly. Make sure that the rockers have the later solid adjuster screws.
If you have the steel pillars (Pt No: 12A210/211) they can be easily machined to enable the rockers to be aligned over the valve stem.
Do not use the alloy rocker pillars as they can fail with stronger valve springs and they make for difficulties in torqueing down the head as the alloy squashes..[frame][/frame]

[Mark Wilson]

I had another look at mine last night, not quite as bad as I thought and would probably last several thousand miles. The hardening is wearing through, though, so rather than risk it I'm going to have to throw yet more money at a set of the Cooper type forged. I'll have to reassess the need for pillar alteration once I've got them. In the absence of a lathe (or the skills to use one) I'm planning to grind and file as carefully as I can, but place a shim between the pillar and the rocker so as to create a smooth interface.

The forged rockers seem to have a wider tip than the pressed ones. Is a small amount of offset acceptable?

[philthehill]

Mark
You have a PM.

Whilst a small amount of offset is acceptable any offset will increase the offset loading on the rocker and rocker shaft leading to increased wear.
It is better to get the alignment right as it will all last longer.
The 12A210/211 rocker pillars (as used on the Cooper S and early 'A' Series) are the best for machining as they are steel and give a very good finished surface unlike the sintered steel pillars.
I find that at least an 1/8" has to be taken out of one side of the rocker pillar to get the alignment right.
The sintered rockers were a cheap solution to the alignment problems in that they are much wider.
The valve centres on the 1275cc 12G940 heads were further apart so exacerbating the alignment problem. With the early 1275cc Cooper S heads (Pt No: 12G185) the valve centres were closer together and needed hardly any re-alignment and there was no need to machine the rocker pillars. But of course the 12G185 head had other problems to contend with like head cracking between valve seats.

Phil

[Mark Wilson]

I do hope your Christmases weren't spoiled by worrying about my rockers☺

All was resolved, as reported on the other side, with some much appreciated help offline from Phil. One point worth noting, though, is that having decided to pay up for what were advertised as new Cooper style forged rockers I was informed by the local manager of the company selling them that he was aware of failures due to faults in their manufacture but hadn't yet persuaded his head office to remove them from their catalogue. He advised me to find a set of sintered rockers on eBay, which I did, at much lower cost. I'm being deliberately vague about the company involved as I don't want to cause any problems for the guy after such good advice, but do be on your guard if buying new rockers.

Engine now complete, well on with the gearbox!

Mark