Saturday, 27 October 2012

Rockers! How to rebuild these

1929 rockers, standards and spindles

-SG- Rockers...a minor can of worms here which I have deliberately avoided up to now!

1. Although there are minor size differences because of casting variations all of the essential dimensions of the arched 1926 to 1929 rockers are the same.

2. The rocker spindles of the early 1926 ones were hollow with grease nipples in the end and the rockers themselves had no grease nipples.

3. At some point, I think later in 1926, the rockers were made with grease nipples and the spindles were solid.

4. Apart from the grease nipple difference the spindles were all the same with one small variation I will cover later. They had a thread under the head of 3/8 x 26 TPI, a plain hardened shank of 5/16 dia. and a short 1/4 BSF threaded bit on the very end.

6. The thread where the ball end (the adjuster) goes in on the rockers was not 1/4 nor 5/16 but 9/32 x 26. Fortuitously this is the same size as the ball end used on quite a few BMC cars (Minis, 1100s etc) and the ball on the BMC part is fine too. The BMC lock nuts are not suitable though as they are just plain nuts and the Norton ones have a small cone shape on one face which is intended to lock up against the contersink recess in the rocker.

7. The exception on the spindles mentioned above is the exhaust one fitted to ES2 and all 1929 engines where the exhaust valve lifter is mounted on an extension of the spindle, ouboard of the 3/8 x 26 thread and under the hexagon head (see photo). This extension is 3/8 diameter, hardened and ground and 5/8 long. The rocker standard for these has a cable stop incorporated in the casting quite close to the foot.

8. The original bearing was a miserable affair with a brass cage and six 3/16 x 3/16 rollers each end.  These tend to dig into the surface of the spindle despite it being hardened and to a lesser extent the rocker bore and most people have thrown them out but in some cases without the need to do so! I say this because, provided the threads on the spindles and the threads in the rocker standard are OK, then one can throw out the brass cage and rollers and substitute crowded 3/16 x 3/8 rollers instead with a small spacer between them in the centre of the rocker. This spacer needs to be 0.500" OD x 0.835" long with a 5/16" clearance bore. These provide more than twice the bearing area of the original design (eight will fit each end) and the rollers are running on an unworn part of the rocker bore/spindle.  From personal experience it works fine.

9. If the rocker standard threads (the 3/8 x 26 ones) are worn remedies are difficult because there is so little material in that part of the standard although I have heard of someone who opened up the thread from 3/8 to 10mm x 26 (a thread used a bit in the light fitting industry) and then had new rocker spindles made to suit.

10.  So, forgetting (9) above, we move on to bronze bushes in the rockers and  new spindles. I have seen various versions of these but the best idea in my view is:
a. Carefully ream out the worn 3/8 thread in the standard to 13/32.
b. Thread the other side of the standard 3/8 x 26 ensuring the two holes line up perfectly.
c. Make a rocker spindle which is stepped under the head with a diameter at that point only of 13/32 with the rest of the spindle being 3/8 and with a 3/8 x 26 thread on the end. The spindle does not need to be hardened but a good finish is very desirable.
d. The bush in the rocker can be a one piece chunk of bronze suitably drilled so that grease can get through it from the grease nipple to the spindle.

11. There is a further alternative to all this and that is to fit needle rollers and a new spindle - not loose needle rollers but an actual race the number of which is B88 (Torrington). The outer diameter of these races is the same as the rocker bore so they can be inserted - one each end of course - and held in with Loctite bearing fit. If desired a thin spacer can be put in between them. The B88 is designed to run on a 1/2" spindle and the best way of achieving this is to make/have made 1/2" tubular spindles with a 5/16" bore. These need to be hardened and ground and just long enough to fit between the rocker standard uprights. These need altering to accept the new spindles by silver soldering a small threaded sleeve 3/8 x 26 into the original hole. This should have a pilot hole in the centre. Then drill straight through the sleeve and the other side 19/64" and ream 5/16". Hold the whole lot together with a 5/16 bolt and nut.

12. I have not mentioned rocker end float up to now. In the original design this was adjusted by loosening the 1/4 BSF nut and backing off the spindle a fraction in the 3/8 x 26 thread, and then tightening up the 1/4 nut again. A rotten idea which I am sure contributes to wear on the 3/8 x 26 threads of both spindle and standard. This end float can be better controlled by adjusting the thickness of the washers which press into the rocker bore in the original set-up. These were 0.6875" dia. and 0.055" thick. With the bronze bush solution, all one needs to do is make the bush the correct length to achieve about 0.005" end float before it is pressed into the rocker. And with the Torrington solution, where one still has to use the washers to close off the rocker bore at either end, make these of a thickness to achieve the end float.

13. I have no doubt many people have effected entirely satisfactory rocker repairs in other ways and I certainly don't want to get into long discussions on alternative methods but we will gladly add any other good solutions to this list.