MG-Cars.net

Welcome to our resource for MG Car Information.

Recommendations

Parts

MG parts spares and accessories are available for MG T Series (TA, MG TB, MG TC, MG TD, MG TF), Magnette, MGA, Twin cam, MGB, MGBGT, MGC, MGC GT, MG Midget, Sprite and other MG models from British car spares company LBCarCo.

MG Midget and Sprite Technical - 1275 rockers

I replaced the rocker shaft on my 1275 midget but the rockers don't seem to line up with the valve stems well at all - many are considerably off centre... Did I screw up or is that normal?
Simon Fryer

Hi Simon

You have to mess around with shims to get them to line up.

Peter
peter burgess

Did you just change the shaft or the whole assembly?
Dave O'Neill 2

I just changed the shaft - all the bits that fit on it are original...
Simon Fryer

As Peter says, add and remove shims as necessary, in order to get the rocker pads positioned as best you can over the valve stems. Due to the valve spacing, you will never get all of the rockers exactly central.

Also, check that the rocker pads are oval, rather than round - assuming that you have the pressed steel rockers. If they are round, a PO has probably fitted rockers from a 1098 engine, which will never sit properly over the valve stems...and won't lift as high, either.
Dave O'Neill 2

thanks Dave & Peter but I'm not sure shims are the answer... there were no shims on there when I took it apart and as I only changed the shaft no dimensions have changed in the process. Might there be another explanation?

Simon Fryer

BTW rocker pads are definitely oval
Simon Fryer

The rockers and pedestals may have been previously matched and 'faced' to optimise their position - and you've mixed up the running order. See if you have any thick and thin ones.
f pollock


Simon,

I did the same thing a couple of weekends ago, replaced the rocker shaft, and found myself scratching my head over the same thing. After examining the contact patch on the rockers, I decided that I *had* put them back exactly as they had come out, even though a few of them appeared a bit off centre. So either the PO muddled them up and I've perpetuated it, or it's always been like that. I decided not to fret about it and put them back like they were.

Either way, the engine runs just fine, and my oil consumption seems to have gone down, which was the aim.
MarkH1

The reason that 1275 rockers don't seem to line up on the rockers is down to the fact that the engine was originally designed with much smaller valves - anyone who has compared a 850 Mini head with a 1275 Cooper S or MG Metro head will know this... The cylinder head stud spacing has remained unaltered but the valve head diameter places the valve stem in a completely different place on 1300 engines. Accordingly the rockers are oval but still do not often sit exactly centrally over the valve stem (unless you add shims) The later (horrible) A+ rocker was a huge lump of scintered steel for the same reason. I suspect if you look at the wear marks on your apparently misspaced rockers you will see that they have always been so...

Cheers

James
James Bilsland

Guys, if my rocker pads are worn, as is the shaft, can I replace them with the scintered type found on minispares? I assume if I grind the pad flat I will have ground through the case hardening.
Robin Cohen

The pads can be faced and retreated but the bushes will need replacing, drilling and reaming to size which is the main cost. I had this done many times on a set of lightened S rockers I religiously swapped from engine to engine but I found the bushes and shafts always prone to wear and readjusting the valves on a regular basis became the norm. About 5 years ago I chucked the forged ones away for new sintered ones and have found nothing but benefits. They are quiet, have never once required adjustment and I'm still using the same (standard) shaft. Some people will argue they give slightly less lift and are therefore undesirable for high lift cams, but it doesn't take a lot of wear for the initial advantage of a numerically higher 1.3 ratio rocker to be wiped off.
f pollock

This thread was discussed between 08/12/2009 and 11/12/2009

MG Midget and Sprite Technical index

This thread is from the archive. The Live MG Midget and Sprite Technical BBS is active now.