Hi Marty, As per the previous posted comment, the shims were introduced under the centre pedestals as the early engines suffered from premature wear in the pedestal bores due to the rocker shaft spinning, which was unwanted. The BMC technical boffins came up with the shim idea to create a 'bow' in the rocker shaft, preventing it from rotating.... A bit 'Heath Robinson', but it's a cheap and simple solution that cured the problem. Looking forward to the next installment 👍.
Firstly thank you both, Carsten and David for the comments, I went a looking in my manual to see what's what. You are both correct, the manual references two shims under the center pedestals. On both the engines I have stripped there was no shims installed. Right now, I'm going to leave as is, I'm not loosening the head off again and replacing the head gaskets again, I've had to do this once already due to the issue with the tappet adjusting screws and getting the pedestals machined in the first place. Thankfully I didn't put the shim in the pedestal with the small amount of clearance, I could just move the rocker shaft with all the bolts tightened with some assistance. Due to there being an anti-rotation pin in the pedestal with the oil way in it I would assume that the misalignment would be to prevent fretting rather than turning. Also, I took the rocker cover off to just check things again and found that I hadn't remembered to open up the split pin in the end of the rocker shaft, so thank you for sparking that "train of thought".
The factory used to install a thin shim in the 2 middle pedestals, apparently to add some tension to further keep the rocker shaft from movement. Some question this.
Hi Marty, As per the previous posted comment, the shims were introduced under the centre pedestals as the early engines suffered from premature wear in the pedestal bores due to the rocker shaft spinning, which was unwanted.
The BMC technical boffins came up with the shim idea to create a 'bow' in the rocker shaft, preventing it from rotating.... A bit 'Heath Robinson', but it's a cheap and simple solution that cured the problem.
Looking forward to the next installment 👍.
Firstly thank you both, Carsten and David for the comments, I went a looking in my manual to see what's what. You are both correct, the manual references two shims under the center pedestals. On both the engines I have stripped there was no shims installed. Right now, I'm going to leave as is, I'm not loosening the head off again and replacing the head gaskets again, I've had to do this once already due to the issue with the tappet adjusting screws and getting the pedestals machined in the first place.
Thankfully I didn't put the shim in the pedestal with the small amount of clearance, I could just move the rocker shaft with all the bolts tightened with some assistance. Due to there being an anti-rotation pin in the pedestal with the oil way in it I would assume that the misalignment would be to prevent fretting rather than turning.
Also, I took the rocker cover off to just check things again and found that I hadn't remembered to open up the split pin in the end of the rocker shaft, so thank you for sparking that "train of thought".
The factory used to install a thin shim in the 2 middle pedestals, apparently to add some tension to further keep the rocker shaft from movement. Some question this.
Hi David, Please see my response to Carsten.