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MG TD TF 1500 - Rocker Shaft Diameter

I have now found the source of the rattle that was loudest when I placed my stethoscope probe on the inlet manifold. The case hardening on the rocker shaft has exfoliated under rockers 4 and 5. I am about to place an order for a new shaft and eight bushes from the Octagon Car Club (they appear to be the cheapest). I have measured the diameter of the shaft where it sits under the pedestals and is thus unworn and it is 0.59" or 14.99 m/m. Will I need to ream out the bushes once I have pressed them in? I don't have a reamer of the sizes above and will have to buy one. Do I need a 15 m/m one? I know that the threads on an EXPAG are metric but though the other dimensions were imperial. 0.59" isn't a standard size and I don't want to buy a metric reamer only to find it is not the correct one.

Thanks in advance

Jan T
J Targosz

Jan. Those bushes will need to be reamed - even if they fit the shaft when loose, they won't when pressed into the rockers. I would use an expanding reamer to take out the I.D. until they fit.
Dave H
Dave Hill

Jan. The bushings need to be honed to fit. Take them to a machine shop to get them done. The clearance between the shaft and the bushing is a lot tighter than you think. Reaming is problematic, and the size of the reamed hole will vary depending on the lubricant used and adjusted the reamer(I'm not talking about an adjustable reamer, there are techniques to make a solid reamer cut oversize or undersize). Again honing is how the rocker arm bushings are fit to the shaft. If it's not right you get low oil pressure.

Butch
R Taras

Most of the dimensions on the XPJM Morris** engine, from which the XPAG*** and XPEG engines were developed, were metric. The ones most known about are the bore at 63.5mm, 66.5mm or 72mm; the stroke at 90mm; the main bearing dia at 52mm and the big end bearing dia at 45mm. However, bore oversizes were imperial, but crank regrinds were metric, which for the first regrind was a common cause of tight bearings.
I think in the UK Bentley was the first to start designing engines using the metric system.
** XPJW when in a Wolseley.
*** the XPAW engine is the same as the XPAG/SC2 engine.
('exfoliate' ??).
R A WILSON

I have now pressed out the original bushes and they are the split type. These don't take kindly to being reamed with a parallel reamer since the cutters "drop" into the join and chatter. Adjustable reamers are parallel so it looks like I will have to use a spiral 15mm one or find someone who has a hone that will accommodate a 15mm bore. However, I eventually bought all the parts I needed from Peter Edney and he tells me that often there is no need to open out the bushes after pressing in. He advised me not to buy a reamer until I have found out for sure. Also has anyone recently priced up the thrust washers that fit next to the rocker shaft spacer springs. They are about 20 thou thick with a 15mm bore, very similar to normal washers. They are about £4 each and you need 10! Their cost is more than the shaft and more than 8 bushes.

Jan T
J Targosz

The new bushes and shaft have arrived. The bushes are an absolute b*****d to fit. They are split and you need to turn up a collar that is a tight fit over the bush and press the bush through this into the rocker. If you don't do this the bush opens as you start to press and you can easily ruin it. Don't ask me how I know. Once I have reamed the bushes to fit the new shaft I will fit the shaft between centres in my lathe, slip a rocker over this and drive it with a catch plate so I can true the faces up really square with the bore. I have tried them with a file and a carbide tool should do the job. I do have a question though. What's the opinion on fitting bronze thrust washers between the rockers and spacer springs. Early OHC MG engines have such washers but instead of springs have aluminium spacer tubes. I do have original steel thrust washers but bronze on steel will be better than steel on steel.

Cheers

Jan T
J Targosz

Jan
When my 53 TD was first put back together, having been taken apart by someone else. I has a set of Bronze spacers that fit between the rocker instead of the springs. The idea was that the engine would end up Stage 5 tuned and had all the other bits to do that. Two 1 1/2"SU's two fuel pumps, Extraction exhaust front pipe with an Arbath dual box tail pipe, TF Larger valves, skimmed head & all moving parts balanced.
I assumed the rocker spacers were to prevent any movement when doing high revs.
They are still fitted now 42 years later and I still get 50 to 60 psi on the oil pressure even though the engine is now somewhat tired.
I removed a lot of the go faster stuff 20 years ago as I did not want o ware it our so fast. I guess as you get older priorities change :)

Interestingly I have noted that there is a little float in the rocker assy. now - possibly about 1/16" overall. So it may be time to look at it again. Even putting back the center Spring and thrust washers would alleviate any slop.
But give the old girl her due. Runs like a top with just a few rattled. I do need a new cam and tappets.
That's on the to-do list.
Rod


R D Jones - Ex Pat

This thread was discussed between 21/06/2016 and 22/06/2016

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