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MG MG Y Type - Rocker Shaft

This has puzzled me for a while. Most of the wear on the rocker shaft occurs underneath the shaft, where maximum pressure from both the pushrods and valve springs is exerted. The oil holes are in the top of the shaft and also line up with the holes in the rocker arms which spurt out oil at realtively high pressure.

What is the logic behind this arrangement and is there any benefit from reversing the shaft so that the oil holes are at the bottom (after drilling a new hole in the shaft to take the oil feed)
Dave
D P Jones

The logic, I believe, David is to prove full oil flow all around the shaft and bush.

Paul
Paul Barrow

Dave, have a read of an article I wrote in John James on-line mag 'Totally T-Type2' issue 27 back in December 2014 called 'Mods and Rockers' you can find it via http://ttypes.org/ttt2/mods-and-rockers This will explain why you have excess oil flowing out of the top of the rocker arms and the shaft not properly lubricated. Although my article was TA (and MPJG) based it also applies to XPAG engines, Mike Sherrell of 'TCs FOR EVER' fame always does this mod to XPAG engines he rebuilds.
Regards, Brian
Brian Rainbow

I cannot understand why the engine continued in production for so long after 1938 without any change to the rocker oil ways in spite of this knowledge. For some reason wear is remarkably small, even in the case where a restrictor is fitted to the oil supply as I did many years ago. Perhaps the improved quality of the oil has helped to reduce wear. Bryan

PS oil emerging from the rockers does help to confirm that it is circulating, and perhaps the rocker cover helps as a oil cooler [if painted black].
B Mellem

Hi Dave,

For about 45 years I have run my rocker shafts upside down in my road TC and my S/C race TC. To do so, it is necessary to drill a new supply hole into the shaft as the shaft must be turned "end-over" to keep the keyways on the correct side. A new hole is easy to drill once the case-hardening has been ground away with a tiny stone in a "Dremmel". I obviously agree that the supply to the rockers should be on the load side. I do not block off the rocker holes as I believe the oil which exits will be shaken along to the valve end which (I believe) needs lubrication like the pushrod ball does.

Under racing conditions it is not uncommon for shafts to break at the supply hole inside the rearmost pedestal. This can happen whether the shaft is inverted or not. HOWEVER ... if the shaft is inverted, it is an opportunity to remove that weak point. Since breaking a shaft about 25 years ago, I now invert the shaft and drill the supply hole in the SIDE of the shaft and grind a groove inside the pedestal from pedestal hole to shaft supply hole. The groove usually breaks in to the 8mm bolt hole so I use a star washer (not split washer) to lock/seal that bolt head.

I have seen several broken shafts at the rear pedestal but Brian's is the first I have heard of breaking at any other point. I have uploaded an image of an article I wrote for MG Car Club of South Australia magazine in the mid 70s. (Hence the old writing.) It describes how adjustments can be made to prevent the shaft "rattling around" in the pedestals. I will need to upload the second page to another post. Perhaps loose pedestals could cause shaft breakage.

Bob Schapel

R L Schapel

Hi Dave,

The second page of the article.

Bob

R L Schapel

Hi there, I have just read your 1970s article, and page 2 states that the cam followers are hardened throughout. This is not correct, the followers are made from chilled cast iron. This means that there was a small billet of iron at each end of the cylindrical hollow in the casting box. One billet would be shaped to roughly form the flat end of the follower and the other to roughly form the concave end, and both would have been dipped in a non-stick solution. When the liquid iron hit these billets the cam follower ends would have heat drawn away, or be chilled, quicker than around the circular body, and this would induce a slight hardening, to the depth of just over 1mm, at the ends.
The holes in the cam follower sides are for the coring out to hold the sand in the middle, thus forming the hollow centres, and the cam followers were probably cast six or more at a time.
After removal from the casting boxes the followers would be centerless ground to give the cylindrical form. Then the flat end (supposedly slightly domed, but not found on new ones I bought years ago) would be ground on either a cylindrical or surface grinder, and the hollow end would be tidied up on a cylindrical grinder. Neither operation would remove much metal to avoid removing what shallow hardening there was. There was no subsequent hardening, and there couldn't be, as the followers might then be harder tham the camshaft lobes, although we all know they both wear rapidly anyway.
R A WILSON

Obviously 'tham' should be 'than', and I checked at least six times !!
R A WILSON

Thanks guys, that cleared up the mystery. I have inverted my rocker shaft, after driling a new hole, lets see what difference that now makes. Inverting the shaft does make more sense to me.
David
D P Jones

Are the cam followers designed to rotate, my concern is if reground the profile may be lost. Why is it that after time the surface shows signs of crazing surely it should work harden. In saying that in my very high mileage engine I have not found a cam follower actually break up.

One word of caution is that I found modern replacement cam follower oil holes are incorrect for the Y low lift cam shaft. Only with the T Type camshaft does the oil holes rise enough in the chest. Bryan
B Mellem

The cam followers are designed to rotate in use. Their positions are set approx 1mm left or right of their respective cam lobes (forward or back along the length of the cam) but their centrelines still intersect when looking along the cam from the front. This can be seen by looking, from above, down the empty follower housings onto a camshaft.
Thus the line of contact of a cam lobe on a follower is longer on one side of the follower centre than on the other side. As the cam rotates, each lobe will put a sideways force spread uniformly along the line of contact. Thus there will be more sideways force one side of the follower centreline than the other, and this will set the follower rotating; this in turn will prevent the lobe from wearing a groove in it's follower.
However, because the rotation creates a sideways force, there must be friction along the line of contact, which rather defeats the purpose of the oil, and probably explains why the follower faces suffer from crazing and pitting. As an aside, if the cam followers were domed, the only points of contact would be in the centres ??
The lack of work hardening may be because the followers are cast, with the ends chill hardened, rather than forged. Oil hardening might have been better, but more expensive.
The follower side holes are not oil holes - see my earlier notes - and the hollow centres will very quickly fill with oil.
R A WILSON

With the replacement followers purchased I found the oil entry holes were drilled a few mm lower than the original ones, so as the cam lift is only about 6mm on the YA these said oil entry holes never raised above the horizon in the chest. No problem for me since I fitted a TF cam. Just something to look out for. Bryan
B Mellem

Thanks R.A.

Yes, I should have re-read my old article before uploading it. In about 1970 I was told, by an old MG specialist, that "chilled" meant the hardening went right through. I have since learnt that was incorrect, so I should modify that bit (or better still, re-write the article). I should also modify the "ground flat" bit. Despite all this I have found that the hardening is deep enough for cam followers to be re-faced. I must chop up an old follower one day to double-check how far they can be refaced.

Thanks for the information re how the followers were made. I had no idea about those details.

Bob Schapel
R L Schapel

Should have also mentioned - I do not think it is a good idea to rotate the rocker shaft, as in the correct position, each time a rocker swivels to open a valve, the shaft and rocker drillings line up and some oil is pumped into the rocker. This oil should not normally go out the top as the balls** pressed in prevent this, but the oil will go down the side drilling to come out by the threads of the ball ended adjusting screw. This oil will dribble down, lubricating both ends of the pushrod, then the sides of the cam follower. The holes in the sides of the followers are from the 'fingers' which hold the centre sand core of each follower during casting, and would not be drilled out later. With a follower on the camshaft base circle these holes are either above or below the housing in the block. Thus they provide a secondary function of allowing oil to flow through a follower*** to lubricate the follower underside. Some oil also gets there from being thrown out as the crank rotates, but in either case that takes time after a cold start, so is another time when wear on the follower face will be high. So ensure the rocker drillings are plugged at the top, and probably better not to rotate the shaft.
** All my rockers are plugged, so I did not know that some, incorrectly, were not plugged.
*** Possibly the people who made the replacement followers did not realise the secondary function of the holes, and put them in an inappropriate position.
R A WILSON

Hi RA,
I have played with XPAGs (and XPAWs) for over 50 years, including owning/working on two Y Tourers, driving a road TC since 1968 and racing a s/c TC "special" since 1972. As a result, I have rebuilt many XPAG engines and accumulated lots of spares, yet, despite seeing dozens of rocker assemblies, I can not remember seeing any which were plugged at the top. Perhaps the plugs were done for a short time by the factory? ... maybe early or late? (Unless they are a mod done by other owners or didn't come that way to Australia.) It might be a good idea but I would be concerned that it might result in lack of lubrication to the valve end.
Bob Schapel
R L Schapel

Hi - my TD was made in 1951 for export, not known where, and came back to the UK in 1960. It was then sold with a replacement engine, which is the one I am referring to, but I do not know if the replacement engine was fitted abroad, or by the importer - I didn't buy the car until 1968. There is a Morris Engines service sheet dated 1938 advising dealers to fit plugs in the rockers if they are missing, but I haven't seen a copy, nor can I find a display on the internet - I would be grateful if anyone can post a link. However, for my engine I cannot believe in the fifties a dealer would remember a 1938 service leaflet, especially after WW2. Thus I assume the plugs in my rockers were fitted by the factory. I have also seen photos of plugged rockers on this forum or in TT2. The plugs also make sense of the rocker cross drilling, otherwise without the plug all the oil would issue from the top, with none going via the pushrods.
However, I did wonder about the valve gear, although with the shrouds almost no oil will get to the valve guides anyway. The interface between the rockers and the valve stems is a problem, as the only way oil can get there is out of the sides of the rockers along the shaft, then generally thrown into the air by the action of the rockers. It is rather haphazard, but in my engine the rocker/valve stem interfaces, as well as the top of the cylinder head, are normally covered with oil when I remove the rocker cover after a run.
Possibly it was just another problem with the XPAG/XPEG, added to the inability to increase it's capacity, that caused Leonard Lord to abandon the engine when Austin and Morris combined, although it is just possible that Lord was a bit biased.
R A WILSON

Sorry, it is TTT2, issue 27 in Dec 2014. Also mentioned by Don Jackson in the Octagon Bulletin, issue 198 in July 1986, which I have not read. I still have not read the actual Morris service sheet.
R A WILSON

Something else to take into account - the XPAG was not produced until 1939, although the XPJM/XPJW engines on which it was based were produced in 1938. However, the service sheet is March 1938, so it is more likely to refer to the previous MPJM/MPJW/MPJG engines, which came out in 1935, although I do not know what their rockers look like. Nevertheless, the engines were similar OHV engines, so I would have thought the warning would still apply - and apparently Mike Sherrell advises to plug the holes.
Gets nice and complicated !
R A WILSON

Attached is an image of rockers on a pre-war Morris 10 engine which has 1 DEC 38 cast into the head. The rockers look the same as XPAG rockers, although they might be slightly lighter in the casting between shaft and adjuster. The holes are not plugged. As with the TB, the engine does not have a timing chain tensioner. The most interesting point is that there is no rectangular oil drain cast between pushrods 4 and 5. ALL the oil had to drain down the pushrod tubes. The pushrods are slimmer than XPAG. Another Morris 10 head I have, dated 1 JUN 39, does have the familiar cast drain.
Bob Schapel

R L Schapel

Thank you for the photo of the Morris XPJM engine. The 1938 service sheet, issued by the Morris Engines service dept, does not seem to have encouraged the engine assemblers to press the ball bearings into the rocker holes. The service sheet may only have applied to the earlier MPJM/MPJW/MPJG engines, and it would be interesting to hear comments from TA owners with original engines, but I think the 'plug' requirement would have carried over to the XPJM/XPJW/XPAG/XPAW/XPEG engines.
The knitting needle pushrods were only fitted to the XPJM/XPJW engines - it was MG who got them changed to the tubular type as they wanted their XPAG engine to rev higher, and they thought the knitting needles would bend.
The rocker sketch in TTT2 issue 27 is slightly unclear; where the ball ended adjusting screw fits the internal thread ends just above the cross-drilling. Below this the hole is opened out to just larger than the thread OD, otherwise the oil would not come out.
(Still a puzzle, and would be nice to know what Don Jackson (Octagon Bulletin) and Mike Sherrell say, and to read the 1938 service sheet).
R A WILSON

I have a spare engine, which I found in a scrapyard forty years ago, but had never really examined. I now find that none of it's rockers is plugged - not sure if that does or does not assist the discussion !
R A WILSON

I don't believe those engine designers were not aware of the lubrication issues, after all the MG overhead cam's were capable of greater specific power outputs than any engines in the world. Perhaps a hot high velocity jet of oil from the rockers expanding into a low velocity spray has something to do with it.
When I first ran my model steam locomotive on air at 20 deg C to my surprise the exhaust blast pipe became coated in ice. We were rather good at engine design then. Bryan
B Mellem

This thread was discussed between 19/08/2016 and 28/09/2016

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