Mods and Rockers

Last year on a trip up to Aviemore for the ‘MG European Event of the Year’ I broke a rocker shaft on my TA. We did about 580 miles on the 4 day trip up to Aviemore, it was a bit windy and wet at times so I wore my cap with the ear flaps down. About 10 miles from Aviemore I took my cap off and could not believe the clatter from the engine.

On arrival at the hotel, I checked the tappets and found them all OK except No 2 exhaust, which was open to 25 thou, but the locknut was tight! I reset it to15 thou and thought that was the end of my problem.

On the first day we did a 100 mile run and the clatter returned, so again that night I checked the tappets, sure enough No 2 exhaust had opened up to 20 thou. I thought it must be a cam follower breaking up, nothing I can do about that so for the remaining few days of the event I reset No2 exhaust every evening after the runs.

It was the best MG event I have ever attended, so after all the final day celebrations we set off home, ear flaps down! I was fully expecting to call the recovery truck out but 3 days later I drove the old girl into the garage at home and immediately drained the oil. I have one of those magnetic drain plugs and was fully expecting to see bits of the broken cam follower stuck to the magnet, but there were no iron filings it was clean as a whistle!

Next morning I started to remove the cam-followers, I took off the rocker cover, undid the 8 bolts on the four rocker pillars and lifted the rocker shaft off. It fell into two parts having broken through the oil-feed hole for No 2 exhaust rocker (see photo 1).

Photo 1 – showing the broken rocker shaft.

Goodness only knows how old the rocker shaft was, but I had never heard of one breaking before, only wearing out. Over the years I had accumulated a number of complete rocker shafts from old engines that I had stripped, so I sorted out what I thought was the best one with least wear on the rocker pads. It was then that I noticed it did not have the small holes in the top of the rocker arms blanked off.

There was a Morris Engines Service Sheet published in March 1938 that told dealers to blank these holes off by hammering 1/8 inch ball bearings into the holes. If you look at photo 2 you can see various rockers with these holes either open or blanked off by various means, including using pop rivets! In photo 2 from left to right the hole is blanked off by a ball bearing, a grub screw, metal rod (too long sadly) and a pop rivet!

Photo 2 – showing various past ‘solutions’ for blanking off the small holes in the rocker arms.

I found an article by Don Jackson in an old ‘Octagon Bulletin’ #198 dated July 1986. It explains that “these holes should have been blanked off in production, so you are only correcting a fault that shouldn’t have occurred in the first place. The result will be proper pressure-fed lubrication of the rocker bushes, improved lubrication of the tappets, and a vast reduction in the amount of oil swilling around in the rocker cover. You will also gain a few pounds per square inch oil pressure as a bonus!” The diagram that Don drew is reproduced below (diagram 1) and explains the problem. If you have ever run your engine with the rocker cover off, the eight holes look like mini ‘oil geysers’, with loads of oil oozing out!

Diagram 1 –Don Jackson’s diagram referred to in the text.

I stripped the rocker shaft assembly down and started to rebuild it with a new rocker shaft. Be aware that the rocker shaft can only be fitted one way. On an MPJG engine the oil feed to the rocker shaft is via an external copper pipe from the main oil gallery in the block to the cylinder head. The feed goes directly under the rear rocker shaft support post and then up through a hole in the post to the rocker shaft. You must ensure that the oil-feed hole in the rocker shaft is at the ‘six o’clock’ position for the rear pillar support, if you get this wrong there will be no oil fed to the rockers. Once this is done you can then start to build up the rocker shaft assembly, starting from pillar number three make sure that the locating spacer washer fits in the key groove in the shaft. I have several rocker shafts with the key groves on different sides, all this means is that you need to turn the rocker pillar though 180 degrees.

In my case, before building up the assembly I had to clean and inspect each rocker arm and then block off the small hole in the top. The method I use is to tap the hole out with a 4BA tap, blow through with an airline to remove any swarf, then screw in a very short 4BA Allen headed grub screw secured using a bit of Loctite. I used 1/8 inch long Allen key headed grub screws purchased off eBay.

I found that I could tap the hole out without drilling it out to the correct 4BA tapping size (see photo 3).

Photo 3 – showing the equipment and materials used for blanking off the holes in the top of the rocker arms (which shouldn’t have been there in the first place!)

This mod is well worth doing on XPAG engines as well, I spoke to my old Aussie mate Mike Sherrell, he told me that he does this mod on all XPAG engines that he builds. Since fitting the new rocker assembly the engine is now a lot quieter, but sadly not as quiet as it should be! Maybe a new set of cam timing gears and a new timing chain will quieten it a bit more, but that can wait for the time being!

Brian Rainbow

Ed’s Note: Brian is Chairman of the MG Octagon Car Club and is also Registrar for the Tickford models, a job he does for the ‘T’ Register of the MG Car Club.

To join the MG Octagon Car Club go to the website – Membership subscriptions are fairly modest at £35 (UK) £37 (EU) and £39 (Rest of World).

14 thoughts on “Mods and Rockers

  1. STEVE says:

    Your rocker shaft doesn’t look warn, and it seems like it was getting enough oil,, maybe I am missing something,, How does plugging the hole in the rocker arm prevent the shaft breakage?


  2. Brian Rainbow says:

    plugging the hole in the rockers is not going to prevent the shaft from breaking! Plugging the holes in the rockers will solve an error in manufacturing that Morris Engines admitted in their Service Sheet in 1938. Oil will take the easiest route out to escape under pressure. They had to drill that hole to allow the oil to travel along the horizontal route to exit over the valve. What they failed to do and realised in 1938 was they should have blocked off the top part of the near vertical hole, hence the instruction to tap an 1/8 inch ball bearing into each hole.

    I had my broken shaft examined by a metallurgist friend at Rolls Royce, he said that the fracture over time was caused by that rocker hole not being slightly countersunk, of the 8 holes in the shaft two were not countersunk I have no idea how old that shaft was, it had been on the car for the 18 years that I have owned it.

  3. Peter Jones says:

    I too had the holes blocked in the rockers of my TC. However having a nice lot of oil swilling about over the very hot head can help cooling so I would think twice about blanking them off an XPAG engine.

    If oil pressure needs to be increased then perhaps looking at the pump and blow off valves would be a better option.

  4. Brian Rainbow says:

    I remember talking to you about it quite a few years ago. Didn’t I supply you with a complete used rocker-shaft, I’m sure that had ball bearings in all the holes. My current TA engine has run with the holes blanked off and still has too much oil lying on top of the head. I doubt whether hot engine oil offers much cooling to the cylinder head as someone suggested. Have you ever seen another OHV engine with holes on top of the rocker fingers? Have a look at BMC A Series and B Series rocker gear, they have no holes on the top, yet have the cam and followers in a similar configuration! Why on earth would Morris Engines publish a service sheet about it if it was not a problem. I have seen quite a few XPAG rocker shafts that were well worn, probably by not being lubricated properly.
    As you say you pays your money and make your choice….
    As you say you pays your money and takes your choice.

    • Martin Moore says:

      Hi Brian ,
      Only just got round to following up this article with the festive season intervening .
      I confirm that you did very kindly provide a complete rocker assembly with the holes suitably blanked off .
      I rebuilt the rockers with new shaft , new bearing inserts and refaced finger ends , though the curvature is a bit of guess work .the complete assembly is fitted to my spare cylindr head which has been called into service far too often in the last few years on account of blown head gaskets . I hope to have sorted this by fitting solid copper gasket and Evans waterless coolant . ( that was paying your money ! )
      Wishing everyone a very happy new year . Martin .
      Afraid this does not provide any more answers ,though I can see the logic in blanking .

  5. Laurent CASTEL says:

    Sorry for last message. A bit short. I guess it’s an error from Morris to initially forgetting blanking the holes. But someone may has discovered that it enhances the lubrication for the valve end of the rocker.

    For information. I’ve watched carefully the DVD “stripping the XPAG” from P. Edney. Althought his engine has many improvements that he explains. The rocker holes are not blanked !


  6. Huib Bruijstens says:

    Looking at that diagram one, I cannot see any oil coming through or out at the pushrod end since that hole is perfectly blocked by the setsrew? Anybody can explain how that should happen?

  7. Sandy Brainsky says:

    My 51 TD with original engine has unblocked holes. If the bulletin was released in 1938, curious that they are still be drilled in 1951? I will say the hole size is much smaller than 1/8 inch. Closer to a 32nd.

  8. Bruce Greaves says:

    Classic case of you pays your money and takes your chance. Oil like other fluids will take the path of least resistance.
    With the Rockers un blocked it will in the main shoot out of the hole as we know, thereby sending less oil to the rocker shaft bushing. With the hole blocked then most or all the oil should go to the bushing. There is no direct oil feed to the valve gear just spray and pray as I see it. The oil from the bushing will end up in the head casting and may help cooling FWIW. I wonder if there is a copy of this 1938 78 year old article from Morris /MG floating about somewhere in the archives ?

  9. Graeme Hogg says:

    I have three sets of XPAG rockers; one set ostensibly TF 1250 , but the other two probably TC or TD. All have the top and screw end oil holes unplugged. The top oil hole is a tad over 2.5mm.
    I also have a set of rockers from an MGB 18GB engine and have the cast rockers and they have open top oil holes but plugged screw end holes. The top hole will take a 2mm drill shank and the original workshop manual states it should be drilled 1.98mm if appropriate when bushes are renewed.
    I also rebuild my Healey 100/6 engine renewing the rocker bushes in the process and they too have open top holes and plugged screw end holes.
    Of note in the MGB manual is that the oil groove in the bushing must be at the bottom of the rocker and which seems to me to be common sense as that is the point of highest loading.
    I have replacement bushes to fit to an XPAG engine I am currently rebuilding and which have a pre-drilled oil hole within the oil groove area and which would appear to be incorrect. I shall re-drill the oil hole in the bush after fitting same with the groove at the bottom.
    Perhaps more oil escapes from the XPAG screw end holes than might be desirable?
    I am with Peter Jones on this issue.

  10. Graeme Hogg says:

    If I may, one more case study that may help to clarify the issue of, to paraphrase, “to plug or not to plug” the top rocker holes. Austin/Morris 1100 (A series engine) workshop manual, published 1965, advises to drill with a no.47 bit through the top hole and a no.43 bit through the screw end hole and plug only the latter with a rivet and secure with a weld.

  11. Steve Ball says:

    I know my rocker cover filled brim full with oil and therefore the tappet chest must also have been full? Mike Sherrell, in TCs Forever More, says his XPAGs do the same. I just went to the shed with tape measure and calculator; my alloy rocker cover holds about 3.5 litres and the tappet chest on an old block appears to hold another 0.9 litres or more. So that’s 4.4 litres of oil that aren’t in the sump.

    I gather the official oil capacity of an XPAG with TC sump is 5.1 litres.

    So my full rocker cover was leaving 0.6 litres which then had to fill the pickup pipe, the pump body and the oil filter, the galleries and the oil drillings throughout the engine…

    This engine destroyed itself within the first 400 miles, after a very, very expensive rebuild, to the puzzlement of all concerned. After reading your article above and doing my maths I reckon any XPAG that is filling its rocker cover should be on the edge of catastrophic oil starvation. Cornering with no sump baffle won’t help this. But this can’t be right or many XPAGs would wear out in super-low mileages. What say ye?

    My engine was rebuilt by a different builder, and is not back in the car yet, so I can’t say whether there was any restriction of the drain passages between head and sump or whether my rockers were badly worn and leaking extra oil. Before it is started I shall be tapping and plugging the rockers in both places to just leave a moistening supply to the tappet adjuster screw and I’ll also check that the oil drains from the head are clear. She’ll also get a proper sump baffle which Sherrell says the original TC lacked and desperately needed, and a 25psi low pressure warning light.

    Many thanks for the article. It may have saved me a lot of bother.

  12. Wm. Hyatt says:

    Typically rocker arms squirt holes are to hose down valve springs to cool them. It is another question if a low RPM, low HP such as XPAG really needs extra cooling oil.


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