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MG TD TF 1500 - Broken rocker shaft?

Has anyone experienced a broken rocker shaft, breaking at the oil feed hole in the rear pedestal?
F Filangeri

You're not alone Frank--There was a discussion about this issue a while back
You need to contact Bob Schapel from South Australia, he has turned his over so the oil hole is at the top and modified the oil supply to suit, he explained how to do it on here but I can't find it in the archives, but it'd be there somewhere

willy
William Revit

Found it
It's under MGY---Rocker shaft in the archives-August 2016
William Revit

Hi Frank,
I have enjoyed watching your Youtube race videos!

Yes, broken shaft at the oil feed is fairly common in competition cars. Less common in quietly driven cars.

The hole is a "stress raiser" in a bad spot. The force of the rear rocker tries to lift the rear of the shaft. I guess more stress in comp cars due to the higher revs, bigger valves with stronger springs against higher combustion pressures.

Easily solved by turning the shaft upside-down (end over end). The supply holes to each rocker finish up on the under-side where the oil supply is needed most. Plenty of oil gets around to the upper side to exit the hole at top to oil the pushrod and valve ends.

The only complication is to arrange another oil feed without weakening the bottom of the shaft. I drill a feed hole in the SIDE of the shaft and grind a groove inside the rear pedestal (NOT the split side) so oil can get to that hole. (Note that the groove might break into the bolt hole, but that doesn't matter as long as you don't use a split washer under the bolt head where oil can leak out.) There are other ways to do it, but I think this is easiest.

I have used this tactic in my race TC for over 30 years without any problems.

Good luck with your repair. Let me know if any of the above needs further explanation.
Bob Schapel
Bob Schapel

Bob,

Glad you are enjoying the videos! More to come starting May. I have come up with an alternate solution after breaking shafts twice and having a friend break one on the dyno recently. See attached pic for a custom pedestal that supports the shaft end. Stole the idea from what I saw on a Spitfire engine. Made an initial run of seven for myself and several other racers. Works really well and would like to see if there is interest in the community to do another run of perhaps 10 or so to keep cost down. Have commitments for two more already. Cost will be in the $225-250 US range. No mods to anything required, just replace the rear pedestal.

Good racing,

Frank


F Filangeri

Hi Frank,
Your idea looks good although the simple fix I described has worked perfectly well for me.

Your idea might have an advantage if running ultra strong valve springs. Then one of those on each end might be needed.

Cheers from South Australia,
Bob
Bob Schapel

Bob,

Just one question on your fix. Do you plug the original oil feed hole in the shaft that now is in the forward pedestal or just let it leak a wee bit?

One other thing I now do is chamfer and polish the original oil feed hole to eliminate any microcracks from the drilling operation. From what I have seen the the holes are left "as drilled".

Frank
F Filangeri

After breaking a shaft, I made a new one from stronger material 4140HT and had it chromed for surface hardness.
I'm surprised no one has had an improved batch made up, but it's probable people wouldn't be willing to pay up for a better shaft.
Charlie
c mac quarrie

Frank,
No real need to plug the original oil feed hole. It finishes up facing upwards at the front, where it should be clamped shut in the front pedestal.

That is another separate issue. The spacer washers in the pedestals should be thinned down slightly if the thicker bolt does not clamp the shaft when it is tight. (I rub spacers down with emery paper on glass.) Fit can be tested using a vice. If the shaft can slop up and down in the pedestals when the bolts are tight, it could cause extra noise and/or upset valve clearance setting. I have found many shafts which are not clamped firmly despite pedestal bolts being tight. The rocker shafts from such situations sometimes have a "hammered" effect at the four points where they go through the pedestals.

I think your chamfer and polish tactic should help. Sharp edges and micro-cracks are not good.

Charlie, I had the rocker shaft in my road TC hard chromed in the early 1970s. It has been untouched since. I did it to repair a worn shaft. So long ago I can't remember if I also flipped that shaft. Better steel must be be an advantage, but the simple "flip and modify supply" costs nothing and is so easy to do.
Bob
Bob Schapel

Last year I spoke with the guys from Rocker Arms Unlimited, the go-to rebuilders of rocker gear. They told me they were so dissatisfied with the poor quality of new (Asian) rocker shafts that they don't order one from the usual suspect, they have originals hard-chromed and centerless-ground back down to the proper diameter.

Other than making one up out of better-quality materials, as Charlie suggests above, this seems the best way to maintain quality. I would say that a good shaft is a necessity especially when the stronger 150# Mark II/TF valve springs, and certainly with a roller cam set-up. I only use 120# springs these days, as I have little need to rev over 5,000RPM in normal driving. If your regular driving frequently leads you over 5,000 RPM use the stronger springs, but expect increased cam, follower and rocker wear, also.

Tom Lange
MGT Repair
t lange

I like your thinking Tom. No need for any more spring tension than is needed.
Lightening valve train components reduces the spring tension requirements. A lot can be removed from cam followers (see image), valve-spring top washers and rockers.
I run old 150# springs in my race TC. I rev it to 6500 most of the time but occasionally 7000. I'm sure the lightening helps that being achievable.

In 1995, when I built the current motor, I planned on some top end mods once the engine was tested. I never got to do them because it went so well as it was. I'm guessing my planned top-end mods are nothing new. I planned to shorten the rocker pedestals, pushrods, valves and springs to save weight. I was going to use more open-coil springs of about the same tension or slightly less. ..... Perhaps one day?
Cheers,
Bob


Bob Schapel

This thread was discussed between 12/04/2022 and 15/04/2022

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