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MG TD TF 1500 - Broken rocker shaft thread

Several months back someone posted some pictures of their broken rocker shaft and there was some discussion about the quality of the new shafts and the differences. I would like to have a look at that thread as the rocker shaft on the engine I am assembling isn't looking all that great. Try as I may I cannot find that thread in the archives. Can someone help me out here?

Thanks
L E D LaVerne

LaVerne. I think that discussion may have been on the MGExp
W A Chasser

Thanks Bill. I had a look there as well and could not find it. I was pretty sure it was on this site, but I have been wrong before and certainly will be again I'm sure.
L E D LaVerne

What would cause a rocker shaft to break other than seized bushings? Seems like there is little torque in that shaft.
Christopher Couper

That was what the discussion was about along with the quality of those supplied today.
L E D LaVerne

Hi LaVerne,

I posted some photos of my broken rocker shaft last year, so it should be in the archives. I put the original shaft back in and took the old shaft down to an engineer to make a new one. He said that it had been cracked for a while, which considering I had only done about 1500kms running my engine in, surprised me. I bought new shafts from Moss, which looked better quality, but I did have them crack tested before fitting. One thing I did notice in this exercise, was that there was play in the pedestals. I slowly sanded down the spacers until I had a slight grip.

Bernie
B W Wood

Bernie could you reactivate that thread for me please.
L E D LaVerne

I tried to find the thread but without luck. I seem to remember some replacement shafts had been drilled from each end rather than through drilled. This led to out of alignment where they met causing a stress point and fracture.
Ray TF 2884
Ray Lee

Ray, try searching by selecting "threads started by me" button.

Frank
TF1414
Frank Cronin

I had a look under threads posted by me and its not there, I also searched the archive because there used to be a couple of threads on this and I cannot find any, so I wonder what happened to them?

Here is one of the photos.

B W Wood

I can remember the discussion it expanded into valve spring strength with roller cams and also a bit by Bob from Aust about turning the shaft over

still looking
William Revit

Thanks for the effort Bernie.
L E D LaVerne


Ahhh-I remember now---------------

You won't find it, it was taken down--

At the time there was a similar dicussion going on in the MGB section, A guy from NSW or Queensland had broken a shaft next to No2 valve, which is quite rare and his shaft had been drilled way off centre and if I remember correctly the hole was much larger than normal leaving decreased wall thickness-

BUT
On this TF TD section the shaft had broken at the oil hole and Bob (Aust) had suggested turning the new shaft over and modifying the pedestal to feed oil into the shaft
The conversation expanded into why it broke, including maybe faulty shaft, valve interfearance, and valve springs, then onto the very high spring pressures used on the roller cam kit, I made a few observations at the time and put forward a suggestion about the roller kit spring strengths which got dismissed, so asked for the spec of the springs, seat pressure and spring rate as there was a bit of a dark area as to if the pressures quoted were actual spring rate or seat pressure and also suggested the use of lighter spring seat pressure if it was seat pressure being quoted and also that a rev kit would enable the spring pressures to be dropped down taking the pressure off the rocker shaft--I think I had quoted a manufacturers name but not 100% sure-----The next day when I went to check the response on here the whole thing had gone and can remember thinking at the time---someone with influence didn't like that then

willy
William Revit

I recall that some shafts were drilled way off center, resulting in very thin walls on one side. Pretty sure there were pictures of new T-series shafts with off center holes. I think it said replacement shafts have been made by various manufacturers over the years with different machining and metals. Common sense tells you that higher spring pressures would exacerbate any weakness, and several suggested hard chroming and rebuilding original if possible. George
George Butz III

LED, I apologize in advance if this post is offends anyone, but the following contains major comments/conclusions from the thread in question. Hope it helps:

---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------

MG TD Broken Rocker Shafts:

P Hehir, New South Wales, Australia
Anyone else experiencing this problem? Seems a few cars here in Oz with the stronger valve springs are having this issue. Info is currently being gathered from owners here & I'll post more details as they come to light. Early indications are that the longitudinal oil gallery on some new shafts is a larger diameter than it was on the original shaft, which reduces the wall section. This gallery is 1/4" (16/64") whereas the original was 11/64". Most breakages occur around the #4 exhaust valve. In some cases this occurs after just a few kilometers. One car broke two, the second after about 2 kilometers! Cheers Peter TD 5801


R Taylor, Australia
Peter, A friend here with an A suffered a broken rocker shaft - a little over mid length from the front. This was a few years ago now. Not sure how long that shaft had been in the car but it was an engine used for sport and touring and had been rebuilt a couple of times prior to the discovery. The owner knows how to rebuild his engines.

We checked the broken ends and discovered the shaft appeared to have been drilled from both ends but not true to centre. The drillings were just off enough to have created a point of weakness under tension. Might be worth considering in terms of supply of replacements. Regards Roger


R L Schapel, South Australia, Australia
Hi guys, the oil supply hole is a weak point and is where the original T series shafts occasionally break. With original valve springs (or the slightly stronger factory springs) it probably only happens after many years of fatigue. Those I know of, were on race cars, so revs might contribute. (harmonics?)

My solution is to turn the shaft over (end for end because the keyways have to stay on the left side). This removes the offending oil supply hole from the stress area. I drill a new supply hole in the right hand SIDE of the shaft and grind a groove inside the pedestal tunnel to take oil around to the hole in the side. Because the groove breaches into the small bolt hole, I use a washer which will not allow oil to escape, from under the bolt head. This operation puts the individual rocker feed holes on the bottom (load) side of the shaft which I see as another improvement.
I have run inverted rocker shafts in my road TC and race TC for about 45 years. I added the side drilling and grooving to my method 22 years ago.

The news of new shafts with less wall thickness and bigger oil supply hole is new to me. I agree they are probably more fragile than originals. Bob Schapel
When the shaft is inverted (end for end) the original oil supply hole becomes a useless hole at the top, inside the front pedestal. However, because this hole is on the TOP of the shaft it is no longer a weak point. The end rockers, when under load, are trying to bend the unsupported ends of the shaft UPWARDS. The top of the shaft, inside the pedestal, is therefore in "compression" (crush) and so a crack won't start there. When the hole was at the bottom, the area around the hole was in "tension" (pulling apart) so the hole provided a weak point for a crack to start.

Thanks guys for the "heads up" on new rocker shafts. I often learn something new on this forum. I bought a new shaft on eBay about a year ago but haven't used it yet. I dug it out of the shed today and found it fits your description with the 1/4" bore and 4mm wall thickness. (Fortunately it does appear to have been drilled very centrally.) I guess it should be OK for me because I don't use high spring pressures. Cheers, Bob Schapel


J Walton, New South Wales, Australia
Roger, on inspection of a two long rocker shafts yesterday at a friend’s place they also had been drilled off centre creating a thin wall on one side and obviously a thicker wall thickness on the opposite side. John...Sydney


J Walton, New South Wales, Australia
Bob, when I looked at the end view of the shaft, that is the thread view, I couldn't see the hole being off centre. However, when I viewed the hole in the broken piece it came obvious it was off centre by 0.030". I would find it to be very difficult to visually determine in a new shaft if the hole was off centre.
I will try and take a photo later today. John...Sydney


t lange, Maine, USA, tlange@acadia.net
A rebuilder here in the States is so dissatisfied with the quality of current rocker shafts that he has originals hard-chromed and then cenerless-ground back to spec. Needless to say, he does my rebuilding. Tom Lange MGT Repair


George Butz, Florida, USA
I have a shaft about 10 years old with an Abingdon Spares sticker on it. Visually the center is straight and smooth. The wall thickness at the ends where threaded is about 4mm. Close up pictures of broken ones would be interesting, and good to trace back to the likely single manufacturer. George


B W Wood, New Zealand
Peter, I am just assembling an engine with Len's Roller cam, lifters and roller rockers with Lens very high pressure springs (170+). I had bought a new long rocker shaft from Moss and just checked it with an ID of 1/4". I have no way of checking for off-centered drilling. I am now a bit worried about using the new shaft, or the one in the car which I think was changed in the mid 70's. Are any of the machinists going to be available for purchase? Bernie TD8570 TF6344


William Revit, Tasmania
The reason for my comment on spring pressures is---and this is on a Chev with much bigger and heavier valves and regular high revs use. We ran 175lb seat pressure to get good results but the end result was the roller followers started cracking out from the roller pin, caused by the follower hammering on the cam with 30thou tappet clearance. Went back to 145lb seat pressure and ran a rev kit on the followers to keep them on the lobe all the time and like that it was super reliable and a lot easier on components like collets, caps rocker gear etc. willy


J Walton, New South Wales, Australia
Unfortunately I was unable to photograph the broken shaft as the battery in the camera went "kaput “so will try again in the next few days. However we measured the offset and the hole was 0.030" off centre with the thinner section exactly over the oil inlet hole. Is it any wonder it broke as that was the position where there was the smallest amount of material? John...Sydney


J Walton, New South Wales, Australia
Exactly Bob I agree 100% of what you are saying. And I also chamfer the oil inlet hole to the shaft.

It is also interesting to note in that the rockers themselves should be checked in accordance with Horst Schach book "The Complete MG TD Restoration Manual where he states on page 92 the casting numbers of the rockers and the location of each. For they are different on the short shaft than that of the long 147/8"shaft.

For those who don't have access to the book the castings numbers of the rockers for the long 147/8"shaft are......

1...168002
2...22557
3...22558
4...168001
5...168002
6...22557
7...22558
8...168001

The lone hole at rear of the shaft aligns with rear tower:

1,4,5,8 - These four rockers have narrow shoulders.
2,3,6,7 - These four rockers have wide shoulders.
Clip and washers both ends and washers at end of each spring.

John...Sydney
WHT

Thank you WHT. Of possible interest to add to the now missing information, The rocker shaft from the TD 1250 is clearly drilled off center. It also is plated. This is the original shaft on the engine.

L E D LaVerne

Interesting that after 57 years of sitting on a shelf assembled that there are raised areas where the rocker bushing grooves sat but yet it hasn't lifted from the shaft.

L E D LaVerne

WHT
That's the thread -or parts there of but there was a lot more than that-----
I couldn't remember how the MGB (MGA) shaft got involved, remembered it as being on another thread, but there it is
Had you saved that back then or is it somewhere in the archives we can find
Cheers
willy
William Revit

If I may intrude, I read that the TF shaft is 7/8ths of an inch longer, is that only on the 1500 engine? I had my shaft out when I replaced #5 rocker and noticed no wear groves in it, I don't have a receipt showing it was replaced during the head rebuild, just a receipt for the head project, but I guess anything is possible. If it's the original shaft, should there be wear groves visable? PJ
PJ Jennings

Hi Willy.

Unfortunately, I did not save the entire thread; just some of the major observations and comments. Hopefully, others can help piece it together since it was an important topic.
WHT

The early 14-inch shaft was replaced by a 14 7/8-inch shaft on later TD engines. The extra length allowed the rocker arms to increase bearing length 1/4" on the 1st, 4th, 5th and 8th rockers. The newer spring allows for addition of thrust washers.

Rocker #4 and #8, TC to Early TD, Part # SA2213/4
Rocker #4 and #8, Late TD to TF, Part # SA2213/5
Rocker #1 and #5, TC to Early TD, Part # SA2214/4
Rocker #1 and #5, Late TD to TF, Part # SA2214/5
Rocker #2 and #6, TC to TD to TF, Part # SA2215/4
Rocker #3 and #7, TC to TD to TF, Part # SA2216/4


WHT

Early and late rocker shaft configuration (should see wear on used shaft):

WHT

All good WHT-thanks
willy
William Revit

My Abingdon Performance Ltd. Roller cam kits have been on the market for 13 years with many hundreds of them sold. My own car had about 60,000 miles on the rocker shaft before I replaced it due to wear & another 20,000 miles on the new replacement.
Engine builders world wide that have Roller Cam experience have no concerns about the spring pressures of my springs (The lowest recommended for any roller cam).More than a few of these engine builders have been in business for 50-60 years, 2nd & 3rd generation.
ONE customer did have a new shaft break after 725 KM or 451 miles!!! More than a year later it has not happened again.
Chet Herbert was producing Roller Cam kits for T types from 1951 to about the early 1970"s with no record of broken rocker shafts.
Len Fanelli
Abingdon Performance Ltd.

Len Fanelli

This thread was discussed between 22/12/2019 and 24/12/2019

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