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MG TD TF 1500 - .015' Valve Cover Tag Factory Explanation
|Over the years a number of questions have appeared about valve covers with the tag for setting the valves at .015", rather than the early .019" or later .012". Various suggestions have been posited for the very occasional occurrence of this tag on a valve cover, all speculatively.|
I was reviewing factory Service Information Bulletins from the 50's the other day, and found two that solve the riddle once and for all. One, dated 1.1.53, notes:
"Commencing at engine No: XPAG/TD.2/24116 a new camshaft [p/n 168553] has been fitted to the TD midget to improve wear on the tappet faces.
With this camshaft the valve clearance has been altered from .019" to .015"."
It goes on to list the new part numbers for the affected parts: camshaft, cylinder head cover assembly and valve clearance plate. The .015" valve cover plate is given p/n 162279
BUT: 2-1/2 months later on 19.3.53, MG issued the SAME document (I have issue 3) about the SAME 168553 cam, in which the only differences are that the .015" figure is replaced with .012", and the part number for the .012" plate is now 168729.
This pretty conclusively proves that for a brief 2.5-month period between January and March, 1953, the factory recommended using .015" as a valve setting, but later changed it to .012" for the same cam.
The instructions to dealers: "Note :- Manuals should have addendum slip added to comply." was clearly NOT followed - or at least I have never seen one!
I'm glad to put this one to rest. Unfortunately, there are other Service Memos that raise more questions than they answer!
|Very interesting and thanks for posting info! George|
|So which cam are we getting when buying a new one in stock configuration?|
|The Original Type Camshaft for MG TC, TD & TF 451-261 sold by Moss has a exhaust and intake valve setting clearance of .012 (hot)|
|Who knows? My guess is that it is closest to the 168553 cam, the .012", which was the last iteration of the standard MOWOG cam. But even that cam can be improved upon, which is why I use the RV grind from Delta Cam. |
There are so many cam grinds that your head will spin. Like engine oils, it's totally a matter of personal preference, and just as consistent as a flip of a coin. Just because a cam has a valve lash of .012 does not mean it is the stock cam!
|Tom, can you post a PDF or a photo of that service bulletin so that I (we?) can update the service manual? Thanks!|
|OK, so my engine # is 24722. This is after the change to .015 and later to .012. Mine are or were set at .015 but tend to be noisy. I don't know if I have the original cam, so it's a toss up as to where to set the clearance. If I go down to .012 will the tappets become louder? I can talk all day about gas turbine engines, but when it comes to piston engines I'm really in the dark most times. Guess I should own a biz jet instead of the TD :-)|
|I have engine 24126 just 10 after the change to .012.|
My builder told me to set to .012 and I had questioned him. he told me about the change.
When it came time to readjust, I set to .012
and it has quieted down a lot. seems to have the power I expected. Happy MG-er
|Tom is there any possibility they were just correcting a typo & that the mention of 15 thou was simply an error? Cheers|
Peter TD 5801
|.... or that going to .012 was quieter with no bad effects?|
|The service sheet is mum on the reasons for the change. It could have been for any of the reasons stated above, although I doubt it would have taken 3-1/2 months to correct a typo. I think the engineers changed their minds, perhaps after complaints of noise - but that's PURELY speculation on my part.|
I think it is safe to say that virtually NO cars will still have the .019 cam; that cam was obsolete 64 years ago, and the standard replacement cam was the .012.
Nowadays the sometimes-recommended setting of .015 is a compromise and/or safety measure, I think. Back when 99% of T-series cams were .012 or .019 (the remainder were racing cams), the settings were obvious. But in these days where there are dozens of cam shops and grinders, and literally dozens of XPAG cams of wildly differing grinds available, absent the grind sheet who knows what the proper setting may be?
Therefore, I suggest that the .015 setting is safe for most cams (NOT Crane cams), even though it may make a slight clatter - better too loose than too tight, which can burn valves. .015 will do no harm, in any case. My personal seat-of-the-pants feel is that with an .012 cam a setting of .012 gives a tad more power, but the difference is not really significant for a street machine.
If you know you have an aftermarket or re-ground cam, look to the cam sheet for setting information (a Crane cam, for instance, will require different settings for intake and exhaust). If you suspect you have an .012 cam, set for either .012 or .015. If it is too noisy at .015, use .012.
|Someone asked for the service bulletins regarding the camshaft modification. Actually there are three (Service Letters #100, #104 and #108). Here is number 100 (hope you can read it as the Original is very light)
|...here's number 104:
|...and finally number 108.|
Hope this helps.
|Oh and the addendum added to the workshop manual looks like this....
|Fascinating Nick! 64 year old Documents. Thank You for Posting!!!|
|Service bulletin 108, at the bottom, mentions how to distinguish between the two camshafts - useful for people whose T, W or Y types still have original camshafts (although probably a bit worn by now).|
|R A WILSON|
|Forgot to say, I have had both camshafts in the past, but never spotted the difference in grooves. I wonder if there were special marks for the AEG122 cam, which is very similar to the early cam - an AEG122 is in my engine, but I don't really want to remove the chain cover to check|
|R A WILSON|
|I have studied the factory blueprints for the various cams, and each one has a different series of grooves in the end.|
|Neat documents, thanks from me also! George|
This thread was discussed between 16/05/2017 and 19/05/2017
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