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MG TD TF 1500 - Cam Identification
|Let's see if I got this right.|
I understand the TD's came with two different cams.
The early ones (to engine 24115) produced a valve lift of .315(8mm) and tappets were set at .019".
The later ones (from engine 24116) had the tappets set at .012" and from what I have read produced a valve lift of .327"(8.3mm).
At this point I assume that the rocker arm ratio remained the same.
If the rocker ratio remains constant and the valve lift is different then the cam/lobe lift must be different.
I am trying to identify my cam by measuring the cam/lobe lift. The lift on my cam is about .220"
Does anyone know what the cam/lobe lift is for the two different cams?
PS: Does anyone know the rocker ratio?
|Mort Resnicoff 50 TD (Mobius)|
|Rocker ratio is 1.5 : 1|
I had stated that it is 1.38 : 1
Where I made the mistake???
Your valve lift should be .330"
All of my cams have a lift of .430"
Thanks for that info.
With a rocker ratio of 1.5:1 My cam lift of
.220" x 1.5 = .330" of valve lift.
This tells me I have the later cam even though I have an early car (engine 1606).
Now the strange part. Per the WSM I should set the tappets to .012". The brass plate on my valve cover says to use .015".
Is there some history here that I am unaware of?
|Mort 50 TD (Mobius)|
|Mort & Len,|
Sure am glad I glanced at this thread. I'm getting around to evaluating rocker shaft height and pushrod lengths and was referencing the 1.38:1 ratio.
Just so happens, I yanked an old cam out of our engine today and it looks a bit sad as do some lifters. Am looking forward to installing our roller lifter cam package.
I think I'll go mike that old one tomorrow, but I don't think that'll solve the mystery. Could not find any numbers or identifying symbols anywhere, either. It looks like both cams might have virtually identical lift as subtracting .007" from the valve lash (.012" versus .019") adds another .0105"- and 8mm rounds up to 8.3mm new lift.
"The brass plate on my valve cover says to use .015"." Did John Swift ever work on your engine? He sets all lash to .015." You sure that's not .012" on the plate?
More than likely your cam has been replaced. During a rebuild, a cam would most likely be replaced, the replacement would be the later cam.
The plate clearly says .015".
It's obvious that the engine has been rebuilt more than once and the cam is the later style. I am trying to understand the .015" instead of .012".
|Mort 50 TD (Mobius)|
A TD would have a valve cover with either the early plate (.019) or the later plate (.012). The .015 plate tells me the original TD valve cover must have been exchanged for one from some other Nuffield product.
I would ignore the plate specification and go with the .012 setting - if your measurements point to the use of the later cam in the earlier engine.
|Mort & fellow "cam followers,"|
I would not use "valve lift" as a method to disclose your camshaft. If you have an "original TD" cam and set the lash down to .012" you too will enjoy about 8.3mm valve lift and be convinced it is the "later" cam.
At last count, there appears to be at least 4 factory cams (Google "Special Tuning for MG midget Engines" thanks to Dave Braun, again), not to mention the popular Crane, other aftermarket suppliers, as well as regrinds!
Of the four MGs (and probably all the others, too), there is one and only one with zero overlap.
Mort- I was under the impression your cam was out, but since it isn't, you can verify if yours is the classic "later" grind fairly easily. Rolling the engine over very slowly, if the exhaust valve opens and closes BEFORE the intake starts to open, there's zero overlap. IF the intake starts to open before the exhaust rocker stops, then it has overlap and is something else.
If you take a degree wheel and your dial indicator, you can document valve events and then compare to cam specifications.
The MG TD started out with .019" lash, and then evolved to the "later" grind with .012" gap. The higher performance AEG 122 went back to the .019" spec, BUT BUT BUT, they said you can go down to .015" for quieter operation. Sound familiar? Did they offer a special .015" plate with this one? The racing "high overlap" shaft #168551 called for .012" on the intake and .019" on the exhaust.
What might be the most important detail of all, is on the bottom of your lifters... are they perfectly flat or crowned? If you haven't already read it, go to Moss Motors, MG T engine internals, and read the INFO under "Tappet Set" item #38 and "Camshaft" Item #61. Lots of valuable information. This is where you can get into trouble mismatching cam with lifters.
For example, our '51 TD has a Crane cam, and the only reason I know this is... the 30 year old receipt for an engine rebuild in the mid 1980s.
Have I confused you enough for one night?
By the way, the cam I just removed has some fairly deep erosion but it might be regrindable. IF someone wants it for a core, I can send it to you or directly to Delta. Might just ship it to them anyway for any future customer (rather than just scrap it). email me firstname.lastname@example.org
That is good info about all the different cams.
I can't currently use your method since the block is stripped down to only the cam and crank remaining. I did put a lifter in each hole and dial indicated the difference in the high and low. I'm pretty sure its the newer cam. See the details above.
|Mort 50 TD (Mobius)|
|Wish we could go back and edit previous posts. I took a second look at the cam specs and that "later" cam does have overlap. Thought that sounded wierd. That's what I get for eating and trying to post at the same time (something about no blood in the brain). But as these events coincide at 45 degrees BTDC and ATDC, there is an issue where different rockers on different cylinders terminate and happen simultaneously with this cam, whereas the other cams' rockers always overlap. Back to dinner!|
|For a great, detailed rundown on the MG TD/TF cams,|
"Where the Rubber Meets the
Road ....... Part II Camshafts and Valvetrain"
By Dave Barnett
Vintage MG Club of Southern California
This thread was discussed between 16/01/2014 and 18/01/2014
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