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MG Midget and Sprite Technical - Cam sproket key dimension

Hi Everyone

Does anyone have an old sprocket or woodruf key that they can measure for me (my only one is buried in my engine!).

I have a 1932 Armstrong Siddeley and I'm hoping that I can use an offset midget (or B if anyone has one of those) woodruf key to bring the cam timing to where it needs to be. A long shot but worth a try! Any help appreciated.
R Cohen

I probably have some, but not sure where. I will have a look.

A-series and B-series use the same key.
Dave O'Neill 2

RC
Just pulled the cam out of a B--
-0.156" wide---(5/32")
-0.600" long
-0.25" deep
The crankshaft key is the same but on some B engines the keyway in the crank is machined in with a flat bottom and the key is a tiddle longer and has a flat on the bottom to suit, so if you were ordering an offset MGB key you would need to make sure it was a cam key,,
- or find out which type of crank key it is
Cheers
willy
William Revit

Thanks William, the sprocket key way that I have is 3/16 so I can't get an off the shelf solution - however the plan now is to machine a 1/4 key in the mill and make one. Thank you again. Worth noting that both the MG and the Armstrong Siddeley that this actually relates to are suprisingly sensitive to getting the cam timing perfect. A couple of degress out (which you almost certainly will have without an adjustable sprocket or offset key) and you lose power.
R Cohen

If the cam is mild such as a std B then the timing is less sensitive. early Bs were timed 110 degrees atdc on inlet lobe, later engines were advanced to 106 degrees atdc. We set them at 108 for std race use. By mistake we once set one at 104, pulled like a steam train out of the bends but struggled at end of straights!
A race cam does detest being retarded whereas an advance of say 2 works well especially with a smaller engine, thinking of 1840 as opposed to 1950 B engines.
With small bore A series we tend to advance a couple of degrees over the larger bore 1275 (or larger) engines
Peter Burgess Tuning

Peter, in the absence of timing data (1932 sidevalve), I am going to time the cam so that the valves are at cross over at TDC (there isn't actally any crossover, rather a 3 degree period when exhaust is closed and inlet closed). I assume that this is the best approach?
R Cohen

It depends if the cam is symmetrical for inlet and ex lobe timing. Quite a few early cams seem to be set like the A series std one 5/45 40/10 so you would have to be 2.5 degrees atdc to get equal overlap. Having said that I am sure you should be in the right ball park with equal lift at TDC as the cam must be really mild
Peter Burgess Tuning

Interesting your findings on timing Peter, my mate has a Jag. engined racer sports car with monster cams, I tend to set cams up 2-3 deg ahead on most engines but this thing--For the circuit it runs, and because of how we gear it to suit it has to have a strong top end(hence the big cams) but also needs to be torquey lower down---Tried lots of different cam grinds but nothing matches these for outright go up high ,so started fiddling with timing and found the inlet cam could be pulled up as much as 8deg without killing the top end with the power coming in noticeably earlier--around 3200 instead of 4000
10deg killed it so 8 it is, BUT if we moved the exhaust up any more than 3 while the inlet was at 8 it would completely kill the top end and go flat right through everywhere
So 8 and 3 is where it is
Nice to have the flexibility of seperate cams for experimenting and Jag's easy fiddle sprockets
William Revit

Interesting Willy, I have always found it a little
daunting messing around with twin cam timing, seem to be so many variables. Did you do it on the track or rolling road?
Peter Burgess Tuning

Atthe track Peter, he's never been on rollers, we just keep fiddling to tailor him to the track--The car has held the over 3 litre sports car record here since the mid 80s up till last year
In 2017 Duttons rolled up with a Mclaren M8F big block Chev and thought they were going to take the record but--no, went home without it
Then last year they came back with the same car and had spent heaps on it and had the widest slicks I've ever seen, they also bought with them a Benneton F1 car to pace themselves against---sole reason, to get the record, which they did---bugger
Sadly now they have the record they didn't come back this year --
The Jag is right at his limit and there's no chance now of him getting the record back so he's having a rest for a while--
William Revit

This thread was discussed between 22/11/2019 and 05/12/2019

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