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MG MGA - Valve timing

I would like to compare the valve timing and cam lift for a 1622 MkII engine with that of an Austin Cambridge A60 of same era. Anyone out there got any or all of that information?

Art
A Pearse

Art,
Have you spoke with someone from one of the big suppliers of cams, such as Crane Cams?

Ray
Ray Ammeter

From the Workshop Manual for the A60, Morris Oxford (Series VI) and 16/60.

Inlet opens TDC
Inlet closes 50 after TDC

exhaust opens 35 before TDC
Exhaust closes 15 after TDC

The above are, of course, in degrees.

I have never possessed one of these cars so am now wondering how come I have a workshop manual.
Malcolm Asquith

I missed the valve lift which is given as 0.312 inches (7.925 mm)
Malcolm Asquith

Malcolm, these sound very weird, apart from exhaust closure. Usually, it is something like:

Ex opens ...... BBDC during the firing stroke
Ex closes .....ATDC during induction
Inlet opens ..... BTDC during exhaust
Inlet closes .....ABDC during compression
where ..... is some small degrees

Ray, good idea!

Art
A Pearse

Although I am no expert, from what I have read, I believe that the A60 engine is the same as the MK3 and Mk4 Magnette. The info for the MG engines is covered in several publications by Niel Cairnes and is all over the 'net,

See Tuning a 1622cc Engine at:
http://www.mgcars.org.uk/farina/garage/1622update.html
For a complete changeover instructions from A60 to MGA version engines.


See: ENGINES for M.G's Their Story after 1935. At:

Http://www.mgexperience.net/article/mgenginehistory.html
Excerpt:


'B' Series Camshafts in M.G. Engines.

Model Cam Timing Lift Part Number Inlet & Exhaust Valves

ZA Magnette to 18101 5;45;40;10 .312" 48G184 1.375" 1.28"
ZA & ZB Magnette 5;45;40;10 .312" 48G184 1.5" 1.28"
All MGA 16;56;51;21 .355" 88G252 1.5" 1.28"
mga twin cam 20;50;50;20 ? 1.6" 1.44"
Mk 3 Magnette to 8067 5;45;40;10 .312" 48G184 1.5" 1.28"
Mk3 & Mk4 Magnette tdc;50;35;15 .312" 12H76 1.5" 1.28"
MGB, MGB GT 16;56;51;21 .355" 88G303 1.56" 1.34"
MGB after Oct '67 16;56;51;21 .355" 12H2746 1.625" 1.34"
The lift on the chart is at the valve, as the rockers act at a ratio of 1.4, the actual lift on the cam lobe is .220" for a .312" lift, and .250" for a .355" lift. The part numbers of BMC change at lot for the same item, depending upon the supplier, hence a 12H76 is also a 12H34. A 48G184 is also a 1H603, 1G2591, 1H1066, and a 88G252 can be a 88G303,12H2746,1H1435,1H729,12H1647, and 12H1656. Clear now?
C Schaefer

Thanks Chuck. Great info.
I take it the figures are inlet open / close, ex open / close, in that order?

Malcolm, I'm reading your figures as inlet closes 50 ABDC and ex opens 35 BBDC.

Art
A Pearse

Neil's book and other tuning guides for MGA are available on my site:

http://www.clancy.ch/Library.html

The factory tuning guide is here (woth more stuff too)

http://www.clancy.ch/Owners_Pack.html
dominic clancy

Art

You are of course correct the figures should be:

Inlet opens TDC
Inlet closes 50 ABDC

Exhaust opens 35 BBDC
Exhaust closes 15 ATDC

Serves me right for being in a hurry.

For the sake of completeness the same manual covers the A55 (MkII) and its Morris and Wolseley equivalents. The figures for those are:

Inlet opens 5 BTDC
Inlet closes 45 ABDC

Exhaust opens 40 BBDC
Exhaust closes 10 ATDC

and from engine 15AMW/UH101, L601 or 15WB/U/H8998, L7563.

Inlet opens TDC
Inlet closes 50 ABDC

Exhaust opens 35 BBDC
Exhaust closes 15 ATDC

so the late A55 cam could be the same as the A60 one.

Apologies.

Malcolm
Malcolm Asquith

Assuming equal lift and profile, the cams are the same.

All three have 230 degrees duration intake and exhaust on 107.5 degree lobe centers. The middle one is installed 5 degrees less retarded than the other two- 2.5 vs. 7.5 degrees late.

Most modern cars have their cams intalled straight up or slightly advanced.

Have fun,
Bill
Bill Eastman

Bill, what do you mean "straight up" ?
A Pearse

Are the camshaft numbers somewhere on the cam? I've looked and haven't been able to find a number.

G Goeppner

Same here. I can't find the part number on my cam.
A Pearse

Straight up = overlap centered at TDC. The intake opens the same amount before TDC as the exhaust closes after. For these cams overlap is 15 degrees soo straight up would be plus/minus 7.5 degrees.

I would guess MG's choice of later cam timing is due to the combination of relatively short, siamesed intake ports, constant depression carbs, and looser 1950s manufacturing tolerances.

Bill
Bill Eastman

This thread was discussed between 25/10/2008 and 29/10/2008

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