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MG MGA - Unknown camshaft

exhaust
John Backman

John, what is the lift (at the pushrod)
Art Pearse

Art,

Measured from the base circumference of the camshaft, the lift is:

Intake: 0.188
Exhaust: 0.192

I cannot give you a gross lift amount as I have not removed the camshaft.

John
John Backman

That doesn't sound right. Stock cam should have 0.250 lift at the cam lobe, 0.355 lift at the output end of the rocker arm.
Barney Gaylord

Cam specialists have software (ie Cam Dr) that can identify any cam profile and then advise what timing you should use. See example here
https://www.youtube.com/watch?v=ImJTSs5g3gY
John, how did you determine your cam timing, using a degree wheel?
Mike
Mike Ellsmore

Might be an Austin camshaft, A55 or A60.

My car has an Austin A60 engine but I installed the MGA cam.
Art Pearse

John
Have you included the .050 in your lift measurements or not-
Also
I know measuring at .050 is the proper more accurate way of checking cams but for comparison reasons you are probably better off measuring at advertised specs which is normal operating specs
The easiest way to 'roughly' measure this and have something to compare to std. type specs is --
Set the valve clearances to a guestimated spec, say .015
Rotate the crank with the degree wheel or whatever fitted and measure your specs then at the point where the valve clearance decreases to 0 lash or close to it. You can use a thin feeler gauge (.002) in there for this. And then check when it loosens up again when you start to get clearance after the valve closes again- This should give you advertised opening and closing points. -If you don't want to jam a thin feeler in there you can just feel the pushrod and you can tell when it looses clearance
It's a bit fiddly but this will give you an advertised duration spec to compare with the older style of advertising timing duration like 25-60 or 30-70 or

cheers willy
William Revit

Also I take it that you measured lift at .050
therefore lobe lift measured by you would equal
.238"
.242"
std MGB= .250" not sure of MGA spec but

willy
.

William Revit

Barney, this was my first go at using a dial gauge miss-reading the gauge lead to the wrong lift figures. The correct numbers are; Exhaust 2.92 lift and Intake 2.88 lift. More than stock.

Mike, I am using a Crane degree wheel. Since I am doing this in car I had to jack up the engine a bit for clearance.

Art, I am fairly sure that I have a MGA 1500 block. Second hand information from the seller indicated a complete engine rebuild in the late 1980s and the Mistress had not seen many miles until I got her. As for the head possibly coming from another line of the MG family, you should know it is the one you sent me several years back (still going strong by the way)!

Willy, thanks for the suggestion on finding open and close. I did use the standard .05 lift as the start and end points with the degree wheel.

After multiple times re-measuring things, the approximate lobe center lines; Exhaust 62* ABDC and Intake 90* BBDC.

Given the high lift and 112* lobe separation in comparison to the APT and Crane Cam specs, it would appear that I have some variation of a performance camshaft. I seems like I will need to dial in some advance for the cam, but the question is how much? Crane Cams timing sheet says the general rule would be 5* for 108* lobe separation or greater. That amount of advance would pull the lobe center lines back into the lobe centerline marking ranges on my degree wheel.

John
John Backman

John
Every cam I dial in I give 3-5deg advance
You will find that some cam manufacturers grind this amount into the cams already for you but most don't
Then there is the problem of some vehicle manufacturers using identical grind camshafts but use retarded sprocket sets to make there engines work harder at idle to get past the pollution requirements - Luckily MG didn't go that way
It always pays to dial them in and as I mentioned I give em between 3 and 5 deg advance

As far as your measurements go for lift
Did you measure your lift by having the dial on 0 on the back of the lobe and rotating till you get max. lift or are you still involving the .050 thing
It needs to be on 0 to start
Sorry to nag at you but if it's your first go at a dial gauge--well we want to help you get it all good

How smooth/choppy boes it idle -
It would be nice to have the advertised duration specs.at normal running clearance just for comparing



cheers
willy
William Revit

John, glad to hear the head worked out OK. I put a B head on mine, its a 1622.
I don't understand how you measured the lift, "from the base circumference of the camshaft" I take this to mean you miked the major and minor axes and the difference is the lift, but you said you did not remove it.
Art Pearse

Art
If he fitts the dial indicator down onto the cam follower or alternatively onto the top of a pushrod and gets sets the dial to zero on the back/base of the lobe and then rotates the cam till max lift, the measurement taken then is lift at the lobe
willy
William Revit

Willy, lift was measured as you suggested. I set the dial to zero and rotated until I got to a maximum figure. As for the idle, with the crank and cam gears set up as stock, the idle is pretty loppy. To smooth it out at all the idle RPM's have to be set around 1,100 or more. RPM was measured electronically, not with the tach.

Art, as you can see I used the method that Willy is suggesting.

Any suggestions on dialing the advance using an adjustable cam gear? Maybe something like loosen up the cam gear, hold the cam in place and turn the crank counter-clockwise? Then re-secure the cam gear?

Also is the amount of advance (in degrees measured from the crank or cam? In other words if I advance the crank 5* the cam will only advance 2.5*. Or should I advance the crank 10* to get a 5* change on the cam?

I have yet to find a good explanation of the actual process of "advancing" the cam. All of the directions get up to the point of suggesting the use of off-set keys or adjustable gears, but stop short of describing the last steps in any detail.

John
John Backman

John
It's measured in crank degrees
BUT moving the cam just for the sake of moving it isn't really going to achieve anything unless you are chasing something in particular
Finding out what the camshaft grind is so that you know what you have is the go
If you have adjustable timing gears--to adjust
Use a texta and mark around the heads of the bolts/washers and then if it slips while you have it loose you have somewhere to go back to-
It's a case of measuring where your timing is as you have done and then if you want to advance say 3deg. for example, loosen the bolts,move the crank backwards a few deg. and tighten up,then measure up again to prove your result
The texta marks are handy as sometimes when you loosen the bolts the cam flicks to the end of the slot but you'll know where to put it back to cause you marked it

Don't just move it forward for the sake of it though as it might already be in front of where it needs to be
Finding out what the cam is, is the issue really
willy
William Revit

The timing card for my Crane Cams fast street cam states, "This cam is ground 1 degree retarded for best lobe size and hardness. Optimum performance will result from installing the cam 5 degrees advanced, as indicated on the timing card".

What that means is, if you install it with straight key and sprocket marks aligned as instructed in the Workshop Manual, resulting cam timing will be 1 degree retarded. Difference between 1d retarded and 5d advance is 6d at the cam, or 12d at the crankshaft, and yes it really is the much change required.

To advance the cam, hold the sprocket still and rotate the cam clockwise by the specified angle. To go from -1 to +5 you need to advance it 6d at the cam. One tooth on a 40-tooth sprocket it 9 degrees. Offset keys are commercially available with 1, 2, 3, 4 degrees offset.

By coincidence, 1/32-inch offset of the cam key results in 3 degrees change of sprocket angle (for the Austin B-series pushrod engine). Camshaft key is 5/32-in thick. Crankshaft key is 6/32-in thick. You can mill 1/32-in steps in a crank key to make a cam key with 1/32" (3 degree) offset.

If you skip the timing chain over one tooth you will advance (or retard) the cam sprocket 9 degrees. If you install a 1/32-in offset cam key you can retard (or advance) cam timing 3 degrees. Do both and you get 9-3=6. Using one straight key and one 3d offset key, you can walk the cam around the clock in 3 degree increments. If you need more accurate cam timing you can use a cam key with different offset.

If you know the exact cam timing you want, you can get there with a tooth skip on an offset key. If you want to experiment with various cam timing, then you might want yo buy a vernier cam sprocket that is infinitely adjustable. In any case you need to measure the resulting cam timing to be sure you got it right.
Barney Gaylord

Why don't they just grind the cam properly without this nonsense?
Art Pearse

Barney
I've never heard of camshaft timing being quoted in camshaft degrees, It's always crank degrees ????
willy
William Revit

The line about -1d grind to +5d final position for the cam is the only reference to the cam shaft position. Everything else on the timing car refers to valve timing related to crankshaft position.

Let's see if the card image will show here. If not then for larger image see http://mgaguru.com/mgtech/power/pics/crane_timing.gif

Note that all set-up angles for open and close are referenced to 0.050-inch lift position on the cam lobe. This is because it is almost impossible to measure the precise point where the ramp begins to rise.

Barney Gaylord

I still tend to think it's crank degrees they are refering to but yeah good point, just depends how you read it really

Looking at this timing card it shows what we were talking about before with some cam grinders grinding to spec and some not
In this particular case it would be VERY important to set up exactly to the card as they are saying that at that spec it would have 5 deg advance , otherwise if fitted on std. timing marks it would actually be 6deg behind spec and that would certainly be enough to kill bottom end power

willy
William Revit

John
I've been poking around on the internet ,having a little look for a cam with your specs or close to
Moss have a cam with exactly the same lift combination as your cam, but don't give other specs. To have exactly the same lift combo would have to be more than a fluke
It might be worth contacting them and tell them what you're up to and see if they would send you the specs for comparison

http://www.mossmotors.com/Shop/ViewProducts.aspx?PlateIndexID=82981

willy
William Revit

Willy,

Thanks for the tip. I appears that the Moss performance cam, 222-273 is the APT B Series Performance Cam VP11. http://www.aptfast.com/Content/how-to.aspx (see the B series link). At least the Moss part number is cross-referenced, but specs appear to differ.

I have questions into both Moss and APT. We will see what turns up.

John
John Backman

Cheers John
Another thing just to keep your eye on is that although .050" lift is the norm for measuring up a cam, again there are differing ways of doing this, some cam manufacturers quote their figures at .050 lift at the lobe, but others quote at .050 actual valve lift measured from the top of the spring cap with the valve clearance set at normal running clearance
Why can't they all do it the same I ask ????????????
When you work it all out there is very little difference in the result but why can't they all just do it the same way.

.050" at lobe-------

or .050" at lobe x 1.426 rocker ratio = .071 minus say .016 tappet clearance = .055

So just 5 thou. difference in this case which would possibly get soaked up with strain in the rocker gear opening the valve so not really a problem but worth keeping in mind all the same just to stay alert when reading specs.

If for example the rocker ratio was drastically different the two different results would be further apart and it would be more important in that case to set up to whichever spec the cam designer quotes

Thought you might be interested for your own info now that you are kitted up and venturing into the crazy but very interesting world of cam timing-----
willy

William Revit

This thread was discussed between 27/04/2015 and 06/05/2015

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