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MG MGA - Unknown camshaft
|My 59 roadster came with a 1500 engine of undetermined condition. A couple of years ago I rebuilt the head when the head gasket blew. Otherwise the compression and oil pressure are fine. This weekend I have been attempting to get a read on the condition and possible fine tuning of the camshaft timing. I did get the camshaft endplay and gear alignment back in spec.|
I have no information regarding the cam or maker. The only stamped markings on the end of the cam is 32.
The cam measurements came out as (taken at .05 lift):
exhaust Open, 59* BBDC; Exhaust Close, 5* BTDC (the latter is a reading at BTDC rather than the expected ATDC).
Exhaust centerline approximately 89* ABDC
Exhaust duration 244*
Intake Open, 17* BTDC, Intake Close, 62* ABDC.
Intake centerline approximately 62* BBDC
Intake duration 259*
Lobe separation 112.5*
Up to now I have been running her with the stock timing, but it appears that I have a non-stock camshaft. Any thoughts regarding the cam timing would be appreciated. The Crane Cam info suggests that for lobe separation of greater than 108*the camshaft timing be advanced 5*.
|John, what is the lift (at the pushrod)|
Measured from the base circumference of the camshaft, the lift is:
I cannot give you a gross lift amount as I have not removed the camshaft.
|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.|
|Cam specialists have software (ie Cam Dr) that can identify any cam profile and then advise what timing you should use. See example here|
John, how did you determine your cam timing, using a degree wheel?
|Might be an Austin camshaft, A55 or A60.|
My car has an Austin A60 engine but I installed the MGA cam.
Have you included the .050 in your lift measurements or not-
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
|Also I take it that you measured lift at .050|
therefore lobe lift measured by you would equal
std MGB= .250" not sure of MGA spec but
|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 1980’s 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.
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
|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.
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, 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.
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
|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.
|Why don't they just grind the cam properly without this nonsense?|
I've never heard of camshaft timing being quoted in camshaft degrees, It's always crank degrees ????
|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.
|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
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
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.
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-----
This thread was discussed between 27/04/2015 and 06/05/2015
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