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MG MGA - Cam Shaft Alignment Out 180 Degrees?

exhaustl started with the need to replace a leaking water pump. While I was at it I wanted to replace the thermostat and timing chain cover (early MGB style). What the heck while I have things open I will replace the timing chain, sprockets and tensioner. Got everything cleaned up and painted and now some 6 weeks later, after painting a good portion of the house, I am finally ready to put her back together.

Since I had not moved anything in disassembly, I figured reassembly would be a snap. That notion evaporated pretty quickly when I went to get the new timing chain cover seal lined up with the crank pulley. Per the workshop manual I lined up the two dots on the crank and camshaft gears only to notice that instead of sitting at TDC the crank was at about 10 degrees

jjb Backman

No such thing as the cam being 180 degrees out of place. If you think it is, then rotate the crankshaft exactly one turn, which turns the cam 1/2 turn, putting it all in correct position.

Your timing chain may be one tooth out of position on one of the sprockets (no difference which sprocket). Then when you align the dots both sprockets will be rotated slightly from nominal (1/2 tooth each), and the crank pulley would be misaligned just as in your picture.

distributor drive gear is commonly misaligned, but easy to fix. Instructions are in the Workshop Manual, but maybe a little vague due to translation. I have the write up on my web site, but success still depends on having the timing chain installed right first.
Barney Gaylord

Not 100% sure about this. If you replace your MGA timing chain cover with a MGB cover (the one with the timing marks on the top) you need to replace the pulley as well. The timing mark for the MGA pulley will be at the bottom whereas the timing mark for the MGB will be at the top (or approx. 11:00 position). This could be the cause of some of your troubles. Also, check University Motors (John Twist) he has videos that may help.


You can install the timing cover with pointers up top, then just file a new notch in the pulley in the appropriate location. No need to change the pulley.
Barney Gaylord


When I put the MGB cover on my 1500 motor I filed a new notch to match the timing marks on top. A dab of white paint in the notch and it showed up well with the strobe.

Steve Gyles

Somewhere down the road I plan on doing this. Curious just how you know where to put the notch?

Larry, the most accurate way is with a piston stop. You can make one from an old spark plug body, with a short length of 1/4" rod welded in instead of the insulator. Round off the end. When screwed in, it stops the piston a few deg BTDC. Rotating the engine the other way it stops it the same deg ATDC. Mark these 2 points on the pulley by the pointer, then bisect them and file your notch there. I think 3/4" projection from the plug threads works OK. Disconnect the starter to avoid an accident!
Art Pearse

The rabbit hole has gotten a bit deeper, but Barney set me straight on the timing chain and sprockets. Mine was just a couple of teeth off. I first tried getting the cam shaft into the correct position with the sprockets and chain on then removing everything and bringing the crank around to TDC but just wasnít able to get to the correct alignment. So back to the MGAGuruís site for details on a manual alignment process Ė this is where the rabbit hole got deeper. The manual process involves disassembly of the rocker assembly so the cam can be turned by hand. The procedure could be done without removing the rocker assembly, but I had other reasons for removal. Not a huge task but I also knew that the aluminum rocker pedestals where in bad shape. Fortunately I had an early MGB assembly with cast iron pedestals for replacements. Of course the MGB assembly was pretty rusty, so it took one evening just to get it torn down and cleaned up. Lastly with the rocker assembly off I will try to install new valve stem seals. So the end is in sight, but first a few more questions.

Since the rocker assembly is out, I have loosened all of the head nuts. My sense in doing so was that the head was torqued well beyond 50 ft-lbs. Should I pull the head and replace the head gasket? What about the studs, replace those as well? I donít know much about the history of the engine other than second hand information that it was rebuilt in the late 1980ís but has not seen many miles. Very good cylinder compression and oil pressure seems to bear this out. On the other hand previous repair work was done with bubble gum and bailing wire so I am reluctant to pass on making sure for myself.

BTW Larry, I believe that mine is a very early MGB timing chain cover so the timing marks are on the bottom.

Thanks, John
jjb Backman

jjb, since you've loosened all the head studs and therefore drained the coolant in my opinion you might just as well lift the cylinder head and inspect the bores, studs and valves. In the case of the studs unscrew them and check for any corrosion or 'waisting' just before the thread starts. I'd use a new gasket.
J H Cole

This thread was discussed between 11/10/2010 and 20/10/2010

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