Long story short, I reinstalled the engine in the car with the cams 180 out ( set them at TDC, but not on the power stroke). So the valves are opening and closing at the wrong time.
Now I need to rotate the camshafts to the “other” TDC.
What is the safest way to do this with the engine in the car and the head attached? I know that valve clearance is an issue when I loosen the cam bolts…and I don’t want to bend any valves.
What position should the crank be in to accommodate loosening the bolts? Do I do both sides at once, systematically loosening the bolts ? Or one side first ?
And stupid question: what if I just rotated the spark plug wires in the distributor housing 180, maintaining the proper firing order ?
So close to starting this beast after a long rebuild…and yet so far…
180 out is half a turn of the camshafts, so they are one full crank turn out?
Do it correctly…
Remove the camshafts. Pay close attention that the valves don’t collide, so if you have two tappets pushed down at the same time (unlikely since both have not been moved, the timing slots are still at 90° to the cam cover sealing surface, the pistons are in the positions they would be in otherwise, right?), you have to remove the upper one first. Remove both camshafts.
Rotate the crank to the proper position.
Reinstall the camshafts and check valve clearances to find bent valves. Assume there are none. Done.
If a cylinder is up but one turn out it should all come together but that engine will be rebuilt again one day… I would be very unhappy to find something „wrong“ with the distributor. But I think this would work.
Just to reinforce what David says, if you remove (or even loosen) the camshafts, then all the valves are closed and remain closed as you rotate the crankshaft the required amount. This pretty much guarantees you won’t hurt any valves during the process. And it’s not that much work to loosen the camshafts until all the valves are closed. Just observe the cam follower buckets for position.
That said, I have never heard anyone refer to the XK engine as an “interference engine”, which tells me that there is no possible combination of piston position and valve position that will cause a clash. This may depend on whether you have domed pistons or not, I don’t know. Which technically means you can just remove the timing chain, rotate the crankshaft, and reset the cam timing. I think the issue that bends valves is when you take the head off the block and lay it on a flat surface, there will be one or more valves fully open such that they extend below the bottom of the head and get bent when you plop the head down on a flat surface.
If I am wrong, someone please chime in!!! The safe thing is certainly to just loosen the cams, with the timing chain disconnected of course.
As far as potential bent valves, a leak down tester should identify any problems without much effort.
Ok, I’m Confused. If you set the cams to TDC the cams should be in the right position to the crankshaft (timed). Are you saying the distributor rotor is pointing to the wrong plug lead? Is the distributor is off by 180 degrees?
the XK is definitely an interference engine. Valves foul each other and the piston can hit the valves no matter what piston is used.
instead of the piston at TDC compression he set it a full turn out (just as if the engine was set to #1 instead of #6). As a result the distributor drive is out by half a turn. In-car re-setting the cams is easy and done in 3-4 hours and then it is all set.
My engine went together this way 20 years ago and wouldn’t fire. I simply swapped the wires at the distributor. It ran that way until the sump had to come off for a non related reason. The oil pump and bronze gear were removed, the crank rotated 360 and then reassembled.
If you want to do it from the top just fully loosen the cams including the chain sprockets and rotate the crank. I’d wait until the valve shims need to be adjust since all of this has to happen anyway. Having to reset the cam timing is a fiddly job that you don’t want to invite for no reason.
And you wouldn’t be the first person to do it. I know I wasn’t the first when we made the same mistake on the engine in the 2+2 18 years ago. Since the wires weren’t where the factory manual says they are I made small labels, 1-6 and stuck on the distributor cap so it was obvious which wire went to which spark plug on the rewired distributor cap.
I had a friend in high school who had purchased an MGA that needed work. After several weeks of trying to get the engine started I stepped in and on a hunch swapped the wires. It started right up. The look on his face was priceless. Fortunately he went on to be a Phd Entomologist, not a mechanic.
I did the same thing when I rebuilt the engine in my 120. You have to remove and reinstall the camshafts several times anyway when you’re shimming the tappets so, really, what’s the big deal about taking your initial clearances, removing the cams, rotating the crank one turn, reshimming the tappets, then replacing the cams?
Thank you all for your advice. I decided to just move the wires. I intend to keep this car for many more years, so chances are at some point I’ll have to adjust the valves again…and that will be the time for correcting the cams.
Good news is the car started ! She’s been off the road for a year while I did my slow & steady “refurbishing”. So that was a sweet and satisfying sound out of her tailpipes.
Now on to getting those rebuilt carbs working as they should !
Best,
Harold
And just for follow up, the likely mistake you made was not installing the cams 180 out, but installing the distributor drive 180 out. A common mistake.
Instead of changing you wires you could just remove the drive dog from the distributor and replace it 180 out.
I’ve not tried this but I understand that you can simply remove the center screw that holds the distributor cam assemby to the shaft and and rotate it , along with the weights 180 degrees. This way you don’t need to rewire the cap - albeit that rewiring the cap is the simplest solution.