Urgent: Timing Help: Urgent
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Urgent: Timing Help: Urgent
Hello, I'd like to say I'm new to the site and Jaguars in general.
The vehicle in question is a fully loaded 1975 XJ12.
We were timing the motor following instructions in a repair manual.
we started by placing the Right hand bank cylinder #1 at top dead center, we installed the head, tappet block and all that comes with it, and then the camshaft, but while torquing down the camshaft while it was in the proper position, we heard a snap.
We did a compression test and realized the snap we heard was the breaking of the first exhaust valve.
This makes NO sense to me if the camshaft has to be in a certain position for timing while at top dead center.
Any help explaining what we did wrong or what to look for next time would be greatly appreciated.
The vehicle in question is a fully loaded 1975 XJ12.
We were timing the motor following instructions in a repair manual.
we started by placing the Right hand bank cylinder #1 at top dead center, we installed the head, tappet block and all that comes with it, and then the camshaft, but while torquing down the camshaft while it was in the proper position, we heard a snap.
We did a compression test and realized the snap we heard was the breaking of the first exhaust valve.
This makes NO sense to me if the camshaft has to be in a certain position for timing while at top dead center.
Any help explaining what we did wrong or what to look for next time would be greatly appreciated.
Senior Member
Joined: May 2009
Posts: 178
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From: San Antonio, TX
Without looking at the manual, I will offer this basic info. It sounds like the camshaft was not in the correct position. The exhaust valve must have been open too far and contacted the piston. Recheck the book, I would think that both valves should have been closed, as if the piston had just reached top dead center on the compression (both valves closed) stroke.
Otherwise, there is possibly not enough piston-to-valve clearance. But that would result from milling material off the flat surface of the head or block. Or it could result from changing to a higher lift cam.
I have a Haynes manual I can dig up tomorrow and see if it has the procedure. What manual did you use?
Otherwise, there is possibly not enough piston-to-valve clearance. But that would result from milling material off the flat surface of the head or block. Or it could result from changing to a higher lift cam.
I have a Haynes manual I can dig up tomorrow and see if it has the procedure. What manual did you use?
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