Triumph Repair: Timing chain Spitfire MK3 1969, cam lobes, compression stroke

Question
QUESTION: I wanted to change my timing chain- (restoring the car)the chain has over a 1/2 of slack.  The quetion is the repair manual said to line up the etched dots on the two sprokets when putting the chain back on, but they aren't lined up now, or with the old chain on- I didn't take the old one off yet.  What should I do?

ANSWER: Hi Ron,
You should not be attempting this without a service manual. However, here is the procedure.

Turn the crank until #4 is at TDC of the compression stroke. Set the valve clearance of # 7 and 8 valve at .050". Turn the crank until #1 is at TDC of the compression stroke. Check the valve clearance of #7 & 8 and move the crank back and forth slowly until you have both #7 and #8 exactly the same clearance what ever that is.

Now be careful not to move the crank or the cam. Note that the mark on the crank sprocket and the cam sprocket are in line with each other and the the open hole in cam sprocket at about 10:00 o-clock has a dot on the cam sprocket next to the hole and you can see a notch in the cam in that hole. Now you can remove the cam sprocket and crank sprocket.

Note that there are 4 holes in the cam sprocket but only two bolts used to secure the sprocket. The sprocket can be rotated 90 deg to get a half tooth adjustment or you can flip the sprocket over and get quarter tooth adjustments.

The end result you are trying to achieve is that #1 and #4 Piston are exactly at TDC and the cam lobes of # 7 and # 8 are exactly the same clearance. This it called "Splitting Overlap" in cam timing. All of this must be done and done exactly as I outlined.
Howard

---------- FOLLOW-UP ----------

QUESTION: Thanks for the fast response and expert advise! Maybe I should leave it up to a mechanic, I do have a repair manual but it seems like a big job that you don't want to get wrong.  I have another questions would there be any harm in removing the sprockets after marking them and then putting on the new chain. My goal is to put a new chain on as the old one looks worn. Then I could adjust the timing via the distributor.  Last question ss there a reason that the dots on the sprockets don't line up as it sits now and it supposedly ran before.


Answer
Ron, cam timing and ignition timing are two different things and neither should be set by guessing. You can mark the sprockets as they are now and just put a new chain on and it may run ok but no one can guess what the cam timing is if you don't want to check it for what ever reason you may have. Incorrect cam timing will effect performance and can cause premature engine failure.

If you have a mechanic do it, at least print my directions and have him or her read the procedure. If the mechanic don't understand the term "Set cam timing by Splitting Overlap" You need to look for a different mechanic.
Howard