QuestionQUESTION: I have been restoring a 1971 TR6 for several years. The other day I fired it up for the first time and all was good but! In setting the timing by the book(not running)It fires up great but then I have to advance timing by moving the distributor by hand for higher RPM's. In looking at the distributor the way the vaccuum is, it is retarding the timing. This is a 22D distributor in looking in books a 19D distributor would be correct but I am still confused as to why you would have a distributor that only retards timing am I looking at something wroung here?
ANSWER: Hi Mike,
Yes, you are looking at something wrong. The 71 TR-6 for the US had two different distributors. Lucas # 41306 and 41352 both of which had vacuum retard units on them. The vacuum advance unit of the 41306 was plugged by the factory and the vacuum advance unit was not used. Generally most cars that use a vacuum retard unit run the vacuum from straight manifold vacuum. On some cars when they wanted to meet emission standards they would run the vacuum through delay valves etc. I believe you can just run straight manifold vacuum to yours if you only have a vacuum retard unit. You should have a centrifugal advance inside. Any time you open the throttle the vacuum lowers and the retard unit advances the timing as does the centrifugal advance. You should check both to see if you are getting advance by RPM only (vacuum plugged)to test the centrifugal advance and then apply vacuum to the retard unit to see that it retards timing. If you have the Lucas # 41352 distributor you should have the ignition timing static at 4 deg. BTDC. With the engine at idle (800 RPM) you will probably see about 4 deg ATDC. You should not change timing to get a better running unless the engine has been modified. If it does not run right with the timing set to factory specs you need to fix what is wrong rather than change timing to try to correct it.
Howard
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QUESTION: Thanks Howard,You certainly know your stuff. I have another question.This one is about the timing spockets for the 1971 TR6. The after market spockets and maybe even the original do not have line up marks. The original spockets I cannot locate. For line up of the cam and crank the book say's to use these marks but if you don't have them it becomes a bit of a guess. With the engine at TDC I have lined the camshaft up with the keyways that have been machined into it. It has a bigger keyway that I will say is at 9:00 and the smaller is say 4:00. I have left the radiator and all out and have run the engine and all appears to be OK. But there is this little guy in the back of my brain that say's check before putting everything together.
AnswerHi Mike,
If you have closely examined the sprocket for the mark (in the web of the sprocket) on the cam sprocket and can not find it, there is a method to time the cam with no marks. I would not try to do it with the key way as that would be too inaccurate.
Almost all street engines "Split Overlap" for cam timing. Over lap if you are not familiar with the term means that at TDC of the exhaust stroke both valves are open at the same time and to split overlap means to have both valves open exactly the same amount. There are several ways to do this. Usually you need a degree wheel to do this but I will show you a method where you don't need a degree wheel.
Set your cam sprocket on with the chain and keys and bolts etc where you think they are about right according the the manual. Remove all of the spark plugs and the valve cover. Adjust both valves of #1 cylinder to .050" accurately when the piston is at TDC of the compression stroke. Then rotate the crank around to TDC of the exhaust stroke and locate EXACT TDC with a coat hanger or such in the plug hole. Now remove the cam sprocket and chain and bolt the cam sprocket on to the cam temperarally. Now rotate the cam slightly back and forth and check valve clearance. The valve clearance will probably still be excessive so rotate the cam slightly until the valve clearance closes up on one of the valves and put a thin feeler gauge in and move the cam until you get a very slight drag on the feeler gauge. Now go down to the cam sprocket and put a marking pen mark on one tooth and also on the backing plate behind that tooth. (Be exact!) now rotate the cam slightly in the other direction to close up the clearance of the other valve and close it up on the thin feeler gauge you just used on the first valve to a "Just drag feel" and go down to the front again and put another mark on the backing plate EXACTLY in line with the mark on the tooth. You will now have two marks on the backing plate. Now measure EXACTLY half way and put a mark there. That is your alignment mark for the cam with the #1 piston at TDC.
If now when you try to align everything you find that the chain is a half tooth off so that you can't align everything use the two different bolt holes in the sprocket. If it still can't be aligned check to see if the cam sprocket can be flipped over giving you two more optional positions. The bolt holes are not exactly aligned with the number of teeth of the sprocket so as to give you two different settings per side of the sprocket.
Once you have completed this, check it by rotating the crankshaft in each direction to close the valve gap of #1 cylinder and mark the back plate and note that each new mark is evenly spaced on either side of your middle mark and that the piston is the same distance down on each side.
Then you can reset the valve clearance to specs and assemble everything back together.
Any problems let me know.
Howard
