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Triumph TR6 - Basic ignition timing

I'm sure the answer to this is buried in previous threads; never the less, a simple question:
My TR6 is an early 1974, CF24228U, with a plain vanilla stock engine. I'm starting a basic tune-up and want to set my timing at the factory setting before I start tweaking. I understand that the timing at idle (800 to 850 rpm's) should be 4 degrees ATDC. Bently indicates that this should be the reading with the vacuum retard hose DISCONNECTED. It seems that in other threads I've read that the reading should be adjusted with the retard CONNECTED. I'm looking for the real starting point.

Below zero in Minneapolis today; let the projects begin!

When things are completely out of whack a static timing of 11 deg BTDC is first used to get the engine started. Then the timing is set to 4 deg ATDC WITH the vacuum retard unit connected. Also, be sure and check that the retard module works - the diaphram can sometimes fail.

Brent B

UK cars never had that vacuum advance unit (which advances the timing when there is a low pressure in the inlet manifold- for emmission reduction, not performance) and they had a static setting of around 11 or 12 degrees. But they also had higher compression heads. USA cars with lower CR will need less advance. The best way to find the optimum timing is to warm the engine up, set static to 12 degrees approx ( vacuum advance canister diconnected permanently) and then with engine on tickover slowly turn the distributor (clamp loosened) slowly, degree by degree until the tickover speed is highest. Use throttle adjustment to keep engine speed around 800, to ensure the centrifugal advance does not begin. Don't forget to retighten that clamp.
P H Cobbold

Actually, it is a vacuum retard unit - the theory being that when the throttle is open the timing follows the distributor centrifugal advance curve, and when the throttle is closed at idle the higher manifold vacuum overrides the spring over the unit and "pulls back" the timing. With engine mods I found the vacuum unit gave too great a timing range for acceptable performance, so it's been disconnected. The timing's now set at 7 deg BTDC at 900 RPM.

Brent B

Keith--I have the same setup on my 72. I could never get it timed using the Bentley method because the idle would rise very high with the retard disconnected. The Bentley method is 'retarded'. Just leave the retard connected and shoot for an initial timing of 4 degrees BTDC (not ATDC). The final timing should be set by the seat of the pants just below detonation (pinging in 3rd gear up an incline). This method works for me and results in good fuel economy/performance.
Rick Orthen

as long as we're discussing basics.
how do you test the advance and retard modules?
also I have a 70 TR6 am I right in thinking this year
has one of each? which side is which?
Ian Kinaid

The manual I have (Haynes) says that the early models had distributors fitted with BOTH advance & retard modules, but the advance units weren't hooked up. The retard module faces back towards the firewall. To test 'em, plug on a clean piece of hose and suck on it. If you get air, the diaphragm is cracked. If it holds, it's ok. The longer you do it, the more likely the car treat you better, too.

Brent B

Let's get it straight. The disy rotor rotates anticlockwise. The vacuum advance capsule uses inlet vacuum to pull the moving contact breaker plate in the clockwise direction. So vacuum in the inlet manifold **advances** the ignition timing ( ie the spark occurs earlier). (This gives longer for the weak off-throttle mixture to burn.)When the trottle is opened the vacuum reduces towards atmospehric and the plate moves clockwise, pulled by the little spring, and the ignition retards. This will happen even if the rpm are too low to operate the centrifugal advance springs (which are in now way affected by the capsule.)
I should know as I've designed and built a solenoid-operated boost-retard unit to replace that vacuum advance unit. This retards the ignition when I hit 6psi boost on the blower by moving the contact breaker about 3mm clockwise, retarding the timing by about 14 degrees.
I agree with Brent in that the vacuum advance is best disconnected, provided the leak into the inlet manifold after removing the hose is plugged up! Use Rick's method , or mine, or and average of both, to get the optimum timing for your engine- which will depend on fuel, compression ratio, engine breathing, altitude, etc etc.
P H Cobbold

I'd concur with you, except that every source I've seen calls it a vacuum retard unit. Also, if you disconnect it, the timing advances. Sounds like a retard unit to me.
Brent B

Is there any question why I'm confused?

Hey, you asked for it! :)
Chris W

Earlier TRs (2/3/4s) had a vacuum capsule facing the front of the car that works as Mr. Cobbold says. The 250 and early 6s (NA market at least) had dual capsules; one faced front and one rear on the same side of the distributor. One would think they would cancel each other out for a net effect of zero, but I'm sure they did something. By late '70 the front capsule was dropped and the rear-facing one was the only one left. This configuration was used to the end of production (NA market at least).
Where this 'retard' capsule is mounted makes it pull the plate counterclockwise. My 72 had a broken one, which I replaced, and the engine then ran 300 RPM slower. Originally (starting sometime in 72) there was a thermo-valve in the top radiator hose that closed the vacuum off if the water temp got too hot. No vacuum=faster idle, so engine fan pulls more air across radiator and cools engine off. Reminded me of that Rube Goldberg Mousetrap thing. For a while it worked in that it would make the engine run faster when stuck in traffic, but it never slowed down (or cooled off). I ended up using Rick's method and junked the thermo valve. Triumph stopped using the thermostatic valve in '75 (but kept the retard unit).
Car is long sold, but it ran best when the vacuum stuff was inop and I advanvced until it pinged!
Jeff Fetner

Anyone care to give me a quick lesson on pinging?

Ping, or preignition, occurs when the fuel/air mixture in the cylinder ignites before the spark occurs - or too early. It is most undesirable since alot of the energy of the fuel explosion opposes the piston motion instead of forcing the piston back down, and engine damage can result.

Generally, it happens when the rpm's are low amd power demand is high, which is why the classic "test" for the TR6 is to try and accelerate hard from 30 to 50 mph in 4th gear. To me the sound of pinging is a fairly loud "clatter" when the pedal is pushed. I'm sure others would describe it differently. So try and accelerate, if you hear a clatter retard the timing 2 degrees and try again.

Another alternative is to use a higher grade of gasoline if you're not already on "premium". The octane rating is a direct correlation of a fuel's tendency to "ping" - lower values have the greater tendency.

Brent B

Use a handheld vacuum pump to apply a vacuum to the unit - you can visibly see if the rotor moves. If the diaphram has a leak, it will not hold the vacuum. The same vacuum pump can be used with a kit to bleed the brakes. It's also helpful for finding fittings and lines that leak. The pumps usually have a small gauge on them to show how much vacuum you are pulling, and the rate of return on the gauge helps to show rate of leaking, if any. The pumps usually cost about $25 (I bought mine several years ago, so cost may now be higher). Check Sears or Eastwood for the pumps.

further to Brent Bs explanation...the other 'undesireable" to pinging is engine damage.
Rick c
Rick Crawford

This thread was discussed between 12/01/2003 and 24/01/2003

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