TR6 Btdc...atc....atdc

[sundown]

Can someone out there please explain to me.I am trying to understand this timing info. When standing in front of the car the engine rotates CW so when the degrees on the pulley are coming around to the pointer that is BTDC is this correct so the 4 hash mark to the left of the large hash mark is the static setting?

 

[dklawson]

Remember that this is a 4 cycle engine so it takes 2 full revolutions of the engine to complete 1 full cycle. The implication for setting the static timing is that you have to be on the correct TDC.

Specifically, you set static timing (typically BTDC) on the firing stroke for cylinder #1. To determine that you are on the firing stroke and not the intake stroke, remove the valve cover and the spark plug for #1. The timing marks should be starting to line up, the piston will be visible through the spark plug hole, and the rocker arms above that cylinder will be "loose". You should be able to wiggle the arms which means the valve springs are not compressed.

Most engines will start on a static timing setting between 5 and 8 degrees BTDC. Many of our older cars will only specify a static timing figure, some will specify a static figure for getting the engine started and then a dynamic timing figure for final tuning. All those figures should be considered starting points, not carved in stone. The published values were determined as compromise figures for an average, new, as-built engine at the time of manufacture. Chances are your engine isn't what it was when it left the factory and fuels have changed.

A more realistic timing can be determined by getting the engine started and up to temperature followed by using the idle speed screws to bring the engine to about 4000 RPM. Use an "advance type" timing light to set the advance to 32 BTDC then lock the distributor down and return the car to a normal idle speed. Test drive the car by accelerating uphill in too high a gear while listening for pinging and knocking. If any bad noises are heard, retard the timing by 2 degrees and repeat your test drive. Keep doing this until no more bad sounds come from stressing the engine. When you reach that point, record what the advance is at idle and record the idle speed you measured the advance at. You have now found the maximum advance your engine can handle for its current condition, state of build, and fuel you use. If you change the build spec or fuel you are using (say dropping from premium to regular) you will need to reset the timing to match the change in fuel.

As far as which of the pointer marks you need to use, I cannot say. I am not sure if your pulleys on the TR6 are marked the same as on our GT6. I would think the manual should show a few pictures explaining which mark is which.

EDIT:
Poolboy added some pics and info about the timing marks at the page in the link below.
https://www.triumphexperience.com/phorum/read.php?2,710268,page=1
and Paul Rego added more information here...
https://www.britishcarforum.com/bcf...-Does-your-TR6-have-timing-degree-marks/page2

 

[poolboy]

BTDC on the right of TDC...0 to 24 degrees on damper
4*ATDC on left of TDC..0 to 16 degrees on damper

To say I'm not a big believer in using the position of the piston within the combustion chamber as indicated by those marks for setting the time for the spark plugs to arc would be an understatement, but if you are, you should get the engine running and warm, disconnect the vacuum retard tube from the bottom of the carb and cap the nipple so it won't be sucking air and disrupting the fuel air mixture.
Then while maintaining idle speed of 850-900 rpms by adjusting the throttle stop (idle speed) screws set the timing in the 12 to 15* BTDC range.
These are the instructions that came back with my distributors from Advanced Distributors.
When or if you decide to reconnect the retard to your distributor, the idle speed will drop and you will need to raise it back up...if the retard is actually working.

 

[TR3driver]

Can someone out there please explain to me.I am trying to understand this timing info. When standing in front of the car the engine rotates CW so when the degrees on the pulley are coming around to the pointer that is BTDC is this correct so the 4 hash mark to the left of the large hash mark is the static setting?

A bit more background:
The 4 to the left of the large mark is actually the factory "dynamic" timing mark; which by US law at the time (EPA mandate) had to be at 4 ATDC. This was an emissions thing, the thought was that by using an incredibly late ignition timing at idle, the throttle would have to be open farther, which raises peak cylinder pressure and promotes more complete combustion (which in turn lowers unburned hydrocarbons in the exhaust, thought to be a major component of smog). To achieve the late timing, the TR6 (& TR250 & Stag) use a vacuum retard module, that pulls the timing back only when the throttle is closed. The "static" timing (which is also the dynamic timing when the vacuum retard is not operating) was around 10 or 12 degrees (depending on year).

There was supposed to be a sticker under the hood explaining the "proper" timing procedure (again by EPA mandate), which was to set 4 ATDC with the retard connected. Unfortunately, many of the manuals were not properly updated, and they say to remove the vacuum line (which is appropriate for non-US models with vacuum advance and not vacuum retard).

Although technically still illegal, many people choose to just disconnect the vacuum retard, back off the idle stop screws to get the idle speed down, and set timing to the "static" figure from the book (or any of the alternate methods outlined above). In some cases, it may be necessary to adjust the linkage to the float bowl vent valve to get the idle down that low without the retard.