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TR6 Tune Up Tips for TR-6

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Mark_Gibson

Mark_Gibson

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Good Morning,

I finished my complete restoration on my 70 TR-6 last summer, and was just happy to get it on the road in time for some car shows. Now that it's coming out of storage for the 2d season, I'm trying to get the final mechanicals in order. The car starts easily and runs OK, but it seems to be lacking in power. I'm pretty sure the timing is too far retarded, but the timing marks are way off, as it seems when the engine was rebuilt the timing chain was installed a tooth or two off! The compression is excellent across all cylinders (new pistons and rings), the head is basically new, and the dwell is set to factory specs (yes, I'm using the original points set up). The oil pressure is almost 100 psi at cold idle, and about 60 at warm, so the mechanical condition of the engine after the rebuild seems OK. The biggest concern is that to advance the timing, the tach cable length is insufficient to reach the tach drive when I turn the dist clockwise. If I retard the distributor and rotate the plug wires one notch over, it is too far advanced and the car won't run. The carbs were rebuilt to factory specs. Any ideas?

Thanks,
 
Mark,
I am glad you asked this question. I have been wondering about this also.
I have seen many mentions that the dynamic timing should be ATDC and usually 4 degrees. That just seems wrong. All the vehicles, military and civilian, that I have worked on for the last 50 or so years were BTDC. I would like to know why these are different. I used to tune my Triumphs but have not had a runner for probably 30 years and I cannot remember the timing setting I used then.
I do remember that in the 60's, all the refrences I could for the TR4 were for static timing. To find the dynamic mark for my TR4 I initially set my TR4 by the static method and then used a timing light to find the dynamic setting. I never did a static procedure again.
I wonder if anyone with a point ignition setup has done this and what they found? Also did they have the vacuum line connected or disconnected when they checked with the timing light. I would do it myself but I do not have the point ignition parts.
I used to do some racing and once I found the initial reference I did fine tune the adjustment, but this method served me very well.
 
[ QUOTE ]
as it seems when the engine was rebuilt the timing chain was installed a tooth or two off!

[/ QUOTE ]

If indeed the cam sprocket was set off that much, I doubt that the car would run at all. Even one tooth off is a lot. Assume the best, just try setting your timing to run centrifugal advance, ie, about 8 degrees BTDC and plug all you vacumn lines that would go to the dizzy.


Bill
 
Setting the timing by the static method is very easy. Frankly, I do not bother with dynamic settings at all. With engine wear levels and available fuels the timing information provided by the factory is just a starting point.
To set the static timing is set as described in Chapter 4, para. 10 of the Haynes manual using a test light. My 1978 version has an excellent Fig 4.10 that shows the early six cylinder timing marks. Basicially find and align the top dead center mark (on my TR250 there is only one) on the crank pulley with the front edge of the pointer on the timing cover, with No. 1 cylinder at TDC. Rotate the engine counterclockwise until the mark on the pulley aligns with the point where the tapered edge of the pointer meets the cover, i.e. 0.57 inches to the right of TDC when looking from the front of the engine. This is 10 deg. BTDC.
Next, having already verified the correct point gap, and with a 12V test lamp inserted between the spade connection of the low tension wire (black & white)coming from the the dizzy, and a good ground, and with the ignition switched on, rotate the dizzy until the light just comes on. If it is already on when you started, rotate it until it just goes off. You are looking for the point when the points just open.
Now tighten the dizzy clamp and road test the car. Listen for pinging in 4th gear "lugging" it up hills at speeds of 30 to 50 mph. Adjust as necessary to retard if pinging is heard.

When you arrive at the setting you like now connect your timing light to see where its at and record that setting for future use.
 
To add to the above, here is an article borrowed from the 6-Pack Site. BTW if you are not a member I recommend you join. Has a very good web site and glossy magazine.

"It is 1970. You own a brand-new TR6. Everything works perfectly, nothing has been modified. The car is “North American Specification”. The distributor under the Conifer Green bonnet is a Lucas 22D6, part #41306, equipped with both vacuum advance and retard. The ignition timing was set by the factory and dealer at 12 degrees BTDC static, 4 degrees ATDC dynamic. All Lucas type 22D distributors have mechanical (also called “centrifugal”) advance. Yours was set by Joe Lucas himself to provide 0 deg advance at idle, and 22 deg at 5000 RPM. The vacuum advance capsule is stamped 4/7/8; it can provide a maximum 16 degrees of vacuum advance. The retard capsule is stamped 3/10/8; it can provide a maximum 16 degrees vacuum retard.



In the examples that follow bear in mind that: TOTAL ADVANCE = STATIC ADVANCE + MECHANICAL ADVANCE + VACUUM ADVANCE - VACUUM RETARD


EXAMPLE 1

You just started your fully warmed up engine, which is idling smoothly at 850 RPM.

-Static Advance = 12 deg BTDC.
The Triumph mechanic set this by rotating the distributor and clamping it. It won’t change in operation, except for gradual variation due to wear of the distributor’s parts.

-Mechanical Advance = Zero.
Mechanical advance is a function of engine speed only, and your distributor is “curved” for zero advance at this engine speed.

-Vacuum Advance = Zero.
Although the manifold vacuum is very high, the vacuum advance unit doesn’t sense it. The vacuum pickup, on top of the front carb, is masked by the throttle butterfly.

-Vacuum Retard = 16 degrees.
Manifold vacuum is high, and the vacuum “signal” runs from the bottom of the rear carb, where no "masking" is occurring, to the vacuum retard capsule, which is providing its max retard value of 16.

TOTAL ADVANCE = 12 deg BTDC + 0 + 0 - 16 deg = 4 degrees ATDC.
This is why you set static timing to 12 deg BTDC with the engine off, but when you idle the engine with a timing light hooked up you see 4 degrees ATDC.


EXAMPLE 2

You are driving downhill in top gear at 65 MPH, stuck behind some pogue in an MG Midget wearing open-knuckle driving gloves and a tweed cap. Engine RPM is 3000. The throttle is partially open, obviously.

-Static Advance = 12 deg BTDC.
The Triumph mechanic set this by rotating the distributor and clamping it. It won’t change in operation.

-Mechanical Advance = 14 deg.
Mechanical advance is a function of engine speed only, and your distributor is “curved” for 14 degrees advance at this engine speed.

-Vacuum Advance = 6 deg (est).
The manifold vacuum is moderate, and the vacuum “signal” runs from the top of the front carb to the vacuum advance capsule, which is providing “some” advance. This increases both fuel economy and tailpipe emissions.

-Vacuum Retard = Near zero.
Although the manifold vacuum is moderate, the vacuum advance unit doesn’t sense much of it. The vacuum pickup, on the bottom of the rear carb, is masked by the throttle butterfly.

TOTAL ADVANCE = 12 deg BTDC + 14 deg + 4 deg - 0 = 30 deg BTDC.
If someone could hook a timing light to your engine right now, they would see 30 degrees BTDC. That’s a lot of advance for such allow RPM, but the engine can tolerate it without pinging because it is only at part-throttle. Notice that the Vacuum Advance is not really providing any “extra power”.


EXAMPLE 3

You’ve "just" pulled out into the passing lane and mashed the accelerator pedal. The engine is still at 3000 RPM, it has not yet responded.

- Static Advance: 12 deg BTDC.
The Triumph mechanic set this by rotating the distributor and clamping it. It won’t change in operation.

-Mechanical Advance = 14 degrees.
Mechanical advance is a function of engine speed only, and your distributor is “curved” for 14 degrees advance at this engine speed.

-Vacuum Advance = Zero. (Surprise!)
The manifold vacuum is low, hence no vacuum advance.

-Vacuum Retard = Zero.
The manifold vacuum is low, hence no vacuum retard.

TOTAL ADVANCE = 12 deg BTDC + 14 deg + 0 - 0 = 26 deg BTDC.
Notice that you now have less advance than when you were “just cruising” at the same engine speed. That’s because the engine is now under load and can tolerate less advance without going to higher-octane fuel. To avoid pinging, that “nice-to-have” vacuum advance economy feature is automatically cut out.


EXAMPLE 4
Victory at last! 110 MPH through the hills, God bless you. Engine RPM 5000 plus, pedal to the floor.

- Static Advance = 12 deg BTDC.
The Triumph mechanic set this by rotating the distributor and clamping it. It won’t change in operation.

-Mechanical Advance = 22 deg.
Mechanical advance is a function of engine speed only, and your distributor is “curved” for its maximum 22 deg advance at this engine speed.

-Vacuum Advance = Zero.
The manifold vacuum is low, hence no vacuum advance. -Vacuum Retard = Zero. The manifold vacuum is low, hence no vacuum retard.

TOTAL ADVANCE = 12 deg BTDC + 22 deg + 0 - 0 = 34 deg BTDC.
Your engine is spinning fast now, and can tolerate more advance even though it is under load.


Points to remember:

-High manifold PRESSURE = low manifold VACUUM. If the car is at sea level on an average 60 degree day, the outside ambient pressure is about 30 inches of mercury (30" Hg). At idle, the manifold pressure is low, say 12" Hg. That means the manifold vacuum is 30" Hg - 12" Hg = 18" Hg. This is a HIGH manifold vacuum at idle! At full throttle, the manifold pressure is high, say 27" Hg. That means the manifold vacuum is 30" Hg - 27" Hg = 3"Hg. This is a *LOW* manifold vacuum at full throttle!

-Vacuum retard is an idle emissions feature. It does little, if anything, at off-idle RPM unless the throttle is closed (such as during an overrun condition).

-Vacuum advance provides part-throttle economy, not high-load or high-RPM power. It was deleted on later cars due to tailpipe emissions, and power did not suffer a whit because of it.

-Vacuum advance and retard are not intended to operate at the same time.

-TOTAL ADVANCE is what you see when you point a strobe gun at the crank pulley with the engine running. This is roughly equivalent to the “Dynamic Advance” referred to in the Bentley manual.

-If your vacuum retard is no longer operational and you set your TOTAL ADVANCE to 4 deg ATDC with a strobe gun, your car will run poorly, since you just set your static timing to 4 deg ATDC instead of 12 deg BTDC.

Suggested further reading: (Available from the VTR Bookstore, hint, hint).
-Tuning Lucas Ignition Systems, Speedsport Motobooks, ISBN 0851130631
-The Complete Official Triumph TR6 & TR250 1967-1976, Robert Bentley, ISBN 0837601088


Tom Marincic" End article.
/ubbthreads/images/graemlins/cheers.gif
As stated at the conclusion of the article a non functioning vacuum retard module will screw things up if you set the timing with a timing light at 4 ATDC.
 
Nice article Andy.... /ubbthreads/images/graemlins/thumbsup.gif Read it twice!
 
Andy:
Great info and in understandable language. Since you are so elequent with the '70 TR6, I thought I would ask if any or all the 74TR6's were set up with the vac retard (dual pots)? My TR6 only has the advance and does not appear to have had anything removed but I know how that goes.
 
Vettedog: I am no expert on the later TR6s, but its my understanding that the dual advance/retard module was used until about 1971, after that the stock distributors have only a vacuum retard module.
I have a Lucas 41202B on my car, which has only a vacuum advance module, but the standard literature says it should have both. Go figure.
Anyways, check the model number on yours. It should be retard only.
Before using the numbers quoted in that article be sure to check the specifications of your model of distributor found in the Bentley manual, starting at page 511. There were subtle diferences in the amounts of mechanical advance and vacuum retard, depending on model year.
I have to repeat, and give credit where its due, that I did not write the article above.
 
Great info, this should go on the knowledge base.
 
Hello Mark,

firstly I would double check the cam timing, that has to correct or you are wasting your time. To get the distributor in the correct physical position requires the drive spindle to be properly orientated. Remove your distributor, with it set to number one firing (and the engine also)look at the drive spindle and see where the offset slot is. If it does not line up with the drive dog (and that is what seems to be the case), remove it and re-insert it so that the slot ends up where the dog is. It will probably take a couple of goes as you get used to the spindle rotating as it engages on the cam.

Alec
 
I have the correct dual advance/retard distributor, freshly rebuilt. I understand the above descriptions of how the ignition system should operate and be set up. Thanks for all the advice guys, I'll keep you posted on the results.

Thanks,
 
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