TR2/3/3A Timing TR3A and Overheating

[TFB]

RAndal
What does vacuum specs 7-14-10 mean?,listed for tr3a.
I forgot about starting rpm advance.
What is vacuum advance+ centrifugal,to equal total?
From the chart it looks like 8.75 at 700,low idle, 14 degrees(total I guess) at 2700and 1.75 at 500.Not sure if idle would go that low to check.
I guess after setting at 8.8 with light you could then check static and see what the difference is.
Never hand started my old tr3,but too much advance kick back can break your leg on an old motorcycle.
I agree with the road test method but feel that may be fine tuning,after initial tuning.
I usually like to set timing by book,then it's one variable elimenated when adjusting carbs.Then back to fine tune ign. timing ,then back to carbs.
Thanks for the great info,I'm here to learn.
Tom

 

[TR3driver]

What does vacuum specs 7-14-10 mean?,listed for tr3a.

That means the vacuum advance should start to move at 7 inches of mercury, and reach 10 (camshaft) degrees of advance at 14 inches of mercury.

I'm sorry the document isn't clearer, I really put it together only for my own reference in sorting this mess out. Never did really finish the research, just got bored and moved on to something else

But the line you are looking at indicates only that that advance unit is what a Triumph owner (Kent Shrack) found on his car. The line just below it indicates that, according to Lucas documentation, a model 40480 distributor should have a model 421953 vacuum advance module, which is rated as 4-11-7.

A given model distributor would always have been fitted with the same (or equivalent) advance module by the factory, but of course the advance modules get replaced separately and so what is found on the car may vary considerably. Many vendors offer a "one size fits all" replacement. Most original modules have both the part number and the advance specs stamped into the housing (although it can be hard to read without a magnifying glass).

Gotta go, more later.

 

[DNK]

What kind of wine does your TR3 like with its cheese, Randall?

 

[TR3driver]

What kind of wine does your TR3 like with its cheese, Randall?

It's partial to 95 octane leaded; but I'm afraid it does get that much any more. Much like it's owner, it had to give up the good stuff.

 

[TR3driver]

What is vacuum advance+ centrifugal,to equal total?

When most people talk about "total" advance, they mean initial advance (the amount you set with the light) plus the centrifugal advance only. That's because they are interested in full throttle performance, when the vacuum advance isn't doing anything. Furthermore, it is usually given in crankshaft degrees (since that is the way it's measured).

Maybe an example will help. I'm going to arbitrarily pick a model 40795(A) distributor, since I believe that is correct for late TR3A. This is the model number given in Practical Hints 6th edition (the driver's handbook published by Triumph and delivered with the car).

The centrifugal advance curve for 40795 (according to Marcel Chichak) ends at 1200 distributor rpm, or 2400 crank rpm; with 10 (cam) degrees of advance, or 20 crankshaft degrees.

According to Lucas documentation, a 40795 would have a model 54413565 vacuum advance, rated 2-6-3.

So, cruising at roughly 60 mph, we would have an actual ignition advance of 30 degrees total; 4 from initial timing, 20 from centrifugal advance, 6 from vacuum advance. This is the highest possible advance.

If you then floor the throttle to pass someone, the vacuum advance drops out, and the actual advance is only 24 degrees.

Does that clarify the situation any?

 

[TR3driver]

Oh, one other comment on "tuning" : In my opinion, initial tuning is only to get the engine running, so you can fine tune it. There are way too many variables to be able to say that one particular number is "right".

Just one example, here in the US, the fuel you buy will vary in composition based on time of year, and even the part of the country where you buy it. Modern cars of course compensate for these changes, but our Triumphs don't.

Practically all cars sold here for the past 20 years or so have had a "knock sensor", so they can silently retard the timing if you use lower quality fuel. Triumphs don't have that feature, so if you hear it knock, you'd best either get off the throttle, or pull over and tweak the timing for the current conditions.

 

[TFB]

Randall,
Great to have these numbers for future.I print most of this stuff to add to manual.
When I set ign. with light I will set at 8,check for smooth advance until 30,and 4 static, as a starting point and see what numbers are on my dis.
Right about the gas.I used to work in refinery.The gas is different everyday.

Thanks
Again,
Tom

 

[TR3driver]

Just to show that sometimes it's the simple things that trip us up, my TR3 has been running a bit hotter than usual this week. Couldn't figure out the problem, but the TR4 temperature gauge I installed last month (along with my own solid state conversion voltage stabilizer) seemed like a prime suspect.

Today it finally dawned on me to check the fan belt, which was <span style="font-weight: bold">very </span>loose. Not sure how it got that way, but I saw that the flat washer installed by the previous owner on the adjustment slot is now folded almost double, so I'm guessing it slipped. On the 20 mile drive home, it ran cooler than it has since I've installed that gauge!

Tomorrow when it's cool, I'll install a heavier, hardened flat washer (aka setup washer).