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Has anyone ever purchased a rebuilt distributor from autozone to fit tr3-4a? It sells around a 100 dollars but the idea it fits different models cautions me. They could not give any information on exactly which model # distributor it was. With new bushings installed, could you just take your weights out of your old dist. and use them in the new one to have the right advance? Any thoughts appreciated, Charlie
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TR4/4A Rebuilt Distributor: TR3-4A
- Thread starter PlaidMan
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DougF
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Don't be concerned about parts being shared between different cars. Not only were some things the same within the same marque, some were shared between marques. The new MGB distributor that is available will also fit the TR3/TR4. Many body parts were also shared.
These companies were working on very limited budgets and did the best they could with what was available.
Think of how many different cars had that TR3/TR4 engine. How about the Rover V8?
I would be more concerned with the quality of rebuild.
These companies were working on very limited budgets and did the best they could with what was available.
Think of how many different cars had that TR3/TR4 engine. How about the Rover V8?
I would be more concerned with the quality of rebuild.
TR3driver
Great Pumpkin - R.I.P
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The difference is in the advance curve, which is pretty much wrong for modern gasoline anyway.
Within a given Lucas distributor (eg DM2 or 25D) the weights were all the same anyway. And AFAIK, they do not interchange across different models. (Certainly DM2 and 25D weights are quite different.)
The advance curve was adjusted by using different springs, and a different advance stop. See
https://www.jcna.com/library/tech/tech0015.html
for more than you ever wanted to know about the subject.
BTW, there were many different advance curves used just in the TR2-4A range of cars. Basically every variation of intake, exhaust or camshaft had a different advance curve. There were even different distributors for the 83mm liners vs 86 in the same car. Most likely, any curve will work well enough, it just won't be optimum. But you have to watch out for undetected knock, as it can destroy your engine. Somewhere, I've got a TR3 piston with the ring lands broken, as a reminder.
Within a given Lucas distributor (eg DM2 or 25D) the weights were all the same anyway. And AFAIK, they do not interchange across different models. (Certainly DM2 and 25D weights are quite different.)
The advance curve was adjusted by using different springs, and a different advance stop. See
https://www.jcna.com/library/tech/tech0015.html
for more than you ever wanted to know about the subject.
BTW, there were many different advance curves used just in the TR2-4A range of cars. Basically every variation of intake, exhaust or camshaft had a different advance curve. There were even different distributors for the 83mm liners vs 86 in the same car. Most likely, any curve will work well enough, it just won't be optimum. But you have to watch out for undetected knock, as it can destroy your engine. Somewhere, I've got a TR3 piston with the ring lands broken, as a reminder.
Hello Charlie,
as an addition to the above, the advance stop is marked in degrees of distributor advance (half of engine advance) so you can see what you have to use as a basis. (That could be wrong of course if a wrong model distributor had been fitted in the past. This is where an accurate manual is invaluable)
Alec
as an addition to the above, the advance stop is marked in degrees of distributor advance (half of engine advance) so you can see what you have to use as a basis. (That could be wrong of course if a wrong model distributor had been fitted in the past. This is where an accurate manual is invaluable)
Alec
TR3driver
Great Pumpkin - R.I.P
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I don't have a good answer for that; short of running the engine on a dyno or installing a knock sensor.Geo Hahn said:
Certainly a good thing to check if you are playing with advance curves; but the problem is knowing how much advance the engine "wants" without knocking under the conditions at hand (engine mods, fuel, intake temp, etc.)Geo Hahn said:
MGTF1250Dave
Jedi Knight
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I will also recommend Jeff at Advanced Distributors. He recently rebuild my TR3A distributor, it took about two weeks total including shipping to and from Hawaii. As I recall his basic service is about $75. Here is a link to his website:
https://www.advanceddistributors.com/
I was very satisfied with the work. The distributor looks and works like new. He will check and re-curve the advance based on your engine modification.
Before you buy a new distributor, IMHO you owe it to yourself and your car to check out Advanced Distributors.
https://www.advanceddistributors.com/
I was very satisfied with the work. The distributor looks and works like new. He will check and re-curve the advance based on your engine modification.
Before you buy a new distributor, IMHO you owe it to yourself and your car to check out Advanced Distributors.
Brosky
Great Pumpkin
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Here is what you get for your money:
https://www.74tr6.com/distributor.htm
OR
https://www.74tr6.com/distributoradjustable.htm
I have four of his distributors, three of which are spares. I have sent at least ten other locals to him and everyone was very happy with what he did for them.
https://www.74tr6.com/distributor.htm
OR
https://www.74tr6.com/distributoradjustable.htm
I have four of his distributors, three of which are spares. I have sent at least ten other locals to him and everyone was very happy with what he did for them.
dklawson
Yoda
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Geo Hahn said:
Typically it's not silent. It's that wonderful knocking and pinging you hear when you put the engine under load while running low octane fuel and too much timing advance. The way around it is to retard the timing until the sound goes away... or run higher octane gas.
Marcel (who wrote the article in the first link of this thread) will tell you (as he told me) that the ONLY way to get a proper advance curve is to make changes to the distributor as part of dyno tuning. I asked him once for assistance in figuring out a new curve for a 23D4 distributor I was working on. He told me he would not give me any suggestions as they would be a wild guesses.
I've only heard good things aboug Jeff's work. I'm sure if he rubuilds your distributor it will be right. You'll also know that the distributor will have the right "as built" curve for your car.
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Yes - Limiting the maximum advance, (centrifugal plus initial, no vacuum) to 32 to 36 degrees at high rpm would be a safe method. In fact, the only practical method for most folks.Geo Hahn said:
"Silent" detonation typically occurs at higher rpm & high loads where other engine noises mask the sound. As TR3 said, it can destroy an engine. The higher the compression ratio & the more radical the cam, the more likely this is to occur.
One of the confusing things is that distributor advance degrees & rpm are used to spec distributor characteristics & are 1/2 that of the engine settings.
Typically, full engine centrifugal advance plus initial advance (no vacuum) should be no more than 32 to 36 degrees total at the maximum centrifugal advance rpm, usually 4,000 to 4,500 rpm. Vacuum advance is only applied at lighter engine loads.
The exact number will depend on engine design, compression ratio, & fuel quality. Too much advance will give very little increase in power, so better to err on the lower side.
Many modified engines, especially with more radical cam timing, will give much better throttle response at lower rpm & or lighter loads with more than original designed advance at lower rpm. Typically 25 crankshaft degrees at 2,500 engine rpm. BUT the high rpm advance of 32 to 36 degrees still must not be exceeded.
Assume the original distributors max. design centrifugal advance was 26 degrees crankshaft (13 degrees marked on distributor cam arm) at 4,000 rpm & the initial timing were set to 15 degrees to obtain good throttle response (possibly 25 degrees advance) at 2,500 rpm. The maximum advance at 4,000 rpm would be 15 degrees initial plus 26 degrees centrifugal, or 41 degrees total. Unheard detonation, & engine damage, would be likely.
To get the desired lower rpm timing increase without exceeding the safe maximum, the centrifugal advance calibration is changed. Typically, the advance control springs would be changed to allow quicker advance to 25 degrees at 2,500 engine rpm, & the centrifugal advance stop changed to limit it to 32 to 36 degrees (engine) at it's maximum advance. ie. 15 degrees initial plus 18 degrees centrifugal (9 degrees marked on centrifugal stop) = 33 degrees total advance.
If you exceed this advance setting, carefully monitor sparkplug condition. Signs of high rpm detonation will be overheated plug electrodes. Or on worse cases, visibly melted electrodes. In this instance, it's likely that piston damage has already occurred.
Folks such as Jeff S. have the equipment, knowledge, & parts to tailor your centrifugal advance to an optimum but safe calibration. If you fill out his engine spec sheet, he can get things pretty close.
D