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TR2/3/3A timing DM2P4 dist, TR3A - vacuum?

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Hello Tom,

as you said that the car tends to stall and is difficult to start hot, that seems to indicate that the mixture is weak.

The timing should vary with engine speed, increasing speed should show more advance. I don't know the spec of your distributor and the speed at which it starts advancing varies by quite a bit from one variant to another. That is what the number code is for on the side of the distributor, there are dozens of variants of the 25D series as with other Lucas types.

Alec
 
Curious? Have you checked the fuel pressure and volume from the pump?

That is an area that I would consider of primary influence.
 
You guys have provided excellent suggestions for my further exploration. As I work on weekends (OSV.org) I'll have to wait 'til Monday to get back to my idle investigation. Really appreciate the detailed diagnoses and paths to pursue.

To answer a few questions:

I'm a little confused, since yesterday you posted that it didn't vary much above 1000 rpm, but today it does. Is that right ? Before setting the timing, I'd back out the idle (throttle) screws all the way, but still have idle at around 1500. I could watch the idle slowly change from 1500 to 1200 to 2000 and back down to 1500, but never slower, and the engine would never die. After first setting the timing yesterday, I started the engine and it began idling around 500, then got slower (never faster) and stopped. I restarted, screwed in the throttle screw to raise the idle to around 800, then watched it slowly drop from 800 to 600 to 400, then die. Again, never got faster, only slower. So I raised the idle to 1000 and it varies slightly between 1000 and 1500 (up and down), but never drops below 1000 and engine never dies.

What does the timing mark do while the idle rpm is varying ? I've read to do only static timing, so I've never tried watching the timing mark with a strobe. (sorry - I'm assuming you're asking about the mark under a strobe)

What work was done on the car before the high, varying idle developed ? I received the car back in February; the high (+/-1500) varying idle existed back then up until I set the timing yesterday. I don't know what work was done prior to my receipt of the car; however, I do know that just before the previous owner sent it to me, he had re-connected the choke cable and choke linkage. Edit: Best I recall, he told me the idle as too fast for the years he owned it, and his mechanic was unable to lower the idle speed.

Carburetor: Lucas 25D, part #40897A. Sounds like a very late 25D.

After setting the timing, it's difficult to start hot, and diesels at shutdown. Prior to timing work it started both cold (with full choke) and hot (no choke) at the absolute first crankover. Never dieseled. I had replaced carb jet seals about two months ago to get the choke to work; at that same time I set and balanced the two H6s. Idle was still around 1500rpm with the throttle screws fully out.

Fuel pump pressure/volume: haven't checked that.

Interesting to consider that the engine seemed to run beautifully *except for that high idle* before I set the timing. I decided to set the timing following a suggestion that incorrect timing can often result in faster than normal warm idle.

When I started the timing work yesterday, I found that the A/R vernier was fully retarded; knob wouldn't turn any further toward "R". While twisting the dist to try to turn off the test light, the copper vacuum line broke at the dist vacuum unit, so I had to cut and refit the line through the compression fitting to the dist.

One footnote: remember that when I tried to set timing with the plug#1 to coil light, the only way I could get it set was by holding the rotor against the spring. Trying to set the timing by the "CCW - CW - light on/off" method was impossible without manually twisting that rotor shaft.

Thanks all.
Tom
 
As an aside to this thread....is it true that the Petronix setup will help keep timing where it should be even if the dist bushing or shaft is worn? Also this is a bit of a long shot but are you sure the throttle stop on the carb closest to the firewall is set where it should be? Karl
 
Karl - thanks for the followup. After I set and balanced the carbs a couple months ago, I re-connected the throttle shafts between the carbs, and fully retracted the firewall side carb throttle screw (so it doesn't hit the stop). Thus the idle is set by only the front carb throttle screw.

Tom
 
Hello Tom,

" Trying to set the timing by the "CCW - CW - light on/off" method was impossible without manually twisting that rotor shaft."
This will give an incorrectly timed engine.
When you let go of the rotor shaft the timing will shift in a retarding direction, by a large amount. I thought that you had understood that by loosing the split clamp bolt that the distributor will rotate (360 degrees if you want). They sometimes can get tight, so it is worth removing the whole assembly and freeing it up. The clamps can get distorted over time and overtightning. Set the timing statically without touching the rotor shaft.

I see no reason not to use a strobe light to time the engine. Static timing is how it would be done when the car was new as strobe timing equipment, if available at all, would be very rare? The difference between static timing and dynamic timing will depend on your distributor, some will have started to advance at idle (approx 700rpm) others may not, in which case static and dynamic will be the same setting.
Really, the timing to book figures is a start, but then you may find that adjusting from this setting is better depending on how the car drives. Fuels have changed since the car was built so in the end you need to adjust the timing to an optimised setting.

Just one point with the carburettors, check the fast idle (choke) screws are clear when the choke is pushed in.

Alec
 
Piman: I thought that you had understood that by loosing the split clamp bolt that the distributor will rotate (360 degrees if you want).

Just to clarify, I loosened that split clamp bolt so I could rotate the distributor.

With the light between ground and the coil, and ignition on, the light was on. Turning the dist *in the full range possible* did not change the light to off for that CW-CCW test. That's what puzzled me.

So when someone suggested that the dist shaft bushing might be very worn and allow shaft play, I (wrongly) guessed that the person was saying that rotational shaft play might be causing the difficulty in setting the timing. So I manually rotated the rotor shaft; that's when the points would change and the light would go off.

Turned out the suggestion on the worn bushing referred to radial play, not rotational play, in the shaft. So my "correction" for play was incorrect. I had no radial play at all, so the worn bushing issue is pretty much moot.

I think the big puzzle for me is that I couldn't set the timing using that CW-CCW technique. Maybe I just didn't rotate the dist enough - altho' it sure felt like there's a limit caused by the vacuum unit touching the engine when turning the dist clockwise, and a "built-in" stop when turning it CCW.

Alec - are you saying I should really be able to rotate the dist a full 360 degrees?

Sorry for being so dense guys. When the vacuum unit and vacuum line hit the engine on turning the dist clockwise, I just figured there was no way to turn the dist a full 360.

Onward through the fog!
Tom
(my learning curve steeps with every breath!
 
hello Tom,

yes, basically, but of course as you have found out, the vacuum unit snags. So, if that is what was stopping you getting the timing spot, the distributor will need to be removed and re fitted so as to re-mesh with the camshaft such that you can adjust in the timing 'window'. Sorry for the cumbersome description but I hope it is clear.
A relatively simple way is to pull the distributor out of the block, you will see the distributor shaft rotate due to the skew on the gear. Make a rough note of how many degrees it turns. Set the engine to TDC on your number one firing point. Set the distributor body approximately where you want it to sit (as per the photo in an early reply?). Turn the rotor to the number one spot in the cap, then turn it as much as it turned when you removed it, in the opposite direction. Re-fit the distributor and it should then end up with the rotor pointing to the number one spot. Don't worry if the first try is wrong, just re do the removal\re-fitting, learning from your first go. You should then be able to set the timing correctly.


Alec
 
It's not quite as easy as that. If you pull the distributor out, you will see that it is driven by an offset dog that goes into an offset slot. That slot has to be in a certain position when #1 cyl is at TDC. If it's not, then the distributor/tach drive has to be removed and repositioned. The dist/tach drive also drives the oil pump.

From the TR3 factory service manual...

This drive is taken from the helical gear on the camshaft through a similar gear unit mounted on the oil pump driving shaft. The shaft has a tongue at the lower-most end which engages the oil pump mounted in the sump.

The helical gear unit is secured to the shaft by a woodruffe key. The upper gear on this unit drives the tachometer and the boss-like extension is fitted with a mills pin to prevent the gear and shaft from rising. The head has an offset recess into which the distributor shaft will seat.

When correctly engaged, the slot in the distributor driving boss, with #1 cyl at TDC on the compression stroke, should assume a position "five minutes to five" (53 deg) with the offset towards the rear of the engine (Fig. 16). In this position the slot will point directly towards the exhaust valve rod sealing tube for #1 cyl, the distributor rotor will face #1 sparking plug, and the keyway in the helical gear will be aligned with the oil dipstick when fitted.

If I had a picture of Fig. 16, the line-up would be much more obvious. I'll see if I can dig one up online. Also, there is a specific procedure for getting all of this lined up properly, as there is the all important engagement of the oil pump that has to be taken into consideration. If you just yank out the distributor drive pedastle, and move the engagement gears, the oil pump drive won't line up with the slot in the pump. I suppose you could futz around with a long screwdriver to align the slot in the pump, but if you want the factory procedure, I'll post it.

Meanwhile I'll see about Fig.16.

Edit: Silly me, why hunt for a picture online when I can just take my own.
 
Hello Mart,

thanks for the clarification. I must admit I assumed that, as later triumphs have, a gear rather than a dog. so it is a little more complicated.
However that being the case it could be more likely that the drive spindle is correct and that the plug leads might be one cylinder out in the cap? This would allow a 90 degree change of effective distributor position.

Alec
 
This could be true, but the only way to tell is to put the engine on TDC of #1 cyl on the compression stroke, pull the distributor and check the slot alignment according to Fig. 16 in my last post.
 
Hello Art,

yes, easily checked, but as you say a bit more of a job to rectify. I take the point about the oil pump drive so some fiddling and trial would be required to pull the drive shaft, move the oil pump shaft x degrees and try to re-insert the distributor drive shaft and hope it picks up the oil pump and allows the shaft to go back into full mesh. If it fails it's a sump off and refit the oil pump after fitting the drive shaft.
I do feel that my suggestion of moving all the plug leads by one post gives an option that could be less trouble?
Alec
 
At least on my TR3A engines, it's been a relatively trivial matter to deal with engaging the pump drive. Chose the right tooth for the gear, then bump the engine over a bit; either by rolling it in gear or just touching the starter. The gear will engage and drop down over the shaft.

Oops, I meant the shaft will engage the oil pump and drop into the slot. I pre-engage the shaft with the gear, then turn the engine to get it to match the oil pump.
 
Good tip Randall. I'll file that in the back in my head for future reference. It would make it alot easier then the method outlined in the factory manual. /bcforum/images/%%GRAEMLIN_URL%%/cheers.gif
 
karls59tr said:
As an aside to this thread....is it true that the Petronix setup will help keep timing where it should be even if the dist bushing or shaft is worn?
Click to expand...
It will help, but an optical pickup system (like a Crane or Lumenition) will help more. The Pertronix is still somewhat sensitive to gap.
 
TR3driver said:
karls59tr said:
As an aside to this thread....is it true that the Petronix setup will help keep timing where it should be even if the dist bushing or shaft is worn?
Click to expand...
It will help, but an optical pickup system (like a Crane or Lumenition) will help more. The Pertronix is still somewhat sensitive to gap.
Click to expand...

The Pertronix uses rotating magnets & a Hall-Effect sensor. This setup is very insensitive to gap changes, eg. .017" gap change = 1 degree dwell change. It is totally insensitive to vertical position variations, & is not subject to optical shutter contamination.
D
 
karls59tr said:
As an aside to this thread....is it true that the Petronix setup will help keep timing where it should be even if the dist bushing or shaft is worn Karl
Click to expand...


Yes it is absolutely true!. It will keep the timing spot on---Keoke-- /bcforum/images/%%GRAEMLIN_URL%%/yesnod.gif
 
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