TR6 Ignition timing problems

[mikeyb]

I had to remove metering unit to replace dodgy fuel pipe to No.2 injector along with the dizzy pedastal to cure an oil leak.

Having previously had a good running car with timing set to 4 ATDC as per the pulley marks, I set the engine to TDC, marked the dizzy/pedastal up and pulled it apart. Having reassembled, setting up drive gear, dizzy & MU up as per the book (yes the correct book, not the erroneous haynes etc.!), I now find the car runs sweetly but not at the 4 ADTC timing mark. More like 20-30 deg ATDC.

 

What worries me is bearing in mind the car was adjusted and ran fine to its prescribed timing mark before, it doesn't at the same position now - which is almost off scale on the pulley.

 

I took the dizzy out again yesterday, pulled it apart to make sure everything inside was moving as it should - it was, although I did find a tiny unused rivet stuck in the bottom - looked similar to those holding the centrifugal weights together. I also changed the vac advance unit (albeit not used on the TR6) as the vernier adjustment has seized on the old and the wheel had been mullered!

The result - no difference whatsoever! By ear the car timed up at an indicated 20 deg BTDC, on the road drove nicely. Timing then rechecked using the vacuum method resulted in an indicated setting of 24 deg BTDC, but with some pinking on the road test. There was also a perceptible increase in fume from the exhaust. So I have ended up back at 20 deg BTDC, the car is a pig to start from cold, tickover is lumpy and hunts but on the road she absolutely flies - way better than ever before.

Still concerned, cannot work out the root cause of this change. Car is off to Le Mans in a couple of weeks so need to get to the bottom of this!

[RogerH]

Hi Mike,

I'm not a tr6 person but my 4A has its static timing BTDC (before) you state yours AFTER TDC - is that right?

 

Could you be one tooth out on the dizzy drive?

 

 

 

Hi Mike,

just read your CT forum posts.

Your last paragraph suggests you have gone from ATDC to 20BTDC with lumpy tick over.

Is 20BTDC too much and should it be a lower figure.

Edited May 23, 2015 by RogerH

[mikeyb]

TR6 CP should be timed dynamically to 4 ADTC according to the workshop manual - this is the setting I inherited with the car and it ran fine at that position before I started. Moving the dizzy drive cog around didn't change the timing mark position on the front pulley, jut the angle that the dizzy pointed to for it to run right.

 

20deg BTDC is way too advanced, but a) she pulls like a train now at that setting without pinking and she will hardly run at all at the correct setting of 4deg ATDC.

 

cheers Mike

Edited May 23, 2015 by mikeyb

[Peter Cobbold]

Mike,

4 ATDC ?????????

I dont recognise that.

I think you have been reading data for timing the USA dual vacuum canister disy. Which was not fitted to CP PI engines

 

What do you mean by "dynamically" ? are you checking the centrifugal advance curve?

 

 

The CP PI engine should be set to 11-12 BTDC static. No revs. No vacuum capsule connected up.

It would run at 4ATDC static but will be horribly retarded and risks burning exhaust valves rapidly.

 

So the 20BTDC you have now is closer to correct, it is not "way too advanced". It would be pretty good for a low compression head, but a little too advanced for a CP 9.5:1 head. But if it doesn't pink then "20" may well be about right because the timing mark could have slipped with age and no longer reflects true TDC.

 

So if it runs like train, note the timing position and enjoy!.

Spark timing is not super-critical anyway:

see third figure here:

https://supertrarged.wordpress.com/2015/02/25/combustion-basics/

At 4ATDC you were abut 15 deg too retarded, so torque would be down around 10%, but it wastes fuel and the engine runs too hot.

 

 

Peter

Edited May 23, 2015 by Peter Cobbold

[peejay4A]

I think you should verify that TDC on the engine is TDC on the pulley. Otherwise you're guessing.

[mikeyb]

Hi Peter, yes I wondered about that setting - it came up when I searched the forum for it. Strange too that the pulley on the car has been"chisel stamped" at that figure.

 

From:

 

http://www.thorden.dk/Teknik/TR6%20Repair%20Operation%20Manual.pdf

 

Sheet 86.35.00 Sheet 1 (page 462 on my reader) states that the 41219 dizzy (mine) should be set to 11 deg BTDC static. I do not know why the manual does not state any figures for timing at idle (dynamic as I would perhaps erroneously call it), however for almost all the other dizzys listed, the stated static timing of 12 deg BTDC looks to correspond to a idle setting of 4 deg ADTC so (maybe incorrectly) I have made the assumption that on the strobe, that will be pretty close to that figure also for my dizzy. Please correct me if my assumptions are wrong!

 

Pete, for my piece of mind, I will go back to first principles and check that TDC really is where the markings show it to be. I will then try a static setting of 11 deg BTDC and check what the strobe says!

 

Thanks to you both.

[peejay4A]

As long as you keep the idle revs below when centrifugal advance (should) begins your strobe ought to read 11 deg btdc. Say around 800rpm. As Peter points out unless you have a U.S. Motor 4 deg atdc is plain wrong.

Edited May 24, 2015 by peejay4A

[Steves_TR6]

The spring loaded weights in the distributor ADVANCE the ignition, so any dynamic reading will at least as advanced as the static setting.

 

Hence it wouldn't be possible to have 11btdc static and 4atdc dynamic.

 

At least that's how I think it works !

 

Steve

[peejay4A]

No advance below 800rpm if the distributor is in proper shape.

[mikeyb]

Car has been running fine all last week - used everyday for work, on a strobe timing setting of 16deg ATDC. (edit BTDC) No pinking, pulling like a train but hunting on tickover.

 

Having messed up the clutch hydraulics on Sunday (another story!), no trip to work for it today, so made up a "piston stop" out of an old spark plug and a bolt, and checked the position of true TDC - it was pretty much spot on where the marks on the pulley said it was!

 

Ran out of daylight at this point, next job will be to re-time statically.

Edited June 2, 2015 by mikeyb

[peejay4A]

If that's a true 16 deg after then it certainly won't pink but I'm surprised it runs at all. It is timed on number 1 cylinder I suppose?

[Peter Cobbold]

16 ATDC is ridiculously retarded. 16BTDC would be acceptable.

[mikeyb]

OOPS sorry - that should have read 16deg BTDC!

[peejay4A]

In that case I'd leave it where it is.

[mikeyb]

Well, found time to static time the car last night. I first of al tried 4 deg ATDC static, a strobe check showed little deviation when idling, however on the road the car was obviously hesitant and unwilling, particualrly at higher revs.

 

I then reset it statically to 12 deg BTDC, strobe check at idle showed it to be running at an indicated 15 deg BTDC, on the subsequent road test, the car revved cleanly all the way up and pulled like a train. So I think that is where I will leave it set!

 

Thanks agan to all that have advised.

[Peter Cobbold]

And here's why that timing is best:

https://supertrarged.wordpress.com/2015/02/25/combustion-basics/

Peter