Timing technicalities

[TR5tar]

Following on from my posts about power loss issues - http://www.tr-register.co.uk/forums/index.php?/topic/48807-power-loss-over-bumpos/?hl=bumpos and http://www.tr-register.co.uk/forums/index.php?/topic/49989-fuel-starvation-or-something-else/?hl=%2Bpower+%2Bloss, I've spent the winter months cleaning connections and changing/upgrading a few components (plugs, coil, rotor arm, distributor cap) - the easy bits in other words. It was as much a learning exercise as anything else.

 

I've run the car out three times over the last three weeks (covering about 100 miles in total), and have not had any loss of power or cutting out issues, like before. However, the running feels a bit lumpy at idle and low speeds, and hesitates slightly on acceleration, particularly from standing and low speeds. I wonder if this isn't unusual, or even if it's the way I'm driving the car to some extent. Maybe I'm just not booting it hard enough.

 

I'm also wondering if there are any timing issues, but as I'm really a novice when it comes to timing, I don't know. My understanding of timing is very basic. I understand that spark plugs fire in a particular order and that they have to fire at the right moment for the car to run properly, but that's about it. I also imagine that changing components (as I've done) might alter the timing, as might quality of fuel, fuel additives used, and temperature presumably. Is that correct? In these colder conditions the temperature gauge still isn't rising much above the 1/4 mark. Should I make some adjustment for running in the colder months?

 

I bought my first timing gun earlier this week. I warmed the engine up and then checked the timing at idle, and I could see that the timing mark was just left of the pointer as viewed from the front of the car looking back. Is that where the mark should appear, or should it be where the pointer indicates? Or, am I not taking the measurement properly?

 

Any tips greatly appreciated.

 

Darren

Edited March 13, 2015 by TR5tar

[peejay4A]

Have you got a workshop manual Darren? It should tell you what you need to know about measuring timing advance and adjusting if necessary. None of the mods you list above will affect the timing. If you're experiencing jerkiness in slow traffic with stumbling on acceleration I would be looking first to make sure that your throttle butterflies are synchronised. There's a bazillion posts on the forum about how to do that as indeed there are posts on timing.

Edited March 13, 2015 by peejay4A

[Peter Cobbold]

Hi Darren,

The 'static timing' for these engines is a round 12BTDC, I think the TR5 book value is 11. Theorotically the pointer on the timing chain cover should point to about 11 btdc on the pulley when the light flashes, at tick over ( assuming a simple strobe device). But the timing marks on the pulley may well have shifted with age. Meaning you have to find TDC and remark them. However, you can still get very cose to the correct timing by loosening the disy clamp until you can with some effort ( ie not too loose!) turn it by hand a few mm to and fro. Wiht the engine warmed up and ticking over, slowly ease the disy to and fro - no more than about 5 mm at its circumference - and stop when you get the position of fastest tickover. Reclamp. While doing this beware of the HT !! - keep hands away from the leads.

Peter

 

Pete's post above may well be a more productive !! Timing iwould have be badly 'out' to cause stumbling.

Edited March 13, 2015 by Peter Cobbold

[TR5tar]

Thanks Pete and Peter.

 

I do have a Haynes workshop manual Pete, but often my knowledge is so basic that I don't know exactly what I'm looking for. For instance, I've heard of butterfly valves in carbs, but I didn't know anything about throttle butterflies on PI cars. I've looked in the manual for information, but cannot even find a listing. I'll look through other threads as you suggest.

 

Same problem when it comes to the timing I'm afraid Peter, as I'm not sure what the figures you mention relate to or what "BTDC" is. From reading on the subject, I do know that "TDC" is top dead centre.

 

Cheers, Darren

[Peter Cobbold]

Thanks Pete and Peter.

 

I do have a Haynes workshop manual Pete, but often my knowledge is so basic that I don't know exactly what I'm looking for. For instance, I've heard of butterfly valves in carbs, but I didn't know anything about throttle butterflies on PI cars. I've looked in the manual for information, but cannot even find a listing. I'll look through other threads as you suggest.

 

Same problem when it comes to the timing I'm afraid Peter, as I'm not sure what the figures you mention relate to or what "BTDC" is. From reading on the subject, I do know that "TDC" is top dead centre.

 

Cheers, Darren

Darren

The PI butterflies do the same job as in carbs, control the flow of air into the engine.

On the PI there are six of them, in three pairs. They are supposed to open in synchrony but the linkage can go off.

The diagrams in manuals, or parts manuals, are often the best place to start to get an idea of how things might work.

 

BTDC is Before TDC. ATDC - after.

There's also BDC etc.

TDC is when the piston is at the very top of its motion. The spark should happen about 10 to 50 degrees BTDC at the end of the compression stroke. The exact time varies with the power demanded and with rpm. The flame is set burning at a time such that the peak combustion pressure always happens at about 15deg ATDC. That way the gas gives the piston the best push.

 

 

I wonder if there might not be demand for beginners' instruction at the IWE, on the PI system and maybe on ignition?

On-car not talking.

If no-one asks no-one gets !!

Over to you - new thread?

 

Peter

Edited March 13, 2015 by Peter Cobbold

[snowric]

before top dead centre. so you start your engine, warm it up. Attch timing light and set it to 11 degrees. press the trigger and point the flash at the crank pulley at the front of the engine. it will then light up the white top deand centre mark on your crank pulley. you compare this line with the metal pointer welded onto the timing chain cover. you move the distributor body or the advance retard dial until the white line is at the mark.

 

sometimes the white mark is not top dead centre as the rubber in the crank pulley gives way.

 

peter posted something on combusiotn recently. as the petrol/air mixture takes time to burn the spark happens before the piston gets to the top (so BTDC) so you get the most out of the air fuel mixture taken into the piston. squashing it also accelerates and improves the efficiency of the explosion.

[Peter Cobbold]

but often my knowledge is so basic that I don't know exactly what I'm looking for.

Darren,

There were a series of books by SC Mudd "Technology for Motor Mechanics", about three volumes I think, that might help you get the basics before diving into manuals. From the late '60s so they predate modern elcectrikery, aimed at first year apprentices. IIRC one was engines, another suspension and transmissions, and another electrics.

 

There may well be better suggestions forthcoming.....

 

Peter

[TR5tar]

Appreciate the further clarification, thanks Peter, Snowy.

 

I've ordered those books you recommend Peter, for a very reasonable 1p each, plus shipping. I'll also put together a thread asking about a hands-on session for complete beginners at the IWE. Good idea.

 

Cheers, Darren

Edited March 14, 2015 by TR5tar

[Steves_TR6]

Hesitation or stumbling on acceleration is often PI related on these engines.

 

The PI system isn't very sophisticated, no electronics whatsoever!, so you can work on it yourself.

 

I went from zero knowledge to a working understanding over a summer of tinkering.

 

Perhaps go along to your local group meeting and chat with the locals, am sure someone will volunteer to help!

 

Failing that talk to Neil Fergussen, he is the man for Pi issue resolution, and a very nice chap too!

 

Steve

[TR5tar]

Thanks Steve. Good to know that it is possible to go from very little knowledge to a good understanding in a relatively short amount of time.

 

One extremely kind forum member has already offered to give me some pointers face-to-face, so that will be great.

 

Darren