a question of timing...

[998automan]

Hi, recently borrowed a timing gun with advance function to check the timing on my 998 with Kent 266 cam. Although running ok this showed 23 degrees BTDC. Question is does this seem to be in the right area for this cam or should I still be using standard timing as per manual (8 degrees +0 -2) Engine builder seemed vague about this when we built it and it seems a long way out to me!     

[wimfournier]

Question is, how many revolutions a minute the engine made when you read these 23 degrees.
The 8 +/- 2 degrees that the book says, is at 800 rpm with the vacuum advance lead disconnected.
The interesting part of a timing gun is, that you can read advance -with the vacuum lead connected- at every engine speed.
The book tells you what advance -by vacuum plus by centrifugal weights- is desirable  at the various speeds you use your engine in every day practice.
The character of the 'cam' you use does not make very much difference to these 'wanted figures'. Because the effect of the cam is only on the filling of the bearning room.
The workshop handbook said:
centrifugal 
26 - 30 deg at 5500 rpm
24 - 28            4800
15 - 19            1800
12 - 16            1600
0   -   4             800
Vacuum starts at 3 in Hg and ends at 15 in Hg at 18 degrees.
So in total you could reach 48 degrees BDP. The figures are ment for 'automatics'.

[998automan]

Hi Thanks for your answer. Engine was running at 1500 rpm when I took the reading as my manual states 1500 rpm vac disconnected rather than 800 for 8 degrees BTDC? Also I disconnected the vac so maybe this is giving me a false reading? If not it sounds like it should be less than 23 degrees at 1500rpm then, nearer 8 - 10 perhaps?

[jockduck]

Hi, How old is your distributor? I was amazed the first time I put a timing gun on my mini, the scatter was so bad the flashes were barely inside the window in the converter cover, on close examination the distributor was a mess, worn pins and weights and slop in the main bushing. All the wear made the thing advance early leading to the engine pinging even on good fuel and correct static timing. Most distributors are made down to a very low standard.
Jock

[998automan]

Hi Jock, Thanks. Dizzy is nearly 30 years old but only 12k miles driven in that time. Have just fitted powerspark electronic ignition which should (I believe) compensate for some of the wear on the shaft? What would be great to know is how do you go about timing engine in if you can`t use original factory settings due to wear or changes to original spec such as my camshaft. Is this a rolling road job or can it be done at home?

[998automan]

Hi, On further investigation I think the timing marker set by the engine builder has moved, is it possible to establish TDC without removing the head? (I do own a dial gauge and have do this once when the head was off.) Thanks all! 

[jockduck]

Yes it can be done through the plug hole using a slim extension on the dial gauge, when you refer to the timing mark are you referring to the "front" pulley? If its an auto there are marks on the torque converter and a pointer. Manuals also have marks on the flywheel of used to.
Jock

[wimfournier]

"There's a hole". This one is not 'in  the bucket', but in the cap surrounding the torque converter. At the top of the cap you find a round rubber plug. Right above the plug there is an arrow painted on the cap pointing to the left. This hole is ment to see precisely TDC. When you turn the torque converter round by applying a screw driver through the square hole (with plastic plug) that is made especially for that purpose at the eleven o clock position of the cap, you can put the screwdriver in the starter ring and push the torque converter in the right direction (anti clockwise) until you see the markers in the hole with the arrow for TDC.

[998automan]

Hi Guys, thanks. It is the timing mark on the pulley. Unfortunately the torque converter marks are not legible as the company that reconditioned the box, re-painted it so that you can no longer see the marks! Any Idea where I can get a slim extension for the dial gauge from?    

[jockduck]

I guess it depends on your dial gauge, I use a wooden skewer which "threads' into the plunger end, could probably get away with a bike spoke. You won't get it 100% vertical but it will do the job.
Jock

[notamini]

Odd you should say it is painted there. Mine has never seen paint. You absolutely sure you're looking at the right place?
Now that I'm here, anyone with the ballast resistor in the ignition heed this warning. Get a spare and be sure it is in the car at all times. Mine quit from rust (46yrs) and left me puzzled and stranded for 1/2 hr. Your car will start and run until you let off the key from START. Then it dies. Fortunately, I had some wire and quick connect terminals. I bypassed the resistor. Do this only for a short trip and only if you must. It can cause your points to weld shut! Could someone tell me what would happen if I had electronic ignition?

[kalkat]

It would depend on what type of ignition it was. Some kits replace everything, but with others you would retain the ballasted coil.

Just as a point of information, ballasted coils have a lower resistance than non ballast types.

[998automan]

Hi, returning to timing once again can anyone tell me what the effect of advancing & retarding timing has on power? Is the ideal to get it firing as close to TDC as this gives the mixture more time to compress or not? Thanks.

[wimfournier]

To understand how you get the most effect of the power your engine is producing, compare it with riding a bycicle.
When you are about to get on the way out of a stand still, you prefer to have the pedal about 30 degrees after 'top dead centre'.
You know that when the crank is 100% vertical, all the power you apply to the pedal has zero effect.
The more degrees the crank has turned after TDC the more effect the power you put on the pedal has, until the crank has turned 90 degrees from TDC.
Techniciens found out that an engine works at its best when the flame front in the burning chamber of the cilinder has reached all the outscirts of the chamber, when de crank has turned 24 degrees from TDC.
Because it takes every time the same time for a spark to build up and spring over at the plugs and -with the engine revs speading up-  the time between TDC en 24 degrees after TDC becomes shorter and shorter, there is need to start up building a spark earlier and earlier, to get it springen over at the right time. So, we have divices on board working with centrifugal power and with vacuum power to advance the spark.
To find the best setting of the ignition, you have to use a dyno meter. Every engine each has its own caracteristics. At the same time you can find the best setting of the carburation.

[kalkat]

Wimfournier has the nub there. Ignition timing with 'funky' cams is a bit of an issue - normally resolved by use of a rolling road/dyno. Have you chexked the dizzy's spindle for slogger? That can really bounce timing about even with pointless ignition!

When the engine was built, was the cam timed properly?

Info here .....

www.theminiforum.co.uk/forums/index.php?showtopic=36988

www.dummett.net/ime/website/ime/c/cam_time.html

Using standard timing wheels and woodruff keys won't necessarily get the cam right. There are offset keys to get some degree of offsets or adjustable and vernier wheels available.

[998automan]

Thanks, interesting stuff. The mini forum list mentions my cam (kent 266) with the following timing information:

Timing: (Intake): 24/56 (Exhaust): 61/29

Can anyone explain what this figure relates to? At the moment I am getting good results by adjusting 2 degrees at a time and road testing, I have currently got to 12 degrees BTDC which is a big improvement on 10 which was a big improvement on 8, so I know I am heading in the right direction! The question is when to stop, can anyone tell me how I will know when I have too much advance and what is likely to happen? I know I could sort all this on a dyno but the nearest one to me is a 2 hour drive away + it all costs money!! (I also feel I am learning more this way than by watching someone else do it!)

Thanks all.
   

[wimfournier]

The critical aspect about advancing ignition is 'pingping'.
When you drive in third or fourth gear and apply the throttle (not so deep that the box goes 'kick down') and you hear the engine pinging, the ignition is to early.
With such early ignition the effect of the burning of the gasses is also less. So you have more economy with a little later ignition then.

The figures 24/56 and 61/29 stand for 'duration'; the time the halve is open.
Duration is the angle in crankshaft degrees that the valve stays off its seat during the lifting cycle of the cam lobe, sais the book.
So, the intake halve opens 24 crankshaft degens before TDC and shuts 56 degens after BDC and, the exhaust halve opens 61 degens after BDC and 28 degens after TDC it is closed again.
More duratiom gives more top power and less gives more bottom power.

[998automan]

Thanks, so keep on advancing until it starts to pink & then retard slightly? 

[wimfournier]

That's the way!

[998automan]

Hi I am still a little confused about the timing holes in the torque converter. The hole in the bottom of the picture is impossible to read as it has been painted grey, is the plate above it anything to do with timing marks? Mine has a gasket under it so assume whatever is underneath it is inside the transmission itself?

Attachments:

[kalkat]

The hole with the pointer in it is the timing 'orifice' ........... winch the engine over to the marks, then rub some paint or chalk into the markings.




Emma

[998automan]

Thanks Emma, do you know if this will still likely to be accurate following an engine rebuild/new cam fitted? 

[richard1]

The timing marks on the converter, at least on my SPI, coincide with those on the fan pulley. But, as mentioned by wimfournie, once you drive it you can set it better, especially in the carburated models.

Set the timing for the highest rpm you can get or just under that. Drive it accelerating at low rpm. If it pings, retard it a bit and try again. The best timing is as far advanced as you can get without pings. It will vary with altitude.

When I set up my Corvair, I was at my office in the city at 6200 ft above sea level. I had it perfect, and drove home, 600 ft lower than the city. It pinged on my way to work each time, so I retarded it a bit to be right for home. When I took to my other home at 1300 ft above sea level, I had to retard it more.

[kalkat]

The timing marks remain accurate as the flywheel/torque converter is keyed to the crank.


Emma

[mra-minis]

Please note until I can purchase the MRA-Minis URL I can be contacted on [e-mail]

Yep, the cam will not perform at it's best if it is not correctly timed in, this is irrelevant to the type of cam, as every cam must be correct to design intent. You do have a little margin either way depending on the result you require.

KENT CAMS do a pretty good vernier timing chain arrangement, but there are similar ones out there by other manufacturers.

The best ignition is a system without a distributor.... ie an ECU, Trigger wheels do a nice kit and will reduce it a little if you want to fit it to an automatic provided you by the timing sensor bracket from me ;-) I make a nice aluminium alloy billet one.

Other than that, a good timing kit and quality chain will also help as it controls the camshaft which drives the distributor, so any slack in the cam timing will reproduce itself in the drive to the distributor, which if worn will just magnify the errors and you have scatter that is on a magnificent scale.

1) make sure your cam timing and system are in good condition
2) make sure your distributor is in good condition
3) make sure all the settings are good.

Incidentally, the SU is a great carburettor and unless worn will NOT be your issue.
check your SU for wear by running your engine at tick over and spraying some WD40 or similar light oil onto the carburettor around the spindle, you don't need to much and if worn you will hear the engine revs rise.

[mra-minis]

Mar 16, 2016 12:40:19 GMT richard1 said:

The timing marks on the converter, at least on my SPI, coincide with those on the fan pulley. But, as mentioned by wimfournie, once you drive it you can set it better, especially in the carburated models.

Set the timing for the highest rpm you can get or just under that. Drive it accelerating at low rpm. If it pings, retard it a bit and try again. The best timing is as far advanced as you can get without pings. It will vary with altitude.

When I set up my Corvair, I was at my office in the city at 6200 ft above sea level. I had it perfect, and drove home, 600 ft lower than the city. It pinged on my way to work each time, so I retarded it a bit to be right for home. When I took to my other home at 1300 ft above sea level, I had to retard it more.

There is a tweak for this.... get a turbo vacuum pot on your dizzy to allow for more pressure related adjustment.

[998automan]

Thanks Emma/Martin, loads of good information there!

[mra-minis]

Sept 9, 2015 15:57:22 GMT 998automan said:

Hi, returning to timing once again can anyone tell me what the effect of advancing & retarding timing has on power? Is the ideal to get it firing as close to TDC as this gives the mixture more time to compress or not? Thanks.

Just thought of a few other things and ways to explain.... the mixture has to fire at a predetermined position in relation to the piston and crankshaft

The advance curve changes the position that the ignition starts to fire, ultimately we are looking for the flame front to start to push the piston down the correct way at the same point mechanically. as your engines speed increases so does your advance, this is due to the time it takes for the ignition of the fuel / air mixture, which takes the same time every time (unless it's turbocharged) so lets say it takes 10 milli second to ignite the fuel/air mixture (we can at this point call it gas) now the crank angle changes at the rate of 1 degree per milli second (at some engine rpm) so to get the gas to ignite at 1 degree ATDC we need to ignite the mixture at about 9 degrees BTDC. now if the crank revs up and now covers 2 degrees per milli second we need to advance the ignition point to 18 degrees BTDC, so your distributor is really a time machine ;-)


Also if it is advanced too much it tries to push it back down the way it came, ie it is still on the up stroke but trying to force through an expanding high pressure flame front of the gas...

With retarded ignition it is forever chasing the piston down and as such will cause over heating issues

Both will result in a loss of power and reliability will be shortened, sometimes very very short.