Ignition timing with Pertronix Ignitor and strobe light

[Lutz Kramer]

Can you check the static timing now with the dual contact plate fitted?

Uups, forgot to do that and already put in the Pertronix again. I will change it again and check the static timing with the contacts, because that does make sense! Thank you for your suggestion!

 

[Lutz Kramer]

To perform the static timing test I decided not to use the Mallory twin contact plate but the Pertronix Module. It opened exactly at 45° BTDC to break the negative circuit which creates a spark. I once again checked the TDC mark on the pulley with the position of piston #1. Everything OK.

I still can't believe that the engine is definitely firing at 45° BTDC at idle!

There is only one possibility left that may cause this phenomenon. The engine was completely overhauled about 8 years ago and thereby was converted to run with unleaded fuel. May be therefore the compression ratio was lowered, which may require a pre igniton earlier than 15°. But 45°???

 

[Jim 58 BN6]

Usually, a conversion to run on unleaded fuel will only involve changing to hardened valves and valve seats, and the compression ratio is left alone. I hate to keep going back to the camshaft, but did you add a "high performance" cam? I assume the rocker arm clearance is also set properly.

It seems to me that if the cam had radical specs, or was somehow a bit advanced, then you could have a situation like this -I can't think of any other reason, given all of the things you have already checked, - but certainly there must be something that I've forgotten or never learned!

Next, I would use a dial indicator, and measure the valves on #1 cylinder to see when the maximum lift occurs on each valve. Then put a mark on the damper/pulley corresponding to each of these each of these measurements. By measuring the distance from the TDC mark to each of these marks, and knowing the circumference of the damper/pulley, you should be able to calculate when the maximum valve lift occurs, then compare it to the cam's specifications. I actually have a camshaft timing disc that is attached to the crank and set to TDC. It then provides this data without any more timing marks or measurements. I'm sure you could find one of these as well.

Sorry to keep coming back to this, but I cannot think of any other causes to your problem. GL, Jim

 

[johnea]

Lutz, Is the centrifugal advance mechanism working properly; when you turn the rotor arm counter clockwise, does it snap back?

 

[Lutz Kramer]

Lutz, Is the centrifugal advance mechanism working properly; when you turn the rotor arm counter clockwise, does it snap back?

I checked this when I changed from the pertonix system to the twin contacts, since I had to pull the module together with the basic plate. I even had to strenghten one of the two little springs because it was to weak. The centrifucal advance mechanism looks like brand new and is moving freely. I tested its function with the strobe light. By increasing rpm to 4000/min you can see that pre ignition is moving about 20-25° and going back as soon as the rpm is back to idle.

 

[Lutz Kramer]

Usually, a conversion to run on unleaded fuel will only involve changing to hardened valves and valve seats, and the compression ratio is left alone. I hate to keep going back to the camshaft, but did you add a "high performance" cam? I assume the rocker arm clearance is also set properly.

It seems to me that if the cam had radical specs, or was somehow a bit advanced, then you could have a situation like this -I can't think of any other reason, given all of the things you have already checked, - but certainly there must be something that I've forgotten or never learned!

Next, I would use a dial indicator, and measure the valves on #1 cylinder to see when the maximum lift occurs on each valve. Then put a mark on the damper/pulley corresponding to each of these each of these measurements. By measuring the distance from the TDC mark to each of these marks, and knowing the circumference of the damper/pulley, you should be able to calculate when the maximum valve lift occurs, then compare it to the cam's specifications. I actually have a camshaft timing disc that is attached to the crank and set to TDC. It then provides this data without any more timing marks or measurements. I'm sure you could find one of these as well.

Sorry to keep coming back to this, but I cannot think of any other causes to your problem. GL, Jim

Hi Jim,
first of all let me thank you for your efforts to find an answer to my questions. I very much appreciate your help!
Unfortunately I can't tell what kind of cam is in the engine, since I only have the invoice of the overhaul but no detailed information about the work performed. To follow your instructions may bring more light into this.

But let me ask one more question because I'm not to experienced in this area. What is the differance between a normal cam and a high performance cam when it comes to the question of andvanced ignition. My understanding is that whenever the piston is in compression stroke almost at TDC then both valves must be closed no matter how long they where open during the intake/exhaust stroke. What could then be the reason having the ignition to take place about 30° earlier?

 

[Jim 58 BN6]

Lutz, You're welcome. This is a perplexing problem. I would bet it's probably a stock cam, and hope that if it is a performance cam, its specifications, or part number would have been noted on the invoice.

To answer your question: High performance camshafts can have higher valve lift, duration, and valve opening overlap. Generally, when one installs a camshaft of this type, a procedure known over here as "degreeing the camshaft" needs to be followed to ensure that the cam is timed properly. Sometimes an adjustable cam gear, or an offset keyway will need to be installed with the cam gear, to properly adjust the cam timing. If the valves are not opening at the right time - I mean a few degrees error, not a lot, the engine will probably run, and the ignition timing MIGHT have to be set to occur earlier (or later), and the engine might seem to run OK with those settings.

If you can measure when the maximum lift of the valves in cylinder #1 occurs, you could compare that result with the stock cam specifications in the repair manual (or Google!). That could at least tell you if the cam timing is close to where it is supposed to be, and then cross that off of your list! The measurements that I described in the previous post shouldn't be too difficult or disruptive. You will have to remove the valve cover, and then mark and measure those points on the damper/pulley, but no major disassembly is needed.

See: https://www.iskycams.com/cam-degreeing.html This is a good explanation of theory, and what's going on, but don't get too caught up in all of the detailed procedures - the site describes what to do during an initial engine build. I am just suggesting a simple way of finding out when the valves are completely open, and comparing that data to the specs.

Cam timing is not only important for correct engine operation, but it is especially important if an engine has overhead cams, a hemispherical combustion chamber, or domed, high-compression pistons. With these situations, there is a real possibility, with even a small timing error, of a valve contacting a piston and jamming - or worse. Fortunately these old Austin engines are fairly low-tech, have flat-topped pistons, and relatively low compression, so unless the cam timing is way out, there isn't much danger of a valve/piston contact.

If your car was running OK, I don't think there is anything to panic about, but this is a mystery, and should be solved! I hope you can figure out what's going on, and that I haven't overthought this, and made the issue any more difficult, or confusing! Jim

 

[Lutz Kramer]

Lutz, You're welcome. This is a perplexing problem. I would bet it's probably a stock cam, and hope that if it is a performance cam, its specifications, or part number would have been noted on the invoice.

To answer your question: High performance camshafts can have higher valve lift, duration, and valve opening overlap. Generally, when one installs a camshaft of this type, a procedure known over here as "degreeing the camshaft" needs to be followed to ensure that the cam is timed properly. Sometimes an adjustable cam gear, or an offset keyway will need to be installed with the cam gear, to properly adjust the cam timing. If the valves are not opening at the right time - I mean a few degrees error, not a lot, the engine will probably run, and the ignition timing MIGHT have to be set to occur earlier (or later), and the engine might seem to run OK with those settings.

If you can measure when the maximum lift of the valves in cylinder #1 occurs, you could compare that result with the stock cam specifications in the repair manual (or Google!). That could at least tell you if the cam timing is close to where it is supposed to be, and then cross that off of your list! The measurements that I described in the previous post shouldn't be too difficult or disruptive. You will have to remove the valve cover, and then mark and measure those points on the damper/pulley, but no major disassembly is needed.

See: https://www.iskycams.com/cam-degreeing.html This is a good explanation of theory, and what's going on, but don't get too caught up in all of the detailed procedures - the site describes what to do during an initial engine build. I am just suggesting a simple way of finding out when the valves are completely open, and comparing that data to the specs.

Cam timing is not only important for correct engine operation, but it is especially important if an engine has overhead cams, a hemispherical combustion chamber, or domed, high-compression pistons. With these situations, there is a real possibility, with even a small timing error, of a valve contacting a piston and jamming - or worse. Fortunately these old Austin engines are fairly low-tech, have flat-topped pistons, and relatively low compression, so unless the cam timing is way out, there isn't much danger of a valve/piston contact.

If your car was running OK, I don't think there is anything to panic about, but this is a mystery, and should be solved! I hope you can figure out what's going on, and that I haven't overthought this, and made the issue any more difficult, or confusing! Jim

Jim, thanks for your extensive explanations. The article which you provided the link for is very interesting and helpful. I will take all the measurements recomended to find out what kind of cam I have and will then continue from there on.

Best regards from Germany
Lutz

 

[Jim 58 BN6]

Lutz, The first measurement is simple: Find out when the #1 intake valve is fully open - the actual lift measurement is not important now - by placing a dial indicator on top of the rocker arm adjustment screw. Rotate the engine by hand, in the correct direction, to find the maximum lift. If you go past, and have to reverse a bit, make sure you go far enough back to again approach the maximum reading from the correct direction (this makes sure the timing chain stays tight).

Once you find that place, accurately make a new mark on the damper/pulley next to the timing pointer (make sure the pointer points to the new mark like it points to the TDC mark). That will occur sometime after TDC, during the intake stroke.

Measure the diameter of the damper, and using a flexible measuring tape, as carefully as you can, measure the distance from the TDC mark to your new mark. Knowing the diameter of the damper, and the arc length you just measured, you can calculate the "central angle", which is where the valve is fully open. Here in an on-line calculator: https://www.1728.org/radians.htm

Just select central angle, and enter the RADIUS of the damper (NOT diameter), and the arc length you just measured. It will then give you the angle. This isn't a precise measurement, we are just looking for an "in the neighborhood" measurement. It would be a lot more work to do it correctly enough to really evaluate the cam's profile, and would require the timing wheel I mentioned.

I found one set of specifications for my 100/6 that say the intake valve should be fully open at 110 degrees after TDC. If your measurements and calculations show a number close to the specification (within a couple of degrees), than maybe it's OK. If you see a 10 degree error, then maybe more/better measurements are necessary. I know I'm a bit verbose, and this must feel you are like "drinking from a fire hose"! Jim

 

[Lutz Kramer]

Lutz, The first measurement is simple: Find out when the #1 intake valve is fully open - the actual lift measurement is not important now - by placing a dial indicator on top of the rocker arm adjustment screw. Rotate the engine by hand, in the correct direction, to find the maximum lift. If you go past, and have to reverse a bit, make sure you go far enough back to again approach the maximum reading from the correct direction (this makes sure the timing chain stays tight).

Once you find that place, accurately make a new mark on the damper/pulley next to the timing pointer (make sure the pointer points to the new mark like it points to the TDC mark). That will occur sometime after TDC, during the intake stroke.

Measure the diameter of the damper, and using a flexible measuring tape, as carefully as you can, measure the distance from the TDC mark to your new mark. Knowing the diameter of the damper, and the arc length you just measured, you can calculate the "central angle", which is where the valve is fully open. Here in an on-line calculator: https://www.1728.org/radians.htm

Just select central angle, and enter the RADIUS of the damper (NOT diameter), and the arc length you just measured. It will then give you the angle. This isn't a precise measurement, we are just looking for an "in the neighborhood" measurement. It would be a lot more work to do it correctly enough to really evaluate the cam's profile, and would require the timing wheel I mentioned.

I found one set of specifications for my 100/6 that say the intake valve should be fully open at 110 degrees after TDC. If your measurements and calculations show a number close to the specification (within a couple of degrees), than maybe it's OK. If you see a 10 degree error, then maybe more/better measurements are necessary. I know I'm a bit verbose, and this must feel you are like "drinking from a fire hose"! Jim

Again, thanks a lot for your information, Jim, which I definitely will use for my further investigations!

 

[Lutz Kramer]

Having done my homework I’m back to present the results.

1. First thing I did was checking whether the factory mark for TDC on the pulley is sitting correct. I mounted a piston stopper into #1 spark plug seat.



Turned the piston clockwise till it was stopped and made a mark on the damper/pulley. Then turned the piston counterclockwise until it was stopped again by the piston stopper and again marked the pulley. The middle of the distance between the two marks corresponded exactly with the TDC factory mark. So, no problem here.


2. I then downloaded a timing disc for the crankschaft, cut it out and fixed it to the pulley, removed the valve cover and placed a dial indicator on top of the valve.




3. I turned the crankshaft clockwise until the dial indicator started to move. From then on I took the readings every 10° and entered the measurements into the following list.


4. First of all I found out that a real hot camshaft must be mounted (290°), which I didn’t know.


5. As far as I can see from the measurements taken the cam seems to be timed with the crankshaft correctly, or does anybody disagree? Different opinions are welcome!


6. So what about the timing of 45° BTDC at idle? New insights? Not really, except another guess!

In German forums I read that with a hot cam you basically have to change the ignition timing about 10° earlier, depends on what kind of engine you have. Others say never ever! But when I transfer the first opinion to my settings I would have to go from 15° BTDC (normal) to a max of 25°. When I do this, the engine just doesn’t stall but is running very rough in idle and I have to set it to 1000 rpm to keep it going. And in those forums they further say, that this behaviour is normal for engines with hot cams and they usually have less power at lower rpm but therefore more power at higher rpm. Who needs it if you don’t go for races?


So question is, should I leave everything as it is (45° BTDC at idle) or should I change to the racing version, which I don’t need, since I seldom run the engine above 4000 rpm???

By the way, now I know why this engine has a fuel consumption of 17 mpg. The intake valves of a 290° cam are opened extremely long and therefore suck in a lot more of air and fuel for a full cycle like normal cams usually do. On the one hand this provides more power but at the same time more fuel is consumed. To bad that you cannot have one without the other.

 

[Jim 58 BN6]

Great work, Lutz, it is very thorough, and well presented! Looking at your data, the maximum intake and exhaust valve lifts do occur very close to what the specifications list for my 100/6 (and I assume that the 3000 must be close to the same). So, I agree that the cam is probably correctly timed, but there does appear to be a lot of "overlap". Like what you have read on the German forums, my experience (whatever that's worth!) using "hot" cams, has also shown me that earlier initial ignition timing is probably necessary, but 45 degrees seems excessive to me as well!

You might check the distributor advance curve, but I don't think that would have an effect on initial timing. However the entire system does work together, so ??? Maybe a Bosch Station could check this.

If it were me, and I were not determined to race or "hot rod" the car, I might consider changing back to the stock camshaft. If you are not experiencing pre-ignition upon acceleration, or running-on after shutting the engine down, and the engine seems happy and runs its best where the timing is now set, then maybe just leave it be - for now. I think 17MPG is a bit low, but may be what is expected with a hot camshaft.

You could also hook up a vacuum gauge and see where you get a maximum vacuum reading at idle. It should be maximum when the timing is about correct, but probably a lower than stock reading if there is a more radical cam. Google the procedures, and interpretations of the vacuum readings - it's been a long time since I've done that!

Another thought: Do the spark plugs look like the fuel mixture is correct, and are the correct heat range? Adding one performance part to a motor can require other parts to be changed or modified. Fuel mixture vs. RPM and load (carb needle profile, etc), might also be affected, and maybe the earlier timing is compensating for another problem.

There must be folks on this BB that have properly set up a Healey with a hot cam, so maybe someone else will comment. Good luck, and I'll try to think of anything else that you could check. Jim

 

[Lutz Kramer]

Jim, thank you for still following my thread and not getting tired to give helpful and excellant answers and recomondations!

I have Healey specs where the standard maximum intake and exhaust valve lifts for a BJ8 are given with 9.36 mm, which is about 20% less than the measurements for my hot cam.

Hopefully there are some guys in this forum who are experienced with the setup of hot cams and are willing to give their comments.

But anyhow my problem is not really a problem, since the car is acutally running perfectly. It's only that I would like to understand what is going on in this engine!

By the way, I found the guy in south Germany who did the engine overhaul in 2007. He is now out of business and over 80 right now, but was realy willing to help. I talked to him on telephone for more than hour. He could only remember having added a power package with a hot cam of 271° or 290°. But he did not have any idear either, what the reason for this strange timing could be.

Lutz

 

[Jim 58 BN6]

Well, "If it ain't broke, don't fix it!" That being said, I agree with you, and would want to know what the heck is going on!

I wonder what else was included in the power package?

One more thing: you mentioned needing a higher engine speed at idle (100RPM?). Another observation of mine is that a hotter cam will require a higher idle speed. Maybe 1000-1200, or higher. If you haven't already tried it, set the idle a bit higher, and see if it will accept less initial advance, and still perform well under load.

I'm glad I was able able to provide some helpful suggestions - but it's much easier to do in person than on-line. It was nice to see your data presented the way it was, and reminded me of some of the data acquisition and reporting that I did before retiring - but I'm not done yet!

Please let us know if you find do find some "smoking gun". Jim

 

[johnea]

Lutz, hotter cams need more initial ignition advance. The total advance however should not exeed 36 degrees. Probably even a bit less . . . . If your distributor is still stock the advance will be too much. In such a case
you need to reduce the advance in the centrifugal mechanism. Jim has made a good suggestion. Hook up a vacuum gauge and see what happens if you turn the distributor. The needle wil fluctuate because of the large overlap. A stock cam presents a much steadier needle . . . .

 

[Lutz Kramer]

Lutz, hotter cams need more initial ignition advance. The total advance however should not exeed 36 degrees. Probably even a bit less . . . . If your distributor is still stock the advance will be too much. In such a case
you need to reduce the advance in the centrifugal mechanism. Jim has made a good suggestion. Hook up a vacuum gauge and see what happens if you turn the distributor. The needle wil fluctuate because of the large overlap. A stock cam presents a much steadier needle . . . .

Thank you, Johnea!

 

[Lutz Kramer]

Since none of the guys of the "hot cam" or "racing" fraction is responding to the question whether a hot or racing cam requires more advanced igniton I think I rather start a new thread with the headline:"Hot cams and advanced ignition" to draw more attention to this issue.

 

[red57]

I run a 283 degree cam and have not noticed a need for more spark advance. I run a Mallory dual point distributor and don't know how the advance curve compares to the Healey distributor. My self induced red line is 6000rpm (occasionally up to 6200 in the heat of the moment). My Mallory hits full advance around 2800rpm (I think you want full advance no later than 3000rpm). I have always set it to max advance of 35-36 degrees, and never paid much attention to where it is at idle (and it drives well - both on the track and the street). I've never heard of anyone advancing beyond 36 or so - more would risk high speed detonation that you would not hear over the other noises and could be catastrophic. As long as you aren't suffering detonation, you probably aren't hurting anything. I'm no engine guru, but I have not heard of any significant timing changes when cams are changed - subtle timing changes on a dyno might result in a bit more power, but I believe those changes would be slight. Doubt if it helps but that's my experience.

 

[CLEAH]

Lutz, I've been reading this in the background and while I am no expert, I have a few observations and a question. You have reported that your car runs fine. You and others have suggested that it should hardly run at all at 45 degrees advance. You have a hotter cam, but that is pretty common. Are you sure the 45 degree reading is correct?

 

[GregW]

Hi Lutz,
I'm curious how you marked your crank pulley for the 15 and 45 degrees. 15 degrees should be 51/64" (about .8") away from the TDC mark, or 20.24mm.