Ignition Timing

[Tom H]

At the 2011 Invasion in Winona, we discovered my ignition timing was about 22 Deg BTDC at 1000 RPM. We tried adjusting it to a more reasonable setting but it ran poorly at anything less than 22. Nevertheless I continued to drive it on my7500 mi road trip. I suspected maybe my damper /pully was mismarked, or possibly shifted on its elastomer band. I just finished checking the TDC mark on the damper/pulley and it seems correct. And it still requires about 20 deg at 750 RPM to run smoothly.

I'm looking for possible explanations. It has the Vizard mod, stroke increased from stock 3.25" to 3.35", custom pistons to maintain stock deck clearance of 0.018", but with reduced dish to achieve CR of 9.3, plus KB grind on the cam. Do these mods account for the needed advance increase?

Is it possible I have the cam mistimed? I doubt it very much, as I assembled it quite carefully, but I have no photo of the installed timing chain. It seems to me that a misstep on the chain would have a much greater effect on proper running.

For those interested in how I confirmed the pulley timing mark, I made a pair of long plastic "feeler gauges", one 0.050" and one 0.060", from sheet styrene, and inserted them into the cylinder thru the #1 spark plug hole. With a deck clearance of 0.018' and a gasket thickness of about 0.030", you have a "squish" area about 0.048". You can tell when you reach TDC, within about 5 degrees. The 0.060 feeler will not insert into the "squish" area at TDC, but the 0.050 one will. 4 deg earlier and 4 deg later the 0.060 will fit into the squish area. I used a wooden extension handle on my crank starter handle to move the crank in small steps .

Tom

 

[Chuck Ingram]

Tom

I would pull the valve cover.Make sure #1 piston is TDC on compression stroke as both valves should be closed.I think a long thin screwdriver would be better to feel the movement when the TDC is met.This is what I have used on both the V 8s
If one valve is not closed then the cam timing may be out one link. I use a button switch to the solenoid to move the engine.When I'm close using this method I rock the car in gear.This way you can go forward or backwords.It eliminates using the crank.

Also a good method for setting the points

 

[RootesRacer]

The first thing I'd suspect is that your crank pulley is not timed correctly or has slipped.

One should never time an engine at idle, you should read the manual and find out what the max advance timing is and set it there (this is a far more important spec than idle because no one ever pinged an engine to death at idle).

You set the timing to the max timing spec (3800 rpm on an alpine) and then see where the idle timing happens to be.

If it (idle timing) is way advanced then the centrifugal mechanism is stuck.

 

[RootesRacer]

Tom

I would pull the valve cover.Make sure #1 piston is TDC on compression stroke as both valves should be closed.I think a long thin screwdriver would be better to feel the movement when the TDC is met.This is what I have used on both the V 8s
If one valve is not closed then the cam timing may be out one link. I use a button switch to the solenoid to move the engine.When I'm close using this method I rock the car in gear.This way you can go forward or backwords.It eliminates using the crank.

Also a good method for setting the points

You really need to do this with a dial indicator and mark the pulley at .050 piston down on both sides of TDC then find the middle (real TDC).
There is so little slope of piston movement near TDC, you really cant find it by looking for the peak since 5 or so degrees of travel doesnt change but a few thousanths of an inch at the piston near TDC.

 

[Tom H]

Chuck, Jarrid makes the same point I tried to. Others have suggested using a stick or screwdriver in thru the spark plus hole. But if you do the math you'll see that over a crank rotation of +5 to -5 deg around TDC the pistion only moves 0.0065" (up and then down). I see that if you move forward and backward (like fine tuning a microscope focus or radio) you CAN get pretty close. But I found it hard to do that fine "nudging" on a 1 ton machine while trying to feel 6 thou difference!

Jarrid, I like your method. I'll try using a 0.100" plastic feeler to find the two points where the piston is about 0.050 down. I'm pretty sure that my pully is marked correctly, based on my tests. But I'll check again using the 0.050 down points. That should show points about +14 and -14 deg.

And I'll check teh timing at 3500 RPM.

Thanks,

Tom

 

[beamdream]

If the cam is stock then you should be able to make up a protractor for the front pulley and establish when the valves open and close in relation to crank rotation e.g. IO 10 degrees BTDC, EO 40 degrees BBDC etc.

If the cam is modified then these same specs are usually available from the supplier.

This the only sure way to establish cam timing without removing the front cover.

 

[RootesRacer]

Chuck, Jarrid makes the same point I tried to. Others have suggested using a stick or screwdriver in thru the spark plus hole. But if you do the math you'll see that over a crank rotation of +5 to -5 deg around TDC the pistion only moves 0.0065" (up and then down). I see that if you move forward and backward (like fine tuning a microscope focus or radio) you CAN get pretty close. But I found it hard to do that fine "nudging" on a 1 ton machine while trying to feel 6 thou difference!

Jarrid, I like your method. I'll try using a 0.100" plastic feeler to find the two points where the piston is about 0.050 down. I'm pretty sure that my pully is marked correctly, based on my tests. But I'll check again using the 0.050 down points. That should show points about +14 and -14 deg.

And I'll check teh timing at 3500 RPM.

Thanks,

Tom

For something like this, you really want to pull the head.

I have seen some spark plug screw in adapters with an extendable shaft to probe piston height. Going from where it hits on one side of TDC, then rotating 340 or so degrees till it hits on the other side could yield reasonable figures.

 

[Chuck Ingram]

For something like this, you really want to pull the head

I think Tom was not looking to pull the head

I was going to suggest pulling the head as that is the most exact way to determine true TDC.At that point a dial indicator will give the exact spot

 

[Tom H]

Chuck, Exactamundo! Not gonna pull the head to satisfy my curiousity! The car has run fine for over 8000 miles since assembly. But I think using my plastic feeler guage of 0.100" will pretty well identifty approx +15 and -15 deg from TDC and allow me to check the TDC mark on the pulley. Then I'll pull the valve cover and check the valve positions at TDC and then check the advance at 3500 RPM.

Beamdream, as noted in first post the cam is NOT stock, it is KB grind. I have the specs. It does open the intake about 10 deg sooner than stock and it does have a different recommnded advance curve than stock. But I don't think that includes an idle advance much off the stock settting. Also the head has the Vizard mod, and crank is reground for 0.100" longer stroke.

Tom

 

[RootesRacer]

How about going to the auto parts store and buying a spark plug "antifouling extension" and fitting a threaded rod with ruts surrounding the extender to become a piston stop?

Radius the end of the rod to avoid a sharp edge but such a device would yield near the same accuracy as the dial indicator method, all without pulling the head.

Just saying.

 

[Chuck Ingram]

How about going to the auto parts store and buying a spark plug "antifouling extension" and fitting a threaded rod with ruts surrounding the extender to become a piston stop?

Radius the end of the rod to avoid a sharp edge but such a device would yield near the same accuracy as the dial indicator method, all without pulling the head.

Just saying.

I think you are a thinker as well.
I use the thin screwdriver. I sanded in my career so much my fingertips are still pretty sensitive

 

[Tom H]

Jarrid,

Why don't you think the use of a plastic feeler gauge will work? Imagine a flexible, styrene, "popsicle stick" that is pretty exactly 0.100" thick. Insert it into the squish area and turn the crank gently until it grips the feeler lightly. Mark the pulley. Then remove the feeler, turn the crank past TDC and reinsert the feeler, keep turning until the feeler will insert into the squish area again. Maybe reverse crank a tiny bit to again grip the feeler. I'm thinking this will find the same +/- TDC point within a few thou at worst.

I've seen this question come up dozens of times and now I think I have a near foolproof, yet simple, method to find the true TDC without pulling the head or tiimng cover. Your idea to locate the point 0.050" or so down was the missing piece. Finding flat styrene of appropriate thickness is pretty easy if you have a hobby shop nearby.

Tom

 

[RootesRacer]

Jarrid,

Why don't you think the use of a plastic feeler gauge will work? Imagine a flexible, styrene, "popsicle stick" that is pretty exactly 0.100" thick. Insert it into the squish area and turn the crank gently until it grips the feeler lightly. Mark the pulley. Then remove the feeler, turn the crank past TDC and reinsert the feeler, keep turning until the feeler will insert into the squish area again. Maybe reverse crank a tiny bit to again grip the feeler. I'm thinking this will find the same +/- TDC point within a few thou at worst.

I've seen this question come up dozens of times and now I think I have a near foolproof, yet simple, method to find the true TDC without pulling the head or tiimng cover. Your idea to locate the point 0.050" or so down was the missing piece. Finding flat styrene of appropriate thickness is pretty easy if you have a hobby shop nearby.

Tom

I think you might be ignoring the carbon mountains on the pistons and squish face.

Not sure how reproducible the stop position is going to be if you cant position the "gauge" on the same terrain.
Its a thought though.

 

[beamdream]

Chuck, Exactamundo! Not gonna pull the head to satisfy my curiousity! The car has run fine for over 8000 miles since assembly. But I think using my plastic feeler guage of 0.100" will pretty well identifty approx +15 and -15 deg from TDC and allow me to check the TDC mark on the pulley. Then I'll pull the valve cover and check the valve positions at TDC and then check the advance at 3500 RPM.

Beamdream, as noted in first post the cam is NOT stock, it is KB grind. I have the specs. It does open the intake about 10 deg sooner than stock and it does have a different recommnded advance curve than stock. But I don't think that includes an idle advance much off the stock settting. Also the head has the Vizard mod, and crank is reground for 0.100" longer stroke.

Tom

What I was trying to say is mark up the pulley to establish if the timing marks are correct.

With the modified cam you should have the valve open / close degree numbers, with this info, if you mark those degrees on the pulley perimeter and check that the valves open and close at these intervals, you can at least establish if the timing marks are either right or wrong.

 

[Bill Blue]

Why not use the time honored piston stop. Isn't the spark plug over the piston?

Bill

 

[Ken Ellis]

What's the relationship between TDC and the woodruff key on the crankshaft? A minimally-invasive check could be made by removing the bolt from the crank end, but not the pulley. Check and mark its location on the pulley, inside the elastomer ring with straightedge and paint marker. Then you should have a repeatable, non-slip reference from which you can determine crank angle. Even if it's not TDC.

Remember to re-install the bolt, of course...

 

[Tom H]

Thanks for the thought, Ken, That would help, and I thought of that. But as you note that bolt can be an issue. I was looking to avoid undoing and redoing that bolt. So I was looking for a "less invasive" approach to checking the timing. As it is, based on my tests so far it looks like the timing mark is correct. That's why I'm looking for better explanation on why "effective" timing could be so far from "normal" .Vizard? Longer stroke? KB grind cam? Misaligned chain? Next step is to try my thicker plastc feeler gauge, to get a higher confidence in the TDC mark. Then check valve timing.

Beamdream, I have the cam specs somewhere, but even with those specs it's pretty hard to ID the exact TDC point. I think finding the crank position where the cam lobe is at the center of its peak is twice as hard as finding the top of the piston position because the cam moves only 1/2 the crank rotation. Or maybe about same difficulty, because of small cam dwell at the peak. Furthermore, any error I would find using this cam approach would leave me still uncertain if the error was in the timing mark on the pulley or in the chain, or even possibly in the cam.

Tom

 

[sunbby]

Thanks for the thought, Ken, That would help, and I thought of that. But as you note that bolt can be an issue. I was looking to avoid undoing and redoing that bolt. So I was looking for a "less invasive" approach to checking the timing. As it is, based on my tests so far it looks like the timing mark is correct. That's why I'm looking for better explanation on why "effective" timing could be so far from "normal" .Vizard? Longer stroke? KB grind cam? Misaligned chain? Next step is to try my thicker plastc feeler gauge, to get a higher confidence in the TDC mark. Then check valve timing.

Beamdream, I have the cam specs somewhere, but even with those specs it's pretty hard to ID the exact TDC point. I think finding the crank position where the cam lobe is at the center of its peak is twice as hard as finding the top of the piston position because the cam moves only 1/2 the crank rotation. Or maybe about same difficulty, because of small cam dwell at the peak. Furthermore, any error I would find using this cam approach would leave me still uncertain if the error was in the timing mark on the pulley or in the chain, or even possibly in the cam.

Tom

Usually you don't try to find the lobe center directly, but try to find the cam timing at a certain opening and closing threshold, such as .040" after opening and .040" before closing (or some other point that is on the steep area of lobe "ramp"). Then you can use your cam specs to determine the lobe center timing.

As for determining the crank position, Bill's method is the best. Remove a spark plug and use a dial gauge or a hard stop. You bring the piston up, _carefully_, to the hard stop from both directions, then TDC is the middle point between these 2 measured points.

When I was racing motorcycles I made my own stop by removing the center of an old spark plug and tapping a bolt through the middle that extended an inch past the end of the plug.

Using these 2 methods you can get pretty accurate cam timing measurements.

 

[RootesRacer]

http://www.ebay.com/itm/COMP-Cams-Piston-Stop-Tool-4795-/370616449943?pt=Motors_Automotive_Tools&hash=item564a763b97&vxp=mtr

 

[beamdream]

Thanks for the thought, Ken, That would help, and I thought of that. But as you note that bolt can be an issue. I was looking to avoid undoing and redoing that bolt. So I was looking for a "less invasive" approach to checking the timing. As it is, based on my tests so far it looks like the timing mark is correct. That's why I'm looking for better explanation on why "effective" timing could be so far from "normal" .Vizard? Longer stroke? KB grind cam? Misaligned chain? Next step is to try my thicker plastc feeler gauge, to get a higher confidence in the TDC mark. Then check valve timing.

Beamdream, I have the cam specs somewhere, but even with those specs it's pretty hard to ID the exact TDC point. I think finding the crank position where the cam lobe is at the center of its peak is twice as hard as finding the top of the piston position because the cam moves only 1/2 the crank rotation. Or maybe about same difficulty, because of small cam dwell at the peak. Furthermore, any error I would find using this cam approach would leave me still uncertain if the error was in the timing mark on the pulley or in the chain, or even possibly in the cam.

Tom

OK at the risk of teaching to suck eggs, let me explain myself a little with the cam timing. First you need to determine if in fact the cam / chain relationship is in order with the crank, having done that you can be prove / disprove that the timing pulley marks are correct / incorrect.

So we are focusing on the fact that the cam to crank timing is correct, after that we can be safe in the knowledge that the timing marks are correct.

As a means to prove this, check the valve opening or closing times with the known data of the cam, ie inlet opens x degrees BTDC, exhaust opens y degrees BBDC etc.

A simple way of doing this is to insert a feeler guage, say two to three thou, at the appropiate rocker arm as you move the crank in DOR, when the rocker nips the feeler you know that this valve is about to be opened, now look at the degree marks on the pulley and establish if they are correct or not. If the numbers are right you have reassured that the timing marks are correct.

Longwinded but I hope of some assistance.