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Ignition Timing

R

RootesRacer

Donation Time
beamdream said:
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.
Click to expand...

Even when the cam is supposedly ground without lobe center offset, often manufacturing tolerances and errors result in the cam be advanced or retarded according to design specs.

Very often we have to install offset keys on the cam to make the cams crankshaft timing accurate according to specs.

That said, if you use an uncorrected cam to verify the crank timing, any error in lobe offset gets multiplied by 2 for the crank.

BTW, I installed a 3 degree offset key in an alpine once.
 
Alpine 1789

Alpine 1789

SAOCA President
Diamond Level Sponsor
R

RootesRacer

Donation Time
Jim Stone said:
I bought one of these, but don't know how to use it. I expected the center rod to be spring loaded, meaning I'd be able to use it to see when the piston was at the top of its travel. But it is fixed, meaning I'd damage the piston if I screwed it down, rotated the engine and it wasn't at the very top. How are these meant to be used?
Click to expand...

Its meant for the piston to hit it, but you are supposed to gently rotate the engine by hand to get the piston to just touch the threaded rod.


You should take out all 4 plugs and squirt oil in the cyls before you begin to ease the force needed to rotate the engines crank.

The piston stop is used in the #1 cyl.

You clock the engine to around 15 or so degrees BTDC (we dont know if its accurate yet) and then screw the rod in till you feel it touches the piston.
Visualizing the threaded rod and the piston, determine what direction you can rotate the crank so it doesnt hit the threaded rod. You will carefully back the crank rotation till the piston hits the rod.
You then mark the BTDC side of the pulley at the timing pointer.
Carefully rotate the engine (remember to visualize the mechanics) till you hit the piston on the ATDC side of the pulley.
Mark this position on the pulley too.

True TDC is the midpoint between the two marks on the pulley.

Test several times to make sure the marks are reproducible and be careful not to slam the piston into the threaded rod or torque a divit in your piston.
 
B

beamdream

Gold Level Sponsor
RootesRacer said:
Even when the cam is supposedly ground without lobe center offset, often manufacturing tolerances and errors result in the cam be advanced or retarded according to design specs.

Very often we have to install offset keys on the cam to make the cams crankshaft timing accurate according to specs.

That said, if you use an uncorrected cam to verify the crank timing, any error in lobe offset gets multiplied by 2 for the crank.

BTW, I installed a 3 degree offset key in an alpine once.
Click to expand...

As I read it, the original post #1 explains that we are running at 22 degrees advance ignition timing, which by all standards is a long way from the norm.

Whilst cam lobe error may contribute to the peak performance of an engine, the excercise here is to verify that the timing marks are correct.

A simple and reasonably accurate way to do that is use of the feeler guage rocker arm clearance method; after all, during initial engine buildup this is a way of verifying that the cam / crank timing agree are correct.
 
T

Tom H

Platinum Level Sponsor
Whew, gettin' deeper into this than I planned! But maybe I'm learning something - or maybe not. I get the idea of how to use the spark plug piston stop tool. Makes sense. But I will first try to use my thick plastic "feeler gauge" approach. I already have that tool. I can see how carbon deposits might mess it up. But if I use 0.120" thick gauge and this then finds the point about 0.070" down, which is about 18 deg before and after TDC, a couple thou carbon won't make much difference. This will tell me if the TDC mark on the pulley is correct.

Dreambeam, I think I understand your suggestion. BUT nowhere in your steps do I see where, when, how we verify that the PISTON is at TDC when the mark on the pulley says it is. Your steps all relate to the valve positions. How do you know where the piston is at any point? At no point in your described method to we do anything to verify the piston position. I see how to use your method to verify the valve timing, and thus the chain/and sprockets alignment, but first I need to verify the crank, pulley, and piston relationship.

Tom
 
B

beamdream

Gold Level Sponsor
Tom H said:
Whew, gettin' deeper into this than I planned! But maybe I'm learning something - or maybe not. I get the idea of how to use the spark plug piston stop tool. Makes sense. But I will first try to use my thick plastic "feeler gauge" approach. I already have that tool. I can see how carbon deposits might mess it up. But if I use 0.120" thick gauge and this then finds the point about 0.070" down, which is about 18 deg before and after TDC, a couple thou carbon won't make much difference. This will tell me if the TDC mark on the pulley is correct.

Dreambeam, I think I understand your suggestion. BUT nowhere in your steps do I see where, when, how we verify that the PISTON is at TDC when the mark on the pulley says it is. Your steps all relate to the valve positions. How do you know where the piston is at any point? At no point in your described method to we do anything to verify the piston position. I see how to use your method to verify the valve timing, and thus the chain/and sprockets alignment, but first I need to verify the crank, pulley, and piston relationship.

Tom
Click to expand...

OK sorry for the lack of info, what we are establishing is that if the valve opening position is correct then so will the TDC mark be correct.

So for instance, if I know that the inlet opens at say 20 degrees BTDC because of the cam spec numbers, I place a mark on the pulley correspondingly at 20 BTDC. Then move the crank in DOR to the point where the #1 rocker arm for #1 inlet valve nips up my feeler guage; I now know that this is the point where this valve is about to open.

If all is correct that pulley 20 degree mark will now be aligned with the front cover pointer, as a consequence of this all the other pulley marks must also be correct including your TDC mark etc.

There is more in the telling unfortunately than the detail, so hang in there.
 
B

beamdream

Gold Level Sponsor
Thinking further on how the distributor timing might be out, have you checked the distributor drive is in the correct position ? If the oil pump has been removed at some stage and not reinstalled correctly then the distributor drive slot will be out of kilter with the cam. Ref. WSM Section B page 32.

Oh and by the way if you are still struggling with the valve timing concept have a look at WSM Section B page 17 re valve timing.
 
Ken Ellis

Ken Ellis

Donation Time
WorkShop Manual -- available for early and late series cars. PDF on our site, under Technical Data, for immediate reference. Also available in print from the popular vendors.
 
T

Tom H

Platinum Level Sponsor
Ken, WSM = Work Shop Manual. There are several versions depending on what Series. For Series V , 1725 engine I use WSM 145.

I think dreambeam is using an earlier one.

Several versions are avialable for download under "Technical Data" on this site.

Dreambeam, I disassembled the engine and rebuilt it 4 years and 8000 miles ago. Bored, stroked, Vizard mod, KB cam. It's possible I mis-aligned the timing chain, but unlikely. I just looked at a photo I took during assembly and the dizzy drive dog is clearly lined up correctly at TDC. ( about 48 Deg as noted on page B16 of WSM 145). (that is, I can SEE in the photo the actual #1 and #4 piston at TDC). I DO understand the cam timing and I know the manual quite well. The cam sprocket has 44 teeth, so if I were off one tooth the dizzy drive would be off more than 8 Deg, from the 48 deg nominal. I think I can discern that it is NOT off that much. I am 99% certain (I'm a careful assembler) that the chain/cam/crank are aligned correctly, but I did not take a photo of the cam/ crank/ chain. And when I assembled it I do not recall for certain if I checked that the TDC timing mark on the pulley damper was in the correct location. I had no reason to check it, it was the original pulley.

But note again, there is NO WAY to verify that the pulley marking is correct by checking only the valve timing. All the info on valve timing (page 25 of WSM 145) is based on the assumption that the marks on the pulley are correct. I will verify the TDC mark by checking piston position at equal points Before and After TDC. Then I can check the valve timing to be sure I have the chain on correct. Then I'll look closely at my dizzy .

IF I use my photo evidence to feel 100% confident that the chain, cam, crank, and oil pump are on correctly THEN I can use valve timing to check the pulley marks. But I'll feel more confident to verify the marks via Piston position tests.

Thanks for the thoughts.

Tom
 
B

beamdream

Gold Level Sponsor
[
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.

Tom[/QUOTE]

OK somewhere along the way I understood you were trying to verify the accuracy of the timing marks; my suggestion was to verify this via the valve timing technique, it now seems you have indeed proven them to be correct particularly as you have also established that the distributor drive slot is correctly aligned.

So what can make the distributor run so far off as it is ? There can only be two possibilities, first as mentioned earlier, the centrifugal advance mechanism or secondly the distributor vacuum mechanism.

By the way, do you know what the manifold vacuum is at idle, just wondering if that cam as any influence on things.
 
T

Tom H

Platinum Level Sponsor
Hey Ken, I tried the link and it got to a page that said it " WikiHow does not yet have an article with this exact name". Could you get back to that article and give me a better link.

Beamdream, you're still missing it. The photo seems pretty sure to show me that the cam, crank, and oil pump are all installed correctly. But the photo was taken after the timing cover was installed but before the pulley was installed. So none of that information confirms that the timing marks on the pulley are correct. So I still need to verify the timing marks on the pulley. IF I assume, from the relatively imprecise photo evidence that the cam, crank and oil pump are correct I could use your valve timing to verify the timing marks. But I think I am better off to use the more direct step of verifying via piston position. A least our discussion, and your oil pump reference caused me to find that photo and give me greater confidence in the chain installation.


Tom
 
R

RootesRacer

Donation Time
The hydrolic method would probably be good unless you have a cracked ring or compression loss, in which case some of the fluid will leak past the piston making the second point at a nearer TDC than the first.

Gonna stick by my first recommendation (or is that the second or third?) and say go with the piston stop, performed with care.
 
B

beamdream

Gold Level Sponsor
Tom H said:
Hey Ken, I tried the link and it got to a page that said it " WikiHow does not yet have an article with this exact name". Could you get back to that article and give me a better link.

Beamdream, you're still missing it. The photo seems pretty sure to show me that the cam, crank, and oil pump are all installed correctly. But the photo was taken after the timing cover was installed but before the pulley was installed. So none of that information confirms that the timing marks on the pulley are correct. So I still need to verify the timing marks on the pulley. IF I assume, from the relatively imprecise photo evidence that the cam, crank and oil pump are correct I could use your valve timing to verify the timing marks. But I think I am better off to use the more direct step of verifying via piston position. A least our discussion, and your oil pump reference caused me to find that photo and give me greater confidence in the chain installation.

OK Tom I am listening to what you are saying and readily admit that I will never be too old to learn.

So let me ask, that if during assembly, you put the crank at TDC and then put the cam out by one tooth, would it then be coincidental that the valve opening / closing points occured at the precribed number of degrees before / after TDC as indicated by the crank pulley marks. If that were to be the case I cant get my head around it.
Click to expand...
 
T

Tom H

Platinum Level Sponsor
Beamdream, I think I see your point. If the cam were off by one tooth and yet the marks lined up, that would be a huge coincidence. So checking via valve timing would be a reasonably valid way, and if the marks are on target via valve timing, it's highly likely that the marks are correct. Which would leave me still scratching my head as to why the most effective timing is around 20 deg at idle. And I'd still then have some doubt about the marks. Similarly, if I used valve timing to check the marks and find they are OFF target, I am even more puzzled - maybe it's the timing chain - or maybe it's the pulley marks themselves. So I return to the obvious, check the pulley marks based on Piston position. Seems more direct, pretty easy, and quite conclusive. I'm going to check it this afternoon. Thanks for your interest and suggestions. It has helped me think this thru a good bit. I hope all the other viewers of this thread are not bored to tears by now! I'll report on TDC findings soon. As well as Dizzy report.

Tom
 
sunbby

sunbby

Past SAOCA President
Donation Time
Hey Tom,

Just curious, how do you know the timing is set to 20deg? Are you using a timing light, is it a simple light or one of those where you can dial in the advance?

Just wondering if you're chasing a measurement equipment issue instead of a "real" timing issue.
 
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