84FromHell

Last week end I replaced my timing chain and gears. I thought I was very careful lining up the timing marks. After it was all back together I started it up and everything seemed ok. On the test drive I noticed the thing was a dog! I checked the timing and found that it was at 4* ATDC. I moved the timing to 6* BTDC (specs) and now I reset it to 11* BTDC and it seems better. What has me a little spooked is that the timing got so far retarded with the new chain. I thought it would be advanced with the new chain . Anyways, now it seems to run as good as it did before I changed the chain. Anyone have input on this? I've been told the simplest way to check the cam timing is to remove the valve cover on the right side, turn the motor until #6 is at TDC on the exhaust/intake stroke, then my timing mark should be at zero. Is this correct, and is there an easier way than pulling the valve cover? thanks guys

Aggravated4life

Best thing to do is to remove the #1 spark plug,remove the distributor and then bump the motor over until it(#1) reaches BTDC and the timing mark on the balancer is near or at 0 degrees.
Ya know,that bump the motor over and feel the compressed air come out of the plug hole,etc.
Get the #1 where its supposed to be then reinstall the distributor(may need to play with the oil pump shaft) and it should be where when you advance it,shouldnt take more then 6 to 8 degrees BTDC to time it.
Many times we make the mistakes and reinstall the distributor off because the oilshaft was turned on removal.
Its not always a tooth off.Try that first.
:)
(Hey Jake,if youre here,chime in...you got some good ideas as always.Jake helped me out with this similiar problem some time back.)
:)

Dr. Evil

Could it be that your old chain had stretched a bit so that with the new one it threw you off?

JAKE

Wow.

This could be complicated. Cam timing and ignition are two different animals, but both use the same name - timing.

Here's the problem. With the distributor installed, if you move the camshaft to a different position, it also moves the distributor, so ignition timing is effected. BUT, if you move the distributor it does not effect the cam timing.

What I need to know is what timing chain set you used. Some have multiple keyways in the crank gear and if not installed correctly, the camshaft will be advanced or retarded.

Sometimes, the dots won't align correctly even with new sets. In these cases, the crank gear must be set exactly at 12 o'clock but the cam gear should be set very slightly toward the 7 o'clock side.

It's hard to explain, but sometimes the camshaft gear will not mesh the chain properly with the dot directly at 6 o'clock. You then have only two options, the five o'clock side or the 7 o'clock side - the 7 o'clock is the way to go.

So based on what you posted, you have a ten degree ignition timing difference.

Assuming before you removed the old chain set you had your initial ignition timing set at 6 degrees BTDC and after it was at 4 degrees ATDC; you've got a 10 degree change.

Something's not right.

Does the engine feel different now? I mean does it seem to have more mid-range and top end; if so you retarded the cam. If it feels stronger down low in the RPM band, you advanced it.

I don't know of any way to check the cam timing (actually it's phasing) by looking at the lifters and the damper. If there is such a way I'd like to know about it because it would save me an awful low of work degreeing in cams.

It's difficult to say specifically what happened, can you post some specific details on what you did in changing the timing set.

Maybe then I can see what may have went wrong.

Jake


[Modified by JAKE, 2:06 PM 4/3/2002]

84FromHell

thanks for the replies.

Jake, here's what I did .. I used a edelbrock double roller chain and gears. I got the one with only one keyway (non variable timing). I did not remove the distributor. I removed the old chain and gears (which had 6* of slack) with the crank gear at 12 and the cam gear at 6. I thought I installed the new stuff the same way, but the timing issue has me wondering. Assuming the timing was at 6* btdc when I started, the chain had 6* of slack, and when I put it all back together the ignition timing was at 4*atdc, that would amount to 16* of retardation in the cam. Which I'm thinking is one tooth.
The "lifter/balancer method" of determining cam timing may not be accurate for degreeing a cam, but the theory is this - #6 and #1 cylinders are twins, but opposite. If #6 is at tdc of the exhaust/intake stroke, then #1 will be tdc on the power stroke and therefore the balancer mark should be aligned with the pointer at 0*.
At any rate I won't be satisfied until I know for sure where I'm at, so I'm going to try the "lifter/balancer" method tonight.
Any thoughts or ideas are appreciated and I'll post what I find out tonight.
Thanks!

Bill

jimbos86vette

Hey Bill,

Just put a vacuum gauge on a manifold vacuum source, and see what your readings are, you should be around 18 to 20 inches of vacuum. This can go up or down depending on altitude. If your off one tooth, you'll have 14 or lower. This is assuming that your cam is a stock grind. It doesn't sound like your off a tooth though, you wouldn't be able to even get close to your original performance by advancing the ignition timing.
This is by far the easiest way to check if your cam timing is correct.

Hope this helps :flag :flag :flag

84FromHell

jimbo I never thought about trying that, but it sounds like a great idea. Unfortunately about an hour too late ;-)
I pulled the right valve cover, put #6 at tdc on the intake stroke and my timing mark looks to be (off the scale) about 16* atdc.
Actually I'm not sure I even have the power I did with the old chain even with ignition timing set at 11* btdc, so I'm pretty sure I installed the timing gears one tooth off on the retarded side. Also yet another reason I think that is because after the install before I even adjusted the ignition timing the thing was a total dog. With a new, tight chain that should have advanced the cam which in turn would have advanced the ignition timing causing my ignition timing to go from 6* btdc to 12* btdc because there was 6* slack in the old chain.
I'm not preaching here, just thinking outloud and if you have a different opinion PLEASE post it before I tear the thing down again lol
thanks!

Bill

jvesalga

Well heck here is my 2 cents. I had the same problem on my 84. From your message I truely believe the gears are aligned correctly,if they were not then you would see a real problem. In timing the ignition you need to disconnect the wire to the distributor that contols the advance mechnism. (like disconnecting the vacuum advane on older cars) it is located just under the windshield wiper motor toward the drivers side of the car, single wire.

Jeez I hope this helps I know how frustrating this can be.

joe

JAKE

Right. I understand now what you're doing now.

Sure. if the #6 piston is at TDC at the conclusion of the compression stroke (and just before if begins the power stroke) the damper TDC mark should closely align with the timing tab zero. Also, both intake and exhaust lifters for the #6 should be dead level and on the base circle of the cam lobes when this check is done.

Problem is the piston will dwell for several degrees at TDC while the cam will move. This is the main problem for not using a dial indicator to find TDC when degreeing in a camshaft.

I remember once counting the number of teeth on the camshaft gear so I would know how many cam degrees each tooth represented. Seems that it was right around that 16 figure too.

I've been trying to think of other ways to eliminate the teeth being off without having to tear into the engine again because I know what a real PIA that is. I just installed a new cam last week end so I'm fresh from the wars and don't want any more front line duty any time soon.

The only thing I can think of is to use a positive stop screwed into the #1 spark plug hole and using a degree wheel verify TDC for the piston. Then with the piston at absolute TDC on the compression stroke (just before the power stroke begins), look at the timing tab and see what the reading is. This will verify the accuracy of the mark on the damper and the pointer on the timing chain cover. It should be dead on zero.

You could then look at the pushrods for the #1 and both should be of equal height and fully into the block (down position), indicating the lifters are on the base circle of the camshaft lobes. If one pushrod is higher than the other, the cam gear is off.

Of course you'll have to pull all the plugs and turn the engine with a 1/2" ratchet or breaker bar DO NOT USE THE STARTER. You can use the center damper bolt to turn the engine.

Having the plugs out makes turning the engine over possible without a lot or compression resistance from the other cylinders.

If I come up with anything else I'll post it.

Anyone else have an alternate plan?

Jake

JAKE

These are definite signs of the cam being off in the retarded position one tooth.

Jake

[SNIP]
Actually I'm not sure I even have the power I did with the old chain even with ignition timing set at 11* btdc, so I'm pretty sure I installed the timing gears one tooth off on the retarded side. Also yet another reason I think that is because after the install before I even adjusted the ignition timing the thing was a total dog.

Bill[/SNIP]


[Modified by JAKE, 12:01 AM 4/4/2002]

JAKE

[SNIP]
(Hey Jake,if youre here,chime in...you got some good ideas as always.Jake helped me out with this similiar problem some time back.)
:)
[/SNIP]

Hey, Bill; how'r things?

I do what I can, but sometimes this stuff keeps me up at night.

Maybe I outta get a "life".

Jake

84FromHell

Jake I think your's was good advice.
To clarify the #6 lifter/balancer theory a bit, this is what I was told .... determine TDC on #6 by turning the motor until the intake and exhaust valves move at the same time (overlap). This puts #6 at TDC (or very close) of the intake stroke. Since #6 and #1 are twins, #1 should be at TDC of the power stroke, therefore the timing pointer should be at 0* Now that I think about it I guess it wouldn't matter if you set #1 or #6 at TDC of the intake stroke because the timing mark should be at 0* in either case. I know I don't have exact TDC using this method, but I think it's close enough to not be off by 16* atdc which is what I'm seeing on my balancer ;-)
I bet doing this job again will be even more fun the second time heheh .. at least I should be a little faster at it :-)

JAKE

Okay, here's the real skinny, as how it see it, on how it works.

True, #1 and #6 are twins, but they are doing the exact OPPOSITE things, even though they rise and fall in unison.

Pistons are at TDC twice on a four stroke engine, once on compression and once on exhaust.

So when the #1 is at TDC on the compression stroke, the #6 is at TDC on the exhaust stroke and vice versa.

Now, when on the EXHAUST stroke, you have the overlap period as the exhaust valve is closing and the intake valve is just beginning to open, meaning both lifters will NOT be on the base circle of the cam and will be moving - one up and the other down. The intake lifter will be moving up - beginning to open the valve and the exhaust lifter will be moving downward closing the exhaust valve.

So my problem is that looking at the #6 won't really tell you what's going on with #1 because both of the #6 lifters are moving.

The real way to do it is to watch #1 and when both are of equal height and fully recessed into the lifter bores, then you know the lifters are on the base circle of the camshaft's lobes.

At that point, the #1 piston should be NEAR TDC, but since the #1 dwells (sits still while the crank is moving) at TDC for several degrees, it's hard to find EXACT TDC by merely watching the lifters.

Another point is that short duration cams will have shorter valve events, so that both valves will open later and close earlier and will be on the base circle while the piston is still a greater distance from actual TDC. The longer the duration of the cam, the later the intake valve will close (arriving at the base circle and not move anymore) and the closer to actual TDC the piston will be.

This is why reversion becomes a problem with long duration cams. Because the intake duration is so long, some of the incoming charge gets pushed back into the intake tract as the piston rises toward TDC. So the longer the intake valve is held open, the more incoming charge get pushed out as piston speed increases enroute to TDC.

Using that method will give you an error range of maybe 4 degrees or so, meaning your mark on the damper can be 2 degrees either side of the ZERO on the timing chain cover pointer. Maybe more, depending on the cam.

But if you use that technique and see that your damper mark is at 16 degrees - give or take a few - then you know the cam's off a tooth or so.

Of course, with the intake manifold installed, you'll have a hard time seeing exactly where the lifters are.

The only other variable I can think of is that the damper and timing chain cover pointer are not matched to each other. Using a pointer meant for a 6-1/4" damper on an engine that has a 8" damper will always give you false readings.

Putting a timing set on one tooth off isn't that hard to do; I've walked that road before.

Hope this helps.

Jake

jimbos86vette

Try a compression check, I always do them after vacuum test to back up diagnosis. If your valve timing is off your compression WILL be low.
I agree with Jake, you must find TRUE tdc to be accurate about cam timing. I've always used vacuum and compression tests for diagnosis of jumped timing chains.

84FromHell

you guys are right ...
I know the lifter/balancer method won't give true TDC, but the idea is to get the CAM at where it would be if the piston WAS at TDC. So setting the cam there, then looking at the balancer to see if you're near 0*. In my case I was 16* after TDC telling me I was one tooth off. I tore it down tonight and yep, I was one tooth off. Why didn't I see that the first time???? lol
thanks for all your help guys!