after aligning the 12, 6 marks on the cam gear with the 12 mark on the crank gear, the balance mark shows 4 deg after tdc. what did i do wrong?


thanks

matt

 

When the two marks are facing each other, the #1 piston is at the bottom of the cylinder.

To set if for 'compression' both marks should be pointing straight up..(12:00 o'clock)

This will put the crank at TDC and the distributor pointing at #1.

Rotate the crank until both marks are at 12 0'clock and your distributor should be pointing at #1 and the balancer pointer should show TDC.

 

Or your balancer has slipped in the hub. It is common for the rubber to eventually wear out causing it to slip.

 

WRONG!!! Both the #1 AND the #6 pistons are at TDC. The #1 piston is at TDC beginning the intake stroke, and the #6 piston is at TDC beginning the power stroke.

With the both sprockets in the 12 o'clock position, the #1 piston is at TDC beginning the power stroke, and the # 6 piston is at TDC beginning the intake stroke.

There are two complete rotations (720°) of the engine in the 4 stroke cycle.

The OP is simply off by 4° unless he located TDC using a piston stop. If so, the damper or crank key way, or both may be off.

RACE ON!!!

 

ATTENTION on DECK. Both my rebuild manual and my FSM say the proper way to install a cam is for the marks to face each other. That is the mark on the crank gear at 12:00 and the mark on the cam gear at 6:00. The key should be at 2:00. Both #1 and #6 will be at TDC. Which one is beginning its power stroke will depend on how you install the distributor. Convention is #1 is starting its power stroke.

I am not trying to start a pizzing contest here simply reporting what my books say as well as what I have been doing for 40 years or so.

 

HOLD THE PHONE.

Don't forget we need to consider what the valves are doing. So it's a bit more complicated than just considering where the rotor's pointed.

If you merely point the rotor at #6 (which would have just closed the exhaust valve) while #1 is waiting for the spark (having just closed the intake valve) to begin the power stroke, I guess you could say you'd have a problem.

Also, neither is at the bottom of the cylinder which is what I believe CFI-EFI was primarily addressing.

Jake

 

WRONG!!! You were doing good, right up until the end. The distributor is not the determining factor as to what stroke the engine is on. The camshaft determines that. If you position the distributor to fire at 6° BTDC as the piston comes to the end of the exhaust stroke, you will have an engine that doesn't run.

The first part of the post is correct. Technically it makes no difference whether both sprockets are at 12 o'clock or if the crank sprocket is at 12 o'clock and the cam sprocket is at 6 o'clock. When crank sprocket dot is at 12 o'clock, the #1 and the #6 pistons are both at TDC. It is the orientation of the camshaft that determines which is starting the power stroke and which is starting the intake stroke. With the 12/6 arrangement, the dots are closer together and it is easier to see when they are properly aligned. As I said in my first post, with the dots at 12/6 the #6 piston is at TDC starting the power stroke. With the dots at 12/12, the #1 piston is at TDC starting the power stroke. When it comes time to install the distributor, the engine is usually rotated to TDC on the power stroke for the #1 cylinder, but there is no reason it couldn't be done with #6 in the position to fire.

RACE ON!!!

 

I have an engine,sans heads, on a stand.Tomorrow I'll do some checking and get back to everyone.

 

thanks for all the replies!

ill try to be clearer this time, maybe my wording confused everyone.

cam gear: timing dot at 12, dowel locator pin at 9, other dot at 6

crank gear: timing dot at 12

crank key at 2

all three dots lined up in a row


after the cover and damper are put on w/o moving crank,
the timing mark is at 4 deg after.

when i pulled off the intake, the rotor was pointed to #1 (front of engine, driver side)

both cam gear(steel) and chain are new -- old gear(nylon) had 1 tooth broken off and chain was stretched.

the cam is new as well.

 

Two things:
1. Never,never try to post anything of a technical nature when your wife is talking about going out for dinner.
2. I was way off base with my comment about TDC and distributors.With the dot on the crank gear at 12:00 and the dot on the cam gear at either 6:00 or 12:00 #1 cylinder will be at TDC completing its compression stroke. Cylinder 6 will be completing its exhaust stroke.


Matt,does your crank gear have one or three marks, a square,a dot and a triangle? The three marks allow you to set the can straight up,dot, or plus or minus 4 degrees,square or triangle.

 

ill have to pull the cover off to look.
whats the advantage of the other settings?
i think the new cam says its alrready 4deg advanced


thanks

matt

 

This is still wrong. Reread post #4, paragraphs 2 and 3. Also post #7, paragraph 2.

RACE ON!!!

 

There are a couple of other things to consider.

The timing chain cover, timing tab and harmonic damper have to all match each other. If you have a bolt on timing tab that's not designed for the damper you're running, the TDC mark on the damper could be in the wrong place or the tab is wrong for your damper. All three work as a matched set.

Another thought is parallex error. When aligning the dots, if you are not viewing them from dead-straight ahead, they may not be correctly aligned with each other.

You could use the positive stop method to find absolute TDC for #1 which would eliminate all doubt.

Also, you didn't install the gears one-tooth off because doing so would result in an error greater than 4 degrees.

Jake

 

Aligning the dots on the timing sprockets is NOT an accurate way to locate TDC. First, you are confusing the issue, with the dowel pin and key way locations. They are not normally taken into account for installing the timing chain. The 4° advance ground into the camshaft has nothing to do with the installation. Hopefully, because the cam is ground with the advance built in, you have a simple, single key way crank sprocket. Regardless, there are only 2 dots to be aligned for the proper installation of the timing chain, one on the crank sprocket and one on the cam sprocket. Because aligning the dots is not an accurate way of locating TDC, your crank position may be off a few degrees. Also your damper ring may have moved, or tolerance stack up may have caused the timing marks to be slightly misaligned. If you want to check your timing marks, you are going to have to precisely locate the piston at TDC using a piston stop. It is most accurately done with the head off, but you can get close with it in place. If you wish to proceed, and would like an explanation as to how to do it, let me know. I'm happy to help.

RACE ON!!!

 

Thats what I said for goodness sakes.TDC is a transition point, from compression to power (assuming you have fuel,air and spark), exhaust transitions to intake.

 

I must have read it wrong. What registered in my head was that you were saying that both #1 and #6 were at TDC of the same stroke. I apologize. However it isn't an "either" situation.
When the crank sprocket is at 12 o'clock, the #1 and the #6 pistons are at TDC. As previously posted, when the CAM sprocket dot is at 12 o'clock, the #1 piston is at TDC at the end of the compression stroke, just beginning the power stroke, and the #6 piston is just finishing the exhaust stroke and beginning the intake stroke. This is the overlap period.

When the CAM sprocket dot is at the 6 o'clock position, the #6 piston is at TDC at the end of the compression stroke, just beginning the power stroke. The #1 piston is just finishing the exhaust stroke and beginning the intake stroke.

RACE ON!!!