2000StreetRod
Moderator Emeritus
- Joined
- May 26, 2009
- Messages
- 10,597
- Reaction score
- 334
- City, State
- Greenville, SC
- Year, Model & Trim Level
- 00 Sport FI, 03 Ltd V8
Background
The SOHC V6 was installed in 4WD models with a balance shaft and in 2WD vehicles without one (4WD engine shown below).
The balance shaft chain tensioner is rather flimsy and prone to failing sooner than the other improved (2002 and later MYs) timing chain related components. Replacing the entire balance shaft chain tensioner requires removal of the block cradle since the tensioner base retaining bolts are in the vertical position. Some members have successfully replaced just the spring portion of the tensioner by bending the pivot post out of position, sliding off the old spring section, sliding on the new spring section, and then bending back the post. It is unknown how much the stress of bending the post reduces its reliability. Some members have just cut the balance shaft chain rather than remove and reinstall the block cradle to correctly replace the tensioner. There has been much discussion on the forum about the need for a functional balance shaft because of the difficulty associated with chain tensioner replacement or because of the desire to replace a balance shaft equipped engine with an available engine with no balance shaft (or vice versa).
Below are the comments I posted in 2010 and still think valid:
"Two types of imbalance associated with the SOHC V6 engine are rotational imbalance and reciprocating imbalance. The crankshaft counter weights reduce rotational imbalance. The balance shaft is used to reduce reciprocating imbalance. That is one reason that the balance shaft rotates much faster than the crankshaft. A symmetrical opposing (flat) engine needs no balance shaft because the reciprocating forces of one piston are offset by those of an opposing piston.
I remember many years ago as inline four cylinder engine displacement increased from year to year that there was a common belief that two liters was the maximum size possible due to vibration concerns. The industry incorporated balance shafts to exceed the two liter limit. Some engines even had two balance shafts rotating in opposite directions.
4WD associated components are all rotationally balanced. I suspect that Ford chose to implement the balance shaft for reduced vibration for customer satisfaction rather than increased serviceability. Ford produced millions of V6 engines (OHV and SOHC) with no balance shafts and no associated recall notices due to premature failure. I'm not aware of any technical service bulletins regarding premature crank failure related to the absence of a balance shaft. Some standard shift performance enthusiasts purchase lightened flywheels for reduced rotational mass and increased throttle response. The negative impact is a slightly less smooth idling engine. I think the balance shaft issue is an analagous trade off.
I would not be concerned about premature crankshaft failure when using an engine with no balance shaft."
Timing the balance shaft requires no special tools and is not complicated. However, it is difficult to describe without multiple drawings or photos. My 2WD SOHC V6 has no balance shaft so I have no photos of one. However, I have access to the 2005 Mustang SOHC V6 Engine Assembly Instructions which surprisingly (since to my knowledge no 4WD Mustangs were manufactured) has a good description with adequate drawings. The instructions are the main source for this procedure. I also used information from my Haynes Repair Manual and my personal experience gained from forum posts.
Balance Shaft Timing Procedure
Rotate crankshaft until the No. 1 piston is at
top dead center.
Install the balance shaft. (It is not necessary to remove the balance shaft to replace the chain or time the balance shaft).
1 Position the balance shaft assembly.
2 Install the bolts and tighten to 27 Nm (20
lb-ft).
NOTE: Due to the gear ratio between the
reversal shaft and the balance shaft, up to 7
complete turns of the balance shaft may be
required to find the correct position.
Align the timing marks. The hole (B) in the assembly should be centered between the two marks (A) on the sprocket and the mark on the balance shaft (C) should be aligned with the bottom of the block casting and on the side close to the crankshaft.
• Install a 4 mm (0.16 in) pin or drill bit to hold the
shaft in place.
Install the balance shaft chain and
crankshaft sprocket.
1 Position the balance shaft tensioner with its pin installed.
2 Install the 2 bolts and tighten to 29 Nm (21
lb-ft).
3 Position the balance shaft chain guide,
install the 2 bolts and tighten to 10 Nm (89
lb-in).
• Remove the pin from the tensioner and the alignment pin from the balance shaft sprocket.
The SOHC V6 was installed in 4WD models with a balance shaft and in 2WD vehicles without one (4WD engine shown below).
The balance shaft chain tensioner is rather flimsy and prone to failing sooner than the other improved (2002 and later MYs) timing chain related components. Replacing the entire balance shaft chain tensioner requires removal of the block cradle since the tensioner base retaining bolts are in the vertical position. Some members have successfully replaced just the spring portion of the tensioner by bending the pivot post out of position, sliding off the old spring section, sliding on the new spring section, and then bending back the post. It is unknown how much the stress of bending the post reduces its reliability. Some members have just cut the balance shaft chain rather than remove and reinstall the block cradle to correctly replace the tensioner. There has been much discussion on the forum about the need for a functional balance shaft because of the difficulty associated with chain tensioner replacement or because of the desire to replace a balance shaft equipped engine with an available engine with no balance shaft (or vice versa).
Below are the comments I posted in 2010 and still think valid:
"Two types of imbalance associated with the SOHC V6 engine are rotational imbalance and reciprocating imbalance. The crankshaft counter weights reduce rotational imbalance. The balance shaft is used to reduce reciprocating imbalance. That is one reason that the balance shaft rotates much faster than the crankshaft. A symmetrical opposing (flat) engine needs no balance shaft because the reciprocating forces of one piston are offset by those of an opposing piston.
I remember many years ago as inline four cylinder engine displacement increased from year to year that there was a common belief that two liters was the maximum size possible due to vibration concerns. The industry incorporated balance shafts to exceed the two liter limit. Some engines even had two balance shafts rotating in opposite directions.
4WD associated components are all rotationally balanced. I suspect that Ford chose to implement the balance shaft for reduced vibration for customer satisfaction rather than increased serviceability. Ford produced millions of V6 engines (OHV and SOHC) with no balance shafts and no associated recall notices due to premature failure. I'm not aware of any technical service bulletins regarding premature crank failure related to the absence of a balance shaft. Some standard shift performance enthusiasts purchase lightened flywheels for reduced rotational mass and increased throttle response. The negative impact is a slightly less smooth idling engine. I think the balance shaft issue is an analagous trade off.
I would not be concerned about premature crankshaft failure when using an engine with no balance shaft."
Timing the balance shaft requires no special tools and is not complicated. However, it is difficult to describe without multiple drawings or photos. My 2WD SOHC V6 has no balance shaft so I have no photos of one. However, I have access to the 2005 Mustang SOHC V6 Engine Assembly Instructions which surprisingly (since to my knowledge no 4WD Mustangs were manufactured) has a good description with adequate drawings. The instructions are the main source for this procedure. I also used information from my Haynes Repair Manual and my personal experience gained from forum posts.
Balance Shaft Timing Procedure
Rotate crankshaft until the No. 1 piston is at
top dead center.
Install the balance shaft. (It is not necessary to remove the balance shaft to replace the chain or time the balance shaft).
1 Position the balance shaft assembly.
2 Install the bolts and tighten to 27 Nm (20
lb-ft).
NOTE: Due to the gear ratio between the
reversal shaft and the balance shaft, up to 7
complete turns of the balance shaft may be
required to find the correct position.
Align the timing marks. The hole (B) in the assembly should be centered between the two marks (A) on the sprocket and the mark on the balance shaft (C) should be aligned with the bottom of the block casting and on the side close to the crankshaft.
• Install a 4 mm (0.16 in) pin or drill bit to hold the
shaft in place.
Install the balance shaft chain and
crankshaft sprocket.
1 Position the balance shaft tensioner with its pin installed.
2 Install the 2 bolts and tighten to 29 Nm (21
lb-ft).
3 Position the balance shaft chain guide,
install the 2 bolts and tighten to 10 Nm (89
lb-in).
• Remove the pin from the tensioner and the alignment pin from the balance shaft sprocket.