Automatic Primary Chain Tensioner
Road Captain
Joined: Nov 2018
Posts: 583
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From: Allegan, Mi
I may be wrong, but are you referring to the cam (not the primary) chain tensioners?
They're still plastic in '07 and up but they did away with the springs and went to a hydraulic system to provide the tension.
They're still plastic in '07 and up but they did away with the springs and went to a hydraulic system to provide the tension.
Seasoned HDF Member
Joined: Sep 2008
Posts: 14,146
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From: San Diego, CA
At the same time they "upgraded" the compensator, and went to the hydraulic cam tensioners, the MoCo went to the automatic primary chain tensioner... Dynas in '06 and the rest in '07.... I believe all three "improvements" were hand in hand with the 96ci engine.
As luck would have it (OK, it's almost a given whenever the MoCo "upgrades" something) the original design was problematic, part # 39929-06A. It caused the primary chain to become too tight, and it could damage associated bearings/seals in the primary/trans due to the over tight primary chain....
The Moco redesigned that tensioner in 2011 (I believe, forget the actual first year it was in production) and it was part #39929-06B. The second version had several improvements made, and was much better than its predecessor.... there are very few over tightening complaints since the redesign...
In the image below, the "B" version is on top, and the problematic "A" version is on the bottom. You can see the "B" version looks like a better piece. It has smaller adjusting teeth, the bottom ramp is more stout for less flex, and a couple other changes that escape me at the moment. All the changes led to a more reliable auto tensioner with much less probability of making the primary chain too tight... If you have a "B" version, either OEM or as a replacement of the "A" tensioner, I wouldn't worry about it...
As luck would have it (OK, it's almost a given whenever the MoCo "upgrades" something) the original design was problematic, part # 39929-06A. It caused the primary chain to become too tight, and it could damage associated bearings/seals in the primary/trans due to the over tight primary chain....
The Moco redesigned that tensioner in 2011 (I believe, forget the actual first year it was in production) and it was part #39929-06B. The second version had several improvements made, and was much better than its predecessor.... there are very few over tightening complaints since the redesign...
In the image below, the "B" version is on top, and the problematic "A" version is on the bottom. You can see the "B" version looks like a better piece. It has smaller adjusting teeth, the bottom ramp is more stout for less flex, and a couple other changes that escape me at the moment. All the changes led to a more reliable auto tensioner with much less probability of making the primary chain too tight... If you have a "B" version, either OEM or as a replacement of the "A" tensioner, I wouldn't worry about it...
Last edited by hattitude; Aug 7, 2019 at 10:18 PM.
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