P15-C Plymouth Manifold Heat Spring Replacement

[Sbonesteel]

Greetings.  I have read all of the P15 service manuals and all of the related posts on this forum I could find but still need a little help with replacement of the thermostatic spring on my exhaust manifold.  My spring and the cover 'weight' are still installed but the spring is obviously broken.  I understand that the 'operating position' (i.e., once the manifold is up to temperature) of that weight (and, accordingly, the attached pivot shaft and flapper) is in the full clockwise position.  How does the cover assembly come off of the pivot shaft so that the spring can be replaced?  It looks like it is just pressed on but I am reluctant to pry on it without at least asking the question.  Appreciate your help.  Thanks!  SMB

[9 foot box]

   There is a 5/16 headed bolt that needs to be loosened.

[Sbonesteel]

On 10/3/2025 at 7:00 PM, 9 foot box said:

   There is a 5/16 headed bolt that needs to be loosened.

Got it, thanks for the reply, was able to access and remove (although it sheared off...not a problem).  Ready to install with a new thermostatic spring.  My counterweight is identical to yours as is the assembly.  However, I see some of the suppliers advertising a 'stop' for the unit, that being a small plate with a hole in it and a fabric/asbestos strap.  Nothing like that was attached to the unit on my '47.  I assume it attaches to the bolt we have discussed (and that mine sheared off but I have replaced) but where?  There are no remnants anywhere on my unit of anything like this and it is unclear to me why a 'stop' is required, as the internal butterfly bottoms out once the spring is up to temperature.  Anybody know where this is supposed to go or have a photo of one installed?  Since I am rebuilding/replacing this unit I would like to make sure it is complete.  Thanks again to all.  SMB

[Sbonesteel]

Got it all installed, new spring and new counterweight, had to adjust the spring 'starting position' one time but it now works like a charm.  Installed without the strap/stop and it does not seem to be required for this installation (probably why there were no remnants of one on my manifold).  Thanks to @9 foot box for the response/aid.  SMB

[9 foot box]

   The part you are missing provides a soft stop of the mechanism when it closes. It’s good that yours had free movement. 

[Sbonesteel]

20 hours ago, 9 foot box said:

   The part you are missing provides a soft stop of the mechanism when it closes. It’s good that yours had free movement. 

Thanks for that.  My counterweight looks different and the bolt bracket has an 'ear' on it that performs the same function, albeit without the 'soft touch'.  What text is that view of the Manifold Heat Control from?  It doesn't show up in any of my multiple manuals/parts lists.  SMB

[9 foot box]

   I’ve been fortunate to find original service manuals and a parts book that has a bit more detail of how components work.   Rick D.

[Sbonesteel]

UNREAL... .  I have the April '47 and October '48 Plymouth P15 Parts Lists, as well as multiple Plymouth service manuals from 42 through 52, all covering in whole or in part the P15 models, and while the parts lists show that strap in the illustrations, NONE OF THEM HAVE THAT ILLUSTRATION from the 'inside' of the assembly, showing that strap in place on the counterweight.  Why it is uniquely there in the Preliminary version and not in the earlier '47 or later '48 is just plain weird.  Thanks again for providing that.  SMB

[Sbonesteel]

14 hours ago, Sbonesteel said:

UNREAL... .  I have the April '47 and October '48 Plymouth P15 Parts Lists, as well as multiple Plymouth service manuals from 42 through 52, all covering in whole or in part the P15 models, and while the parts lists show that strap in the illustrations, NONE OF THEM HAVE THAT ILLUSTRATION from the 'inside' of the assembly, showing that strap in place on the counterweight.  Why it is uniquely there in the Preliminary version and not in the earlier '47 or later '48 is just plain weird.  Thanks again for providing that.  SMB

OK my vision is getting poor I guess... .  Your Preliminary List is from January 1946, not '48, so it pre-dates all of my editions, so that illustration was an earlier version of the manifold heat assembly.  Here is a photo of the counterweight type in my '47, which seems to have added the metal ear to serve as the 'stop' for the unit.