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 Author  Topic: Rework of Mufflers
Bridge Carney

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Post a Reply To This Topic    Reply With Quotes     Edit Message     View Profile of Bridge Carney  Posted on: Mar 6, 2010 - 8:52am
I'm about done on the rework of the mufflers for my PT-157 model. Quite a challenge but rewarding to build based on actual information! Two quick photos attached. Note that the horizontal rod and vertical rods are to scale! To do this I used musical wire as they have GREAT granularity in sizes. For the vertical rods (based on my scale) I used .0092" wire. The horizontal rod is a .013" (I think). A little tough to cut music wire but results are forever.

Based on the fabulous collection of ELCO PT blueprint microfilm that Dick has brought to light I have been able to complete the linkages for the PT-157's silencing mufflers. I note that these details from the blueprints were not available from any other source previously. Even the hunting I've done with other sites on PTs did not have such detail. So thanks to Dick for bringing this detail, and I'm sure many others yet to be reviewed and/or discovered, to light. However it also showed that as close as my mufflers were to being accurate, they are not accurate according to the ELCO blueprints. So I'll be fabricating a new set and replace my mufflers and the section of the PT-157 book, in due time, with new photos and details

In one of the more enlightening pieces of this puzzle is that many of clearest photos of the mufflers in books (some attached) show the butterfly flapper valves line across as perfectly horizontal. However the blueprints show that the butterfly would be at an angle once the whole muffler assembly is mount to the boat's transom. A closer inspection then of in-the-theater photos, such as the PT-109's stern while aboard the transport, you do see that the butterfly valves are on an angle. These photos are less clear but once you know what to look for it is evident.

Similarly the linkages from the horizontal rotating bar to the vertical rods used to open/close the valves were connected by (surprisingly) ball/socket type linkages. Sort of makes sense as the flapper valves linkage arms were actually on an off angle to the horizontal bar and linkages so the ball/socket joint would alleviate the binding and accommodate the dissimilar axis situation. Somewhere late in the PT's production cycle that butterfly valves (and collars) were put horizontal which allowed the butterfly and horizontal rods to be on the same axis. This allowed the use of, as we see in later blueprints, vertical rod's linkages to be simplified to the use of spilt rod yokes replacing the ball/socket approach. This change certainly was less expensive in production and likely would be a bit more reliable. Can't imagine that an exposed ball/socket joint would have faired well to the seawater conditions over time.

To top it off many blueprints, at least in the muffler series (Roll-4, around 460-479), show which PTs used which version of mufflers, flapper valves, collars etc. So although there is no stern view photo of the PT-157, we now know from blueprints what it did have for mufflers.

Changes in production comes as no surprise. My father, US Air Force in WWII, said that especially for B-17's the changes were so frequent that no two B-17s were the same. For the reason each B-17 had a cabinet on board for the drawings and references for THAT plane.

Am I having fun or what!!


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Frank J Andruss Sr


Post a Reply To This Topic    Reply With Quotes     Edit Message     View Profile of Frank J Andruss Sr   Send Email To Frank J Andruss Sr Posted on: Mar 6, 2010 - 9:21am

A very nice job on those Mufflars indeed. Thank you for sharing the photos, and I hope you will be posting many more to show us that wonderful model of the boat. I love seeing the work of those who build these boats. I am always impressed with how things are done and constructed. I have asked many more of you to show your work here, but I think my request has fallen on deaf ears...............

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Jeff D


Post a Reply To This Topic    Reply With Quotes     Edit Message     View Profile of Jeff D   Send Email To Jeff D Posted on: Mar 8, 2010 - 3:23am
Great work Bridge, especially considering that the height of the linkage arms is about 2 fingerprint ridges wide...

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Drew Cook


Post a Reply To This Topic    Reply With Quotes     Edit Message     View Profile of Drew Cook  Posted on: Mar 8, 2010 - 5:03pm

Great job on the mufflers, flaps, rods and linkages. The corrosion work on the mufflers below the waterline looks neat, too.

Total Posts: 1289 | Joined: Oct 19, 2006 - 10:44am | IP Logged

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