Some mechanics just don't get it!

[Carpediem44DB]

I had the engines surveyed on the Carver 506 with Volvo 74TAMDs completed yesterday. For the most part the engines are in good shape and run well. One of the first things the surveyor and I noticed right away though were the Zinc plugs. The last mechanic that installed them used teflon tape on the threads! They are not supposed to be isolated/insulated from the component they are tasked to protect! Does he not know what the purpose of the zincs are or how they work? There is no need to seal threads on a brass tapered pipe fitting for components that are at static pressure. This stuff drives me nuts! I'm sure he charged the owner $120/hr for his service to boot.
Carpe Diem

 

[joeyleggz]

I had the engines surveyed on the Carver 506 with Volvo 74TAMDs completed yesterday. For the most part the engines are in good shape and run well. One of the first things the surveyor and I noticed right away though were the Zinc plugs. The last mechanic that installed them used teflon tape on the threads! They are not supposed to be isolated/insulated from the component they are tasked to protect! Does he not know what the purpose of the zincs are or how they work? There is no need to seal threads on a brass tapered pipe fitting for components that are at static pressure. This stuff drives me nuts! I'm sure he charged the owner $120/hr for his service to boot.
Carpe Diem

Agreed but I think the tapered threads eventually cut through the Teflon tape and tighten down all the way if there’s any question you can always verify with a continuity test from the brass plug to a bare part on the motor

 

[hughespat57]

A common misconception, the Teflon fills the void spaces between the threads, it is no sufficiently strong enough to prevent metal to metal contact on face of the threads. The is particularly true due to the tapered nature of NPT or "national pipe thread".

However you are also correct in that with a soft brass tape is not really needed to get a good seal.

Marine https://www.sbmar.com/articles/myths-using-pipe-dope-threads/

Black iron gas lines (which are required to be a continuous ground)

 

[Carpediem44DB]

Good points but also what’s the point in taking unnecessary steps? The the caps are not likely to leak and unless one really grossly over torques the cap the dope is not needed to act as an anti seize. Minor points I know. Thanks for the clarification and Tony’s post as well.
I’ll discuss it with the surveyor as well for grins.
Cheers

 

[dtfeld]

If that's the list from your survey, You're in GREAT SHAPE!!!!

 

[juggernaut1]

The OEM Kohler generator pencil zincs for my boat come with thread seal pre applied.

 

[Carpediem44DB]

If that's the list from your survey, You're in GREAT SHAPE!!!!

The list is actually pretty short, The 1200 hr 21KW Kohler Gen set needs a water pump and the port engine fresh water pump is showing signs that the seal is failing and there is a small leak at the rear crankshaft seal. In all for a 21 year old boat with 600 hrs on the engines it could have been a lot worse. The owner recently had the region's premier Volvo Dealer do a 1000 hr factory service so I expected to have a short list on survey.

 

[Steve S]

Sorry that I am late to the party... Threads are my business... for the last 35 years.

An NPT thread is not normally a "dry seal" thread as when tightened, the thread flanks will compress but since the crest and the root of the thread are truncated, they leave a spiral, open area for fluid or gas to escape unless a sealant of some type is used.

Now an NPTF or "Dry Seal" thread differs from an NPT thread in the amount of crest and root truncation. Because the NPTF thread is not truncated like an NPT thread, the roots and crest engage first and continuing tightening pressure will compress them and then the flanks creating a leak proof seal.

However this action will only occur correctly one time. After that the mating parts should either be replaced or considered an NPT thread as the roots and crest will become truncated from the action of the tightening pressure.

I would think teflon tape would "rub" away along the flanks of the thread allowing somewhat of a metal to metal contact. However I believe a "die electric" grease would also serve the purpose of a sealant in the brass anode fittings.

 

[joeyleggz]

Steve wins!!!

 

[Blueone]

Steve wins!!!View attachment 97981

Ya ...but he had descriptive pictures... not sure that was fair

 

[Steve S]

Ya ...but he had descriptive pictures... not sure that was fair

They are actually from a 750 slide 2.5 day training presentation I helped develop.

 

[Carpediem44DB]

Learn something new every day! Thanks for the lesson. So many things in life come from tribal knowledge the way grampa did it. I always love being enlightened by the specialists who have studied the theory behind what most consider a mundane practice.
Thanks for sharing

 

[Blueone]

They are actually from a 750 slide 2.5 day training presentation I helped develop.

I know your pain... I live in the world of machining SAE J1926-1 ports in every size in Ni-hard, HiSyl moly, steel and ductile.... it’s a lonely existence

Here are some good size ones in a Cummins fuel manifold

 

[Steve S]

Nice! I spent almost 20 years working for Greenfield Industries / Kennametal / WIDIA and sold Metcut Port Contour cutters to a number of customers in Northern Illinois back when I was a field guy.

 

[Blueone]

Nice! I spent almost 20 years working for Greenfield Industries / Kennametal / WIDIA and sold Metcut Port Contour cutters to a number of customers in Northern Illinois back when I was a field guy.

I am mostly using Allied right now for production... they do a fair amount of testing for us.. which takes out a bit of the sting

 

[Steve S]

In their infinite wisdom, Kennametal shut down Metcut and quit making those tools. One of the reasons I moved on. It wasn’t the company I had joined. Bean counters took over the executive management, instead of people that understood machining.