PRV leak

Mofosheee · Nov 14, 2025

The new prv on my 850 has had a small leak leak since installation.
Confirmed good prv / timing case cover threads and installed a new copper washer............. still leaks, but not as much.

To seal things up, would I be going down the wrong path to use a wrap or two of #50 aviation grade silk or kevlar thread at the copper washer location of the prv threads?

Thank you!

kommando · Nov 14, 2025

When faced with such issues a Dowty washer is the fix I go for and it always works. Finding the right size is the hardest bit of the process, I can check tomorrow.

concours · Nov 14, 2025

Mofosheee said:
The new prv on my 850 has had a small leak leak since installation.
Confirmed good prv / timing case cover threads and installed a new copper washer............. still leaks, but not as much.

To seal things up, would I be going down the wrong path to use a wrap or two of #50 aviation grade silk or kevlar thread at the copper washer location of the prv threads?

Thank you!

Yes, that is the wrong path. The threads are not designed to seal.
The copper washer is where the sealing occurs.
Inspect mating surfaces for imperfections. Repair as needed. Use Loctite 518 as a dressing on a new copper washer.

marshg246 · Nov 14, 2025

Mofosheee said:
The new prv on my 850 has had a small leak leak since installation.
Confirmed good prv / timing case cover threads and installed a new copper washer............. still leaks, but not as much.

To seal things up, would I be going down the wrong path to use a wrap or two of #50 aviation grade silk or kevlar thread at the copper washer location of the prv threads?

Thank you!

Assuming the surfaces are good, I would try again with new washers and back off a bit on tightening. Over tightening can cause leaks just as under tightening.

You should use Teflon tape but the one for gas and oil, not plumbing or this:

Edit: I initially put the wrong picture - this is the correct picture:

It is basically liquid Teflon tape and works very well - is messy to use.

robs ss · Nov 15, 2025

Mofosheee said:
The new prv on my 850 has had a small leak leak since installation.
Confirmed good prv / timing case cover threads and installed a new copper washer............. still leaks, but not as much.

To seal things up, would I be going down the wrong path to use a wrap or two of #50 aviation grade silk or kevlar thread at the copper washer location of the prv threads?

Thank you!

Are you annealing the copper washer? If you're not, you may as well use a steel one
Cheers

kommando · Nov 15, 2025

kommando said:
When faced with such issues a Dowty washer is the fix I go for and it always works. Finding the right size is the hardest bit of the process, I can check tomorrow.

An M22 fits well, note there is no ISO standard for Dowty washers so makers can vary dimensions if they wish. This one has a 30mm OD which matches the Hex well

Mofosheee · Nov 15, 2025

Yes, I annealed. All mating surfaces and threads appeared good. I probably overtightened as Greg mentioned.

Dowty washers arrive Monday.

https://www.amazon.com/dp/B0BJ8XNZC5?ref_=ppx_hzod_title_dt_b_fed_asin_title_0_0

Locktite and Permatex is always good to have on hand.

CanukNortonNut · Nov 15, 2025

I had problems with a SRM oil pressure release valve. The early ones came with red fibre type washers and these leaked. They later changed back to copper. A smear of Wellseal on both sides of the gasket or Hylomar would work.

PRV leak

Similar threads