R&R WTC motor shaft Seal... Help needed

[Wax Savage]

Hi guys. I’m prepping a 70mm R&R WTC equipped with dual motors for Subfest 2026. I’m not coming up with a way to retain the 4mm driveshaft’s screw-on endcaps used as a water-seal.

The endcaps hold a 4mm I.D. silicone O-ring inside (see photo). When I run the motors the driveshafts grip the O-ring/endcap assembly and spin the endcaps off or, on depending on whether the motors are running forward or reverse. Tightening the endcap is not an option. If I screw the endcaps on fully, the O-rings get squashed and bind up the driveshaft/motor. Also, the endcap gets hot quickly.

Anyone familiar with R&R WTC’s come up with a fix for this problem?

Thanks!!
Wax Savage

[redboat219]

threadlock?
Bore out the endcap hole slightly larger than 4mm

[Subculture]

Are you running the shafts in the dry? They're designed to run solely in the wet which cools the assembly and the water lubricates the seal.

[Wax Savage]

threadlock?
Bore out the endcap hole slightly larger than 4mm

Thanks for the reply. Threadlock may be good. Do you know if thread-lock is waterproof? Bob suggested using super-glue on the threads to lock the endcap. Why do you recommend the over-bore on the endcap? What is your experience?
Thanks!
Wax

[Wax Savage]

Are you running the shafts in the dry? They're designed to run solely in the wet which cools the assembly and the water lubricates the seal.

I am testing the WTC/driveshafts on my workbench at the moment. The endcaps spin on tight or spin completely loose when I run the motors. I did not intend to attempt imersion of the WTC in water until I had the driveshaft water seals (endcaps) secured.
Wax

[redboat219]

Shaft might be catching on endcap causing it to turn.

[Fishb0y]

I’m curious why you’re not following Bob’s advice?

[Subculture]

Not generally advisable to use silicone grease or oil on silicone rubber. You should use a ptfe grease

[Wax Savage]

I’m curious why you’re not following Bob’s advice?

I am intending to use Bob's recommendation. This thread is to research any possible cures others have discovered/developed before I commit to putting CA glue on machine threads.

[RCSubGuy]

I just ordered some 4mm cup seals off of Amazon (thanks to Nicholas' DiveTribe link). I'll whip up some housings for them. In theory, I could make them a simple install over the existing R&R output seal housings. Should have something ready for testing by the end of the week. I'll show them in this week's video.

[Subculture]

] BTW.., reference your suggestion, did you mean PENN REEL GREASE?

Sorry autocorrect messed up my post, it should have read PTFE grease.

You can contact Permatex and ask them if your lubricant is suitable for silicone o-rings.

I've never had an issue with o-ring glands, they work well enough especially if not going for very high speed drive. They're more common in the UK becaus o-rings were simply a lot easier to source and even those could be hard to find in certain sizes- it was really difficult finding stuff for this hobby before the internet opened up supply chains. The builders of much legacy hardware stick with what is tried and tested.

Ron Perrott used to supply the glands with a locking ring, but he seems to have discontinued them on his later products, perhaps he felt them unnecessary as even a locking collar can loosen without some kind of thread locking compound. You can also use blue Loctite anaerobic thread locker like 242 or 243, which should prevent the threads from unwinding but still allow the seal to be cracked open if required for maintenance.

[Wax Savage]

I just ordered some 4mm cup seals off of Amazon (thanks to Nicholas' DiveTribe link). I'll whip up some housings for them. In theory, I could make them a simple install over the existing R&R output seal housings. Should have something ready for testing by the end of the week. I'll show them in this week's video.

Thanks for stepping up, Bob. I will hold off on gluing the R&R endcaps on until I hear more about your proposed 'aftermarket' endcaps research.

[trout]

Help me understand we’re in my memory banks I have a wire crossed. I thought the rule was:
silicon o-rings and silicon oil = bad
petroleum o-rings and petroleum oil = bad
silicon o-rings and petroleum oil = good
petroleum o-rings and silicon oil = good
Did I mis-remember these rules? Is the world topsy-turvy?

[redboat219]

According to Google Gemini

The fundamental rule of chemical compatibility for polymers and lubricants is "like dissolves like." When an O-ring material chemically resembles the lubricant applied to it, the elastomer absorbs the fluid, causing it to swell, soften, lose its structural integrity, and ultimately fail.

Here is the breakdown of your four statements:

1. Silicone O-rings + Silicone Oil = BAD (True)

• What happens: The silicone O-ring will absorb the silicone oil.
• The result: Extreme swelling, softening, and tearing under pressure.
• Exception: Fluorosilicone (FVMQ) is an engineered alternative that resists this cross-contamination better than standard silicone.

2. Petroleum O-rings + Petroleum Oil = BAD (False)

• Correction: This is actually a GOOD combination.
• Why: The most common "petroleum-resistant" O-rings are made of Nitrile (NBR/Buna-N), Viton (FKM), or Neoprene. These materials are explicitly designed to withstand mineral oils, grease, and fuels without degrading.
• Note: If you meant natural rubber (which is rare in industrial sealing), petroleum would indeed rot it. However, standard oil-resistant O-rings love petroleum.

3. Silicone O-rings + Petroleum Oil = GOOD (False)

• Correction: This is a BAD combination.
• What happens: Standard silicone rubber has incredibly poor resistance to petroleum products, mineral oils, and fuels.
• The result: The petroleum causes the silicone matrix to degrade, swell heavily, and fail quickly.

4. Petroleum O-rings + Silicone Oil = GOOD (True)

• Why: Nitrile (NBR), Neoprene, and EPDM O-rings do not share chemical structures with silicone.
• The result: Silicone oil or grease acts as an excellent, completely inert lubricant that helps install these O-rings without causing any swelling or degradation.

[Subculture]

Seems to be conflicting information out there e.g.

https://www.polymax.co.uk/o-rings/silicone-rubber-o-ring-grease/?srsltid=AfmBOorTfx8CoeLYzbjr6sEij6CU0f8jV6-snOfxFvrcWAhilk38MhDC