# Near loss of rear main seal **URL:** \ **Category:** Aerovee\ **Created:** [October 10, 2026, 4:10pm UTC](https://sonexpilots.org/t/near-loss-of-rear-main-seal/6111 "2026-10-10T16:10:02Z")\ **Posts on this page:** 10\ **Page:** 1
**Author:** ![Bryan\_Cotton](https://sonexpilots.org/user_avatar/sonexpilots.org/bryan_cotton/32/760_2.png) [@Bryan\_Cotton](https://sonexpilots.org/u/Bryan_Cotton)\ **Post date:** [October 10, 2026, 4:10pm UTC](https://sonexpilots.org/t/near-loss-of-rear-main-seal/6111/1 "2026-10-10T16:10:02Z")
So I’ve recently had an opportunity to pull my AeroVee off again. Discovered this: ![Screenshot_20261010-104544](https://sonexpilots.org/uploads/default/original/2X/5/5316f2fb0b33f4c2a068dacae44219b42e5cfae9.jpeg) I remember that seal wanted to come out when I installed it. I pushed it back in with my seal installation tool until the RTV was set - so I thought. It must have tried to escape after I bolted on the flywheel. You can see the rub marks. ![Screenshot_20261010-104524](https://sonexpilots.org/uploads/default/original/2X/c/c149b2bd3cbb8e79036502745199be3e0a7dc91c.jpeg) So going forward, I’ll RTV the seal in, hold it with the installation tool, and let it cure for 24 hours. I’ve always just chucked the flywheel on right away. Tool is in this old thread: > [@Rear main seal installation tool](https://sonexpilots.org/t/rear-main-seal-installation-tool/928): > > Rear main seal installation tool Posted: Sun Aug 11, 2024 9:07 pm by Bryan Cotton I have a regular VW tool but it interferes with the dowel pins. So I used the gland nut to center the tool on the flywheel, and transferred one hole to the tool. Drilled that hole, then pinned it to the flywheel and transferred all the other holes. The dowels are 5/16", but I went up a couple of sizes for the final holes. [[Screenshot\_20240811-142733.png]](https://web.archive.org/web/20240821023207/https://sonexbuilders.net/download/file.php?id=5643&mode=view)Re: Rear main seal installation tool Posted: Sun Aug 11,… Interestingly I can’t pull the seal off by hand. So it is glued in, but in a non-optimal position. ---
**Author:** ![SirPD](https://sonexpilots.org/user_avatar/sonexpilots.org/sirpd/32/941_2.png) [@SirPD](https://sonexpilots.org/u/SirPD)\ **Post date:** [October 10, 2026, 4:49pm UTC](https://sonexpilots.org/t/near-loss-of-rear-main-seal/6111/2 "2026-10-10T16:49:11Z")
Hi Bryan, just wondering about the seal, in my much younger auto racing days, we ocassionally had seals blow out because of, and you know this i am sure, high internal crankcase pressures. In my cases it was instigated by larger piston to bore clearences for reduced friction on piston. my question, could there be case venting problem at high rpm! Or maybe just not enough cure time on rtv? Let us know what you find out!! ---
**Author:** ![Bryan\_Cotton](https://sonexpilots.org/user_avatar/sonexpilots.org/bryan_cotton/32/760_2.png) [@Bryan\_Cotton](https://sonexpilots.org/u/Bryan_Cotton)\ **Post date:** [October 10, 2026, 5:02pm UTC](https://sonexpilots.org/t/near-loss-of-rear-main-seal/6111/3 "2026-10-10T17:02:46Z")
Joe, I think it was cure time. Although the motor sees its share of high RPM, I’m pretty sure the seal slid out after installation and stopped when it hit the flywheel, then cured. ---
**Author:** ![Ausparry](https://sonexpilots.org/letter_avatar_proxy/v4/letter/a/e47774/32.png) [@Ausparry](https://sonexpilots.org/u/Ausparry)\ **Post date:** [October 10, 2026, 9:24pm UTC](https://sonexpilots.org/t/near-loss-of-rear-main-seal/6111/4 "2026-10-10T21:24:07Z")
You could use the green loctite (648 I think) bearing retainer and it should seal well and not come out depending on what temperature you see there. Rotax use it in a lot of places on there engines but they are partly liquid cooled. I think it needs around 180C to remove again but it’s been a while since I looked that up. There could also be other bearing retainers out there that can handle higher temps. ---
**Author:** ![The\_Flying\_Squirrel](https://sonexpilots.org/letter_avatar_proxy/v4/letter/t/848f3c/32.png) [@The\_Flying\_Squirrel](https://sonexpilots.org/u/The_Flying_Squirrel)\ **Post date:** [October 12, 2026, 12:29am UTC](https://sonexpilots.org/t/near-loss-of-rear-main-seal/6111/5 "2026-10-12T00:29:08Z")
With 10 hours on my fully rebuilt Aerovee 2.1, I nave noticed oil leaking around the flywheel area. It has only been leaking the last few hours, and I know I have seen the oil pressure over 100 with running it in the colder Montana weather. I recently removed both pressure relief plungers and polished them to make sure they moved easily in their bores. I suppose I should baffle off part of the oil cooler and warm it longer prior to my run up. Anyway today I looked closely and the rear main seal is pushed rearward on one side, cocking it in the bore. Likely the result of too much pressure. Looks like I too will get a chance to remove an engine. And be more careful to keep the pressure below 100psi. ---
**Author:** ![Bryan\_Cotton](https://sonexpilots.org/user_avatar/sonexpilots.org/bryan_cotton/32/760_2.png) [@Bryan\_Cotton](https://sonexpilots.org/u/Bryan_Cotton)\ **Post date:** [October 12, 2026, 1:37am UTC](https://sonexpilots.org/t/near-loss-of-rear-main-seal/6111/6 "2026-10-12T01:37:55Z")
I’m not sure oil pressure would push out the seal, but crankcase pressure definitely will. How is your breather? Edit: check out my tool for torquing and loosening the gland nut. Scroll down to the 8/11/24 post. > [@Torquing the gland nut](https://sonexpilots.org/t/torquing-the-gland-nut/929): > > Torquing the gland nut Posted: Sat Feb 03, 2024 2:43 pm by Bryan Cotton I wish I had thought of this before. This poorly made 2x4 tool bolts across the top mounting holes. Lets the person react the torque of the breaker bar or torque wrench nearly in plane. The person holding the half prop also grabs one side of it. gland nut torque setup.png (585 KiB) Viewed 2347 times Re: Torquing the gland nut Posted: Tue Feb 06, 2024 11:42 am by Bryan Cotton Will one of these tools work on an Aerove… . ---
**Author:** ![The\_Flying\_Squirrel](https://sonexpilots.org/letter_avatar_proxy/v4/letter/t/848f3c/32.png) [@The\_Flying\_Squirrel](https://sonexpilots.org/u/The_Flying_Squirrel)\ **Post date:** [October 12, 2026, 2:35am UTC](https://sonexpilots.org/t/near-loss-of-rear-main-seal/6111/7 "2026-10-12T02:35:29Z")
The breather and oil separator were thoroughly cleaned during the rebuild. No oil is coming from the small escape hole on the top of the aluminum pipe, nor is any coming from the drain tube of the oil separator. I’ll have to investigate further. Thanks. ---
**Author:** ![Bryan\_Cotton](https://sonexpilots.org/user_avatar/sonexpilots.org/bryan_cotton/32/760_2.png) [@Bryan\_Cotton](https://sonexpilots.org/u/Bryan_Cotton)\ **Post date:** [October 12, 2026, 5:04pm UTC](https://sonexpilots.org/t/near-loss-of-rear-main-seal/6111/8 "2026-10-12T17:04:36Z")
I think on the next seal that I’ll only put RTV on half of the seal - like the half sticking out in the picture. The wet RTV acts as a lubricant that makes it easier to go in and out. If the inside half is dry, that may help retention plus have the side benefit of less opportunity to clog up the drain back to the case. ---
**Author:** ![ysifly2](https://sonexpilots.org/letter_avatar_proxy/v4/letter/y/e0b2c6/32.png) [@ysifly2](https://sonexpilots.org/u/ysifly2)\ **Post date:** [October 12, 2026, 5:24pm UTC](https://sonexpilots.org/t/near-loss-of-rear-main-seal/6111/9 "2026-10-12T17:24:37Z")
just as a reference point: Lycoming service instruction calls for Dow Corning 737 Neutral Cure Sealant and if that is not available, Pliobond #20 may be used. ---
**Author:** ![Bryan\_Cotton](https://sonexpilots.org/user_avatar/sonexpilots.org/bryan_cotton/32/760_2.png) [@Bryan\_Cotton](https://sonexpilots.org/u/Bryan_Cotton)\ **Post date:** [October 19, 2026, 6:26pm UTC](https://sonexpilots.org/t/near-loss-of-rear-main-seal/6111/10 "2026-10-19T18:26:51Z")
Here’s my RTV application. I was shooting for the outside half of the seal. ![Screenshot_20261019-130950](https://sonexpilots.org/uploads/default/original/2X/b/b75939f15dd69ba3a64ca9e9aacfcf80ff8bb5fb.jpeg) After driving the seal in, I took the installation tool off and cleaned up the squeeze out. Then put the seal back on. The 24 hour clock is running. ![Screenshot_20261019-130934](https://sonexpilots.org/uploads/default/original/2X/8/895eb7221be0e4e95db39cd9abec88229d7d5160.jpeg) The back of the seal has no RTV and should have more traction.