Author Topic: Gaskets for OS LA's? (Read 2484 times)

Jim Howell · « **on:** March 02, 2011, 07:08:57 PM »

I have a couple of OS 25 LA-S and a couple of OS 46 LA-S NIB engines. I have some metal replacement backplates for these engines as well as some PA NVA's.

When I removed the backplates, I have discovered that the plastic (?) backplates with the remote NVA have no gasket. (I guess this makes sense that the plastic will deform sufficiently under compression load to provide adequate sealing.) I had thought that I could find gasket sets for the OS 25 FP and OS 40 FP and use them. No luck so far.

I recognize that I can use a thin layer of silicone RTV, but I'm cautious about that - I've been known to be overly fat-fingered at times - and would prefer to use that as my fall-back solution.

So,..., what are you folks using for replacement gaskets?

Jim Howell
Huntsville, AL

Bill Hummel · « **Reply #1 on:** March 02, 2011, 07:13:04 PM »

RSM Distribution sells laser-cut gaskets for a variety of engines, including those you mentioned. Very fair prices, great service!

Jim Howell · « **Reply #2 on:** March 02, 2011, 07:31:14 PM »

Quote from: Bill Hummel on March 02, 2011, 07:13:04 PM

RSM Distribution sells laser-cut gaskets for a variety of engines, including those you mentioned. Very fair prices, great service!

Bill,
Thanks for the vector. Yes, I've ordered stuff from Eric/RSM in the past, but only kits. And you are correct, always great service! Just checked the e-store web site and found the items I need! Thanks so much! Just goes to show that I need to poke around and check on what else might be available from my "known suppliers".

Jim Howell

kenneth cook · « **Reply #3 on:** March 02, 2011, 10:46:38 PM »

Jim, I posted this once before. I had put a FP backplate on my LA.25 due to all the concerns for the plastic backplate problems. To date, I myself never had a problem with the plastic as to breaking, distorting, bad starts, etc. I know the possibilities exist and I've heard from many, but this is based on my experience. Nonetheless, I switched the part out only to discover some problems and this is with the LA.25 only. The engine initially worked fine but due to some vibration problems the runs I was getting were inconsistent and that was resolved later. I put the plane aside for a few months and when I returned to it I went to turn the prop over only to discover it was hard to turn. I thought this was odd and almost felt like the cylinder had something in it. I dismantled and cleaned it only to find nothing so I reoiled and off to the field. I ran it and everything was going well then it sounded like the engine was sagging which was odd due to a fairly rich run. I switched props tried again and same results. When the plane landed I picked it up to find this engine binding again. I took the engine apart at the field wondering if the backplate was too far into the case. I found just the opposite in which it was not and it was allowing the rod to work off of the crankpin enough to cause a bad bind. I went home and compared the heights of each backplate discovering the plastic indeed does protrude more into the case by a few thousandths. I ended up sanding the case on a piece of glass with sandpaper so there's no going back to the plastic for me at this point. I'm currently using a metal one on my .15 with no problems but the others seem to be working just fine with plastic. This may just be a isolated incident but I thought I would make mention of it. I prefer metal myself its just something to look into. Ken

Andrew Tinsley · « **Reply #4 on:** March 03, 2011, 06:19:40 AM »

Hi Jim,
On the first couple of LA 46s I replaced the plastic backplate with FP ones, Before they got difficult to find! I cut my own gaskets, but I will use The RSM ones in future, not worth cutting them at Eric's prices.
My later LA 46s are still being run with the plastic backplates and RTV silicone, plus some loctite on the screws. They have been used an awful lot, both by myself and people that I have lent them to (yes, I must be an idiot to do that!). I have never had a problem. I have a nagging suspicion that people either tighten them too little and they come loose because of vibration, or they really do overtighten them and deform the plastic causing leaks.
RTV and loctite plus the correct torque on the screws seems to be a bullet proof solution, or is it?

Regards,

Andrew.

Jim Howell · « **Reply #5 on:** March 04, 2011, 06:44:19 AM »

Quote from: kenneth cook on March 02, 2011, 10:46:38 PM

Jim, I posted this once before. I had put a FP backplate on my LA.25 due to all the concerns for the plastic backplate problems. ....

Kenneth,

Thanks to you and Andrew for the additional insights. My motivation for replacing the backplates is a combination of 1) looks of metal vs. plastic, 2) rumor and innuendo about the plastic backplate, and, 3) wanting to eliminate the rear/remote NVA to gain usable space on short-nosed profiles. I know I could have taken a razor saw to the rear NVA, but that would have left the dark blue with a ragged edge. Thanks for the "warning" about checking the depth of the backplate. My new one is CNC milled, but it could still be off.

Thanks,
Jim

Bill Little · « **Reply #6 on:** March 05, 2011, 10:47:02 PM »

HI Jim,

I have always been a proponent of replacing the plastic back plate with a metal one. Why? Because I have seen two guys at the same contest have a problem with the plastic ones leaking. To me, once i get the plane in the air, I want as few problems as possible. Hence I use a metal back plate. So far, I have not heard of a single person having a leaking metal back plate on the LA engines. Plenty have had the problem with plastic ones for whatever reasons. Why risk it?

it's kinda like taking off in the car for a 1000 mile trip with a sheet metal screw in the tire. I've seen them run for a LONG time like that, but why risk having it go flat, just because it "can, possibly", hold air?

Big Bear

Geoff Goodworth · « **Reply #7 on:** March 05, 2011, 11:35:08 PM »

While the absence of gaskets with the nylon backplate is theoretically appropriate, both my recently purchased LA 46s had the paper back plate. Also, compared the nylon backplates to find that the depth from the face of the flange to the face of the piece inside the crankcase was the same as a metal FP 40 backplate, the flange is about .5mm (.020") thicker. Also the pan-head screws have shallower heads than the socket screws thet I replaced them with.

Cheers, Geoff

Brett Buck · « **Reply #8 on:** March 05, 2011, 11:41:36 PM »

Quote from: Jim Howell on March 02, 2011, 07:08:57 PM

I recognize that I can use a thin layer of silicone RTV, but I'm cautious about that - I've been known to be overly fat-fingered at times - and would prefer to use that as my fall-back solution.

I don't grasp the concern with the RTV, and I certainly wouldn't use a thin layer. I would clean everything with lacquer thinner, run about a 3/32 diameter bead around the flange, and stuff it in there. A bunch will squeeze out but that ensures you don't have any gaps. Put the screws in, wait a few days, and forget about it.

Brett

Andrew Tinsley · « **Reply #9 on:** March 06, 2011, 09:34:30 AM »

Hello Brett,
Should have been a little more specific. I certainly put a decent sized bead on the flange. However it finishes up as a thin layer once you tighten the screws!

Regards,

Andrew.

Brett Buck · « **Reply #10 on:** March 06, 2011, 05:14:09 PM »

Quote from: Andrew Tinsley on March 06, 2011, 09:34:30 AM

Hello Brett,
Should have been a little more specific. I certainly put a decent sized bead on the flange. However it finishes up as a thin layer once you tighten the screws!

Regards,

Andrew.