Parts Source: KNOTS2U
 

They've been around awhile, but no posts on this forum with links:

https://www.knots2u.net/categories/c...37-models.html

Interior and exterior plastics, mods, electronics, engine compartment, lighting, etc.

On Knots2U's website under Cessna/337/interior they list a primer overhaul kit selling 50 cent o-rings for some 3 bucks apiece but the applicability description states in bold type "for non-fuel injected engines". I'd be willing to pay the premium for the correct parts but I called and asked about the discrepancy and could not receive confirmation that these are in fact correct. I've never been able to ascertain the proper part number for fuel resistant o-rings for this application. If anyone has the correct part number I'd very much appreciate knowing it. The mentioned "kit" uses MS29513-012 o-rings but I don't believe they have the proper cross-section. The primer seals appear smaller than standard.

SteveG,

Two ways to go - get the kit from Aircraft Spruce P/N 05-03637, or buy the O-rings directly; MS29513-012. Make sure you use some fuel lube on these to keep them "fresh". For some reason (I have forgot), I used MS28775-012. Yes, I know these are for hydraulics, but its something I documented a while ago.

Regards,
Jeff

Jeff,

Thanks for the response. The Aircraft Spruce kit is exactly the same thing as the Knots2U kit but a buck less expensive. Any idea why both list C337 as applicable but both specify in bold type "for non-fuel injected engines"? I seem to recall trying a dash 12 o-ring once before but the cross-section was too large for the bore diameter. If you've used these successfully I try again. Although I've never used the primers for their intended cold start purpose I'd like to have them working if for no other reason than to seal the fuel line, otherwise you literally have raw fuel inside the cabin.

Regards, Steve G.

Primers
 

I am not sure why they reference that "non-fuel injected..." can't say I noticed. At any rate, I resealed my primers with the kit, and I had no problems. It is important to have the fuel seal lube, hence why the kit costs more. I have since bought a tube of that stuff after rebuilding the fuel valve on my Stinson, so from now on I will just by the o-rings. I replaced mine about two years ago, they fit well and have had no problems with leaks or otherwise.
Jeff

Steve and all,

More info on o-rings than you probably want. You hear terms like Viton, fluorocarbon and Buna-N...well, I am not here as an expert, but sharing my experience with o-rings over the years. If I am incorrect in any of these statements cause my memory is poor - just be kind in how you correct me.

MS29513 or rings are Buna-N, and designed for fuels (jet fuel, etc). These o-rings are great for cold temperatures (I mean really cold, not just "have to wear a jacket" cold). I believe they have shelf life, which tell you that they do not age as well.

MS28775 / M83248 and old NAS 1593 are made of Fluorocarbon. They are similar to Viton o-rings (Viton is trademark of Dupont), in that they have similar properties. Fluorocarbon o-rings tend to stand-up better to the constant immersion in the fuel for a primer. That is why I use the MS28775-012 in my primers (I knew I would remember why). I think McFarlane kits use the M83248/1-012 - which cross references to the NAS1593-012 (which Cessna calls for) and the MS28775-012. Fluorocarbon is not as good as Buna-N in extreme cold, but I can tell you from experience from working in the high Arctic maintaining aircraft, I did not see a problem between the two types....

So, in summary...there are a few options of o-rings, and as near as I can tell, most Cessna aircraft (150-210 and the 337) use the same primer.

Jeff

Jeff,

The only time one can have too much information is when it's misinformation. Thanks for your time and consideration in creating an extensive post adding to the collective wisdom of this website.