The International Cessna^® 170 Association

cfiatzph wrote:What are the correct o rings? and how many do I need to rebuild the primer. I don't think my parts manual shows this.

Oh yes it does. I seem to remember you have a 170A. The primer is item 34-37 on page 61. The o-ring packing for the primer is listed right under it as an AN6227-7

If you have a B model it's on page 69 item 37-11 with the o-ring listed under it as the same as the A model a AN6227-7.

Sorry I don't have a '48 170 parts manual YET.

BTW a AN6227-7 crosses to a MS28775-012.

My parts manual did not show the breakdown of the primer assembly either...just the assembly as a whole, unless I overlooked something. On the search for O rings for my primer, I took the proper route and went to my A&P. So you know what he did? He pulls out this blue plastic box holding an assortment of O rings identical to the box of O rings the lady at NAPA had Composition material is nitrile, which my information says is good for immersion in all fossil fuels. Went down a size from the size I got at NAPA, and my problem is solved

I ran across the following while browsing Cessna Single-engine service letters and thought it might be a helpful reference to anyone in need of a fuel primer rebuild. Service letter 78-73 says that using NAS1593-012 o-rings "provides smoother primer operation, improved sealing, and longer service life" than the original AN6227-7 o-ring. They recommend replacing them at the next 100 hr. inspection. According to Geniune Aircraft Hardware Co. NAS1593 o-rings are made of Viton. Aircraft Spruce doesn't show the NAS o-ring but does sell MS29513-012 o-rings that "are resistant to fuel and are ideal for applications such as fuel ... primers." I then stumbled on McFarlane's website which seems to have the latest and greatest o-rings ever (for 13 times the price of an MS29513-012): "The MCM83248 series o-rings are 'fuel proof' FAA-PMA replacement o-rings. Only McFarlane has FAA approval to replace the old, less fuel resistant nitrile (MS series) and synthetic rubber (NAS series) o-rings with the latest fuel proof fluorocarbon o-rings! Flurocarbon rubber is commonly known as Viton. It is an advanced rubber that has extremely good fuel and heat resistance and is ideally suited for aircraft fuel system applications." So for the primer the o-ring you need is MCM83248/1-012. Here's a link if you need to order: http://www.mcfarlane-aviation.com/Produ ... 48%2F1-012&

John,

Go to your A&P and get the correct orings.

At this year's annaul A&P finds the prime leaking. I have a 170A and the primer does not have o-rings but a leather packing of some sort. Anyone know what I am talking about. A&P thinks he has it repaired with fuel lube or whatever. Do it need to look for a newer type primer?

Curtis, there are several mfr's primers out there in the field, and it's possible that your primer is different than others. What mfr do you have? Kohler? Does it have a part number/model on it?

As a follow-on to this question: The original rubber O-rings are guilty of failing eventually (although what isn't?)... and a newer product called "Viton" is a flourocarbon O-ring which has better survivability in fuel.

See: http://www.mcfarlane-aviation.com/Produ ... 48%2F1-012&

I replaced the "O" rings in my primer about twenty years ago and they still seem to be working fine. As I remember I got them at the corner hardware store in the plumbing repair parts department for about a dime each.
I haven't lost a helluva lot of sleep for lack of traceability on their ancestry.

Cessna has part numbers for the primer lines (0500106-79,80) but they appear to be just 1/8" copper tubing, is this correct??

That is what I remember from looking at them just the other day Karl. At least if I was going to go replace them I'd be taking my supply of 1/8" copper tube to the airplane expecting to make my own.

The primer lines are just simply 1/8th inch copper tubing.

Suggestion.

If you're in the process of making new primer lines, now is the ideal time to acquire another primer orifice plug. a 1/8th inch tubing tee and the necessary parts to prime the bottom of both intake manifolds. Makes for much smoother starting on cold starts.
Of course, the very best system is to get a six cylinder flow splitter and prime to the intake ports on all cylinders. That really works good on a cold engine.

If you have and installed manifold pressure gauge in the right side (like some factory original options)... you will have lost the ability to plumb the primer over there. Check your cylinders to see if you have a 1/8" pipe-plug on top of the rocker-box area, adjacent to the intake valves. Not 170-original, but that's where the GO-300s were primed, and you might have those cylinders. If so, you might be able to prime each cyl.

Thanks All for the information. I noticed last month that where the primer line goes thru the firewall I had a fuel leak. I snugged up the fittings but checking it again the other day it still seems to be leaking. I am assuming that the copper has work hardened and is cracked. I checked the part numbers Hill Aircraft and they don' t have it.

1/8" copper line must be "double-flared" in order to properly seal.

gahorn wrote:1/8" copper line must be "double-flared" in order to properly seal.

George, are you sure about this? I have never seen a flaring tool that will double flare 1/8" tubing for AN fittings.