Correct material selection for o ring inside the end of the exhaust cam?

I need an o ring, part number 118018, but it is not in stock at ricambi, and seems like something I should be able to get through McMaster easy enough. My question is which material is most appropriate? I assume viton is a good choice, but there are a few different types of that. There is soft and hard, and square, and x shape. And then there are other polymers completely. It resides inside the cam shaft, so high heat and exposure to oil are the criteria. Any advice on the material would be appreciated, thanks!

 

Looks like viton (medium softness) is a reasonable choice, McMaster makes it pretty easy, I just have to order a pack of 50! At least it's only $6

 

Don't think so, part number was confirmed with Daniel at Ricambi, and I learned through McMaster that the last three numbers are the size of the o ring. It's called the "dash number". So maybe that's why there is another part with the same number?

 

50 should be enough .

 

The one that is on there currently is blue/green color, is there any significance to that? I know the color can sometimes identify the material, but blu/green was not an option from mcmaster

 

Thanks dflett! I will check them out

 

I was really just trying to learn a little bit about material compatability so that I can buy o rings (or seals etc) from a parts supplier that doesn't necessarily specialize in Ferrari. I have a nice caliper, and McMaster is sweet. A lot of the o rings, seals, tubing, bearings, and hardware (nuts bolts etc), are common to many other applications.

I know viton will work, but I am still curious if there is any advantage to a different material or shape? Kind of like Verrel's quad seals (which are just o rings in the "X" cross sectional shape. I am pretty sure I saw a post somewhere, where some one used that style o ring (the X) for the cam seals. The square shape also seamed like it could have advantages as well. Maybe some of you guys have tried this already?

 

I just measured the o ring with my caliper and what I thought was the dash number is not correct. It was close, and I did not have the o ring or caliper at work, so I thought maybe that's how they came up with the part number, but no.

 

For the other 3 guys with USA spec 83' qv's (with smog equipment in tact...)

The size for that o ring part number 118018 is 3/8" id x 1/2" od with a thickness of 1/16" dash number 012. The viton fluoroelastomer rubber version is part number 9464k17 for a pack of 100 through McMaster $6.82

 

It is a European car, so most likely it is metric sizing, but...

I got the size by measuring the o ring I took off (in mm), and then converted to inches and chose the one that was closest. I am assuming that the one I took off was the correct part, but who knows.

Bell metric probably has one specifically in metric size. I will check for fun.

 

Belmetric does not have them

 

You are tough one to please Brian. When I was asking for help, you said nothing. When I found a reasonable alternative, you are chastising me. I measured both the shear shaft and o ring, and the o ring is not hard at all. It is not failed either, I am changing it because I have it all apart already. I figured in the fact that is most likely a little smaller from being compressed. I am going to order "the correct" part and post pics and dimensions of both. My thought is that many vendors are sourcing a suitable replacement, especially on an old car. I may be wrong. But the reason I post any question on here is to learn, and your insults are not appreciated. If you have information you would like to share, then by all means share. I am incredibly careful, ask when I have questions, and consult professional mechanics when needed. I wasn't aware that this o ring was such a critical component of this car.

 

Classy. You were not helping me at all, you were trolling, then telling me I am stupid after I figured out an alternative plan. Let's keep in mind we are talking about a non critical o ring that is specific to one model year. Sometimes it's more convenient to be able to source parts from somewhere else. I get it, it's easy to source one from a Ferrari parts supplier, but some time in the future it may not be. It's nice to have alternatives. I hope you get a lot of satisfaction out of being such a jerk .

A couple other folks chimed in above with the same thought, but without the attitude. It's a shame, as you are obviously very knowledgeable, I think you have been on here too long and have lost your patience.