Cast Iron to PVC Fernco Donut Woes

[Scott123]

Based on my pipe dimensions and a call to Fernco, I've got the right donut size. Without the PVC, the donut slides into the CI pretty comfortably, and, outside the CI, the PVC slides in as well. But, inside the CI, no amount of manhandling is getting this PVC pipe into this coupling.

I've tried:

1. Liquid soap as a lubricant.
2. Inserting the donut halfway into the CI and then hammering the PVC using a wood board
3. Tapering the edge of the PVC

The PVC is so sharp now that it's cutting into the ribs inside the donut.

I'm considering

1. Reaming the CI opening with either a drum sanding bit or maybe a grind off wheel
2. Heating the CI
3. Heating the donut in the hopes that it might get a bit more malleable/compressible
4. Sanding the (neoprene?) donut with very fine grit paper
5. All of the above

My CI opening is maybe 1/32" less than 3". I'm not finding any drum sanding 2.5" bits that I can get my hands on today locally. Heating and sanding the donut also makes me a little nervous, since replacing it is a two hour drive.

This thing is really kicking my behind. Any advice is welcome.

 

[Fitter30]

Pipes just butt together not insert into on another.

 

[Sponsor]

 

[Scott123]

Pipes just butt together not insert into on another.

This is the type of coupling I'm using:

https://terrylove.com/forums/index....nto-old-cast-iron-hub-help.91843/#post-662638

When the donut is inside the cast iron, there's presently no way I can slide the PVC into the donut.

 

[Terry]

If I can, I pick up several different donuts to see which one works best with what I'm working with.
I have better luck with donuts that don't alter the size. If I have a 4" hub, I pick up a 4" donut and use a 4x3 flush bush if I'm need 3" pipe in there.

I do bevel the end of the PVC pipe to help with guiding it in. And yes on the 2x4 that you can hammer on.

 

[Reach4]

I have never done it. But I wonder if you put the PVC 1/3 of the way into the donut, put the donut 1/3 of the way into the hub, and start pounding each.

 

[Tuttles Revenge]

I've shaved off some of the rubber to get a fit before.. I'd do that a million times before I tried shaving the inside of a CI hub..

And sometimes you have to start the pipe in the donut and the donut in the CI hub.. then place a 2x4 over (Helper holds the 2x4) and slam the S**t out of it with a sledge hammer

 

[Scott123]

Thanks, everyone

I got it in. Pretty much There's about a 1/4" gap between the PVC and the cast iron pipe. It's messing with my OCD, but, I've hammered it enough and, as far as I can recall, the old steel pipe that was in there with lead had a gap as well.

I ground down the CI opening with this

https://www.harborfreight.com/3-inch-polycarbide-abrasive-wheel-brush-94014.html

for about 20 minutes, focusing on the first inch. It didn't do much, but it was all I had, and I couldn't find the right drum sander bit locally- nor could I make one.

I also sanded both the inside and the outside of the donut, paying special attention to the seams that formed where the two pieces were joined together. If I were to do this again, I'd probably be a bit more conscientious about the grits. I started with a sanding sponge, which was a bit too coarse, and then finished with 600, which helped a bit, but didn't really remove the scratches from the sponge.

I talked to Fernco and they confirmed that heat can help- up to the intermittent temp of 140. So I soaked the donut in 140 water for about 10 minutes and I heated the cast iron hub to about 140 as well, before the attempt.

I think, in theory, these donuts are great, in practice... I'm not so sure. Even with the perfect size donut, very old cast iron hubs may not be made to the kind of specs that donuts require.

Fernco told me that the next size down would be too loose, but, if I were to do this again, I'd probably go with that one, combined with some of this:

https://www.lowes.com/pd/Oatey-10-3-oz-Plastic-Seal-Soil-Pipe-Thread-Sealant/5001781787

That is, if I can find a tube that can still flow. The tube I bought for this job from Ace Hardware was way too old and the sealant was hard as a rock.

Thanks, everyone, again.

Edit: One more thing I'd do differently the next time - If the fit was a little tight, I wouldn't go with a heavier hammer or more elbow grease. It required some pretty forceful hits, but, if you really wail on it, you just end up cutting into the donut and potentially trashing it. I'm about 90% certain my seal is still okay, but only time will tell.