Riviera Two Group piston seal problem - Page 4

August 11th, 2021, 12:52 pm

Thanks, I've contacted the seller to confirm dimensions. I'm waiting for the owner to return from a trip before moving forward. It looks like the donor assembly will work.

August 12th, 2021, 3:24 am

Good to hear!
as a backup solution, a HB'er is selling a Riviera in parts
[FS] Parting out Zacconi Riviera Eagle
You might be able to get a piston or the entire gouphead there.
cheers,
Rob

August 12th, 2021, 1:31 pm

Thanks, the ebay seller confirmed that his piston it too large for this group. He's got lots of Riviera stuff, so will keep him in mind.

I have contacted the fellow parting out the riviera and hopefully he has what I need. I still need to find out how much the owner wants to invest in the machine, the meter is running...

#34: Post by **RobAnybody** » August 12th, 2021, 2:35 pm

I was looking at the photos of the piston rod again, would it be possible to re-work the rod to get a better fit?
As you mentioned

cuppajoe wrote:The thread tolerances are a bit sloppy and when you tighten it onto the piston it throws the rod out of alignment. My guess is it's due to the butchery, which removed the flat at the top of the threads.

I guess it is the last 1-2 mm of thread that is pushing the piston out of alignment since the thread in the piston most likely doesn't run all the way to the bottom of the hole.
If you could make a bevel at the end on the rod (with a bastard file or a grind stone) and clear up the thread with a thread file you should be able to make it work again.
cheers,
Rob

August 12th, 2021, 2:58 pm

The problem was created by someone doing exactly that. My guess is they were replacing the original piston with a newer or older version that was taller.

What is causing the piston to misalign is the poor job of grinding on the rod, which should have been done on a lathe.

#36: Post by **RobAnybody** » August 12th, 2021, 3:46 pm

ah, so the piston is pushed off axis by the neck of the thread on the rod (circled in red) and not by the bottom of the thread (circled in green)?

#37: Post by **drgary** » August 12th, 2021, 6:21 pm

This seems obvious, which probably means it's already been considered and rejected. I would entirely remove the corrupted threads that are higher up on the piston rod and then secure the piston on the rod with a medium strength, food-safe threadlocker. The threadlocker won't be cheap but not a dealbreaker either. The piston will be correctly aligned by the threads on the bottom of the piston rod. Before attempting this I would thread the piston onto the rod short of engaging the corrupted threads and see if it aligns properly.

August 12th, 2021, 9:24 pm

Rob - That's it exactly. I'm waiting to hear if the owner had ever used this machine as is as I can see no way how it could have functioned, and it was a death trap.

Dr Gary - That is a consideration, but after 35 years as a camera tech I have an aversion to kludging. If it was my personal machine I might be tempted. The proper repair is to replace the piston/rod assembly. At this point I have no idea what the condition is of the other group.

Here's what greeted me after removing the bottom cover. The white lead from the power cord was pinched between the element base and the tube fitting. The wire wasn't for high heat and the insulation had melted, exposing the conductor and creating a dead short to the base. The tubing was also bent out of shape, a real hack job.