View Full Version : Mycom Screw Seal Cap

11-09-2013, 12:22 AM
Hi Guys

I've been overhauling Mycom Screws for some time but the one thing that I still find difficult at times , is sliding the unloader piston back in the cylinder bore, after installing a new o ring and cap seal, without destroying the new cap seal . Before anyone asks..... yes, I am pushing it into the bore from the side with the eased edge. Anyone got a sure fire trick for doing this every time? One thing I have had some success with is, Put it in a ring compressor over night and try it the next day, but that isn't always possible to do.

C Ice

11-09-2013, 05:04 AM
Hi C Ice
We had a similar problem, our solution was to make a sleeve with a slim internal taper, this fitted into the eased edge and is the same size as the bore.This allows the piston to be pushed into the bore without any lip for the cap seal to catch on.
This sleeve bolts onto the housing.
See the attached photos.


11-09-2013, 08:14 AM
Now, that's what an Engineer would do!
Impressive Paul!
Having access to a machine shop must of helped though?
Self centre-ing as well with the chamfer.

11-09-2013, 08:38 AM
It takes a lot of pure skill to install them, so I have no trouble!

My experience says

- a fine cylinder bore finish 1200 wet & dry is helpful.
- fit "0" ring then cap seal without damaging lip on each side.
- lip must always stay inside "0" ring groove.l
- install piston in cylinder with a coating of oil in cylinder & some on cap seal,but start one side first so basically unload piston is being inserted on a very slight angle.

Slowly & carefully tap piston in on the very slight angle working around so cap seal entering bore bit by bit.
If cap seal lip appears to come out of groove use flat blade screw driver to gently ease it back in groove. You will have very limited success if you try to put piston in without inserting on angle.

This cannot be rushed & if unsure pull it out & try again.

As seals are very expensive $100-300 AUD you want to get it right first time.
With this method I would guarantee I could do it 100% of the time without damage.

Otherwise make a tool like Paul

11-09-2013, 11:19 AM
Hi Ranger
We used to do the same as you but it is very time consuming and as you say they are expensive so we decided to come up with a foolproof way of fitting them that could be done by anyone. Since using this sleeve we have never damaged a cap seal.
We have made them for 160, 200, 250 and 320 Mycoms. We got the idea from the piston installation sleeves used on Hasegawa compressors.
Grizzly, thanks for the rep points only too happy to help.

11-09-2013, 11:48 AM
Thanks guys, that was all great information!

C Ice