Shellacking A 51 Hood Required?

[benbot517]

Hello, this is a stupid question, but is shellacking a 51 hood in place a necessary step? Would sealing the threads with silicon grease work? Also, is there typically a gap between a 51 nib and its hood? I installed a new nib in mind, and want to make sure everything goes back together ok. Thanks!

[mitto]

Shellacking the vac 51 hood as well that of the non-recessed hood of an aero 51 is a must. Shellacing the hood of the aero 51 with an O ring is also recommended. The nib tip should not be sitting on the hood tip neither too tightly nor too loosely.

[Glenn-SC]

Shellacking the vac 51 hood as well that of the non-recessed hood of an aero 51 is a must.

 

 

Why?

[FarmBoy]

As found in Parker's Service Manual (1967 Revised)

 

"The next step in assembly is to apply a small amount of "51" cement or rubber solution in the barrel threads and assemble the clutch ring to the barrel. Using finger pressure only, screw the shell down snugly against the clutch ring. The rubber friction grip may be used in this operation. We do not recommend the use of section pliers for this purpose unless extreme caution is used."

 

So, apparently Parker found it necessary to use something to seal the hoods onto 51s.

[Glenn-SC]

"Because it says so in the book." has never been my favorite answer.

 

Why is shellack required?

 

I understand sealing the threads so that ink can not leak through via capillary action.
But why use a glue, especially one that requires heat to release?

[benbot517]

Thats whats Im wondering

[benbot517]

Because, while Im certainly ready to shellack it in place, Id like to know if theres a solution that would make the pen easier to work on in the future.

[pajaro]

There is a thread sealant marketed by Main Street Pens. There are other thread sealants marketed by Loctite. Most do require some heat to soften or loosen the sealant.

[FarmBoy]

Parker Service Manual doesnt indicate what 51 cement is, nor does it say what rubber solution is.

 

Shellac is listed as a solution as Shellac Cement in an earlier service Manual.

 

Frank Dubiel swore by rubber cement, a lot of the first generation collector-restorers used the same.

 

Shellac works as does rosin based sealant. I suppose Loktite would also work. But after 100s of 51s we know Shellac is reversible and when used the hoods stay in place.

 

Not even the Syndicate requires you to use shellac, they still have 51 cement.

Edited January 14, 2019 by FarmBoy

[benbot517]

I guess my real question is: is a shellack or other cement-material necessary, or would something like silicon grease work simply for the purpose of sealing the hood? While shellack can certainly be heated to release the hood, Im curious for cleaning sake if something like silicon grease would provide any negatives. Cleaning is certainly one of the not-so-great areas of a 51, and if the hood remained easily unscrewable this may be remidied. Ive heard warnings against over tightening the hoods of 51s for fear of cracking, and that shellack is used to mitigate that risk by firmly securing the hood, however if one was careful about their tightening would there be any other negatives to using silicon grease as opposed to shellack/cementing material?

[mitto]

You need a sealant to keep the threads from leaking and silicone grease is NOT a sealant.

 

Further, using silicone grease may result in increasing the risk of overtightening.

Edited January 14, 2019 by mitto

[Glenn-SC]

I disagree that silicone grease is not a sealant.

It is certainly a water (and ink) repellent, and would perform the function of preventing the ink from passing through the threads as well as a rosin or shellac will (i.e. as long as you had a complete/contiguous application around the threads).

 

The real assumption is that there was a "design compromise" made on the design of the hood.

That is, if the hood was torqued tight enough to hold in place (i.e. not come loose) and to prevent the ink from leaking the hood would/could crack.

If the torque of the hood threads were "loosened up" enough to prevent the hood from cracking then ink could seep through the threads.

 

The use of a combined glue/sealant solves the problem; the glue keeps the hood in place and from unscrewing and coming loose and the sealant prevents the ink from leaking through the looser threads.

 

.

Edited January 14, 2019 by Glenn-SC

[Uncial]

Silicone grease can degrade over time and become ineffective. How long that might be I'm unsure but I suspect it's effective life would be considerably less than shellac. Certain inks will strip the grease over multiple uses. I discovered this in relation to a piston filler greasing. Ultimately though, silicone grease doesn't 'stick' something in position, so while it may be an effective ink barrier for a time, it won't prevent a pen part from becoming loose.

[Glenn-SC]

Remember that the sealant in the threads is static (I.e. is not moving like in an application to a piston).

 

The ink would only contact a portion of the sealant as it works its way through the threads. It silicone was applied to the entire thread surface l imagine that it would take quite a while for the seal to be compromised.

 

I am surprised that silicone is degraded by ink.

[Uncial]

I wish I could recall what ink it was. I do know it wasn't any of the usual suspects, but it completely stripped the grease off a Pelikan tortoise piston to the point that the entire mechanism popped out of the back. I remember at the time it was mentioned by someone else here on FPN. If one ink can do it, it's not beyond the bounds of possibility that another ink will do the same.

[Glenn-SC]

Yeah, I would like to identify that ink as well.

Since many piston-filler FPs are in use and silicone grease is the recommended lubricant/sealant for them I would think that this (or any ink) decomposing the silicone would be a big issue.

 

So what did you use as a replacement for the silicone?

[Ron Z]

Frank Dubiel swore by rubber cement, a lot of the first generation collector-restorers used the same.

 

....and the current generation of pen mechanics swears AT rubber cement. We know better now, and have better materials available to us. For the curious, rubber cement really does not work. It isn't worth buying a bottle of the stuff to try it out. It also contains solvents to keep the cement liquid until exposed to air.

 

Todd is right, Parker did not define what their 51 cement was in any of their repair manuals. I have seen evidence while working on mint (as in the machining dust was still in the barrel) vacumatic 51s that Parker used a rosin thread sealant. Most of the pen mechanics use shellac because it sets harder than thread sealant, and it keeps the casual owner from loosening the hood and screwing up the alignment. But if the shell wasn't over tightened, it is still easy to get off with some heat. With shellac just snug, not tight, is sufficient to hold the hood on, while allowing it to come off relatively easily.

 

The problem with silicone grease beside the fact that it is not a sealant (sorry Glenn, I disagree), is that its lubricating properties make it rather easy to over tighten the hood, which can cause stress cracks from the edge of the hood down. Indeed, less tightening is needed when you use shellac or thread sealant.

 

Ink doesn't break down the silicone, rather it washes it off. That washing off is what causes piston seals to stick on the barrel wall. It is minimal and lasts a long time with the right product. The silicone oil like that which comes with TWSBI pens, is most likely dimethicone (think silicone personal lubricant) and prone to washing off. Indeed you want it to wash off, except inside your pen.

 

Different silicone greases have different properties. Molykote 111 is a food grade silicone grease that is thicker than others, and resists washing off. The application notes say that it is designed for use with 0-rings, and safe for use with most plastics. I assume that the "most" is a lawyer clause, allowing for wiggle room for some of the off the scale or less common materials. Reading the MSDS and application notes provided by the manufacturers, and posted on line, is always enlightening.

 

By the way, no "K" in shellac.

[mitto]

Thanks, Ron, for coming to my rescue.

[benbot517]

I thought it looked wrong... oops!

Thats good info. The last thing I want to do is over tighten here. Thanks everyone!

[pajaro]

This issue comes up from time to time. It is probably important that it be discussed for the benefit of those new to the 51. It would probably seem clever to most to use something other than shellac or sealant, especially if silicone lube is on hand. I don't plan to ever take off another 51 hood.