As a Montblanc fountain pen collector, as well as restoring vintage and classic pens, the opportunity to acquire this wonderful Montblanc Peter the Great Limited Edition 4810 was irresistible "Fools rush in where others fear to tread"!
I knew the pen would arrive with problems. The dealer who sold it to me had previously had it returned from a customer who had complained that it would not fill correctly. There are obviously a number of reasons why a piston filling fountain would not fill properly.
Carefully dismantling the pen barrel, removing piston assembly and removing the pierced overlay, the first problem could easily be seen. For some reason, the section had been forced away from the barrel. I knew from previous service and restoration work on similar Montblanc's, that metal overlays can become loose and rotate on the barrel. However, to force the section away from barrel would mean that the barrel was too short or the overlay was too long. The image below shows the gap of around 1.0 mm between barrel and section.
Measuring the length of the barrel, compared to my own Peter the Great, for some reason the barrel of the pen with forced away section was exactly 1.0 mm shorter. It appears that a previous owner had attempted to reduce the length of the barrel, in order to prevent the overly rotating on the barrel. This did not explain why the barrel had been turned down 1.0 mm when only 0.10 mm would have been sufficient to secure the rotating overlay.
I turned my attention to the piston filling assembly. The piston seal itself was badly scared, again this could be a contributing factor as to why the pen would not fill properly. This was not normal wear, something within the pen barrel could have only caused this type of damage! (see image below)
Using a borescope, I inspected the internal bore of the barrel. The front 90% of the bore was smooth with no scratches. The threads which hold the piston assembly in place were also undamaged. Just below the internal threads, a shoulder which acts as the transition between internal threads and bore had been damaged when someone had previously attempted to remove the piston. I suspect the damage was caused by a sharp metal instrument. As to how and why this damage occurred remains a mystery!
I can only speculate that when the piston assembly was previously removed, the piston became detached from the sliding piston rod. This would normally require the piston to be pushed out of the rear of the barrel using a wooden dowel, accessed from the front end of the barrel. Damage to the internal retaining lip of the piston was consistent with the damage to the rear of the piston bore if a sharp instrument had been used to 'pick' out the piston from the rear of the barrel.
This again would have caused filling problems. Ink is drawn up into the barrel by suction/vacuum effect as the piston is retracted within the barrel. The vacuum created within the barrel, which holds the ink from running back out of the nib, was being lost as the piston seal passed over the damaged part of the bore at the rear of piston travel.
I subsequently discovered that the pen had been returned to Montblanc in Hamberg for repair after the initial attempt to fix the rotating overlay had failed. Being a limited edition, a replacement barrel would have probably had to of been specially manufactured. Montblanc quoted €720 for the repair, not surprisingly, the customer declined this quote. The pen was returned, and the "butchery" began.
Hepworth Dixon Repair and Restoration.
There were two problems which had to be overcome.
Increasing the length of the barrel to achieve the correct length to securely locate and lock overlay in place, without applying undue pressure on the section.
Either fully bore out the barrel to remove the damaged rear end section and substitute the piston seal with one of a larger diameter. Alternatively, manufacture a modified piston having a greater length, so that when the piston was fully retracted, the seal remained within the undamaged bore of the barrel.
Three piston seals are shown below. The left-hand seal is the original from the pen itself. Center, is the piston and seal I manufactured with a greater diameter, to accommodate a full re-bore of the barrel. The right-hand piston and seal to fit the existing bore, being longer, thus preventing the seal from reaching the internally damaged bore at the rear of the barrel.
To increase the length of the barrel, I turned up a brass collar with a spigot. Bored a recess in the brass rear section of the barrel to accommodate collar spigot. Using epoxy resin, the spigot was glued into the rear of the barrel. Carefully mounted in a lathe collet, the extension collar was turned to match both external and internal diameters of existing barrel. Having precisely measured the length of the metal overlay, the collar at the rear of the barrel was turned down to the exact length of the overlay, plus a margin to ensure the overlay would be a tight fit when the pen was re-assembled. Finally, the brass collar was sprayed with enamel to colour match the pen's green barrel.
Now it was time to make the decision. Fully bore out the barrel and use the increased diameter piston and seal, or use the extended piston and seal? I choose to go down the route of the extended piston. Fully boring out the barrel to remove damaged area would have been possible, but ensuring an ultra smooth finish to the bore would be more difficult.
The length of piston travel would also have to be modified to accommodate the extra 6.0 mm length of the piston. The piston slide had to be reduced by the same 6.0 mm. This could not be achieved by simply turning off the rear end. The plastic piston slide has a brass insert at the rear, which acts as the engagement of the spiral worm drive. The piston slide had to be shortened from the front end and a new piston locating recess formed.
Below is the re-assembled, modified piston and turning knob assembly. The second image shows the lengthened barrel with its extension collar colour matched to the barrel.
I would have to point out that due to the modified piston assembly, the barrel ink capacity has been reduced by approximately 10%.
The fully re-assembled 'Peter the Great' fountain pen is now fully functional, draws and holds ink perfectly. A tricky and complicated repair, but well worth the effort.
