Author Topic: Plunger frame  (Read 310 times)

Online Superflash

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Plunger frame
« on: 22.03. 2020 05:25 »
Hey guys. There truly are times when I hate all things tech with a passion. This is my 4th attempt to get the photo file sizes small enough to post.  *problem* *problem*. So ... While waiting for the engine bits to be done, I thought Id move on to the chassis. A local guy here who has a pretty amazing selection of Brit bike stuff sold me a fairly decent plunger frame. Only thing missing were the plungers themselves. But that's ok, because a few months back, I grabbed a pair of sub-frames that had the plungers fitted. The springs look shot, and the axle thingy's need rechroming, but the basic units are all there, and seem to work ok. The thing that interested me was the difference in the castings for the actual plunger mounts. On these sub-frames, there's a fairy big gusset where the pillion peg holes are. So I'm guessing they must be off a really old (pre 49) set up? The frame I bought has these gussets scalloped out as per all the parts lists I've seen, so am happy that they haven't been tampered with. The frame is stamped ZA7S 217** which if I'm right means it is a 49-52 type frame.
Anyway, had a go at mounting in the engine cases, and they went straight in with no fuss. So hopefully that means that the frame is pretty well square and true. Cheers
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Offline Swarfcut

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Re: Plunger frame
« Reply #1 on: 22.03. 2020 08:28 »
  SF.. Looks a lucky find.  The rear  frame column supports "gussets" are  the same each side and will have the identical forging numbers possibly still visible under the paint and dirt, below the footrest holes.   Pre-'53 frames don't have the lug for a prop stand.   Late frames have a plate on the headstock for the steering lock pin. The  rear axle lugs differ in the position of the grease nipples. Late point backwards, early point out. Otherwise the plunger parts are the same on A,B,M models.

 Apart from a basic straightness check, (the top tube sometimes bows behind the headstock on sidecar bikes) head race condition etc, the other things to check are the stand pivot mount holes and the flat part of the footrest lug under the saddle tube. This is where the stand stops often wear away a hollow, so stand then goes further over centre and then lies too low. Easy to rectify now, not so when the bike is all back together and its a hernia lift to get it off the stand. The stand stops also wear, but can be built up.

 As you have found it is easy to mount the cases and gearbox. Not so to load a completely dressed unit. It is far easier to assemble crank, cases and gearbox into the frame and rebuild the motor on this stable footing.

 Swarfy.
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Online Superflash

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Re: Plunger frame
« Reply #2 on: 23.03. 2020 07:15 »
Thanks for the advice Swarfy. Have taken the cases out and had a good look underneath around the center stand lugs. All appears to be sweet as. Same around the head stock.  I recall seeing a thread here regarding side stand lugs, but don't remember anything about working out where exactly to weld one on. Any thoughts or guidance? Cheers Tony.
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Offline Swarfcut

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Re: Plunger frame
« Reply #3 on: 23.03. 2020 12:38 »
Esteemed Member GB may be able to help with some pix and dimensions. Aftermarket prop stands are bit of a worry, most being sourced from areas where the raw material is recycled oil tankers. There have been several  failures, noted on the Forum.

 Plunger Frame. Additional. There are a couple of steel sleeves to join the front and rear of the frame sections, where the the front motor mount long stud passes through. Often mislaid, but easy to make as the are just a thin walled tube. Folks think the long through stud does the job alone. No, it needs a bit of extra help. These are not shown in parts diagrams, but adding them give more stability to the frame joint at this point.

 Swarfy.
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Online Greybeard

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Re: Plunger frame
« Reply #4 on: 23.03. 2020 13:36 »
I recall seeing a thread here regarding side stand lugs, but don't remember anything about working out where exactly to weld one on. Any thoughts or guidance? Cheers Tony.
On my '55 Plunger the side stand lug goes around the frame tube so was brazed on during manufacture. If you need more details let me know.
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Offline Nourish

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Re: Plunger frame
« Reply #5 on: 24.03. 2020 11:12 »
Surely that sub frame with the large gussets is not off a twin frame - the lower rails should protrude towards the front of the engine - they don't appear to be long enough - unless that picture is telling lies!
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Online Rex

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Re: Plunger frame
« Reply #6 on: 24.03. 2020 12:51 »
I thought the same.
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Online JulianS

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Re: Plunger frame
« Reply #7 on: 24.03. 2020 13:09 »
And no hole for the substantial sidecar mounting lug found on the twin and M series frame.
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Online Superflash

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Re: Plunger frame
« Reply #8 on: 25.03. 2020 02:07 »
Yep. That's why I was interested in what it might be off. The bottom rails are straight, and not bowed in like on the complete frame I have. Also, at the end of the bottom rails, there 2 bolt holes that have been drilled in to a flat bar that's welded on to the tube. I'm wondering if they could be some sort of after market jobbie for turning rigid frames into sprung? Not that any of it matters, as I was only after the plunger units anyway. They're the same height as what is needed for my frame, so once the service tool arrives to get them out, the 2 sub-frames will just go into my ever increasing pile of interesting, but useless bits....Cheers
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Offline Swarfcut

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Re: Plunger frame
« Reply #9 on: 25.03. 2020 08:29 »
       SF By the highly polished chromework on the springs, this mystery is more likely the remains of some custom build. The profile of the basic forging looks the same as usual, with that larger sheet addition just welded in place.  May also have the same forging number as your better frame.

      Once the  top column cap and upper and lower pinch bolts are removed, and with the tops and bottom spread a little, the centre column comes out. A stubborn one (where the sliders have seized to the column) will need a removal tool that screws into the thread where the cap goes on the top of the column.  Banging a drift down the middle will simply knock out the pushed in dust cap at the bottom of the column, so try driving upwards first. With exposed springs as you have, freeing off will be a whole lot easier than a fully shrouded unit, as here you have easy access to the exposed column and sliders.
  Thread on the column top is fine and easily damaged.

      Springs are not under great tension and with the column removed the whole plunger unit can be eased sideways enough to put in a piece of threaded bar, washers and nuts to compress the springs just a little to allow safe removal. Hooligans (like me) just give it a  sideways kick.

Cheers.

 Swarfy.
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Online ironhead

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Re: Plunger frame
« Reply #10 on: 25.03. 2020 08:41 »
Surely that sub frame with the large gussets is not off a twin frame - the lower rails should protrude towards the front of the engine - they don't appear to be long enough - unless that picture is telling lies!

That sub-frame is from a B33 / 31. With extra gusseting added.
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