4G Engine Shock Absorber Spring Plate.

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John.reader
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4G Engine Shock Absorber Spring Plate.

Postby John.reader » Fri Aug 14, 2020 11:06 am

If I could ask for some more advice. When the shock absorber nut on the crankshaft is done up tight, should the spring plate be locked solid, or should it be able to turn. I bought a new crankshaft sleeve nut and the hardened washer from Drags, and when I tighten it up, with the pressed steel spring plate that I have, the nut bottoms out on the end of the crankshaft shock absorber sleeve and the spring plate is still able to turn. When I do the same thing with the thicker and seemingly better quality spring plate which I also have, the plate is locked solid and cannot turn. (See picture. The pressed steel spring plate is laying on the bench underneath.)
On Drags web site on the page for the hardened washer 1294-18 it says that "The simple addition of a washer between the nut and the spring cup allows the spring to move without turning the nut," which surely means that the spring plate must be able to turn otherwise why would Drags go to the trouble of making and selling the hardened washer, which wouldn't be needed if everything had to be locked up tight.
Now I always thought that the perceived wisdom on this was that every thing should be done up tight, but reading what Drags say it does make sense that the spring plate should be able to turn.
So which is correct, all locked up solid, or the crankshaft nut done up tight and bottoming on the S/A sleeve and the spring plate able to turn? If its the latter, its no trouble to turn a little bit off of the shoulder on the crankshaft nut to give the spring plate a little bit of play to allow it to move, but I don't want to do this if the whole assembly should be locked up solid.
Once again, any advice would be much appreciated.
Regards, John.
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paul.jameson
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Re: 4G Engine Shock Absorber Spring Plate.

Postby paul.jameson » Sat Aug 15, 2020 7:33 pm

As far as I can determine, the pressed steel plate was superseded by the machined plate which is on the end of your crankshaft. I have used both over the years and find that the pressed steel version tends to break the hardened washer and then becomes even more free than before. So I use the machined version on my bikes these days.
Paul Jameson
36 4G, 37 VH, 54 KH(A), 75 Healey 1000/4, 52/53 ex ISDT KHA (project).
Former Machine Registrar & Archivist, General Secretary and Single Spares Organiser (over a 25 year period).
Now Archivist once more - but not Machine Registrar.

John.reader
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Re: 4G Engine Shock Absorber Spring Plate.

Postby John.reader » Sun Aug 16, 2020 11:43 am

Thank you Paul, that's the information that I needed. I rather thought that that was the case as since my previous post I have been looking at some of the parts of the pre war version that I had in my spares box, and on that version the spring plate is definitely able to turn, even when the two nuts are locked up tight. I'll tighten it all up but will make sure the machined spring plate is still able to move. Many thanks for your help, kind regards, John.

Pete.Silson
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Re: 4G Engine Shock Absorber Spring Plate.

Postby Pete.Silson » Sun Aug 16, 2020 12:21 pm

I believe that the pre-war 4G spring plate should engage with the crankshaft splines when the nuts are done up and is therefore not free to rotate.

4G shock absorber 1.JPG
This seems like a much better idea than the later ones which can rotate and allow the nut to wind off resulting in damaged chaincases. Maybe your pre-war plate is from a single not a 4G?

Pete

John.reader
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Re: 4G Engine Shock Absorber Spring Plate.

Postby John.reader » Sun Aug 16, 2020 5:05 pm

Hi Peter and thank you for your reply. From looking at your picture you are quite right and the pre-war spring plate does not turn on the crankshaft as I thought. As you can see on the right in my picture, my spring plate has no splines to stop it rotating but having seen yours I can now see that they were there, but have been broken off in the distant past. I took this shock absorber assembly from a iron 4G which I know hasn't been touched since the nineteen sixty's if then, so I assumed that the plain hole in the spring plate was original. Not so. What I am building here is a pre war engine, but I'm using Mark 1 crankshafts and rods, as the originals were the white metalled rods and the crankshafts were badly damaged, presumable by driving with the big ends out. this means that I have to use the later shock absorber assembly as the rear crankshaft has the split pin arrangement rather than the flat on the shaft as was used earlier. I know that I could grind a flat on the later shaft, but really the threads are not that good and I didn't want to reduce them even more. This brings me back to the original question, should the later spring plate be able to turn, or should it be locked up solid. I think that letting it turn might be best as if its done up tight then the turning effect of the spring will eventually force it round taking the nut with it, whereas if the nut is locked tight against the S/A sleeve, but the spring plate can move easily then the twisting effect of the spring can move the plate without putting too much twist on the nut which hopefully means it won't come undone. Unfortunately there is no chance of the spring being able to move on the spring plate or the sliding member as the Draganfly spring is a bit small on the ID and has to be forced over the the components at either end. Hopefully the split pin and plenty of locktite will hold it.
Again any advice much appreciated.
Kind regards, John.
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roland robinson
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Re: 4G Engine Shock Absorber Spring Plate.

Postby roland robinson » Sun Aug 16, 2020 10:15 pm

John,

I have had a look at the crankshaft shock absorbers on a 1929 'Colt', a 1935 'Cammy', a 1952 VB and a 1956 'Square Four'. On none of them could I find any evidence that the spring plate was designed to rotate.It is just a case of doing the nuts up tight and using the locking device provided which is what I have done for years with absolutely no trouble. In the case of the 'Colt' and the 'Cammy' there is no extra locking and relies on the nut being tight but I do apply loctight now which of course was not available when the bikes were new.

Roland.

John.reader
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Re: 4G Engine Shock Absorber Spring Plate.

Postby John.reader » Mon Aug 17, 2020 2:09 pm

Hi Roland, and thank you for taking the trouble to check your crankshaft shock absorbers for me. What you say about doing the nut up tight with loctite is what I have always done in the past without trouble. I am being distracted by what Drags are saying on their site about fitting the hardened washer between the spring plate and the nut to stop the nut being forced undone by the spring plate moving to allow the twisting load of the spring as it is compressed.

Just out of interest this is what Drags say about it.
"The shock absorber nut on the SQ4 has a tendency to come undone due to the rotational movement of the spring that causes the nut to turn by ever so small an amount. It has this effect in both directions but the nut only ever turns anti-clockwise because in the other direction it has to tighten the spring, which is too hard to do. Locking mechanisms only delay the inevitable result of the nut trepanning its way through the primary chaincase that has to be repaired with a baked bean tin or similar. The simple addition of a washer between the nut and the spring cup allows the spring to move without turning the nut."

I'm more confused than ever now, but I think that just doing it up tight as I have done before might be best. Thank you for your help, Regards, John.

John.reader
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Re: 4G Engine Shock Absorber Spring Plate.

Postby John.reader » Mon Aug 17, 2020 5:11 pm

Just to add to the confusion, here is a picture of my existing spring plate, and as you can see from the marks on the face, it has been locked up tight in the past, but has then been forced to turn by the action of the spring. The damage is caused by hardened shock absorber sleeve gouging the face of the softer spring plate. The problem with this later type of shock absorber is that there is no positive location of the spring plate, it only relies on being nipped up by the nut, unlike the earlier version which locates in the splines, although mine had all broken off anyway. Perhaps Drags have got a point here, (see above) I'm more confused than ever. Of course the other problem here is that the nut can only be tightened to the nearest flat in order to get the split pin in, unlike the earlier fully adjustable version. So if the nut is tight just past the split pin slot what do you do, force it up another flat and risk stripping the thread, or back it off to the previous slot. Not sure, what does every one else do? Regards John.
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