DT 400 E Barrel Retention Nuts

[UK_DT]

Having removed the head and barrel of my DT400E for painting, I note that the barrel is held on with 4 long nuts. 

On looking at the online exploded engine diagrams there appears to be what is described as a Washer plate that sits between the nut and the barrel (item 16 shown here Engine Diagram CMSNL). Given the appearance of the Washer Plate, am I right to assume that it is only a part required on first assembly as the serrations suggest it is a permanent install?

I didn't retrieve these when I stripped the top end and having measured the distance from where the nut seats to the underside of the barrel (approx 33mm) and compared it with the minimum distance from the bottom of the nut to the engine casing when it is fully screwed in (approx 23mm) it appears that the nuts will secure the barrel when torqued down.

Just want to know if I should have retrieved these washers or that they are either permanently fitted? Hope that makes sense.

 

[Snakebite68]

Someone else will give better advice, but to me it looks like a sacrificial part.
The question is probably: Does it still look in good condition or does it look 'used'..?
It may just be so that the other parts don't 'weld' themselves to the barrel or crack under the expansion & contraction of an air cooled engine.

[NE0]

Pretty sure I've seen these before on barrels on other bikes, I think their purpose is to centralise the long studs through the barrel, so the barrel fits correctly, as you first tighten the nuts up, they press into the top of the barrel and stay there. If the barrel is stripped/sand blasted and the like then you'd probably have to replace one or two. In the distant past studs that went through drilled barrels suffered from corrosion and you could never get the barrel off, these centralising washers (sacrificial as Snake points out) keep the studs in the correct place and the studs exposed between the cooling fins but not corroded onto the barrel but more importantly centralising the barrel and cylinder head.

[Snakebite68]

6 hours ago, NE0 said:

Pretty sure I've seen these before on barrels on other bikes, I think their purpose is to centralise the long studs through the barrel, so the barrel fits correctly, as you first tighten the nuts up, they press into the top of the barrel and stay there. If the barrel is stripped/sand blasted and the like then you'd probably have to replace one or two. In the distant past studs that went through drilled barrels suffered from corrosion and you could never get the barrel off, these centralising washers (sacrificial as Snake points out) keep the studs in the correct place and the studs exposed between the cooling fins but not corroded onto the barrel but more importantly centralising the barrel and cylinder head.

Aaah, that rings a bell from long ago!
Question: Can you see the head bolt shafts through the veins of the barrel (when in) or are they enclosed?

It looks like a case of: If they look ok, it's fine, if they look screwed, replace...

The old adage is: If it ain't broke, don't fix it (but when I have ever listened to myself...)!