Washer under valve spring collar

[John.Newbury]

Can anyone tell me the function of the Halite washer under bottom collar of valve springs? I note that these appear in the VH diagrams but not in the NH and Drags descibe them as for singles. Personally I have never seen them on post war NH models but have I missed something or were they only fitted to VH models over a limited period?

[nevhunter]

The VH runs vERY strong springs standard. I think they are too strong unles you are competing with it as the exhaust cams often wear badly on pre 51 models. I am not familiar with the washers but could they be for heat insulation, particularly on the exhaust. Nev

[pete.collings]

The valve springs for the HS (Terrys VS 513) are very strong, I think to prevent valve bounce with high lift MK1 cams and high revs. I had fitted a set to a VHA head, but removed them and replaced with a standard VH set ( VS422). Unless you work the motor hard and rev it a lot, standard springs are fine, and I am not sure they are as strong as Nev suggests, whereas the HS springs certainly are. This assumption is based on springs for the alloy head, I'm less sure about iron head valve springs (VS20), but think they are shorter and of thicker wire.
The hallite washers are indeed used to reduce heat transfer to the valve springs, and perhaps give a better seating to the spring bottom cups, so they don't wear the alloy on the head if the spring/cup rotates. They can be fitted to other OHV singles if desired, check that they fit snugly with the locating ridge on the valve guide.
As an aside, I was helping a friend, an experienced mechanic, who had the top end of a VH belonging to another friend in pieces. The VH ran fine at around 50mph, but if worked hard at 70mph lost compression, which returned on cooling. There appeared to be two possible causes, lack of clearance on the head/barrel face around the studs (which might cause the head to expand slightly and break the head/barrel spigot joint when very hot), or alloy pushrods that may have been home made with the incorrect grade of alloy (which expanded too much when hot and gave negative valve clearances).
I gave my friend some thin copper sheet (ca. 10 thou, used on hot water tanks) to make a ring to sit on the barrel spigot, as this method had worked on a VHA head with too deep a seating when matched with a new alloy barrel, and this now appears to have cured the problem with the stripped bike.
So two questions from this episode, firstly what grade of alloy should be used if making new pushrods with ends taken from iron pushrods, and has anyone else had this problem?
Secondly, I saw that new PB valve guides had been made for the head, but that the exhaust guide had no rebate at the bottom end. VH alloy head exhaust guides used to have a reputation for coming loose ( the one in my first VH purchased in 1970 did!), due to the build up of hard deposits on the valve catching the bottom of the guide (hence the rebate), has the move to lead free petrol and improved oils lessened this problem, and removed the need for a rebate?

[John.Newbury]

Thanks guys, interesting stuff, most useful.

[david.anderson]

John
The steel in your valve springs will start to be damaged when the heat exceeds 200C. The springs will lose tension and will not fully regain their strength. The area around the exhaust port will reach temperatures around 230C fairly quickly in an air cooled engine. There is only about 12mm of head between the exhaust port and the valve spring and as such temperatures at the base of the spring will quickly exceed 200C. Exhaust port temperatures of over 250C can be expected for prolonged high speed. The use of a halite washer is essential to insulate the exhaust spring and should also be fitted to the inlet spring.
David

[david.anderson]

Peter
The earlier VH springs vs20 are also a very strong spring (too strong). I found they cannot be used with a high lift cam such as the hs cam as they will become coil bound if used with the alloy head. The vs422 spring (VG and late VH) is not strong enough (particularly for the heavier 1 3/4" exhaust valve) and will allow the valve to bounce if revs are taken to the upper limit ( I have a bent exhaust valve to prove it).
I use steel pushrods with an iron barrel and alloy pushrods with an alloy barrel. I have tried steel rods with the alloy barrel and found that the valve clearances opened up by about .004” when hot. As such it is more than likely that they would close by a similar amount if reversed which dependant on the cam type and clearance could hold the valves open (and cause burnt seats).
I have 3 alloy heads, all of which have suffered from a loose exhaust guide. One head has been enlarged for the guide to a point where the shoulder would have been eliminated so a larger than standard shoulder was machined on the guide and the bottom valve spring collar was turned out to suit. I have never heard of a guide that does not seat on a shoulder.
David