valves and guides for NH

[Paul Gasson]

I do not think you will find iron expands very much so you will not get the same advantage as you would with aluminium for example. I did cool the guides in the freezer for 24 hours but you have to be able to fit them quickly or they will gain temperature fast. Its most important to make sure you have the correct interference before you start as someone mentioned. Also remember that iron is great under compression force but does not like to be shocked and the guide can shatter if you tap it in. I use my Triumph tool which locates in the valve seat and a threaded section passes through the guide hole. Quickly fit the cooled guide over the shaft, fit a nut and wind it in as fast as possible. Get everything ready in advance and practice a couple of times before going for it!

[JohnnyBeckett]

hi Paul that is a good way to fit the guides and less chance of braking then i do not like hammering some types of guides in i try and use a press, but i think your way is better you do not have to messabout with setting it up in the press

[volker.halbach]

I did some measuring. The old guides have an OD of 0.6255", the new ones from Single Spares at least 0.001" more. The guide holes in the head are 0.6240". I assume an interference fit of more than 0.002" on an iron head is too tight and will cause the problems Nev mentioned. Strangely, most people seem to fit these guides without turning them down. I don't have a lathe, so I am wondering whether to give up and go to a machine shop after the lockdown or trying to get guides of the proper size. Are the Draganfly guides the same?

[JohnnyBeckett]

hi drags are saying all their guides are 5/8 " ( 0.6250 )OD for the singles engines

[volker.halbach]

Thanks, yes, they say the "nominal" size is 5/8"; but "nominal" probably means only "close" to 5/8", because something is added for the interference fit.

[paul.jameson]

I may have some NOS original guides still. The open valve 350 engine used to eat them.

[Paul Gasson]

I have some guides around somewhere as well so can measure and let you know what I find. Selective assembly is what you will probably need.

[JohnnyBeckett]

hi i would think after all these years of having problems with getting and fitting the right valves and guides that drags or the club would be able to get the ones of the right material that works without giving problems and if you look on this forum you will see lots of members having the same problems

[nevhunter]

Most of these problems emerged with the widespread use of so called "stainless" valves . Anyone who has used stainless spokes will know how they weld together and can't be tightened or undone unless some of the "special" lubricant is still there. There are MANY different forms of stainless steel', some of it pretty ordinary for engine use.
Valve and guide metals have to be COMPATIBLE to work in the hot and sparsely lubricated situation they are in. They must also have the required minimum running fits and a good surface finish. IF or when a valve seizes it can cause a fair bit of damage.. "Normal" wear is smooth with no sign of GALLING. Once the surface is rough the wear is then very rapid, This generally happens with the exhaust valve. "stainless" also expands more with heat so you have to increase the tappet clearances, particularly with Side Valve engines. Nitriding helps stop galling by forming a very hard surface. Refacing the seat will go through it, so don't. You can build up the seats with inconel or stellite for the exhausts but you'd want it done to a "decent " bit of steel to be worth it. Nev

[adrie.degraaff]

"Normal" wear is smooth with no sign of GALLING.

If i put GALLING through translation it comes back as shaving but it is more like melting on the stem and than pushed up to a ridge.
New-old-stock valves don't have that problem.
Something similar happened with the frontwheel barings of the first discbrake cars with strut coilspring, it was hanging in rubber the disc made electricity and it had to earth through the baring, they made a earth wire on the strut to solve it.