Ariel Owners Motorcycle Club

The channel for the exhaust valve on my NH350 is quite badly corroded, as per the pic. Can't see it causing a running problem but is this otherwise normal?

is it corroded or just soot build up?
Try clean it first and check the clearance of the valve stem in the guide.
If o.k. then give the valve a light rub in and put it back together again.

Thanks, the valve clears fine but it looks like the end of the channel has started to flake off, I suppose it could be a lot of soot, didn't want to clean too aggressively in case it is delicate. It seemed to work before so will give it another clean and put back together, thanks again.

First time dismantling a motorcycle engine (initially to change head gasket), and now feel quite foolish as I realise the "channel" I mention is actually the valve guide and not an integral part of the cylinder head. So next stupid question, assuming I can source a new exhaust valve and guide how do you remove the guide? Eg does it pull out from the top (rocker) side or from underneath? Should it push out with a gently tap with a Hanmer and drift?

hi Mike if the valve guide is not broken i would not change it , you can be opening a can of worms if you look on the forum you see members are having problems with getting the right guides and valves that works ok, and you can remove the guide with a drift and hammer like you say or make a little extractor , ( like you have to remove bushes ) to pull it out and pull the new one in or use a press , if you look on this forum you will see a post about NH valve and guides and i think you need to have a look at the posts before you do anything

The best option seems to be the easiest and cheapest, sold! Thanks

That's o.k. there was a picture with it !

removing the guide; I would heat the head up on a electric stove to a point where it sizzels when you spit on it.
Then use a drift with a step in it. You probaly have to make that yourself from a suitable piece of round bar.
Make it snug fitting inside the valve guide, note that inlet and exhaust valves have different diameter of stem.
So if you want to take out the inlet guide make a second one.
Use welders glove to handle the hot head and have everything ready at hand, (obviously).
I use two sturdy blocks of wood to put the head upside down on so the guide can fall in between the blocks, or one block with a hole, whatever.
But, after fitting a new guide + valve you need to have the valve seat in the head lined up .
You have to get that done at a machine shop that knows a thing or two about classic bikes..
Maybe -also- get yourself a copy of Waller or some other manual about Ariels and read up before you actually start doing things.

If you mount a new valveguide, which is concentric, it should not be necessary to line it up with the valve seat.
But unfortunately most of the valveguides, you buy on the internet today is not concentric. Some of them are very unconcentric. Nearly scrap.
Latest time I changed a set, which was on my model A, I didn't even have to use coarse paste to grind the valves. Fine paste was enough. Those guides were concentric!

If you are drifting out the guide and you have new ones to insert then here is a little tool I made to assist with this operation on my 1946 VB600 side valve. It will work perfectly for a OHV engine.
I turned down a suitable old drift to fit and removed the chamfered part so it was square. Then made a Bronze collar to fit the shank and sit square to the thicker end. You can use it with out the bronze collar to drift out the guide ( pre Heating the head will assist this) as damage to the old guide is not important. However when drifting in the new one ( pre heat the head again ) you don't want to peen over the top of the guide so using the bronze collar is important. Being softer than the guides damage will only occur on the bronze collar.
The picture shows the component parts. very simple to make. The calibrated pin going though the shank ( actually a nail brad !) is to locate the shown guide to a required depth when drifting it in as there is no ridge to halt the insertion on this guide shown. It is actually from my 1933 Austin 10/4 where I replaced all guides a few weeks ago.

Cheers
Gary

I followed the advice here on removal and installation. With heat, it was not difficult at all.

However, i ended up buying new valves and guides from draganfly (reasonably priced), and mailed them with the head to a machine/engine shop to have the guides installed, reamed and valves lapped in. It took about 3 months, but was only 50 Canadian dollars (minus shipping). So, assuming you are not in rural Canada, you can probably get the head, new guides, and new valves to a machine shop and have it done right for quite cheap. They will need the specs that appear in the workshop manual.

I would not lose sleep over it, as with a few clicks of the mouse you can have new valves, guides, and a profession shop installing them.