valves and guides for NH

[volker.halbach]

I am about to replace the valves and guides on my open 1937 head on my 1937 NH. I got new valves and guides from the Single Spares. I thought it would be a simple job, but now doubts crept up after going through some older posts and checking measurements. I have now a couple of questions:

1. There were posts that the materials of the club valves and guides don't match and valves tend to stick. How do I identify the problematic combination? The guides are cast iron, the valves have shiny stems after I cleaned off the grease.

2. I have only 2 thou clearance between exhaust stem and guide before fitting, exactly the same as between inlet valve and its guide. Waller says it should be at least 3 thou for exhaust. Of course, I can ream the guide, but maybe that's the reason for sticking valves.

3. I checked the outer diameter of the new guides. Compared to the old ones they have 1.5 thou oversize. Of course, I don't know what size the old guides were before fitting. They needed some force to come out and were not loose in the head. My worry is not that I don't get the new guides in with the cold/hot method. I am rather thinking that they are too tight once fitted. Should I worry? Does anyone know what OD guides should have?

Thanks,
Volker

[adrie.degraaff]

2. It will even seize with 5 thou unless they are differend valves.

[volker.halbach]

Thanks, Adrie. The new valves don't have any markings, so hard to tell what it is. They came covered in grease without any label, so hard to identify. Do you remember anything that may identify them? It seems £24 are down the drains. I can reuse the old inlet valve, but the exhaust is worn with more than 3 thou chafed away at the top. Draganfly is out of stock.

[adrie.degraaff]

If you dril the old guide bigger and make a brass insert than you can use the valve becouse in brass there is no problem.

[JohnnyBeckett]

hi i would get on to pete at single spares i think he will sort it out ,for you, i know their has been a lot problems with valves and guides and what the valve stems are made of and i thought the ones you get from club spares where ok and made of the right grade materials

[Paul Gasson]

Hello Volker, I can add some information from my experiences with a 1955 NH which has the benefit of enclosed and possibly better lubricated valve stems. I rebuilt the head with new old stock valves & guides and just accepted them as supplied, the exhaust valve stuck after a short while. I bought more valves from the club and checked everything on assembly, it was all in tolerance so it went together again and after a few 100s of miles the exhaust valve stuck again. I found a company who have made valve guides for Ariels in the past, cannot remember the name and they said there has to be a difference in surface materials (chrome plated stem) and the guides have to be made from the correct grade of iron. I could buy stainless valves but they were not chrome plated. Apparently, because of current petrol we use it creates higher temperature around the exhaust valve? I bought more guides from Draganfly and valves from G & S Valves which are Pulsed Plasma Nitride coated! I used a reamer to open up the clearance to top limit which I think was 0.004", after a few 100s of miles there was regular popping in the exhaust, I think air was being drawn down the guide, also exhaust valve stuck again. I bought more guides and valves from the same suppliers and this time I used a rotary hone in the guide once fitted to get about 0.003" clearance. Finally, I have a bike that runs well. I am sorry this is a long story and I am sure others will have different experiences, all I can say is that after over a year of trying and frustration, this worked for me. I feel it was important to have a smooth surface inside the guide and many I bought and looked at were very rough, so it might be worth looking at this. I never had a problem with the outside diameter of the guides. Good luck Paul

[volker.halbach]

Thanks to all. Paul, thanks for the long story. Obviously, I wished you didn't have such a long story to tell and the solution were easier; but it's really helpful.The inside of the guides is not really smooth, telling from how the ball gauge feels in the bore. Can you say more on your rotary hone for this small diameter, please, and where I can get one? Perhaps the solution is really the surface in the guide. Of course, I have the additional challenge that I don't get any oil from above into the exhaust guide, only some grease at best.

[Paul Gasson]

I bought them from USA because I could not find anything suitable in my area at a realistic price. Mine came from eBay seller bracketracer and they are called Flex-hone or ball hone silicon carbide 240 grit, they seem to be a car focussed seller. I used 5/16" for inlet and 11/32" for exhaust but you may chose different sizes, I think they were tight in the guides so a smaller size may be better? If you do this, take care and just a little at a time with oil on the hone. It looks like you are in the UK? If you are and would like to borrow mine rather than buy some it is not a problem, just send me a private message and I can post them to you. You may need to balance smooth finish against bore diameter, it is easy to be smooth and too large unless you are making guides. My father was also a big Ariel enthusiast and although he had exactly the same problem as we are discussing, he might have said the rough surface was good because it help oil or grease! I hope you find a good solution and share it with us, if you do something different works it might be helpful on my open rocker machine when it needs an overhaul. Paul

[nevhunter]

Adrie, Brass (Copper zinc) is no good. You will need a bronze (Copper tin.)plus a few things. On open valved with cast iron heads engines use cast iron. That's what they always had. Nitride the stems or chrome them. Stainless will gall and wear out in no time at all once the stem surface roughs up it becomes a file. Waller is spot on with 3 thou,EX and a bit over one on the inlet. I have always used adjustable reamers to get the final size and finish and do it in the lathe (will help to keep the bore parallel). If the guide was tight to remove from the head make the new one the same size unless the surface is rough in which case you add a bit to allow for the rough finish. Don't force a tight guide in or you risk cracking the head near the port end. You'll B*gger the valve end anyhow drifting it in and it will require more reaming after fitting. Guides where the bore is not concentric with the outside mean you have to remove too much metal to dress the seat. Try hard to avoid that situation. Nev

[volker.halbach]

Thanks. Nitrided stems can prevent wear, but it seems they cannot prevent the seizing of the exhaust valve in the guide. Paul solved the problem with a brush hone, and I think I try the same and then fit nitrided valves. So far I knew the flex-hones only as tools for deglazing cylinder bores and didn't realize they made them in tiny sizes as well.

How do you fit guides? I thought about heating up the head and putting the guides in the freezer to avoid any damage to the hole; but with the temperature difference I might lose any feeling for whether the guide is a tight fit or not.