[Thomas]

Hm, I am not sure. In this quenched-only condition, the steel is very hard and brittle and often not useful for engineering applications. The condition is very aptly described as "glass hard". Note the forces applied to the tappets.

In a second step, known as tempering, the hardness can be reduced and the desired service properties (hardness, tensile strength and toughness) of the steel can be adjusted. In this process, the steel is heated again, depending on the alloy content and desired properties. This produces the desired service hardness. The higher the tempering temperature, the lower the hardness. On the other hand, toughness increases.

However, this all depends on the material, whose composition I do not know. Another method is nitriding, which is used to harden GS valves. But you can hardly do that yourself. As I said, I obviously don't need to machine my tappets. Given the uncertain outcome of hardening, that's just as well.

[wessex_man]

You could machine a high tensile bolt to suit warm and oil quench. Find it works well.

[Thomas]

Before going into a more demanding job like grinding and hardening the tappets (thank you Rick) I re-considered Paul's important remark about the face radius. I agree that it should be equal to the distance between the centre of the shaft and the centre of the tappet. This radius is about 45mm and the tappet has a diameter of about 10mm. With these numbers the resulting height for the tappet surface from edge to edge is only 0.3mm. Scrutinising the two tappets surfaces again shows that both are slightly convex, indeed, and match well with this number. The outer phase at the inlet tappet is just "faking" the required round cross-section. It appears that a previous owner has exaggeratedly ground off the edge without calculating the required form.

[Rick Parkington]

Hi Thomas, I agree with the guys, there should be a radius on the adjuster face - so I'd guess this adjuster has been made by another owner. Whether you can grind a radius onto this one depends on the hardening process used. 'Case hardening' is a surface treatment usually no more than 0.040" (1mm) deep - and that's when done professionally; done in a home workshop it will be a lot less - but it may have been hardened all the way through by another process. I have made these from 'silver steel' hardened and tempered and those are 'through hard' but it's hard to know what has been used. Personally I would put a radius on as you suggest and watch to see if there is serious wear. The great thing about open valves is that if there is bad wear the metal dust does not get into the engine oil! That's how I came to make my own adjusters - I wouldn't try it on a bike with enclosed valves because if they broke they could fill the engine with dangerous sharp pieces! But they didn't break so it was a good lesson that it was okay to make my own adjusters.
Cheers Rick

[Thomas]

Yes, Paul, that is what I would have expected, too.  I believe, I am not able to change that. Actually a spare seems to be requiredn but there is none in the club shop. If there is no better solution, I need to use the present tappets.
Thomas

[phutton]

Neither tappet looks right to me, Thomas! I would have expected there to be a radius on the face equal to the distance between the centre of the shaft and the centre of the tappet. This gives as near as possible a rolling action. Unfortunately, I haven't got spare to check that.

[shorrog]

Hi Thomas
Yes I would leave it but there are others on the forum who are much more knowledgeable than me, so I would see what they say.
Graham

[Thomas]

Hi Graham, I am not sure, indeed, and need some expert opinion. That's the reason why I ask. The hardened layer is the issue. Like you I wonder if the rectangular cross-section might be a problem for the valve cap. I simply don't know. I take you answer as an advice to leave it untouched, right?

Cheers, Thomas

[shorrog]

Hi Thomas, are you sure its a problem?  If you do grind I would just provide a small chamfer, its a lot easier to remove than to put back on! Also if its case hardenend you dont want to break through the hardend layer.
Graham

[Thomas]

Hi all!

I noticed that my exhaust valve tappet has a more rectangular cross-section in contrast to the inlet tappet. I know that this is not good and that the tappets are hardened. I believe I should grind it as the inlet tapped (clamped in a drill?). Do I have to pay special attention to anything?

Cheers, Thomas