Grinding Tappets Flat Without a Crown

[JeffR1]

I have a newly ground camshaft for my 51 Bentley 4.25 litre engine, and I need to clean up the tappets; they require that they be ground flat with no crown on them, and I can't find anyone that wants to do this.
No one seems to have the equipment anymore to grind them flat.
I've posted over at the RR/Bentley forums that I've belonged to for many years, and I'm not getting the responses I'd hoped for, just 1, to find someone with a lathe and a tool post grinder.

I've contacted many machine shops, most just ignore me.
The last one is Egge Machine shop in California and I' waiting for the owner to comment.
New lifters are available at £78.00 each, and I would pay this, except they are made oversize and one is expected to have them ground to fit the block.
That is just not practical to have that done, and I'm sure that finding someone to do that would be nearly impossible.
Plus those lifters are ground to match their (Introcar's) ground cams, the one I have is from Flying Spares.

I'll just post these photos I have, they explain what's going on.

 

[Bayless]

I wish I had some advice. It seems like grinding a flat top should be a simple job for any machine shop. I'm surprised you are having trouble finding someone to do it. Or maybe it is a more complex job than I expect.

 

[JeffR1]

There is a problem, when ever you rotate something round, the outer edge of the circle always turns faster then the centre, so when you do that to a tappet, more material is removed from the outside then the centre, creating a dome in the middle, even when the tappet is ground against a dressed flat stone.
So I've been told.

I came across a Porsche forum and the followers are ground flat, the stone was turning, but not the follower (I think; it was hard to tell from the photo)
Something tells me I'm going to be lapping them by hand _ that will take a long time.
Photo 6 above shows where I've started with a piece of glass, some 220 grit paper and oil.

Most of them are pretty flat, but the one in the photo is the exception.

 

[Bayless]

Thanks, I learned a bit from your post. Hand lapping does sound like a slow process too.

 

[JeffR1]

A friend of mine (Tom) that I have known for a very long time, ground them flat for me.
He knew of a retired machinist that kept all his equipment and had the correct machine to do it on.
Each lifter was clamped into a V-Block, and that in turn was clamped onto the machines magnetic bed and they were ground 1 at time _ took Tom 4 hours.
They were beautifully done, and I have one installed on the exhaust and it rotates as it should _ Thank God !
I was told that the newer cams won't fit in my block, the spacing is different, it wasn't meant for that block... on and on...
It was most frustrating getting any correct information, and then finally near the end of all this, I was told an old style camshaft was removed from an R-Type Bentley and a new unused NOS cam from an S1 was fitted.
I don't understand these guys at the unwillingness to give out info... What ever...

Here's that thread over at the RR/Bentley Australian forums for anyone who wants to have a look.
And a photo of the freshly ground lifters.

Australian RR Forums: Correct Tappet/Lifter Grinding

 

[Bayless]

Happy to hear you solved it.

 

[Cis]

I would have thought you could do it clamped to the bed of a pillar drill, with undersized flathead bits attachment & a spot of grinding paste

 

[JeffR1]

I would have thought you could do it clamped to the bed of a pillar drill, with undersized flathead bits attachment & a spot of grinding paste

Well... Maybe.
I think a bit more accuracy would be needed then what could be achieved doing it that way.
Thanks just the same.

 

[JeffR1]

Well, I jumped the gun, only No.1 exhaust tappet rotates, all the other exhaust tappets do not.
I've lubricated the tappets and cam with moly grease, so maybe a proper cam break in grease, and hopefully things will bed in.
I just don't know... Or maybe the cam is ground incorrectly ?

I have no idea at this point even if the intake tappets will rotate, I'll know when the head is on.

 

[mctriumph]

You can reface the tappets as needed , but have them Rockwelled for hardness as you might cut
through the layer that was treated.
Mad dog

 

[JeffR1]

You can reface the tappets as needed , but have them Rockwelled for hardness as you might cut
through the layer that was treated.
Mad dog

Thanks for that, but only no more then 4 to 5 thou was removed, I don't think it will be a problem.
This quote is from one o the RR members on the Australian forum.

"The cast iron tappet faces were cast to "chills" that make them extremely hard. HB900".

I don't exactly know what that means and I could not find any real explanation of it, but I', assuming that's very hard and deep enough to clean up the surface.

A friend of a friend flattened the lifters for me with this special grinding machine, a V-block and a magnetic clamping bad.

 

[mctriumph]

I have had brand new tappets checked that were too soft to use. Better part of valor when doing
a motor you care about.
Mad Dog