Sykes Pickavant valve grinding tool

[Nick Lettington]

I bought a set of valve cutters today that came with a tool for refacing valve seat grinding stones. A few questions... 

what is the difference between using a valve seat cutter and a valve seat grinder? 

Is it an either-or or does one have reason for using both?

Can I get replacement stones anywhere?

And does anyone have the instructions? 

TIA

   

[Tony Griffiths]

I've never seen one, let alone used one, but I imagine that the grinder is to clean up lightly damaged seats or to give a better finish to those cut. As the valevs are lapped in afterwards, the grinder seems, perhaps, a step too far.

[Howard Wright]

Hi Nick

I bought a cheapo Chinese set of valve seat cutters that came with a grind stone.  I gave the seat a very quick grind after using the cutter and then found the valve lapping was very quick.

Cheers

Howard

[Parazine]

I have a Black & Decker Vibo-Centric valve seat grinding tool, very old but functional. It's a similar idea to the above with rotating stones driven by a drill to grind the seats.

The key thing is that you need to use it for just a few seconds on each seat as it will remove the material very quickly. If you overdo the grinding, you'll end up with a bill for putting inserts in!

[Ruairidh Dunford]

I agree - a very light touch with a freshly dressed stone is all that is required. Practise first!

[Stuart Giles]

From my experience, If the valve seat cutters aren't tungsten carbide, they will dull very quickly cutting seats on an early A7 block, ordinary carbon or HSS cutters won't touch modern hard valve seats. 

If starting from scratch on an A7 block after opening the valve throat for big valves as in the photo below, I cut the seat, and then finish it by grinding with the B & D vibro centric tool, as Ruairidh indicates, dressing the stone regularly is key to getting a decent finish and accurate 45 degree or whatever angle.


I have the B & D valve grinding machine too, once the stone in this has been dressed with a diamond, the finish on the seat is better than an 'out of the box' new valve. The B & D user manual for the two machines says that the valves don't need any lapping after this treatment. But I do give them a minute or two with some fine paste to achieve a 'full blue' print across the valve seat.



this pic has some of the stones used with the vibro-centric tool, they are the same as used in a couple of other makes of valve seat grinders, they have a rather odd 9/16" fine thread. Maybe the OPs Sykes tool will use the same size.

[Tony Griffiths]

On the subject of dressing grinding wheels - you really don't need one of these by Wickman - I've always found that, for the typical, greatly abused double-ended grinder, dressing the stone with the first type below never gives a decent finish. The second item is far better - though of course, it's all by eye and while the finish is first-class, it might not be at a perfect right-angle to the side faces. Available here
[url=https://www.ebay.co.uk/itm/Diamond-Grinding-Disc-Wheel-Stone-Dresser-Welding-Tool-Dressing-Bench-Grinder/363061203558?hash=item5488225266:g:kR4AAOSw49pfITW9][/url]

[Stuart Giles]

For my bench grinder I use a piece of so called Quartz to dress the wheels: https://www.mad4tools.com/silverline-sil...el-dresser
A chunk of silicon carbide like this is also really useful for re-shaping mounted grinding points for doing porting where 'off the peg' items are often not the right shape or size for the profile you might want to achieve.

But for precision grinding stones such as those on the Vibro Centric tool or the valve grinder, it really needs to be a jig mounted single point diamond run across the surface. In the OP's photo, the jig for the seat grinder stones appears to be the angled spring loaded plunger; the single point diamond would be fitted at 90 degrees to that plunger.

[Nick Lettington]

On the basis that this thing is a jig for dressing stones I am fairly confident that you assemble it as below to shape the stone...


  20201101_150833.jpg (Size: 176.44 KB / Downloads: 228)

Then insert the guide into the valve guide to centre the stone on the seat...


  20201101_150805.jpg (Size: 156.05 KB / Downloads: 228)

Reading a little between the lines, a cutter is good for softer seats and a stone essential for hardened seats? So presumably the cast iron seven block valve seat can be cleaned up with either?

I wonder how much diamond is left on the tip of the bolt... and if it is possible to cut and fix a disk of carborundum stone with epoxy to an old centre...

[Ruairidh Dunford]

That set up looks good to me Nick - cutting stones are available, you would want to check they fit your tool however...

https://www.ebay.co.uk/itm/254281977579