By Dave Monyhan (retired),
In the previous issue of Tech Notes we talked about selecting a valve seat stone. As you’ll recall, Goodson carries six abrasive formulas for a variety of applications. Today, we’re going to share some tips on getting the most out of your valve seat stones.
Now that you’ve chosen your seat stone, dressing is your next step. The diamond is your friend, but only if it has a sharp point. The diamond’s job when dressing a stone is to remove enough material to expose fresh abrasive. A flat spot without a point will only close off the grains of abrasive and smooth over the bond, actually preventing the grinding wheel from doing its job.
Tech Tip: Regardless of which abrasive you select and the application you are working on, you can make almost any abrasive grinding wheel function differently simply by changing the speed in which you traverse the diamond across the wheel. If you dress slowly you will close off the grains and bond and make the stone act like a finishing type of abrasive and if you traverse at a rapid pace across the wheel you will make it very aggressive. A medium speed is what you’ll use the most. Goodson offers six different types of abrasive, so you don’t have to adjust your dressing technique each and every time you grind, but if you’re in a pinch, give this a try.
We just discussed the importance of having a sharp diamond to dress the wheel, but I want to call your attention to the diamond holder or dressing arm for your seat stone dresser. Most dressing arms have a threaded hole for the diamond to be inserted. These threads will attract grinding dust and must be cleaned periodically. A valve guide brush and some compressed air do a pretty good job. Inspect the threads to insure they are not worn and if you wish, run a tap through it once or twice a year to keep the threads in good order.
Stone Holders are the real workhorses of seat grinding as they have a couple of responsibilities to perform every time they are used. One, of course, is to hold the grinding stone concentrically, and two is to maintain a glove like fit to the OD of the valve guide pilot.
Some stone holders like the Kwik-Way unit are rebuildable, meaning you can replace the shaft, bearing and drive cap as needed. All other stone holders that I know of are used until they become unusable and are then replaced. Regardless of the brand you have there is one area you cannot allow to be compromised and that is the ID of the inner sleeve. A good rule of thumb is if the ID of the inner sleeve is worn by .001” to .0015” it should be replaced. The same can be said for pilot tops. And if the combined wear of the pilot and holder is more than .002”, they should both be replaced.
We recommend you use leather washers on stone holders. This will absorb vibrations as well as help prevent the stone from seizing on the stone holder. Be sure to inspect the threads where the stone is screwed on. These threads will also attract grinding dust and if you don’t clean them, it can cause the stone to seize onto the threads making removal of the stone quite difficult. Goodson does offer a stone removal tool for both Sioux and Kwik-Way style stone holders that works quite well in assisting the removal of the stone but prevention is your best bet.
Pilots are probably one of the biggest inventories you have in the shop as they’re required for every .001” of an inch to cover the valve guide IDs your shop will encounter every day. Pilots are made from High-Speed Steel and, yes, they are hardened to provide long life. However they will wear and if they wear too much you can have chatter, and possibly have stone a come apart on you which can cause injury to both the head you’re reworking and to your body. Don’t let this happen to you.
Pilot top sizes are different. Sioux is .385”, Kwik-Way is .437”, Black & Decker, Snap-On, Winona Van Norman are all .375”. The wear tolerance on the top of the pilot is .0015” and if you have wear on the top of the pilot and wear on the ID of the stone holder, well you can imagine that you are not going to be able to grind accurately or safely. So if the top is worn…..replace that pilot!
Goodson also recommends the use of bounce springs. The bounce spring has been around a long time, and they come in different lengths, but I am amazed by the number of people I encounter that don’t know to use a bounce spring. The bounce spring does just what the name says – it creates bounce. First insert the pilot into the valve guide bore, then place the correct length bounce spring over the pilot, then place the stone holder on top of the pilot and you see that the stone holder is suspended above the valve seat. This allows you to start the rotation of the stone prior to making contact with the seat, it allows you to control when the seat stone makes contact with the valve seat and also lifts the stone off the seat preventing drag or stop and start lines on the valve seat. I also believe because we have pressure pushing up while the stone is pressing down, this helps prevent chatter.
One other thing for maintenance is the drive tool you use to rotate the stone holders when grinding seats. Whether it is electric or air you need to maintain these very expensive drive tools so you get maximum life from your investment.
Air tools can get contaminated with grinding particles from the air hose coupling. The air coupling can get dropped on the floor, picking up tiny particles of grit, dirt or whatever. When you connect it to your air tools you actually force those contaminants right into the workings of the air tool. I like to see dedicated air line for specific air tools versus the lone airline that does everything from blowing off the work bench to being used to drive an air tool. Also you need to use the Marvel Mystery Oil monthly so that the air tool is properly lubricated. Take a good look at the drive end and note any wear so you can get it fixed before you are in the middle of a job and a down air tool prevents you from an on time delivery to your customer.
Most electric drive tools come with permanently sealed bearings so no maintenance there but the gears do require lubrication on a yearly basis. Always check your manufacturer’s instruction manual for details on how to add grease to these gears. Do not over-fill the grease requirement! The brushes that run against the armature should be inspected by removing the cap and looking to see how much wear has occurred. These brushes are spring loaded and are designed to wear over time. I suggest you inspect the brushes every 90 days or so depending on use to, again, prevent down time at the wrong time. Also contact the manufacturer to get the correct brushes for your electric drive tool.
We covered a lot in this article, but understand that we’ve only scratched the surface. Keep an eye out for more in the future.
As always, you can call us anytime Monday to Friday and speak to any of the techs in our tech services department. And be sure to check out the Goodson online Technical Library.