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Had some really ugly exhaust valves on a set of heads I was working on. Didn't feel like waiting for new ones to arrive or going to the machine shop and waiting for them to finally get around to it so I whipped up this tool. Took about 3 hours to figure, design and fab. The grey plastic is nylon I had here but if I was buying I would buy square for ease of fab. To get the valve on center start with the pneumatic grinder first which is a 5/8" hole drilled on a V-Block and then the two hold down holes drilled into the base on a 45 deg after a rough mock up by eye approx where I wanted the valve to be during grinding. After drilling the base then I split the nylon in half at the 5/8" hole so I could clamp the grinder in. The base is 1" thick steel I had and you really need something quite weighty for this. 1/4" pr plywood I dont think would be enough. With this config I can hang the drill off the valve stem and it holds. Once I had the grinder fit to the base I used a very small pointed bit in the chuck to scribe the center line for the nylon that holds the valve and I drilled that 8mm and then the two holes for mounting and with the valve reversed using an angle finder from the vale stem to a long 5/8" bolt I cut the threads off installed in the grinder fixture to get true 45 degrees laid out. After mounting everything as you see here I put the valve stem into a drill running in reverse at full speed so it spins the valve against the stones rotation, with the grinder spinning about half speed ( its a very fast grinder ) and it did an absolutely perfect job of these valves. I dont think I have ever had better done which I was pretty surprised myself. Blue test came out great and none leak at all during mock up with gas poured into the ports on the backside of the valves. I had the nylon but bought the grinder for 20 bucks. Figured some of you guys would appreciate this.
The only tricky part was getting a truly concentric stone as most are kind of wobbly. I had a box full so I had a few but be sure you get a concentric stone for this or you might splooge your valves.
Yeah it was a fun little project. I follow simple criteria on all works; I try and work with what I have and I had all the parts to build it ( had previously bought the grinder for porting ) on hand so it was easy. Function first and foremost is my focus it must achieve the desired result. Followed by usage analysis so if this was a tool I was using daily? I would have taken a completely different approach or simply bought one. In this case I do enough of these to need some solution but not enough to warrant a new tool buy and I most of all enjoy a good challenge. I also follow the rule of simplicity whenever and wherever possible and this one I thought would go over well here for other self doer and the sloppy crew. Worth mentioning that the valve shown in the fixture is not in grinding position, the position is on one half of the stone face.
What do you mean doing them in the heads? Lapping them clean?
Yes i meant if they are basically undamaged. Since you focused/mentoned exhaust I was thinking they may have looked like every set of exhaust valves Ive removed, which is pretty ugly, but easily fixed by lapping them in the head.
I do that too if they are in good shape. Before disassembly I always test each valve with a gas pour in the ports and usually even on clean heads find one or two bleeders. These 823 heads Im working on now came off a high mile LY6 and the exhaust valves were all bleeding fluid and all severely pitted. Seeing as we are now entering the phase of high mile cores with LS engines I figured this wont be the last ones I work on so maybe I could save these and this is what I came up with after digging around and thinking on it some. There is no way these valves would be any good with a lap only so my hand was forced. Now I have a handy little tool for next time. What surprised me most was at least 3 valves were not centered anymore. Meaning the contact face was not truly concentric to the valve stem which lapping alone wouldnt reveal. Grinding did and they are true now.
The valve seats in the 823 are quite different than cathedral heads. To my surprise they still look like new, not a mark on them. The valves took all the abuse. Valve guides too you would swear they were brand new. Wiggle test was so tight I was pleasantly surprised. GM upped their game with these heads thats for sure. 3 angle grind from the factory as well
I did recently have a pair of 243 that were almost as bad as these but the seats were thrashed so I sold them.
After a few mins of thought next time I get a set of pooched seats I think I'll try and make a cutter out of an old valve. Maybe braze in some carbide or something? Not sure about an abrasive, but you have me thinking now...
Could always pony up and buy some stones or a cutter, they are not that expensive. I was having fun using things I had and wanted to get this project moving forward so I whipped this grinder up. It will serve use for many engines, not just LS and if the valve stem is different dia all thats required is to drill out another stand and mount it.
As with in the machining industry,make the valve holding fixture with V grooves in the upper and lower sections to be able to hold various stem diameters.
Yeah trouble is I spin the valve in the fixture which is why I used nylon and drilled in exactly 8mm, i would have preferred teflon but I dont know where my stash is stashed and this nylon bar I had 8' of it so thats that. I did have heat build up on a few valves and could feel the drill loading up against the resistance of the slightly gooey plastic so I had to stop and let it cool a few times especially on the non true valves. Once cooled it retained diameter and still fit tight on the stem. The most surprising result of this whole project was the three badly out of true valves. There were a couple others that were slightly off but within 15 seconds of grinding they were good. The bad ones took minutes to grind clean. This set up is slow though, it takes material off at a snails pace and doesnt even spark its an easy way to not overdo anything.
Regarding the v block etc as I said if I was going to do lots of these I would have taken a completely different tack, this was a quick 3hr tour on an afternoons result
08-08-2018, 08:43 AM
Valve grinding fixture on the cheap 
