jhall Posted February 6, 2005 Report Share Posted February 6, 2005 BBobynski, I'm continuing rework on my '97 Deville N*. Got the Timeserts into the block and pulled the heads down for inspection (I previously asked about valve spring compression force and the cracks on the valve keeper rings). I cleaned the valves and started inspection on everything. I noted that the all the exhaust valves had pitting - something I thought might be cleaned up when I lapped the valves. Unfortunately, this did not happen. Have a look at the "before and "after" pics of an exhaust valve. The intake valves look great - smooth faces, no pitts or grooves. The exhaust valves appear to be in not-so-good shape. At $30 each, I'm not crazy about replacing the exhaust valves but I don't want them to burn out of the seats. Any ideas?. Based on my past experience with the way they look, they either need refacing or replacing. Refacing will add some fun in keeping the margin height correct and making sure the machine shop accurately measures stem height- so I think they may need to be tossed out. Or am I just worrying too much and the leak rate will not hurt anything?? Link to comment Share on other sites More sharing options...
jhall Posted February 7, 2005 Author Report Share Posted February 7, 2005 At $30 each, I'm not crazy about replacing the exhaust valves My goof. The exhaust valves are actually about $13 each. The intakes are the ones that are almost $30 each, but none of these need replacing (whew) . Link to comment Share on other sites More sharing options...
Ranger Posted February 7, 2005 Report Share Posted February 7, 2005 At $30 each, I'm not crazy about replacing the exhaust valves My goof. The exhaust valves are actually about $13 each. The intakes are the ones that are almost $30 each, but none of these need replacing (whew) . Hmm, why the big price difference? Link to comment Share on other sites More sharing options...
jhall Posted February 7, 2005 Author Report Share Posted February 7, 2005 Hmm, why the big price difference? Not sure. The intake valves are a bit larger, but the exhaust valves run hotter and typically require better heat-resistant materials. Link to comment Share on other sites More sharing options...
jhall Posted February 9, 2005 Author Report Share Posted February 9, 2005 The valves are fine. Used exhaust valves start to look like that. Normal. I would personally not replace them unless you just want to spend the $$$. OK, gave it some thought and looked at the scenario of poor seating and possible valve burn. I took the heads to a machine shop that is supposed to have a good reputation for doing this work. I'm hoping the exhaust valves can be cleaned up rather than replaced, but I've located some and I'm prepared to buy new ones if needed. The shop tech seemed to know what he was doing. He asked if I had the valve specs and said that he would check the face seal areas with blue dye during rework of the heads. Keeping my fingers crossed...... One question I have regarding stem height measurement that is not clear in the Helms manual - Is the stem height checked from the top of the stem seal base (after the seal is installed) or from the aluminum landing where the seal and spring sit? It seems the aluminum land is the proper spot, but the illustration in the manual shows two measurement points - neither of which are labeled. Link to comment Share on other sites More sharing options...
Dloch Posted February 9, 2005 Report Share Posted February 9, 2005 Generally the height is checked from the spring pocket. If you are going to grind the seats and the valves I would use a spring height checker that would go between the retainer and seat, and check the before grinding height and then check again after the grind. The difference will be how nuch further the stem of the valve has risen. I don't remember the max stem height you can have before you have problem, I.E. the plunger of the lifter is compressed enough to hold the valve off the seat. I'm sure Guru knows that number off the top of his head. So as not to have a problem, if you know the distance the valve has sunken by the difference between the before grind height versus the after grind height you will know how much you need to grind off the stem of the valve. Also you may want to reshim the valve spring to get the correct installed height again. Dennis Link to comment Share on other sites More sharing options...
jhall Posted February 10, 2005 Author Report Share Posted February 10, 2005 Generally the height is checked from the spring pocket. That's the trick. The spring sits on the valve stem seal when everything is assembled, so I'm not sure whether to measure at the top of the seal land or at the aluminum land on the head. The manual is simply not clear on this and actually shows two measuring points - one at the seal land and one at the aluminum land. Maybe this accounts accounts for the high / low measurements, but I don't want to take a chance. I've already pulled the heads down (and cleaned 'em good enough to eat off them!). I guess I could go back to the shop and reassemble the exhaust valves and get some "before" values. This may prevent problems. I'll talk with the tech. The max / min stem height numbers are in the manual, so no problem there. Actually getting a tool in close enough to make a good measurement is going to be a challenge. I've got a friend who's a very good tool maker that has offered to make up a go / no-go gauge for me, so I'll probably do this to prevent crashing of parts later on. Also you may want to reshim the valve spring to get the correct installed height again. According to the manual, this is a definate no no. Apparently, the springs are running at maximum permissable compression. The manual states that shimming will cause coil collision and "bottoming" of the spring - a very bad thing. Thanks for the comments. Link to comment Share on other sites More sharing options...
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