Fellas - I'm working on the valves and valve guides for a project and I'm getting some strange results. I measured the valve guide ID with a split ball/small hole gauge and a mic (down to the tenth thousandth) and felt pretty good about my results - valve to valve guide clearance was right around .002" which is where I expected it to be on a low-mile engine. However, next I measured it by installing the valve in the guide, pushing it out .400" (to simulate valve being open) and then using dial indicator on the valve to measure amount of wiggle. When I was measuring side to side (perpendicular to rocker arm) I was getting about .004" of movement, indicating .002" of clearance. However, when I moved the dial indicator parallel with the rocker arm, I got .010" of movement, for .005" clearance, which is a big difference. I realize valve guides were oblong, but I didn't expect this much of a variation. I then switched to a snap gauge, which allows me to measure a bit more accurately than the split ball gauge because I can measure the larger axis of the valve guide as well as the narrow axis. I got measurements on the larger axis (parallel to the rocker arm) that were larger than what I got with the split ball gauge, but only by a few tenth of a hundredth thousandth (example - .3747" instead of .3743"). However, I didn't see any readings that indicated .005" of clearance like I saw with the dial indicator method. Any ideas on what I should be using as the most accurate method? Thanks Scott
A dial bore gauge is probably what you should be using.... https://goodson.com/products/p-310-sunnen-valve-guide-gauge-set But lately I've realized that the engines I'm working on don't need to last 100k miles, so when the guides are like yours are, I just run them and don't worry about it.
Tight valve to guide clearances need the tightest valve head to seat runout....Other wise you'll gall or stick valves...My vintage O/T racing junk is done on Newen single axis valve machine....running .0008 intake an .0012 exhaust on air cooled engines... If I care about a street.... engine the cost of valve work is not a factor. But if the head on street engine was with in factory specs ,I would run it..On higher performace I would not risk sloppy guides that can break off a valve head
To start with if you are talking to a machinist a "tenth" is commonly recognized as a ten thousandth. Just to ease the verbiage of writing a sentence. If you are measuring the valve to guide clearance by wiggling the valve back and forth you normally do not use any kind of a gauge. Wiggling the valve is commonly done by someone who has done it for years and is all about deciding if you need to take a closer look. IE its sloppy I better check this out or its tight and I better check this out (tight is probably uncommon). If you are measuring with a dial indicator your measurements are dependent on how far away from the guide you are measuring. The farther away from the guide the larger the measurement. Its an angle thing. Clean the ends of the guide prior to measuring then use a snap gauge. If you are building something that is actually going to be driven then measure the both ends and the middle. It is important that the bore of the guide be straight as it is that a cylinder be straight. Stressed yet? Don't be its not brain surgery. Unless you measure your life by the thousandth of a second close is cool.
I've looked for a used Sunnen setup, but no luck yet. In the meantime, it's a snap gauge, split ball gauge, and dial indicator.
Not running tight clearances, just street stuff at .002" - .003". The problem is that my dial indicator measurements don't jive with my other ones. thanks
Ok, if the wiggle is just to get an idea, then I'm good. On the dial indicator measurement, I opened the valve to factory spec - .400" and then tested. On the split ball and snap gauge measurements, the valve guides were clean and I did three measurements. Thanks
Make a sketch of the guide and the valve, and see how much you'd expect the valve head to move sideways with the wear that you see with the snap gauge. Geometry.... Sounds to me like they're worn enough that if you want it perfect, it needs guides. If you're not going to put a lot of miles on it, and it doesn't have to be perfect, just put it together and run it.
Well Scott... What's the worst that can happen. That's right. Do nothing and what's going to happen. The world won't end tomorrow. How about, what's it going to do. Will it improve things? If so, by how much. Leaps and bounds or just probably be better. Reading the comments I'm again thinking, if you have the money to spend why not spend it. Yet really, why do valve guides and not replace valves? Check the valve for deposits and ask how they got there. And again, how much do you need to spend. Some of it will be guides, some valve stem. Some will be from valve seals maybe? As far as it goes though, don't think you always have to, just that if you ain't the guy doing it, he's going to want it done just to avoid the risk of you being unhappy if budda-bing becomes budda-boom in another year or two. I do the pull out a bit and see if there is wiggle up and down. I also pull out the valve and see if it has a suction when the end is finger sealed. Sounds like you went scientific and measured. Hmm. That's cool, but you still say you are going to talk to your machinist. I think your over thinking, and soon over spending. It's popular. I was of the understanding the wear to the valve guide would be apparently worn inline not side to side due to the one direction action. The wear on the valve shaft however would appear to be cir***ferential? Appears to be so? But it also got me wondering about it's rotation. No clue. I'm going to have a closer look next time things are apart. But as far as it goes, my wiggle to check for wear has been slide out, check up and down not side to side so I really can't say. I also new I had this nicely drawn image and had to post it.
I agree with you on the inability to measure the ID of an oblong or oval hole with a split ball gauge. It's just going to measure the narrowest portion. As for replacing the guides, these engines apparently do not use replaceable guides. Guides that are out of spec are just reamed and honed oversize. On a related note, one of the pairs of heads I'm checking has .015" thicker valve stems, but the machinist who did this left the clearance wayyy too tight on some of the guides - I measured .0005" (not a typo!). Several of the exhaust valves were galled and I had trouble getting several of them out of the heads. Not sure how many miles the engine had on it after the rebuild, but some of the valves/valve guides definitely weren't happy. Thanks for the input
Overthink things is what I do. Overspend, too, but I'm trying to get better at that. As for the wiggle test and the pop check/pop test - I've already done that on these heads and they p***ed. I actually filmed myself doing these tests; it'll be posted on my next YouTube video on this engine rebuild. Will probably be out later this week. I do plan to replace the valves, valve seals of course, and the valve springs as well. I did test the springs and they were within spec (200# open - 1.397" - with +/- 8# variance) but these engines run roller cams and I'll be going with an aftermarket cam with more lift/duration. Thanks
Overthinking is common and extremely common on the HAMB. Sometimes I think that people forget the most important part of the equation when it comes to "traditional" hot rods. FUN!!! If someone is stressing over minor stuff, they are not having some. Stress is not fun at all.
Years ago, Enco had inexpensive dial bore gauges. They worked very well. That would be my suggestion. I know of some shops that have go-no go gauges if they do the same thing repeatedly. The basis of good machine work is measuring in accurate and repeatable results. To measure something 4 times and get 4 different results should let the user know there is something wrong.
I enjoy the challenge of figuring something out, so overthinking isn't always stressful to me. Thanks
I'll have to source some dial bore gauges for the next iteration of this. I hear you on accurate and REPEATABLE results. I'm getting better, but will need a lot more reps before I'm comfortable.
I'm with you. I get wrapped up in "****ysis paralysis" and, if I don't break out of it soon, the project won't get finished.
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