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Thread: valve guides
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3rd May 2017, 08:11 PM #1
valve guides
My first attempt at making car valve guides didn't go to plan ! I cut the cast iron bar into pieces long enough to do two guides , holding each end in the 3 jaw chuck and turn the OD . Well it was going great until I drilled the 3/8" bore down the guides, something went wrong I have a non-concentric bore at one end of the guide. I used a pilot drill and then a 9mm drill and finally then a reamer . Something wandered, the pilot drill maybe . Next attempt I will use a 4 jaw chuck and try drilling half way and turn the guide around and drill the other end . Is it better to do this type of job without a pilot hole and instead just start the bore with a larger diam. drill that will not flex ?
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3rd May 2017, 08:23 PM #2Member
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How long is the piece? How small was the pilot? Tail stock aligned? Bit of drag on tail stock while drilling? I almost always centre drill, pilot and step up slowly. Only time I have had a run off is when I fed the pilot in a little too aggressively and steered it off centre. That was in 4140 bar....
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3rd May 2017, 08:36 PM #3Golden Member
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I have had the same problem making valve guides, or any sort of small diameter bushing really, unless it is bored to ensure concentricity to the O/D. To overcome the problem have finished the I/D to size then held the guide on a mandrel to turn or grind to the required size.
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3rd May 2017, 08:38 PM #4future machinist
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How long are the valve guides ?.
Also have you though about turning the OD on a mandrel ?BETTER TO HAVE TOOLS YOU DON'T NEED THAN TO NEED TOOLS YOU DON'T HAVE
Andre
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3rd May 2017, 09:14 PM #5
The guides are only 2 5/8" long but the problem is I need high accuracy . I am thinking of trying no pilot and instead use a short stubby 9mm drill from each end , the longer drills tend to start chattering at the beginning and then settle down. Boring would be possible but tricky because it's a small bore and the thin boring bar would flex I think.
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3rd May 2017, 09:59 PM #6Mechanical Butcher
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Try boring the hole first, then provide it with 60 degree countersinks and turn the OD between centres.
It has to be long enough for the driving dog.
Jordan
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3rd May 2017, 10:10 PM #7Most Valued Member
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The classic way of doing this is a bored pilot hole maybe 2 diameters deep then a D bit drill/reamer. Very, very standard deep hole drilling operation for gun work.
If you google D bit reamers et al you'll find out more than you ever wanted to know.
Drilling from both ends - good luck with that idea.
IME drills tend not to wander far off centre unless they're buggered, you've done something bad or the item you're drilling isn't coaxial with the spindle bore. I note you held them in a 3 jaw chuck, just how good are the jaws in that chuck? I *never* use a 3 jaw for precision work, I use a really, really good 4 jaw that I know has damn near perfect jaws. Or a collet chuck. Both guarantee me that the workpiece axis is in line with the spindle axis.
Drilling/reaming then turning the OD on a mandrel is a good way of dealing with this as others have said.
PDW
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4th May 2017, 08:23 PM #8
guides
The second go has been better and successful . I turned the OD of the guide blank to around plus ten thou over the desired size which is .631" ( the old worn guides measure .6315" , these were very tight ) . I then used the 4 jaw and pilot drilled half way , then the larger drills to 9.3mm . I removed the guide turned it around re-centred it and did the same . While still in the chuck I ran the adjustable hand reamer through , carefully creeping up onto the optimum size for the valve stems , The guide is a tad tight ATM but I plan on using the valve as a mandrel to turn the guide OD to size. The two guides on the left are the buggered non-concentric ones
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4th May 2017, 08:50 PM #9Pink 10EE owner
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I take it you will still turn the OD to size on a mandrel so the ID is concentric to the OD?
I am certainly no expert on head repairs, but I guess that you install the guides, then the valve taper in the head has to be recut with a tool that uses the installed valve guide ID as a guide..Gold, the colour of choice for the discerning person.
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4th May 2017, 09:27 PM #10
Yep, with cast iron valve seats they typically use a HSS seat cutter , the cutter fits onto a pilot , the pilot is inserted into the valve guide , the cutter is manually turned . Ideally the seat width should be no wider than around 1/16" , if the seat is too wide , the cutters come in 15 and 60 degrees, you use these angles in order to narrow the valve seat .
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6th May 2017, 10:25 PM #11Senior Member
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have made hundreds of guides both ground and turned. Yep use a mandrel it's the only way. If it's only the odd few after makeing the guides plus ten thou you then turn a mandrel on the lathe out of scrap (no centre or tail stock)I would knurl it or centre punch for min surface area then turn to same size as reamed bore. Then twist on and finish turn/polish to size. You can usually twist off but if not pair of multis with alloy jaws lightly gripped and it will twist off. Ideally ream or I preferred hone to size once installed in the head.
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7th May 2017, 07:26 PM #12Mechanical Butcher
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12th May 2017, 08:54 AM #13Most Valued Member
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Learning a bit from this. I have a carby that has a worn throttle shaft & body. It means that the motor leans out (at idle) due to extra air getting through the worn throttle journal. The usual fix is either throw away the carby or bore out the journals and sleeve them with a bronze or brass bush. I have had limited success making these 8mm ID x 9mm OD bushes nicely concentric. I'll have another look at my methods...
SimonGirl, I don't wanna know about your mild-mannered alter ego or anything like that." I mean, you tell me you're, uh, super-mega-ultra-lightning babe? That's all right with me. I'm good. I'm good.
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12th May 2017, 04:03 PM #14Mechanical Butcher
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It's not hard to make short concentric bushes, if you turn the outside and bore the inside without removing from the lathe chuck.
Jordan
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12th May 2017, 07:01 PM #15Most Valued Member
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Same issue as the OP. If for whatever reason your initial hole is not concentric, then the reamer will follow. Turning the OD will not make the ID concentric if it is slightly off. Finishing the OD on a mandrel means that any eccentricty created while drilling, reaming the ID will be removed. This is what I like about that idea.
Of course, investigating and fixing the reason for turning an eccentric ID is the best option if possible.
SimonGirl, I don't wanna know about your mild-mannered alter ego or anything like that." I mean, you tell me you're, uh, super-mega-ultra-lightning babe? That's all right with me. I'm good. I'm good.
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