Valve guide clearance

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pishta

pishta

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Not Slant specific but applies to all guide installs: What's the stem to guide clearance on a .315 (8mm) valve stem? I'm using a bronze guide and once I pressed it in, I need to ream it and I don't quite know what the spec is for the ID of the guide. In the FSM is says 0.315 +.0018/+.0010. Is this the callout for the guide reamer size? ~0.3160- 0.3168? I've never seen a tolerance with 2 plusses. See Pic

20230516_073730.jpg
 
The other callout is to place a dial indicator on tip of valve and see if the deflection is <.20mm rocking inside guide. Seals are poly lock so you. Ant check this unless you pull the seals off and it's a PITA as these are pressed on like Ford 302s, bottle caps and take a friggin slide hammer and collet to remove without heating and melting the rubber inside it.
 
pishta said:
In the FSM is says 0.315 +.0018/+.0010.
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This is telling you that the resulting hole needs to end up between 0.3168" on the high side and 0.316" on the small side. That way a nomimal 0.315 valve stem will always clear. Just a different way to specify the hole size, you could use any combination of numbers as long as the target ends up in the right range. What size tooling you use in up to you. I would start with a good .3160" reamer because if it cuts a couple tenths oversize it's no biggie and you can get a second shot at it if it is a little tight. One .316" reamer may cut to a different diameter than the next one, so that kind of thing is generally not called out.
 
66fs said:
Also you can run intakes tighter than exhaust.
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Kinda reads the opposite ( min .316 exhaust, .3162 intake) in the FSM. Is this from experience? I've NEVER done guides so this is all new to me. I was stoked when the valves slid in when I got them pressed in then they all bound about in the middle of the guide. I was able to coax 2 of them in with a little force and some grease but the other 2, no chance. None were as smooth as the old guides obviously. Need to be reamed for sure. FSM never mentioned this (Is it just a given?) or they did not expect softer bronze guides to be used? I had the option to buy either, thought bronze would be better but I dont think they are as I'm not running chromed valves. What's the benefit?
 
Bronze guides can be run tighter than cast iron guides because of the better lubricating properties of the Bronze. I can only give ball park numbers, 0.001" for Br & 0.002-3" for CI.
 
All I got is, after I gave United Peed World in Tampa 4 bones to go through a set of ported, big valve J heads, Mag flux, everything, when I broke em down fer heavy springs, some of the bronze guides were so tight, I could not pull the valves out. And Half had carbon on em. I also destroyed 2 or 3 rental VS compressors. Over 15 years ago.... BUT they have been on a running street/strip mill over a decade. Was also a daily driver for over 2 years.
 
pishta said:
Kinda reads the opposite ( min .316 exhaust, .3162 intake) in the FSM. Is this from experience? I've NEVER done guides so this is all new to me. I was stoked when the valves slid in when I got them pressed in then they all bound about in the middle of the guide. I was able to coax 2 of them in with a little force and some grease but the other 2, no chance. None were as smooth as the old guides obviously. Need to be reamed for sure. FSM never mentioned this (Is it just a given?) or they did not expect softer bronze guides to be used? I had the option to buy either, thought bronze would be better but I dont think they are as I'm not running chromed valves. What's the benefit?
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Lets take 273, 318, and 340 specs from the 1968 Plymouth service manual as an example. All guides were spec'd .374 to .375. Intake valve stem was spec'd from .372 to .373, clearance from .001 to .003. Exhaust stem was spec'd from .371 to .372 with clearance at .002 to .004. When measured, 340 and 360 HP intake 4 groove stems were .0005 smaller than your typical small block 2 groove stems. Logically as metal heats it expands. Exhaust valves run hotter than intake valves. The metal in the guide is expanding making the guide ID smaller and the valve stem is expanding making the stem larger. Higher temperatures make this expansion more on the exhaust valve and guide than the intake exhaust and guide. I always ran minimum clearance and had different reamers to get where I wanted to be. Another thing you can do is polish the stems to make the valve job last longer, not to add clearance but to make sure the stem slides smoothly in the guide. Bronze is a nice material for guides. You can get reamers from places like Goodson.
 
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Head heating up along with the guides. Would not both expand and open up? Along with the stem... wonder if the different materials (cast iron/aluminum, bronze and steel) all expand at different quotients. All I know for certain is these things need to be opened a tad.
 
The different materials expand at different rates. If you have a liner that expands faster/more than the cast iron head it is mounted in, the hole will actually close up a little until the head catches up. We're talking small amounts, but...
Same reason that you need a more significant shrink fit when setting steel into aluminum than steel into steel. Aluminum expands more and your insert could come loose if the interferance fit isn't enough.
 
pishta said:
Head heating up along with the guides. Would not both expand and open up? Along with the stem... wonder if the different materials (cast iron/aluminum, bronze and steel) all expand at different quotients. All I know for certain is these things need to be opened a tad.
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Guides almost always need finish sizing, they tighten up when they are installed, SOME are intentionally "flared" at the valve head end of the stem to account for the "hot end" expansion, I am not familiar with this particular engine tho'. Always better a tick loose than tight on the exhaust, Goodson sells guide-sized ball hones to finish sizing after straight reaming to a minimum nominal dia. A lot of exh. stems are ground smaller to give more clearance with the same guide dimension as the intake.
 
You have cooler intake charge coming in though I wouldn't call it cold, now remember the intake valve is in the combustion chamber the guide isn't so no they're not going to expand at the same rate or time even if they were the same material. Exhaust valves well obviously you have very high temps going through the exhaust Port where the valve is not only hot so is the guide because the entire Port is. So they came up with .0015-2 int and .003-4 exh.. it has to keep the seat round so the valve isn't moving around and hammering it into a different shape so you know you get guys that run them a lot looser all of these Speedmaster heads people are buying the guides are you could just drop the valve from a couple feet in the air and it'll land in the guide. Because these parts go hand in hand with performance hand in hand with racing and hand in hand with we're not going to drive this very long it's going to get gone through and refreshed every season and so the valve job gets retouched on and on and on and on and on
 
All good input. I'll ream em to the minimum and send it. I got an adjustable to save buying 2 sizes. Now I gotta find my micrometer!
 
OK, I got the valves to slide in after carefully measuring the valve stems and using the smallest in the tightest guide and so on. I had 4 .315 (8mm) valves, and they measured .3161,2,3 and 4 using a .0001 micrometer and its 'clutch' end. (If these are accurate or not, they are all measured the same way so at least the variances are noted) and I was able to find an order of installation that allows all of them to slide in to their guides with just a tad of interference but all are light fingertip push and pull capable, especially at the operating zone of lift. Im not sure what .001 clearance feels like but these fit so well that they draw a considerable amount of vacuum and pressure when I plug the guide hole end with my finger. My adjustable reamer shows up on monday and I dont know if I even need it anymore. Do bronze guides with their lube type metallurgy even allow the steel stems to possibly hang against a 50lb (?) closed dual spring?
 
There is a small amount of wiggle at valve, just enough to feel a rocking at .500 lift.
 
This project is blooming in a bad way. so I get the exhaust valves mounted up (no issues there) and I'm poking around with the spring compressor after I pick the 4 tightest exhaust guides and drive them in. I get 3 springs installed and notice the #4 valve has a different tone when I pop the valve onto the seat. I put a light under the valve and I can see light through the exhaust port. What the hell? I clean the seat (nothing on it) and try it again. light. Im able to put a .0025 feeler gauge in there on a closed valve? I paint the seat and spin the valve onto the seat and only 25% of the seat is hitting the valve. Good grief, this pathetic head shop (who cut this head 1.7mm , .066" when the limit was .020! ) must have used the stone mandrel in a worn valve guide and had it off .012" at 2" (that is the way to test the guides on this motor, deflection at stem without seal when closed). So I'm gonna take this head (for what its worth) and get all 8 seats ground with the new guides installed when my reamer shows up. Its already a day late....:-(
 
66fs said:
I hope you are not returning to the same shop.
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heck no, they are out of business! New owner........:rolleyes: and I work at a new facility that has closer shops. Maybe the 8mm mandrel they used on the Sioux was bent?
 
pishta said:
heck no, they are out of business! New owner........:rolleyes: and I work at a new facility that has closer shops. Maybe the 8mm mandrel they used on the Sioux was bent?
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Machine shops are dropping like flys around here, but if you need a good one, Wayne’s in riverside has recently done some very nice work for me.
 
pishta said:
heck no, they are out of business! New owner........:rolleyes: and I work at a new facility that has closer shops. Maybe the 8mm mandrel they used on the Sioux was bent?
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Hard to tell, more likely the guides are not on the same center as the originals. Of course you should do the valve job after new guides are installed.
 
$25 later at my new head shop and were good to go! Cut the seat (3 angle again) on a Serdi, checked the other 7 seats and told me my ex valves were past their cut limit (1mm @ side minimum) so he recommended new ex valves but said these will work fine for another 100K. I hope this closes this book on this head! He doesnt know how that 3 angle was so off on that one seat while the other 7 were correct. Guides are just cylinders press fit into the AL head. Is it possible the original guide was bad, I mean this variance was huge. I still have all the guides and none look like eggs. Weird, but water under the bridge now.
 
Higher end shops hone the guides to the finish size instead of reaming. A reamer doesn't put the necessary crosshatch in the guide for oil retention, otherwise, oil would just shoot on past and into the ports. Just think if you bored your cylinders with a boring bar and didn't hone them to put a crosshatch in them. Reaming is faster and they make more profit, but you don't get a quality job.
 
Got the motor fired up last night, ran like a top! Let it heat soak, and adjusted the valves hot. Smoked for about 10 minutes while I revved it up and down a few times but then tapered off to no visible smoke, I guess the new rings set? Whatever, all 4 fireing now, I got great vacuum, barely any blowby out the valve cover vent and no water leaks. I'd call this a 2 month schooling on heads, guides, seats and gaskets!
 
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