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| Minimum Valve to piston clearance https://www.slantsix.org/forum/viewtopic.php?t=51125 |
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| Author: | Rick Covalt [ Sat Feb 16, 2013 4:41 am ] |
| Post subject: | Minimum Valve to piston clearance |
I am seeing numbers all over the place for this . I will be checking my valve to piston clearance soon, so what am I looking for as a minimum? Rick |
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| Author: | Dart270 [ Sat Feb 16, 2013 4:47 am ] |
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I have always used 0.090". Lou |
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| Author: | Rick Covalt [ Sat Feb 16, 2013 6:26 am ] |
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Thanks Lou! |
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| Author: | Doctor Dodge [ Sat Feb 16, 2013 8:51 am ] |
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I have run as close as .060 DD |
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| Author: | Rick Covalt [ Sat Feb 16, 2013 9:53 am ] |
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I am hoping not to have to notch my pistons but we shall see later today! Rick |
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| Author: | CNC-Dude [ Sat Feb 16, 2013 10:28 am ] |
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Also axial clearance around the valve is as important as the depth also. |
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| Author: | Rick Covalt [ Sat Feb 16, 2013 11:19 am ] |
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Quote: Also axial clearance the valve is as important as the depth also.
Got it!Thanks |
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| Author: | Charrlie_S [ Sun Feb 17, 2013 4:33 am ] |
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hell, just use the pistons as positive valve closing devices.  Mostly I have seen .080 intake, and .100 exhaust, recommended. I had one of my 170 motors that was quite a bit closer. When I pulled the head after several years, each piston had two small "eyebrows". 
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| Author: | Rick Covalt [ Sun Feb 17, 2013 12:00 pm ] |
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[quote]What valve lash does your cam have. Solid or hydraulic....Also, TDC usually isn't where the intake valve is closest to the piston, its actually 10-20° ATDC that it's the closest, so you'll need to check there. The exhaust valve is closest between 10-20° BTDC.[quote] My cam is a solid lifter, custom cam from Oregon Cams. 1672 exhaust lobe, 977 Intake ground on 105 LSA. Actual measured lift at the valve is .525 intake and .515 exhaust. Piston is .023 in the hole. I installed the cam and lined up the marks and it came in at 96 degrees. I moved the gear and re-checked and it was @ 101.5, That is where left it. I set the valves to zero lash and installed the head with 2 valves and test springs and no head gasket. I set up my dial gauge on the retainer so I could take actual measurements instead of using clay. I rotated close to TDC and took measurements at 5 degree intervals. Here is what I got Intake 10 BTDC .085 Clearance 5 BTDC .022 0 TDC -.002 5 ATDC -.010 10 ATDC -.007 15 ATDC .025 Exhaust 15 BTDC .165 10 BTDC .140 5 BTDC .138 0 TDC .147 5 ATDC .182 10 ATDC .223 |
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| Author: | CNC-Dude [ Sun Feb 17, 2013 4:39 pm ] |
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Don't forget to add your valve lash as part of your clearance along with the head gasket thickness you end up using. |
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| Author: | Rick Covalt [ Sun Feb 17, 2013 5:57 pm ] |
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Quote: Don't forget to add your valve lash as part of your clearance along with the head gasket thickness you end up using
Yes, with a .020 lash and a .040 compressed head gasket I am still at only .050 clearance. I may squeak by with that but now is the time to cut them a bit. There is a chance that this same short block will be getting a Jeffrey head and a bigger cam, so I might as well cut the pistons for that cam now.Rick |
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| Author: | Dart270 [ Sun Feb 17, 2013 9:56 pm ] |
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Don't forget not all pistons get cut the same way (symmetry across the front/rear of the #3 - #4 split). Been there, and had to reshape the notches with the short block together. Not hard, but a bummer... Charlie's response to my valve notch job on the hypereut Chev 2.8L V6 pistons, by hand with a die grinder was... "Bruuutal." This is Charlie we're talking about here too.  Hey, it worked...Lou |
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| Author: | Rick Covalt [ Mon Feb 18, 2013 5:14 pm ] |
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Got all the pistons marked for the shop to cut, but do they need to know the valve angle to know what angle to cut them? If yes does anyone have that number off the top of their head? Rick |
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| Author: | Fopar [ Mon Feb 18, 2013 6:33 pm ] |
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Use a big socket seting on the valve head and measure the angle off the head surface. Richard |
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| Author: | ceej [ Mon Feb 18, 2013 9:02 pm ] |
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No head gasket, zero valve lash. 0.100" My grandaughter still hasn't forgiven me for what I did to the play-doh... If you've got that clearance, once you have a head gasket in there, you won't have a problem when you start tossing feeler gauges in to check the valves hot. CJ |
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