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Author
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Topic: Valve to piston clearance
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Rustang
Gearhead Posts: 733
From: Clarion PA
Registered: Nov 2000
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posted 07-19-2001 09:19 PM
   
Just slid my new cam in and checked piston to valve. The intake is about .082" and the exhaust is .095". This was checked with checking springs and dial indicator with slightly tighter valve lash than recommended and a used head gasket.  My last cam was on the ragged edge too, but I don't recall numbers. I was wondering what some of you guys have gotten away with?
I do know that with the old cam I was told to assemble everything as I would run it with the springs and everything, and set the proper valve lash. then slide .100" feeler gauges on the intake and .120" on the exhaust. turn the motor over carefully and if nothing clunks, it should be okay. Is this too close?
Here's a link to some pictures after running my old cam, one showing a circle in the carbon where the exhaust valve may have been too close!
http://www.rustang-racing.cityslide.com/albums/album_image.cfm/717582/51171/446179 ------------------
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bluestreek
Gearhead Posts: 1724
From: Athens,GA
Registered: Jul 2001
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posted 07-20-2001 10:38 AM
.80 - .100 should work fine as long as cam gears, sprockets, or chains are not worn, cam is degreed properly, and valve lash is not set too tight(check with engine warmed up if possible)..Also use high quality springs to eliminate the chance of valve floating.. If you don't want to chance it, then just get a head gasket that will make the tolerance that you feel safe with.. "When it comes to high performance, you can do what everybody else is doing, or you can take a chance and try to get a little more!!.. That's what I call "ragged edge".. "No performance boundaries are ever broken without some kind of chance or sacrifice"..Dan H.
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Rustang1
Gearhead Posts: 110
From:
Registered: Nov 2000
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posted 07-20-2001 01:28 PM
Thanks Bluestreek. I'm gonna put my old cam back in tonight and compare the two. If it is tighter than my new cam, I'm going to take a chance on it. If it has more clearance, I think my next step will be to find some 1.70:1 rockers. That should give me another .011". Anybody ever run big block Chevy rockers on a Cleveland? I'm told they'll bolt right on. My current head gasket is Fel-Pro #1021 that is .041" thick. I don't know what all head gasket options I have with this "Clevor" combination ------------------
1968 Mustang,Clevor,C4
1969 Torino 351C 4spd
1978 F150 460 C6
1978 F150 351W C6
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steve'66
Gearhead Posts: 8826
From: Sonoma,CA,USA
Registered: Mar 2000
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posted 07-20-2001 01:43 PM
Rustang,You probably know this, but...
You can change your cam timing to gain valve-piston clearance. Did you degree the cam(s) yet? SteveW
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bluestreek
Gearhead Posts: 1724
From: Athens,GA
Registered: Jul 2001
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posted 07-20-2001 02:11 PM
Yes, you can use BB chevy rockers.. Less ratio with the lifters will factor into more valve clearance and less lift and also are easier on you entire valve train.. As you may know, more valve lift moves the HP up in the rpm range, and more duration creates more effective "flow" throughout the entire rpm range.. The trick is to keep the velocity up on the air/fuel mixture at the most efficient rpm range of your induction combination..Nascar 355 ci engines can produce 700-800 HP with only a 390 CFM restrictor carb @ 8000-9000 rpms.. :O
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Butch Jennings
Gearhead Posts: 624
From: No. California
Registered: Apr 2000
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posted 07-20-2001 03:40 PM
Duration has more effect on moving the power up or down on the rpm scale than lift by a long shot....in fact lift has very little to do with where on the rpm scale an engine makes power.------------------
Butch
460 powered 1967 Comet Cyclone
10.271 @ 130.069
Butcher's Home Page
"Friends don't let friends drive Chevys"
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Rustang1
Gearhead Posts: 110
From:
Registered: Nov 2000
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posted 07-20-2001 04:56 PM
I also disagree with the 700-800hp with 390 cfm. they only run the restrictors at Talladega and Daytona, and this limits HP to 450-500. (Still impressive!)------------------
1968 Mustang,Clevor,C4
1969 Torino 351C 4spd
1978 F150 460 C6
1978 F150 351W C6
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Rustang
Gearhead Posts: 733
From: Clarion PA
Registered: Nov 2000
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posted 07-20-2001 05:53 PM
Steve, I checked it at 4 degrees advanced. I'm fairly comfortable with the intake clearance, but the exhaust clearance scares me. I didn't check the cam at any other setting because, if I'm thinking correctly, as the piston comes up to TDC during overlap, advancing the cam will mean the exhaust valve is closing earlier. Therefore retarding the cam less than the 4 degrees advanced should mean exhaust valve clearance will worsen.------------------
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steve'66
Gearhead Posts: 8826
From: Sonoma,CA,USA
Registered: Mar 2000
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posted 07-20-2001 08:14 PM
Rustang,That's true, advancing the cam's centerline makes the intake valve open earlier btdc, and the exhaust valve closes earlier btdc too. You'd have to advance it a little more to help exhaust valve clearance, at the expense of some intake clearance. Good luck  SteveW
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Rustang
Gearhead Posts: 733
From: Clarion PA
Registered: Nov 2000
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posted 07-20-2001 09:48 PM
I was just talking with a guy that does alot of dirt track engines, and he checks valve/piston clearance as follows: He says remove the head gasket, set the valve lash to zero, and rotate the motor. If nothing hits, he's pretty confident you won't have clearance problems. ------------------
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kid vishus
Gearhead Posts: 6098
From: middle of NC
Registered: Oct 2000
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posted 07-20-2001 10:04 PM
I dont know about that method of checking. Sounds like a good way to bend some stuff. My engine guy builds lots of dirt track motors and he clays every one of 'em up. One very reputable shop here has always figured a minimum of .070 on the intake, and .080 on the exhuast. But, they also say you have to really keep an eye on the springs, and your driving style, one free-rev, and it's time to replace some valves.
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Rustang
Gearhead Posts: 733
From: Clarion PA
Registered: Nov 2000
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posted 07-20-2001 10:20 PM
Kid, thanks for your reply. Do you know if that .070 and .080 figures are checked with full valve lash and head gasket installed?------------------
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steve'66
Gearhead Posts: 8826
From: Sonoma,CA,USA
Registered: Mar 2000
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posted 07-20-2001 10:25 PM
Rustang,You have more exhaust clearance than intake now. I'm interested in how your old cam checks out. I think you're fine with the clearances you have now, BTW. SteveW
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kid vishus
Gearhead Posts: 6098
From: middle of NC
Registered: Oct 2000
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posted 07-20-2001 10:26 PM
I think so,but I wont swear to it. They are pricey so I quit going there. When we checked mine, we used a head gasket and set the lash tighter than specs, but my intakes still touched the pistons, even with .100 clearance. We never checked the exhuast valves, but they didnt show any signs of touching. Although, none of the intake valves hit hard enuff to bend them.
I also had .035 piston to head clearance, and they touched too. And I was told that was proper clearance for the piston to chamber. But, the pistons hit hard enuff, they flattened the tips of the domes, and tried to cock four of the pistons in the bores hard enuff that they cracked the cylinders in a partially filled block.[This message has been edited by kid vishus (edited 07-20-2001).]
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Rustang
Gearhead Posts: 733
From: Clarion PA
Registered: Nov 2000
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posted 07-20-2001 10:57 PM
With my old cam I ran .080" intake, .102 exhaust. When I pulled the heads, 4 of the eight pistons had faint marks in the carbon where it looked like the exhaust valves had touched. (for a picture see the link above) I'm pretty sure that my valve springs are stiff enough, and I did over-rev the motor once this summer, when I didn't have a rev chip in and free revved to 8500+. I can only guess if that's the case, though. One other question, Kid, have you ever ran BBChevy rockers? (1.70:1) I'm wondering if they would drop right in, or if they would require different length pushrods or something?------------------
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bluestreek
Gearhead Posts: 1724
From: Athens,GA
Registered: Jul 2001
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posted 07-22-2001 10:53 AM
Prostock blueprinting specs requires at least .100 valve to piston clearance on intake and exhaust.. Circle track blueprinting only requires .80 intake and .100 exhaust.. Both require .010 piston to deck clearance using a .035 head gasket..
Hope this helps.
Dan
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Rustang
Gearhead Posts: 733
From: Clarion PA
Registered: Nov 2000
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posted 07-22-2001 06:15 PM
I scrounged up a pair of BBC 1.70:1 roller rockers (Crane Gold) to see if it helped my situation. I now have .115" on the exhaust!  I'm giving up a little lift (.663 vs. .675) but I'll take that over bent valves any day! The roller pattern on the valve looks perfect and pushrod clearance is good. The only problem I could detect is the rocker casting is very close (.030") to the retainer.
So now do I tell people they're Chevy rockers, or are they 1.7:1 ratio Cleveland rockers?!? Oh, and thanks for everyone's input! This site rules!------------------
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SteveLaRiviere
Administrator Posts: 43151
From: Saco, Maine
Registered: May 99
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posted 07-22-2001 08:04 PM
Tell them you have Crane roller rockers.  ------------------
'70 Mustang Mach 1 M code 351C 4V/FMX/3.25 open
'72 Mustang Sprint Coupe 351C 4V/FMX/4.30 Trac Lok
'94 F-150 XL 5.8L/E4OD/3.55 Limited Slip
'97 Probe GTS 2.5L DOHC
Ford. The closer you look, the better WE look!
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steve'66
Gearhead Posts: 8826
From: Sonoma,CA,USA
Registered: Mar 2000
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posted 07-22-2001 08:13 PM
Rustang,That sounds like the best bet! Go get 'em.  SteveW
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bluestreek
Gearhead Posts: 1724
From: Athens,GA
Registered: Jul 2001
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posted 07-22-2001 11:20 PM
Glad to hear you got it worked out.. As for the rockers........ Don't tell em anything!!!
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