Adequate valve to piston clearance?
#2465393
03/12/18 08:28 PM
03/12/18 08:28 PM
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Joined: Jan 2007
Posts: 2,212 Minnesota
peabodyracing
OP
top fuel
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OP
top fuel
Joined: Jan 2007
Posts: 2,212
Minnesota
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Started lining things up to reassemble my 426 wedge after a very long hibernation, and am now concerned.
I bought a rebuilt set of 906 heads some time back, with new valves in place. Comparing these to my old set of 906's I noticed the new valves sit 'higher' in the combustion chamber than the old ones ( which I'd reground at least once years ago)
Since my engine has domed pistons, I assembled things with head gasket, using the clay on top of piston routine. Set valve clearance according to cam specs and turned the engine over twice in the normal rotation direction.
The first time I did this I was somewhat shocked by how close the intake valve appeared, so I started over and did it all a second time.
It looks like I've about 18 thousandths clearance between intake valve and the piston valve relief. My assumption is this is too tight.
I had run this cam years ago in the engine, long enough to break it in, but had not made it to the track with the car before putting it away. At that time the old heads were installed, with the valves sitting deeper in the seats. There's got to be 25+ thousandths difference in valve height on the seat, between old and new heads.
Cam is not really radical, with .550 lift. I'd not anticipated this concern till today.
Opinions please? Thanks in advance.
Lead, follow or get the hell out of the way
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Re: Adequate valve to piston clearance?
[Re: peabodyracing]
#2465397
03/12/18 08:40 PM
03/12/18 08:40 PM
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Joined: Aug 2003
Posts: 43,230 Bend,OR USA
Cab_Burge
I Win
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I Win
Joined: Aug 2003
Posts: 43,230
Bend,OR USA
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You can have the valves ground down to get them to sit in the seats a little further or buy or rent the tools needed to cut the piston valve reliefs deeper. Are you checking all eight cylinders for P to V clearances? If not do that now before finding out later that you should have I raced several different NHRA legal 1963 426 M. W. motors, both 415 and 425 HP and the stock rods are not all the exact same length, same as any Mopar OEM rod sets from the factory My last 425 HP short block had .009 difference in rod lengths Same thing on rocker arm ratio,, they are not all the same Good luck, take the time now to get all parts to fit correctly I have ran the intake to piston valve clearances as close as .029 on my original 415 HP short block due to having the heads cut to reduce the CC from 86.0 CC + to 81.5 CC based on checking ONLY one chamber in each head and not rechecking the P to V clearances I got lucky on that on, not so on other parts changing without doing all the clearance checking Never ASSUME anything on any motors, ever
Mr.Cab Racing and winning with Mopars since 1964. (Old F--t, Huh)
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Re: Adequate valve to piston clearance?
[Re: peabodyracing]
#2465425
03/12/18 09:34 PM
03/12/18 09:34 PM
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Joined: Sep 2014
Posts: 4,457 Washington
madscientist
master
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master
Joined: Sep 2014
Posts: 4,457
Washington
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Did you measure the clearance with clay?
Just because you think it won't make it true. Horsepower is KING. To dispute this is stupid. C. Alston
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Re: Adequate valve to piston clearance?
[Re: madscientist]
#2465570
03/13/18 12:27 AM
03/13/18 12:27 AM
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Joined: Oct 2011
Posts: 3,036 bean town ....Ca
WHITEDART
master
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master
Joined: Oct 2011
Posts: 3,036
bean town ....Ca
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Did you measure the clearance with clay? this is what I would do or use the valve drop method.. are you able to mock it up with a set of checking Springs.... you need room you can face the valve and shrink the margin.. I think this is better then sinking the valve..
Last edited by WHITEDART; 03/13/18 12:29 AM.
In the 8s N/A.with Brett miller W8's 5.07 at 133 at 2700lb
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Re: Adequate valve to piston clearance?
[Re: peabodyracing]
#2465582
03/13/18 12:53 AM
03/13/18 12:53 AM
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Joined: Sep 2015
Posts: 1,096 Australia
ozymaxwedge
super stock
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super stock
Joined: Sep 2015
Posts: 1,096
Australia
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OP said he has 18thou clearance, he needs another 100th to be safe. Is that about right ?
1963 Plymouth Max Wedge 1971 Barracuda
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Re: Adequate valve to piston clearance?
[Re: Dave Hall]
#2465621
03/13/18 02:18 AM
03/13/18 02:18 AM
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Joined: Feb 2005
Posts: 20,185 PA.
pittsburghracer
"Little"John
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"Little"John
Joined: Feb 2005
Posts: 20,185
PA.
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I can’t afford putting my stuff together praying that all goes right under the bare minimum clearances so I take time and make it right the first time. Good luck.
1970 Duster Edelbrock headed 408 5.984@112.52 422 Indy headed small block 5.982@112.56 mph 9.42@138.27
Livin and lovin life one day at a time
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Re: Adequate valve to piston clearance?
[Re: Dave Hall]
#2465631
03/13/18 04:01 AM
03/13/18 04:01 AM
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Joined: Dec 2009
Posts: 20,647 in a cattle trailer down by th...
Guitar Jones
Paddle faster! I hear banjo music!
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Paddle faster! I hear banjo music!
Joined: Dec 2009
Posts: 20,647
in a cattle trailer down by th...
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You could retard the cam some. A couple of degrees should get it above .050 and it will be fine. This is what I would do first. You didn't say what the exhaust clearance was. If it's more than enough then moving the cam timing should get you where you need to be. Don't worry about changing the power band either. It's something like 4 degrees of cam timing changes the power band 200 RPM.
"Follow me the wise man said, but he walked behind"
'92 D250 Club Cab CTD, 47RH conversion, pump tweaks, injectors, rear disc and hydroboost conversion. '74 W200 Crew Cab 360, NV4500, D44, D60 and NP205 divorced transfer case. Rear disc and hydroboost conversion. 2019 1500 Long Horn Crew Cab 4WD, 5.7 Hemi.
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Re: Adequate valve to piston clearance?
[Re: Dave Hall]
#2465652
03/13/18 09:20 AM
03/13/18 09:20 AM
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Joined: Jan 2007
Posts: 2,212 Minnesota
peabodyracing
OP
top fuel
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OP
top fuel
Joined: Jan 2007
Posts: 2,212
Minnesota
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Thanks much for all the good input!
I did measure using clay. I use a composition head gasket. The heads have the regular valve springs on them; didn't have a set of lightweight springs for this purpose.
I didn't measure at zero lash. I'd set valve lash per cam mfr's info. There was plenty of clearance on the exhaust side.
This used to be a 4 speed car, and 7000 RPM was not unheard of. It's now an automatic and I've switched a number of other things to try and avoid twisting it that hard.
Having said all that, I'd not thought of retarding the cam. That would seem a good option at this point, particularly since I appear to be flush with clearance on the exhaust side. Been too many years. I'll pursue that and recheck.
Cab, I will check all cylinders. Your point on rod length was another one I'd not considered.
Thank you again guys for all your wisdom! It's great to be able to come on here and run this sort of stuff by you all.
Lead, follow or get the hell out of the way
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Re: Adequate valve to piston clearance?
[Re: peabodyracing]
#2465887
03/13/18 05:29 PM
03/13/18 05:29 PM
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Joined: Jun 2003
Posts: 52,972 Romeo MI
MR_P_BODY
Master
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Master
Joined: Jun 2003
Posts: 52,972
Romeo MI
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A few questions for ya.. is this a street car.. (assuming its a street/strip set up) you can put the timing back to give you more clearance.. what head gaskets thickness.. can you give the open/close specs on the can(this will help tell you if you can move the cam.. I just cut a set of pistons yesterday to lower my compression.. you can also cut the valve pockets to help if you dont want to move the cam.. ( I always use a zero lash to get my setting.. just saying)
Last edited by MR_P_BODY; 03/13/18 05:32 PM.
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Re: Adequate valve to piston clearance?
[Re: MR_P_BODY]
#2465979
03/13/18 08:01 PM
03/13/18 08:01 PM
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Joined: Jan 2007
Posts: 2,212 Minnesota
peabodyracing
OP
top fuel
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OP
top fuel
Joined: Jan 2007
Posts: 2,212
Minnesota
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A few questions for ya.. is this a street car.. (assuming its a street/strip set up) you can put the timing back to give you more clearance.. what head gaskets thickness.. can you give the open/close specs on the can(this will help tell you if you can move the cam.. I just cut a set of pistons yesterday to lower my compression.. you can also cut the valve pockets to help if you dont want to move the cam.. ( I always use a zero lash to get my setting.. just saying) Thanks for your questions. I use a FelPro composition head gasket that measures right around .040" thick. I measured the amount the intake valves protrude into the combustion chamber and get just shy of .080" which causes me to wonder if there's something amiss on the heads/valves. This is even more than I guessed at just looking at them. Anyway, cam specs: Duration @ .050 261 Lobe lift 368 lobe separation 103 seat duration @ .020 295 gross valve lift .552 lash (hot) .026 .028 I'd not driven the car on the street for many years. Trying to avoid taking it completely apart to cut pistons, etc. My intent was to get the car going again (after 20 years of sitting) and make some passes with it for old time's sake. I've had the car since the early 70's. Mid 90's I'd switched the car from 4 speed to automatic, and at that time bought this cam after consulting with the supplier. Put the cam in, broke it in and took the car out on the road to try out the 727 only to run into a bunch of problems. Fought with it for a few weeks and ultimately just put it away for another day. Life then got in the way. Over the 20 years I had someone reputable go back through the 727, bought a new converter, changed the gears from 4:89 to 4:56 and welded up a new set of fenderwell headers for it, but that was the extent of progress. This winter I've gone through all the brakes, fuel system, the carburetor, and so on. So my preference is to find a solution that will allow me to bolt the top end back together and go from there. If it all works, great. If not, who knows. I gotta admit I burned out on drag racing back then, so still not sure how deep I want to get financially into the whole deal. Anyway, thanks in advance for your thoughts. I'll shut up now.
Lead, follow or get the hell out of the way
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Re: Adequate valve to piston clearance?
[Re: peabodyracing]
#2465983
03/13/18 08:12 PM
03/13/18 08:12 PM
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Joined: Jun 2003
Posts: 52,972 Romeo MI
MR_P_BODY
Master
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Master
Joined: Jun 2003
Posts: 52,972
Romeo MI
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From the sound of things the easiest and cheapest thing to do would retard the cam 4* then check it (thats a pretty tight LSA so retarding it will help you.. sounds like a old cam)
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Re: Adequate valve to piston clearance?
[Re: MR_P_BODY]
#2466016
03/13/18 08:59 PM
03/13/18 08:59 PM
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Joined: Jan 2007
Posts: 2,212 Minnesota
peabodyracing
OP
top fuel
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OP
top fuel
Joined: Jan 2007
Posts: 2,212
Minnesota
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Thanks for your input. Doubly so now that I see you're recovering from a stroke. Hope you're back to 100% very soon.
Again, thanks and best wishes.
Lead, follow or get the hell out of the way
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