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| Comp 252° cam valve adjustment specs https://slantsix.org/forum/viewtopic.php?t=10179 |
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| Author: | SlantSixDan [ Sat Aug 21, 2004 3:00 pm ] |
| Post subject: | Comp 252° cam valve adjustment specs |
I was just over at Red Slant's place investigating complaints of rough/high idle, poor performance and miscellaneous driveability faults. Found some miscellaneous problems (blown vacuum advance, idle mixture set WAY too rich, idle speed set too high, trans kickdown adjusted WAY too short -- 3rd gear before you can get across an intersection!) and all of those will certainly contribute to poor performance and driveability. The shop that did his engine assembly installed the Comp 252S cam Red supplied and adjusted the valves to the specs provided by Comp Cam. Those specs call for the intakes to be set at 0.010" (same as stock) and the exhausts at 0.012" (way tighter than stock 0.020"). The roughness and power reduction Red's car exhibits are typical, in my experience, of borderline too-tight valve adjustment. This 252° cam isn't very much different from the '71-'80 stock cam or the MP P4120243 cam (244°), both of which call for 0.010" and 0.020". I feel that readjusting the tappets to 0.010" - 0.011" (intake) and 0.020" - 0.022" (exhaust) will improve the idle and driveability of Red's engine. That said, perhaps there is something about this particular cam grind that allows or requires a tighter exhaust adjustment -- I've never used this camshaft. Anyone? |
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| Author: | Pierre [ Sat Aug 21, 2004 5:47 pm ] |
| Post subject: | |
If the shop adjusted them when the engine was cold they probably are too tight now after driving.... |
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| Author: | Slant6Rat [ Sat Aug 21, 2004 6:34 pm ] |
| Post subject: | |
Speaking of clearance, what clearance should I run on my slant with a MoPar cam with 460 L and 268 D? I don't have the cam spec sheet! Motors never been fired up. What is the biggest valve combination I can use with the the head? Thanks. |
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| Author: | SlantSixDan [ Sun Aug 22, 2004 8:17 am ] |
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Quote: If the shop adjusted them when the engine was cold they probably are too tight now after driving....
Right, of course, but I don't think that's what's going on here. I'm fairly certain they adjusted them hot, just to an improper spec.
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| Author: | DusterIdiot [ Sun Aug 22, 2004 9:09 am ] |
| Post subject: | That's correct... |
The specs for the 252 and 264 are lashed at .010 intake hot, and .012 exhaust cold... FYI on the 252 it has an LSA of 110, intake centerline of 106 (degree it in at 4 degrees advanced), duration @.050 is 215.... The tight lash is due to them using a standardized lobe from their library in the 'Solids' section, the lash increases the bigger the lobe gets (if you order a grind with the magnum or Xtreme lobes the lash is anywhere from .015 to .020 on either intake or exhaust side...). You might have to tear the timing cover off the slant and re-degree the cam, I'd guess that they just connected the 'dots' and things are not right. After that I'd think that the blank wasn't finished right... ??? -D.Idiot |
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| Author: | Dart270 [ Sun Aug 22, 2004 9:42 am ] |
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Why not just try lashing the cam to 0.016"-0.020" on the exhausts and see how it runs? If it's a fresh motor, you can even reuse the valve cover gasket and it'll be a free test...  I usually take the aftermarket cam lash specs as "recommendations" and play around with them. Lou |
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| Author: | SlantSixDan [ Sun Aug 22, 2004 1:33 pm ] |
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Quote: The specs for the 252 and 264 are lashed at .010 intake hot, and .012 exhaust cold...
That may be the spec, but it ain't gonna work *at all*. 0.012" cold on the exhausts is going to equal almost zero lash when hot.This confirms my suspicion that Comp is out to lunch on this spec. Also had a few private e-mails from people who've used this cam, and the consensus is to use 0.010" and 0.020", intake/exhaust, hot. |
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| Author: | DusterIdiot [ Sun Aug 22, 2004 1:59 pm ] |
| Post subject: | Whoops... |
They should be .010 hot and .012 hot...I have that spec and my duster with the Hpak is running fine. My bad. (although Comp does have a cam lobe that is spec'd for a "0" lash...don't know what you'd need that for...) Hope you get it figured out, I think Doc even recommended like .008 and .016 for the 'hot rod setting' on this cam, but I can't get it to run like that (.008 makes the idle choppy, and the .016 makes it worse). good luck, -D.Idiot |
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| Author: | Doctor Dodge [ Mon Aug 23, 2004 8:48 am ] |
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Quote: Why not just try lashing the cam to 0.016"-0.020" on the exhausts and see how it runs? If it's a fresh motor, you can even reuse the valve cover gasket and it'll be a free test...
Lou has the right idea, you have to pop the valve cover and check to see if the shop lashed the valves correctly to begain with, then try some different settings to see if you can get an idle / performance improvement. I usually take the aftermarket cam lash specs as "recommendations" and play around with them. Lou I have been able to run the exhaust lash a little looser (.016) on this cam and it did improve the idle quality with the engine it was in. Any looser and it started to get noisy. DD |
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| Author: | Dennis Weaver [ Mon Aug 23, 2004 11:56 am ] |
| Post subject: | |
I've got the 264S cam, keep it set to .010 Int/.012Ex hot and it has run just fine for years. Almost too smooth an idle... D/W |
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