Setting Valve Lash
Thread Starter
Racer
Joined: Jan 2008
Posts: 338
Likes: 0
Setting Valve Lash
Gentlemen,
I have an aftermarket 427 BBC that came in my Corvette, but no idea what cam is installed. I need to set the valve lash but I have no idea what spacing to use. It has iron heads and solid lifters.
Any advice would be greatly appreciated,
Thanks
I have an aftermarket 427 BBC that came in my Corvette, but no idea what cam is installed. I need to set the valve lash but I have no idea what spacing to use. It has iron heads and solid lifters.
Any advice would be greatly appreciated,
Thanks
Drifting
Joined: Aug 2005
Posts: 1,682
Likes: 3
From: League City TX
There is no way to guess at it.
The only way your going to know is to open the engine up, look at the cam, and hope it has ID info on one end.
Short of that, all you can do is check your current lash, hope that its close to specs, and maintain it in that area from here on.
The only way your going to know is to open the engine up, look at the cam, and hope it has ID info on one end.
Short of that, all you can do is check your current lash, hope that its close to specs, and maintain it in that area from here on.
Race Director
Joined: Nov 2002
Posts: 12,142
Likes: 54
From: Taylor Michigan
How do you know its a solid lifter engine?....if it has 5/16 pushrods it could be a hydraulic cam...the 3/8 th's and 7/16 ths push rods are for solid lifter cams....if its determined to be a performance cam, then the lash could be 22-26 intake to exhaust or variances of the two..... The size of the pushrod guide plates will also help the cam identity
Thread Starter
Racer
Joined: Jan 2008
Posts: 338
Likes: 0
I initially thought it had hydraulic lifters, but I followed the hydraulic lifter adjustment (1/2 to 3/4 turn past zero lash) and I believe all of the valves are cracked open. The starter spins and there is no compression. When this happens, does that mean solid lifters?
Thanks for the info, I will check the lifter diameter
Thanks for the info, I will check the lifter diameter
Race Director
Joined: May 2006
Posts: 18,689
Likes: 2,572
Definitely sounds like solids. You can only guess as others have stated, unless you tear engine apart and hope cam has markings, and set for something in the mid .020's, like .025.
Last edited by MelWff; May 23, 2011 at 03:37 PM.
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Melting Slicks
Joined: Oct 2002
Posts: 2,317
Likes: 111
From: St Louis MO
Rather than tear the engine apart to look for cam numbers, you could degree the cam checking intake and exhaust duration at .050", .006", and max lift, and see which cam it matches best with. Unless it's a newer aftermarket tight-lash solid cam, you'd be safe to set about .025" lash.
If you do want to look for a cam number, it's often on the front of the cam so all that's necessary is to pull the water pump, the harmonic damper, remove the timing chain cover and cam timing gear.
Good luck!
If you do want to look for a cam number, it's often on the front of the cam so all that's necessary is to pull the water pump, the harmonic damper, remove the timing chain cover and cam timing gear.
Good luck!
Melting Slicks
Joined: Aug 2008
Posts: 2,200
Likes: 3
From: Lehigh county Pennsylvania
The same thing happened to me ~40 years ago...bought my used vette with solid cam and no idea what to set the lash at.
Once I removed the stick, I still can't identify it. Neither can the chevy dealer or speed shops. I was screwed. You probably are too.
I'm no valve train expert by any stretch of the imagination, but guessing at solid lifter valve lash is bad practice in my book.
Drifting
Joined: Aug 2005
Posts: 1,682
Likes: 3
From: League City TX
The most common "once upon a time" was .025-.026"
Today you see a lot of .016"-.020"
Tight lash solids are typically .011-.013"
Team Owner
Joined: Apr 1999
Posts: 21,953
Likes: 1,445
From: Reno Nevada
2024 C3 of the Year Finalist- Modified
You really can't go wrong setting them right around .018 - .020 Those old school cams from yester year could run the big lash setting because of the wimpy ramps and spring pressure. With todays stuff it would cause damage with .030 lash.
Just a general rule for a street motor is: It depends on the amount of mechanical noise when it's running. If it sounds like the push rods are beating the rockers to death you have too much lash
Melting Slicks
Joined: Oct 2002
Posts: 2,317
Likes: 111
From: St Louis MO
BTW, the timing chain cover CAN be removed without dropping the oil pan (takes a bit of pulling to free it), but snip the inner corners off the inner flange which holds the oil pan seal to reinstall it - use some of RTV to help seal it.
Race Director
Joined: Jan 2000
Posts: 12,399
Likes: 247
From: San Jose CA
Help is on the way - from the Chevy Power book, seventh edition, that cam has part number 3927140 and is ID'd as 33927141. Its specs are 256/268 degrees at .050 tappet lift; .469/.483" gross lift with 1.5 rockers, and a 112 deg LSA. It was the first design racing cam. Use with springs 3927142. Lash is .024/.026".
BTW, the timing chain cover CAN be removed without dropping the oil pan (takes a bit of pulling to free it), but snip the inner corners off the inner flange which holds the oil pan seal to reinstall it - use some of RTV to help seal it.
BTW, the timing chain cover CAN be removed without dropping the oil pan (takes a bit of pulling to free it), but snip the inner corners off the inner flange which holds the oil pan seal to reinstall it - use some of RTV to help seal it.
Last edited by Shark Racer; May 25, 2011 at 10:46 AM.
