Valve lash clearance on Cragar OHV

mngreen

mngreen

Senior Member
[FONT=&quot]Would anyone happen to know what the proper valve lash clearances should be (hot and cold) on a vintage Cragar OHV conversion on a Ford Model B block? I have contacted Steve Serr of the new Miller OHV repops but his pertains to his new aluminum head; mine is old skool iron.[/FONT]

[FONT=&quot]Thanks,[/FONT]

[FONT=&quot]Mike Green[/FONT]
 
Mike, on my steel OHVs, I feel comfortable running .008" on intakes and .012" on the exhaust. I doubt you are going to run it hot enough to worry about heat dissipation on the exhaust valve, but if you think you may then add a couple thousandths more lash on the exhaust valves.
 
Measured cold or hot?

Charlie Yapp thinks I should try .012" intake, .015" exhaust, measured cold.
 
Well, with less intake lash, you get less valve lift. Granted it is marginal but with 1½:1 rocker arms, it does amount to something. This also affects the duration too. The biggest thing you are after is to make sure the valve has adequate time in the 'seated' position to dissipate its heat into the head to keep warpage at bay. Outside of that, excessive lash just wastes energy and creates a noise. Any idea whose camshaft you are using?
 
Well, let me take a stab at this.... and compare it to the mechanical brake system of the Model-A. If a brake rod has wear in a clevis pin (i.e.: lash) we must depress the brake pedal a tad to tighten up the clearance before we see the brake shoes begin to move. The same applies with valve adjustment. If the peak lift of the cam lobe were .300", then with .000" lash the gross lift at the valve would be .450" (providing it has 1.5 rockers). If the the lash were set to 50 thousands clearance, then depending on the rocker arm configuration, you would only see (at max) .400" lift of the valve because the cam lifter must rise an addition .050" before the pushrod makes contact with the rocker arm and it can start pushing the valve open. I hope I have worded this to make sense.

.
 
BRENT in 10-uh-C said:
Well, with less intake lash, you get less valve lift. Granted it is marginal but with 1½:1 rocker arms, it does amount to something. This also affects the duration too. The biggest thing you are after is to make sure the valve has adequate time in the 'seated' position to dissipate its heat into the head to keep warpage at bay. Outside of that, excessive lash just wastes energy and creates a noise. Any idea whose camshaft you are using?
Click to expand...

The third word..........less is more.......no?:confused:
 
Valve clearance depends on the cam being used. Cragars and Denver Millers had 1.25:1 rocker arm ratios. Steve Serr's has 1.5:1. If using a stock B cam, multiply the B settings by 1.25 and set the valve lash at that. The original Cragars used 1928 style Buick rocker arms.
 
Mr. Brierley:

Please pardon my ignorance, but I don't have the stock B setting either. Could you please provide the lash I should have on my Cragar using the stock B cam?

Just for a newbie, be kind: :rolleyes:

COLD: .xxx" intake, .xxx" exhaust
HOT: .xxx: intake, .xxx" exhaust

Thanks,

Mike Green
 
I didn't put in any numbers because it seems everybody and his second cousin sets them differently. I recommend .012" on the intakes and .014" on the exhausts for the B cam. On an OHV conversion you must be aware of the rocker arm ratio, and if it has many miles on it, the rocker arms can be worn and make it difficult to get an accurate reading. BTW, nice talking with you on the phone the other day!
 
Jim Brierley said:
I didn't put in any numbers because it seems everybody and his second cousin sets them differently. I recommend .012" on the intakes and .014" on the exhausts for the B cam. On an OHV conversion you must be aware of the rocker arm ratio, and if it has many miles on it, the rocker arms can be worn and make it difficult to get an accurate reading. BTW, nice talking with you on the phone the other day!
Click to expand...

So for the record, if anyone else out there needs to know, taking into account the 1.25 to 1 rocker arm ratio for a vintage Cragar OHV, lash clearance using a stock B camshaft are as follows:

COLD: .015" intake, .018" exhaust

NOW....after getting that bit of trivia cleared up.....back to reality! Turns out that my valves have beaten their way into the Cragar seats thus causing the valve stems to migrate into the rocker arm causing a cupping on the rocker to valve stem surface, so valid lash measurements go out the window! :p

Looks like a valve job is in order :(
 
Take a compression test first, the valves may be OK. If compression is good, just remove the rocker arm assembly and have the rockers re-faced. This should be done on a valve machine with a radius put on them.
 
Compression at 100 to 102 psi on all four cylinders. After loosening the 3 valves I tightened previously (putting it back the way it was before I messed with it) the engine is running great, just a little knocking.
 
mngreen said:
Compression at 100 to 102 psi on all four cylinders. After loosening the 3 valves I tightened previously (putting it back the way it was before I messed with it) the engine is running great, just a little knocking.
Click to expand...

valve noise, at lease you know they are closing. :D
 
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