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Loaded valve train vs non loaded

General engine tech -- Drag Racing to Circle Track

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Steve.k
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Loaded valve train vs non loaded

Post by Steve.k » Mon May 18, 2020 10:21 am

How much do you guys see loaded valve train in terms of lift losses as compared to non. Say with checker springs. Is .020 common?

Walter R. Malik
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Re: Loaded valve train vs non loaded

Post by Walter R. Malik » Mon May 18, 2020 11:45 am

Steve.k wrote:
Mon May 18, 2020 10:21 am
How much do you guys see loaded valve train in terms of lift losses as compared to non. Say with checker springs. Is .020 common?
Sometimes, more... depends a lot on the compliance of THAT particular valve train.
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Re: Loaded valve train vs non loaded

Post by tuffxf » Mon May 18, 2020 11:50 am

Same answer as Walter,
Just remember any deflection between checking springs and the real deal will come back when the push rod pole vaults back to being straight in a running engine.
What have you found with the oil pressure deal Steve?
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Re: Loaded valve train vs non loaded

Post by Steve.k » Mon May 18, 2020 11:56 am

Nothing yet. Going to dive into bottom end again today. Im checking my cam lift today. The cam originally cut for 1.8 rockers. Net lift should be .780. Im getting.743 to .733 on some with 1.73 rockers and lash of .012. Cold. Just checking lobe lift. Some of you mentioned before that my cam was a little light to kick over the 800hp. I apologize in advance for not listening. I get mule headed you know. Lol.

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Re: Loaded valve train vs non loaded

Post by tuffxf » Mon May 18, 2020 1:32 pm

How are you checking lift, with checking springs or real springs?
Geometry will play a part as well
What sort of cam numbers do you have, What numbers at 200 thou ? What lobe lift?
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Re: Loaded valve train vs non loaded

Post by Steve.k » Mon May 18, 2020 3:24 pm

I checked both ways. With no load was close to .760. No lash with checker springs. The cam is .435 lobe lift and 266 -272@.050. Just pulled some intake pushrods. They are touching. I took a lot of material from holes. Not enough i guess. That explains a lot.

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Re: Loaded valve train vs non loaded

Post by tuffxf » Mon May 18, 2020 3:38 pm

How much duration at 200 thou Steve?
That will give a better indication of what sort of lobe you have
Not unusual for a push rod to have a little rub what pushrods and how much open pressure?
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Re: Loaded valve train vs non loaded

Post by PackardV8 » Mon May 18, 2020 3:43 pm

Steve.k wrote:
Mon May 18, 2020 10:21 am
How much do you guys see loaded valve train in terms of lift losses as compared to non. Say with checker springs. Is .020 common?
Sort of a 'how high is up?" question. As mentioned, it depends.

Valve spring seat and open pressure
Cam lobe lift and intensity
Pushrod stiffness, length, diameter
Rocker arm stiffness
Stud diameter or shaft rocker?
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Re: Loaded valve train vs non loaded

Post by DCal » Mon May 18, 2020 4:30 pm

Way back in my day we thought that an .080 wall pushrod was the way to go but of course we know better now. The difference between a light checking spring and the actual running spring could often be an additional .025-.030 piston to valve clearance and in the case of one S/S hemi it was .060 additional clearance.

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Re: Loaded valve train vs non loaded

Post by Walter R. Malik » Tue May 19, 2020 9:43 am

tuffxf wrote:
Mon May 18, 2020 3:38 pm

Not unusual for a push rod to have a little rub what pushrods and how much open pressure?
Cheers
Exactly ... as long as there is clearance when it is at rest. Touching slightly while running and oscillating can actually be a good thing to dampen some harmonics.
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Re: Loaded valve train vs non loaded

Post by Steve.k » Wed May 20, 2020 3:50 pm

3/8 pushrods .083 on recommendation of mfg. 729 lbs open.
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tuffxf
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Re: Loaded valve train vs non loaded

Post by tuffxf » Wed May 20, 2020 4:22 pm

Gday Steve,
Minimum I would have would be a quality 3/8 in .135 wall, preferably 7/16 in .135wall
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Re: Loaded valve train vs non loaded

Post by Steve.k » Wed May 20, 2020 5:24 pm

Why do the pushrod guys recommend you less if more is better. Thats what i wanna know.

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Re: Loaded valve train vs non loaded

Post by ClassAct » Wed May 20, 2020 5:34 pm

Steve.k wrote:
Wed May 20, 2020 5:24 pm
Why do the pushrod guys recommend you less if more is better. Thats what i wanna know.
They don’t want you to think they make weak pushrods. You can’t get a pushrod too big. Ever.

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Re: Loaded valve train vs non loaded

Post by tuffxf » Wed May 20, 2020 5:37 pm

G,day Steve,
Good question, imo that pushrod is only any good for a mild flat tappet application, 400 lbs or so over the nose,
Cheers

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