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Tractor Pulling Discussion Forum

Head shaving and rocker ratio/relationship

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Clarence Bareni

03-01-2005 15:19:36




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I'm not the smartest individual in the world, but I have a question.
When shaving the head 50 or 100thds, or where ever the head happens to end up over years, the distance left changes the factory relationship between push tube length and rocker arm movement, or the originial starting point !
Will this change lessen the amount of valve opening, from factory spec to a new lessor desired spec, or less valve movement.
100thds going thru a ratio starts to add up

any input
thanks bud barenie

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Earl S.

03-01-2005 18:07:56




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 Re: Head shaving and rocker ratio/relationship in reply to Clarence Barenie, 03-01-2005 15:19:36  
Bud, There has been some good tips here. But if you will do a google search for (Rocker Arm Geometry) you will find some high performance info that applies to stock engine,and modified tractor engines.One of the other things that is overlooked is pushrods. When you increase rocker ratio and in some cases spring pressures (or both) these old tractor pushrods are long and very weak. So be aware of pushrod flexing, not bending. Contact people like Smith Brothers Pushrods They may have a web site if not here is a old phone number 800 367-1533.Know your spring pressures and don't be afraid to invest in some custom made pushrods .You will find it is money well spent.Are you degreeing your cams? Are you checking more than just #1 cyl? You should. I hope this helps. email if you need help.Earl In Illinois

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Clarence Barenie

03-01-2005 18:28:27




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 EARL S DO YOU REMEMBER ME in reply to Earl S., 03-01-2005 18:07:56  
SEPTEMBER 2001

AFTER MY FIRST PULL, I WAS ASKING ABOUT RIM WIDTH,
YOU TOLD ME I NEVER LISTENED TO THE BOARD, PAY ATTENTION TO WHAT THE OTHER GUY'S ARE DOING , AND DON'T OVER DO WHAT THE MFG WAS DOING !


i have not forgot



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Butch(OH)

03-01-2005 17:01:46




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 Re: Head shaving and rocker ratio/relationship in reply to Clarence Barenie, 03-01-2005 15:19:36  
Usualy just a lurker here but saying it makes no differance is not correct, yes it does affect rocker geometry which in turn does affect both total lift and timing. Is it correct and alright to run it that way? depends on your definition of those words. We are not talking large gains to be had unless it was way off to start with. If you wish to assume it was correct before you shaved the head shim the rocker shaft up the same amount you take off the head.Otherwise getting the rocker geometry right is a bit detailed in your case because you first must make sure the rocker ratios are right, if they have been reground thats a big if. On race engines with roller rockers we strived to achieve a contact point that was centered on the valve at 50% lift. Your engine may have not had that condition when new. All this may be rocket science for your application but I always like free, except for my labor, HP increses. Your question is a good one that never even crossed the minds of most of the motorheads who came into my shop wanting as much as could be taken off their heads. Your smarter than you give yourself credit for.

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LW

03-01-2005 19:07:52




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 Re: Head shaving and rocker ratio/relationship in reply to Butch(OH), 03-01-2005 17:01:46  
Well you gave him the most important information right there at 50% lift the center of the rocker tip should center the valve, the tip should also stay in a .060 to .080 window on the valve center through its travel. rocker stand height is also a big player I have yet to see a tractor engine that the valvetrain geometry was correct from the factory.



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Carney

03-01-2005 17:52:59




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 Re: Head shaving and rocker ratio/relationship in reply to Butch(OH), 03-01-2005 17:01:46  
Finaly someone who understands this. Most people just argue and say it makes no difference. What about making the rocker posts correct height so that the rocker arm contact points are perpindicular ( or 90 deg.) to the valve stem at half valve lift as well as centered on the valve stem for max lift and less wear and friction. As the rocker rotates through its arc the vertical travel is lessoned the further it mooves off from perpindicular to the valve.

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CLARENCE BARENIE

03-01-2005 19:51:40




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 Re: Head shaving and rocker ratio/relationship in reply to Carney, 03-01-2005 17:52:59  
AFTER ALL THINGS ARE SAID AN DONE, AFTER A VISUAL INSPECTION OF ROCKER ON STEM PLACEMENT, THEN YOU ADJUST!
QUESTION
WHAT IS 50% LIFT,(I KNOW WHAT THAT MEANS) BUT HOW IS THIS ACHIEVED !!


I THINK I GOT LUCKY TONIGHT !

THANK'S GUYS



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Butch(OH)

03-01-2005 21:14:24




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 Re: Head shaving and rocker ratio/relationship in reply to CLARENCE BARENIE, 03-01-2005 19:51:40  
Install your head with an old gasket of the same thickness of your new one or a properly torqued new gasket. Install the rockers and push rods for one cylinder and set lash per book cold setting. if only hot setting is given rule of thumb is add .002 to intake lash and .003 to exhaust. Set up an dial indicator and zero it with valve all the way closed. Then run the cam through a complete cycle noting the total lift at the valve. While you have your calculator and paper out it is always fun to check it against specs shipped with a cam. If your grinder gives lobe specs multiply times rocker ratio to get theoretical lift at valve. Dont be suprized when it comes up short. Things bend, usualy total lift is listed at zero lash, and grinders lie. Back to your question, divide the total lift at the valve by 2 and that is 50% lift. Then turn the crank until tha reading is reached on the indicator. You might as well eyeball it the first time. We used the same product used to set up hypoid gears, prussion (spelling?) bluing on the contact area of the rocker. The amount used is critical to good readings and you will have to cut and try. When you have it right you crank the lift up half way and then back it up to fully closed. loosen rocker carefully and look to see where the mark stops. After I posted (smarted off?) above it came to me that where the adjustments are made for lash has a big effect on how much shaving the head affects the rocker geometry. On the Chebbys and others wher the lash is set with a nut on the center stud it has a tremendous effect. On a shaft mounted rocker where the adjustment is a screw on the pushrod end of the rocker the effect is less but none the less there. This is because the adjusting the screw affects the true ratio of the rocker arm. If you want to get real scientific and have everything the correct and as good as it can get your rockers center of pivot to center of stem contact needs to be exactly the same as the distance from the center of the rocker shaft to the center of the valve stem. The height of the rocker pivot needs to be such that at 50% lift a line drawn from the top of the valve, through the centerline of the rocker shaft is exactly at 90 degrees to the push rods. If all this is done your rocker geometry will be as good as it can be. You then adjust the pushrod length to get correct lash. Confused yet? LOL good luck with it.

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LW

03-01-2005 20:46:39




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 Re: Head shaving and rocker ratio/relationship in reply to CLARENCE BARENIE, 03-01-2005 19:51:40  
Put a dial indicator on the valve with your lash set where you will run take the max lift divide by 2 roll it through to that # and that will be the 50% mark.



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Butch(OH)

03-01-2005 21:15:42




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 Re: Head shaving and rocker ratio/relationship in reply to LW, 03-01-2005 20:46:39  
sorry LW, did it again, you guys type faster than me.



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Carney

03-01-2005 16:52:09




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 Re: Head shaving and rocker ratio/relationship in reply to Clarence Barenie, 03-01-2005 15:19:36  
Adjusting the rocker arm screw will take up that adjustment but not exactly. The distance from the center of the rocker arm pivot to pushrod top is lowered when the head is shaved. So by adjusting the screw the rocker to compensate it will moove at a slightly different angle than it did, you will lose a slight amount of total valve lift. This can be corrected with shorter push rods.



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Butch(OH)

03-01-2005 17:02:54




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 Re: Head shaving and rocker ratio/relationship in reply to Carney, 03-01-2005 16:52:09  
sorry, you posted while I was typing



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Mike Aylward

03-01-2005 15:25:32




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 Re: Head shaving and rocker ratio/relationship in reply to Clarence Barenie, 03-01-2005 15:19:36  
Bud, you will take up this amount in the valve adjustment. Your valve will open the same amount as it did, providing you can compensate for this lost height. What you are doing by shaving the head will, in effect, make your push rods "longer". You will have to adjust your valve clearance to compensate for this fact by backing out your adjusters. Just be sure that your rockers can compensate for this. Hope this helps. Mike

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clarence barenie

03-01-2005 15:43:51




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 Re: Head shaving and rocker ratio/relationship in reply to Mike Aylward, 03-01-2005 15:25:32  
mike
For got about that, I KNOW, just trying to maintain what the old engineer's started with.

At one time i thought i was smarter than them !


thanks mike !



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42Farmall

03-01-2005 16:59:02




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 Re: Head shaving and rocker ratio/relationship in reply to clarence barenie, 03-01-2005 15:43:51  
If you have your cam reground, it will "shorten" your pushrods!



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Clarence Barenie

03-01-2005 17:10:23




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 Re: Head shaving and rocker ratio/relationship in reply to 42Farmall, 03-01-2005 16:59:02  
this is starting to get complex!
I have an oem start dimension, first the head is shaved, than i change cam profile!
In the old days, with a bad head an a copper head gasket, I have seen where the rocker impacts the valve stem, and how it could pop a valve, so IHAVE TO DRAW PICTURE'S OF THE PROBLEM.
So this maeans a cam job could be a great thing, as long as you trail the math !

And then we add in the years of distructing, or cleaning up the lifters.

Gentlemen !!!!
I am learning, Thank you !

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Butch(OH)

03-01-2005 17:54:41




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 Re: Head shaving and rocker ratio/relationship in reply to Clarence Barenie, 03-01-2005 17:10:23  
A reground, usualy smaller base circle, cam might just cancell out the material you took off the head and everything will be peachykeen with the rockers. Just remember the things I bring up are fine points but if enough things are changed it can become a problem, in severe cases like you mention it can snap valvestems. Now I am going to jump off of here before some regular comes on here and tells me he's been grinding a foot of his heads for 37.8 years with no problem, lol. Knowing you need to at least eyeball the rockers means you have most of this figured out. If you find a problem usualy shimming the rockershaft of shortening the pushrods is the easiest best cures. Good luck

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clarence barenie

03-01-2005 18:37:01




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 Re: Head shaving and rocker ratio/relationship in reply to Butch(OH), 03-01-2005 17:54:41  
BUTCH (OH)
going vertical was what i had in mind !
and then a cam grind !

and then several postings with great opinion's

just tractor pulling at 1750rpm's but it all happens at really low rpm's, the air is gone , mometium is dropping as well as vaccuum !

thank you sir !!
hope we can pull your chain again !



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