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Old 02-12-2013, 06:24 PM
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tbi 350 questions on pushrod lengths

I have a tbi 350 I am building with .040 bore kieth black flat top pistons with valve reliefs stock 5.7 rods trued the block deck vortec 906 heads rv hyd non roller rv cam my question is with the setup I described with rocker arm and pushrods do I use because the vortec push rods are shorter than the tbi pushrods and I'm using flat hyd lifters that match the cam their not roller ...any suggestions will be appriciated

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Old 02-12-2013, 07:52 PM
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I edited the thread title

Please dont use "help" as a thread title. Place some information in the thread title to help the members know what you need help on.
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Old 02-12-2013, 08:10 PM
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Thank u sir I'm still trying to figure the forum out I appreciate your help
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Old 02-13-2013, 12:56 PM
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Quote:
Originally Posted by Birdog 101 View Post
I have a tbi 350 I am building with .040 bore kieth black flat top pistons with valve reliefs stock 5.7 rods trued the block deck vortec 906 heads rv hyd non roller rv cam my question is with the setup I described with rocker arm and pushrods do I use because the vortec push rods are shorter than the tbi pushrods and I'm using flat hyd lifters that match the cam their not roller ...any suggestions will be appriciated
The L31 head uses a self guiding rocker, the head has no factory pushrod guide which used to be part of the pass through holes on the head for the push rods. So the choice of rocker is either stay with the self-guided types (whether the factory sliding tip with the ball and socket fulcrum, aftermarket with roller tip still using the ball and socket fulcrum or the roller tip with a roller trunion as the fulcrum) or go with the older design un-guided rocker.

You can go to un-guided rockers of any of the previous stated styles but since the heads have no cast in pushrod guides they must be modified to accept the available "hot rod" sheetmetal guide. This requires milling the existing cast stud bosses down, tapping their stud holes to accept hex style screw in studs. The hex is used to position and secure the guide plates aqs well as position and support the rocker. This requires that you use compatible push rods that will say they are "hardened" or are "heat treated" in their description. This is necessary to provide a wearing surface where the pushrod passes through the guide plate. Note that all studs use a 7/16ths coarse thread base into the head but they come with either a 3/8ths or 7/16ths fine thread upper that passes through the rocker. The upper threaded diameter of the stud and the rocker's pass through hole of the ball or trunion MUST match each other. This is also true of the press in studs should you retain them, they are 3/8ths and MUST use rockers with 3/8ths pass through holes in the ball or trunion.

In either case of self-guiding or not self-guiding rockers the pushrod will be the longer version used with flat tappets. The flat tappet style lifter is shorter than the OEM hydraulic roller tappet type lifter of the L31 engine so the older, longer length push rods need to be used with the flat tappet lifter whether they are solids or hydraulics. If you change to aftermarket rockers especially if the ratio changes from OEM 1.5 to 1.6 or ball and socket change to the roller fulcrum, and/or you change to guide-plates with screw in studs, and/or you go to a more aggressive lift cam then you really need to check the alignment of the rocker's contact patch on the valve stems to select the lenght of push rod that keeps the contact patch properly aligned. This requires the purchase and use of an adjustable length test push rod to determine the proper push rod length before you purchase any push rods. They end up being one of the last parts you procure before final assembly of the engine.

One other caution, do not mix self-guiding rockers with sheetmetal push rod guides. One or the other, never both. If both are used there is a risk of binding the moving parts of the valve train.

Bogie

Last edited by oldbogie; 02-13-2013 at 01:04 PM.
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Old 02-13-2013, 04:35 PM
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I think I under stand what u are saying so since I am pretty much stock on the came I can use the standerd tbi set up for the now are the rockers the same in tbi vs vortec.
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Old 02-13-2013, 05:24 PM
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Quote:
Originally Posted by Birdog 101 View Post
I think I under stand what u are saying so since I am pretty much stock on the came I can use the standerd tbi set up for the now are the rockers the same in tbi vs vortec.
The TBI Swirl Port engines and the L31 Vortec engines use the same factory rocker arm which is:
- self-guiding having a ratio of 1.5.
- both make sliding contact at the valve stem
- Both use a ball and socket fulcrum on a 3/8ths stud
- for both, the stud is pressed into the head

The push rods of the TBI Swirl Port engine can be different lengths depending on the cam type used in the block. Some TBI engines came with flat tappet cams, some came with roller tappet cams. No 350 Vortec came with a flat tappet cam, however, some 1996 350 Vortecs came with Swirl Port heads and TBI but all 350 Vortec engines use the same short push rod.

- flat tappet cams use the older and longer 7.8 inch push rod
- factory roller tappet cams use the 7.2 inch push rod
- aftermarket roller tappet cams need to be measured they will most likely be something other than 7.2 inches
- all factory style push rods will have a spherical end with an oil hole for each end of the rod. The sphere may be a formed part of the push rod or it may be a welded on ball

Bogie
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Old 02-13-2013, 08:29 PM
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Thank u so much for your help I greatly appreciate all the info ..I think I'm ready to start measuring and adjusting....thanks again for the help
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