Pontiac V8 engine
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===Studs and guideplates=== | ===Studs and guideplates=== | ||
====The bottleneck stud==== | ====The bottleneck stud==== | ||
| − | [[File:Pont stk stud.jpg|thumb|500px|Stock type Pontiac bottleneck stud]]Pontiac heads like the 6X and practically all other heads likely to be used in a performance-orientated build | + | [[File:Pont stk stud.jpg|thumb|500px|Stock type Pontiac bottleneck stud]]Pontiac heads like the 6X and practically all other production Pontiac heads likely to be used in a performance-orientated build originally had screw in ''bottleneck'' studs and steel guideplates. There are some exceptions to this, like the Ram Air IV and "Ram Air II" round port heads, which used a straight 7/16" stud with an adjuster nut/lock nut. |
| − | The usual D-port | + | The usual stock D-port arrangement is a "net lash" set-up. Because the rocker stud is 7/16" OD at the bottom, the rocker arm and pivot ball is also made to fit a 7/16" OD stud, so the stock rocker arm and ball can be reused with a straight 7/16" stud. The '''top''' of the bottleneck stud is threaded for a 3/8-24 nut, to be torqued to 15 ft/lb to retain the rocker arm. |
<br style="clear:both"/> | <br style="clear:both"/> | ||
| − | + | The stock Pontiac net lash lifter preload adjustment may be adversely affected by any of the following: | |
| − | *Block deck height | + | *Block deck height change |
| − | *Head deck height | + | *Head deck height change |
| − | *Head stud boss height | + | *Head stud boss height change |
*Rocker arm brand/design | *Rocker arm brand/design | ||
*Cam base circle size | *Cam base circle size | ||
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*Valve stem length | *Valve stem length | ||
*Head gasket thickness | *Head gasket thickness | ||
| − | So if any of the above changes are made, the stock Pontiac bottleneck stud/net lash set-up may no longer preload the lifter properly. Unless the studs are changed to allow for an adjustable valve train, different length push rods may be needed to set the lifter preload. For that reason it is always advisable to use straight studs to replace the bottleneck studs. A good replacement is ARP p/n 190-4003 w/hex nuts, or p/n 190-4203 w/12-point nuts. Be aware that there can be clearance issues between the polyloc and valve cover if polylocs are used. Check the clearances carefully; you might be able to use a shorter polyloc. If possible (and the valve cover are so equipped) keep the oil drippers. The oil drippers are a separate piece from the valve covers on the RA II/IV engines. | + | So if any of the above changes are made, the stock Pontiac bottleneck stud/net lash set-up may no longer preload the lifter properly. Unless the studs are changed to allow for an adjustable valve train, different length push rods may be needed to set the lifter preload. For that reason it is always advisable to use straight studs to replace the bottleneck studs. A good replacement is ARP '''p/n 190-4003''' w/hex nuts, or p/n '''190-4203''' w/12-point nuts. Be aware that there can be clearance issues between the polyloc and valve cover if polylocs are used. Check the clearances carefully; you might be able to use a shorter polyloc. If possible (and the valve cover are so equipped) keep the oil drippers. The oil drippers are a separate piece from the valve covers on the RA II/IV engines. |
While it is not recommended, the bottleneck studs will sometimes work as an adjustable valve train if a stock SBC lock nut is used and the camshaft is very mild. But this does nothing for the inherently weaker design of the bottleneck stud. | While it is not recommended, the bottleneck studs will sometimes work as an adjustable valve train if a stock SBC lock nut is used and the camshaft is very mild. But this does nothing for the inherently weaker design of the bottleneck stud. | ||
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