Vortec L31 cylinder head
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* Head bolts (required only if the original head bolts are either missing or unusable for some reason) | * Head bolts (required only if the original head bolts are either missing or unusable for some reason) | ||
* Head gaskets ([http://www.crankshaftcoalition.com/wiki/Head_gasket#Re-using_head_gaskets generally required] any time heads are re-installed) | * Head gaskets ([http://www.crankshaftcoalition.com/wiki/Head_gasket#Re-using_head_gaskets generally required] any time heads are re-installed) | ||
| − | * Grinding down valve guides or the use of different retainers and springs, or ghetto grinding the stock retainers, etc., to work with a camshaft having somewhere around 0. | + | * Grinding down valve guides or the use of different retainers and springs, or ghetto grinding the stock retainers, etc., to work with a camshaft having somewhere around 0.450" or more valve lift. |
{{Note1}} The clearance between the retainer and the seal has to be checked during the engine mock up phase of the build to determine exactly what the clearance is with the cam, retainer, valve stem seal, valve locks and rocker arm/rocker arm ratio used. | {{Note1}} The clearance between the retainer and the seal has to be checked during the engine mock up phase of the build to determine exactly what the clearance is with the cam, retainer, valve stem seal, valve locks and rocker arm/rocker arm ratio used. | ||
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Vortec heads come equipped with valves having a 30 degree back cut to help flow. Unlike previous SBC valves, Vortec valves have just one groove for the keepers instead of two grooves (earlier valves had one groove for the keepers, the second (lower) groove was for the oil control O-ring); Vortec heads use a positive-type valve stem oil seal and do not use the tin oil shield seen for years on SBC heads, nor do Vortec heads use exhaust valve rotators. | Vortec heads come equipped with valves having a 30 degree back cut to help flow. Unlike previous SBC valves, Vortec valves have just one groove for the keepers instead of two grooves (earlier valves had one groove for the keepers, the second (lower) groove was for the oil control O-ring); Vortec heads use a positive-type valve stem oil seal and do not use the tin oil shield seen for years on SBC heads, nor do Vortec heads use exhaust valve rotators. | ||
| − | ==Valve springs== | + | ==Valve springs and retainers== |
[[File:Vortec beehive.jpg|thumb|left|300px|Straight wound spring, Left; Beehive spring, right]] | [[File:Vortec beehive.jpg|thumb|left|300px|Straight wound spring, Left; Beehive spring, right]] | ||
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The stock Vortec valve springs are single wound without a damper and are 1.250" diameter. The damping is done by the spring ID being a close fit to the 0.900" guide boss OD; this damps the spring without the added cost of an inner flat wound damper seen on the Gen 1 SBC throughout its production. | The stock Vortec valve springs are single wound without a damper and are 1.250" diameter. The damping is done by the spring ID being a close fit to the 0.900" guide boss OD; this damps the spring without the added cost of an inner flat wound damper seen on the Gen 1 SBC throughout its production. | ||
| − | The stock springs are not suited for high performance use or for lifts above about 0.420" using stock retainers. There are several replacements for the stock springs, among the best is the beehive spring and retainer combination from Comp Cams, originally designed for the | + | The stock springs are not suited for high performance use or for lifts above about 0.420" using stock retainers. There are several replacements for the stock springs, among the best is the beehive spring and retainer combination from Comp Cams, originally designed for the LS engine series. There are two Comp Cams part numbers for the different spring rates: |
*'''[http://www.compcams.com/WhatsNew/NewsDetails.aspx?ListHistoryID=164462240 26915]'''- 105 pounds at 1.8" installed height; 293 pounds at 1.2" (according to Competition Products catalog info); spring rate 313 lbs./in (according to Summit Racing catalog info) | *'''[http://www.compcams.com/WhatsNew/NewsDetails.aspx?ListHistoryID=164462240 26915]'''- 105 pounds at 1.8" installed height; 293 pounds at 1.2" (according to Competition Products catalog info); spring rate 313 lbs./in (according to Summit Racing catalog info) | ||
*'''[http://www.compcams.com/WhatsNew/NewsDetails.aspx?ListHistoryID=1166393320 26918]'''- 125 pounds at 1.8" installed height; 367 pounds at 1.15" | *'''[http://www.compcams.com/WhatsNew/NewsDetails.aspx?ListHistoryID=1166393320 26918]'''- 125 pounds at 1.8" installed height; 367 pounds at 1.15" | ||
| − | + | Either of the beehive springs above need to be installed using the correct retainer for a Vortec valve, like Comp Cams p/n 787 (steel) or p/n 788 (titanium), NOT a retainer originally for the LSx engines; the LSx engines have 8mm metric valve stems. Also note the specs are with an installed height of 1.8". The image below shows the difference in installed height when using different retainers: | |
| − | Either of | + | |
[[File:787-LEFT; 774-RIGHT (Gen III).gif|frame|left|300px|Retainer p/n 787 left; p/n 774 right]] | [[File:787-LEFT; 774-RIGHT (Gen III).gif|frame|left|300px|Retainer p/n 787 left; p/n 774 right]] | ||
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| − | + | On the other end of the cost scale is the use of inexpensive "Z-28/LT-1" springs (or any spring with a ~1.70" installed height and a 1.25" OD) with the damper removed along with the stock retainers that have had some of the bottom ground off to provide more clearance (sometimes referred to as the "ghetto grind"). This will allow more lift (in the area of 0.500") without changing the guide boss height or diameter. | |
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| + | Chevrolet recommends using the Crane Cam 10309-1 drop-in valve spring/retainer kit which is good for .550” lift (this allows about 0.025" between the retainer and seal) with no machining. | ||
| + | When retaining the factory boss and seals, be sure the valve seals are driven on all the way. You need to check that they are before installing this kit. Use a 3/8” drive 1/2” socket and a soft mallet to gently drive the seals fully home. | ||
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| + | ==Spring seat== | ||
| + | Use reduced hex head bolts or 12 point fasteners to give more clearance if a larger seat like for a 1.44" OD spring is used. | ||
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| + | ==Valve guide boss== | ||
| + | [[File:900 guide boss1.jpg|thumb|450px|left|Stock Vortec boss is 0.900"OD]] | ||
| + | For performance use, often the guide boss will be shortened to allow more lift without retainer to seal clearance problems. Along with that, the guide boss OD can be machined down from 0.900" to a smaller diameter so aftermarket springs (double or with dampers) can be used. At the same time the boss can be machined to use a commonly available positive seal like 0.530". | ||
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| + | ===Valve guide boss modification=== | ||
| + | [[File:VORTEC GUIDE BOSS MODIFIED.jpg|thumb|250px|Before (right) and after]] | ||
| + | In order to fit one of the commonly available smaller diameter positive type valve stem oil seals, the tops of the guide boss needs to be turned down. To fit springs with a smaller ID like double or those with a damper, the guide boss needs to be modified by shortening and decreasing the OD of the boss. | ||
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| + | ===Tooling=== | ||
| + | [[File:Tool.jpg|thumb|450px|Comp tooling]] | ||
| + | Crane and Comp Cams sell cutters to machine the guide boss diameter using a hand drill. The arbor and cutters should be used with valve guides that are in good condition because the arbor uses the guide to locate the cutters. | ||
| + | Some Comp Cams part numbers: | ||
| + | *4718- spring seat cutter, 1.440" OD | ||
| + | *4726- valve guide cutter, 0.530" OD | ||
| + | *4732- 11/32" arbor for cutting tools | ||
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| + | ;From an article by editor Jeff Smith: | ||
| + | <blockquote>The Comp Cams cutter increases the spring-seat diameter while simultaneously reducing the outside diameter (od) of the guide boss. The Crane tool also cuts the valve-guide-seal diameter at the same time. Comp sells a separate tool that cuts a new guide seal and reduces the guide height to create additional retainer-to-seal clearance. Both cutters machine the top of the guide down to a 0.530-inch diameter, which is the standard size for positive-type aftermarket seals. This requires purchasing new valve-guide seals, since the factory uses a 0.560-inch guide to locate the seals. Another way to go is to have a machine shop cut the guide boss diameter to around 0.760 inch and reduce the seal height and use either the Crane H-11 tool steel spring (PN 99846) or the Comp spring (PN 981). | ||
| + | </blockquote> | ||
==Rocker arm studs== | ==Rocker arm studs== | ||
| − | Production L31 Vortec heads come with pressed in studs. For high performance and/or solid lifter applications, screw in studs are highly recommended. The pressed studs can be pinned, but this is a stop-gap measure that should be done only in cases where the spring pressures/engine RPM/lobe intensity will not be excessive and the budget is limited. Otherwise use ARP | + | Production L31 Vortec heads come with pressed in 3/8" studs. For high performance and/or solid lifter applications, screw in studs are highly recommended. The pressed studs can be pinned, but this is a stop-gap measure that should be done only in cases where the spring pressures/engine RPM/lobe intensity will not be excessive and/or the budget is limited. Otherwise use ARP screw in studs or their equivalent. While home builders have successfully installed screw in studs without specialized equipment, unless the builder is well versed in doing this type of work, i.e. drilling straight, correctly located holes and tapping them, this is better left to a professional machinist/machine shop. At the least, a fixture to guide the drill bit and tap should be used. |
| − | Guide plates can also be installed at this time if desired. If not, non shouldered studs can be used instead of studs having shoulders and a hex for tightening (this type of stud is tightened by "double nutting"). | + | Guide plates can also be installed at this time if desired. Consider the Isky adjustable guide plates. If not using guide plates, non shouldered studs can be used instead of studs having shoulders and a hex for tightening (this type of stud is tightened by "double nutting"). <br> |
| + | {{Note1}}If using guide plates, non self aligning rockers need to be used. If guide plates are not used, self aligning rockers MUST be used. | ||
| − | ==Exhaust seats== | + | ==Exhaust valve seats== |
Not long after the L31 Vortec head was introduced, there was much made of the supposed difference in flow between the Vortec heads that came with the hardened exhaust seat inserts as opposed to the heads that had induction hardened seats. This was largely due to an incorrect, though oft-repeated statement made by a car magazine that said in essence the c/n 906 head was to be avoided because of the exhaust seat insert being vastly inferior to the heads with induction hardened exhaust seats. | Not long after the L31 Vortec head was introduced, there was much made of the supposed difference in flow between the Vortec heads that came with the hardened exhaust seat inserts as opposed to the heads that had induction hardened seats. This was largely due to an incorrect, though oft-repeated statement made by a car magazine that said in essence the c/n 906 head was to be avoided because of the exhaust seat insert being vastly inferior to the heads with induction hardened exhaust seats. | ||
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|[[File:Hard insert seat vortec 906.jpg|thumb|center|400px|Hardened insert Vortec exhaust seat]] | |[[File:Hard insert seat vortec 906.jpg|thumb|center|400px|Hardened insert Vortec exhaust seat]] | ||
| − | |[[File:Induction hardened seat vortec.jpg|thumb|center|400px|Induction hardened Vortec exhaust seat, note the | + | |[[File:Induction hardened seat vortec.jpg|thumb|center|400px|Induction hardened Vortec exhaust seat, note the discolored area around seat]] |
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==Pushrod guide holes== | ==Pushrod guide holes== | ||
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