Building Chevy LT1 engines
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==Overview== | ==Overview== | ||
Info on the inspection and rebuilding of the Chevy Gen II LT1 engine. | Info on the inspection and rebuilding of the Chevy Gen II LT1 engine. | ||
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| − | + | ==Vehicles that used the LT1== | |
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[[File:Lt1 chart1.gif]] | [[File:Lt1 chart1.gif]] | ||
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<Blockquote>Compared to the 1991 Chevy 350 L98 with TPI, the LT1 made 20 percent more horsepower, got better fuel mileage, and had a much broader torque band with 90 percent of its peak torque available from just over 1,000 rpm all the way up to nearly 6,000 rpm.<br><br> | <Blockquote>Compared to the 1991 Chevy 350 L98 with TPI, the LT1 made 20 percent more horsepower, got better fuel mileage, and had a much broader torque band with 90 percent of its peak torque available from just over 1,000 rpm all the way up to nearly 6,000 rpm.<br><br> | ||
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GM Powertrain accomplished all of this by reverse cooling the engine so they could bump the compression ratio up to 10.5 to 1, tweaking the airflow in and out of the engine, and using sophisticated electronic controls for both fuel and ignition. This combination gave the LT1 300 hp in 1992 and ultimately led to the 1996 LT4 that used better heads, more cam timing, roller rockers and sequential fuel injection to make 330 hp.<br><br> | GM Powertrain accomplished all of this by reverse cooling the engine so they could bump the compression ratio up to 10.5 to 1, tweaking the airflow in and out of the engine, and using sophisticated electronic controls for both fuel and ignition. This combination gave the LT1 300 hp in 1992 and ultimately led to the 1996 LT4 that used better heads, more cam timing, roller rockers and sequential fuel injection to make 330 hp.<br><br> | ||
Although the LT1 was only around for five years, there were two-bolt and four-bolt blocks, aluminum and cast iron heads, regular and H.O. cams that came with long and short dowels, and three different front covers. There was also the "Baby LT1," the 265 cid version that was the standard engine in the Caprice from 1994-‘96. With all that in mind, let’s take a look at this family of engines and see what goes where.<br><br> | Although the LT1 was only around for five years, there were two-bolt and four-bolt blocks, aluminum and cast iron heads, regular and H.O. cams that came with long and short dowels, and three different front covers. There was also the "Baby LT1," the 265 cid version that was the standard engine in the Caprice from 1994-‘96. With all that in mind, let’s take a look at this family of engines and see what goes where.<br><br> | ||
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'''BLOCKS'''<br> | '''BLOCKS'''<br> | ||
| + | [[File:Lt1 block.gif|right]] | ||
'''350''' – There are two blocks, one with two-bolt mains and one with four-bolt mains. They both have the same 10125327 casting number, so there’s no sure way to know which one you have until you get the pan off. However, if it came out of a Corvette, it should be a four-bolt block, and if it came out of anything else, it was supposed to be a two-bolt. GM used the two-bolt block for everything but the Corvette because it had plenty of strength and it weighed a little bit less.<br><br> | '''350''' – There are two blocks, one with two-bolt mains and one with four-bolt mains. They both have the same 10125327 casting number, so there’s no sure way to know which one you have until you get the pan off. However, if it came out of a Corvette, it should be a four-bolt block, and if it came out of anything else, it was supposed to be a two-bolt. GM used the two-bolt block for everything but the Corvette because it had plenty of strength and it weighed a little bit less.<br><br> | ||
'''265''' – There was only one block used for the 265 cid version of the LT1. It’s a 10168588 casting that had the numbers "4.3" cast on the side, too. It’s real easy to spot if the heads are off because of the small 3.74" bore.<br><br> | '''265''' – There was only one block used for the 265 cid version of the LT1. It’s a 10168588 casting that had the numbers "4.3" cast on the side, too. It’s real easy to spot if the heads are off because of the small 3.74" bore.<br><br> | ||
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The cam gear had to match the cam and the distributor drive, so there were two different gears used, depending on the year and the application.<br><br> | The cam gear had to match the cam and the distributor drive, so there were two different gears used, depending on the year and the application.<br><br> | ||
The original cam had a small, tapered hole in the center and a short dowel pin. It was used with the cam gear that had the small hole in the center with 16 splines in it. See the photo. It was connected to the distributor with a short drive shaft that was splined on both ends. The cam gear is a GM p/n 10128349. This combination was used from 1992-‘95 on the aluminum-headed motors.<br><br> | The original cam had a small, tapered hole in the center and a short dowel pin. It was used with the cam gear that had the small hole in the center with 16 splines in it. See the photo. It was connected to the distributor with a short drive shaft that was splined on both ends. The cam gear is a GM p/n 10128349. This combination was used from 1992-‘95 on the aluminum-headed motors.<br><br> | ||
| − | GM had some problems with the early distributor due to both carbon tracking and moisture, so a new sealed distributor with a vacuum port was introduced on the iron-headed 265s and 350s in 1994 and used on all LT1s in 1995. The new distributor was located with a pilot shaft and driven by a pin, so both the cam and the gear were changed. The cam had a large, deep hole in the center for the pilot shaft and a longer dowel pin to drive the distributor.<br><br> | + | [[File:Lt1 opti.gif|right]] |
| + | GM had some problems with the early Optispark distributor due to both carbon tracking and moisture, so a new sealed distributor with a vacuum port (red arrow, right) was introduced on the iron-headed 265s and 350s in 1994 and used on all LT1s in 1995. The new distributor was located with a pilot shaft and driven by a pin, so both the cam and the gear were changed. The cam had a large, deep hole in the center for the pilot shaft and a longer dowel pin to drive the distributor.<br><br> | ||
The cam gear had a bigger hole and it didn’t have the splines that were found in the early gear. The pilot shaft for the distributor extends through the hole in the cam gear and seats in the hole in the cam; the distributor is driven by the long dowel pin that sticks up through the cam gear. The cam gear is a GM p/n 10206039.<br><br> | The cam gear had a bigger hole and it didn’t have the splines that were found in the early gear. The pilot shaft for the distributor extends through the hole in the cam gear and seats in the hole in the cam; the distributor is driven by the long dowel pin that sticks up through the cam gear. The cam gear is a GM p/n 10206039.<br><br> | ||
'''FRONT COVERS'''<br> | '''FRONT COVERS'''<br> | ||
[[File:Lt1 fr cover.gif|right]] | [[File:Lt1 fr cover.gif|right]] | ||
| − | The front covers have been changed three times, once because of the changes that were made to the distributor and once due to OBD II. | + | The front covers have been changed three times, once because of the changes that were made to the distributor and once due to OBD II. The original cover had three holes, one for the crank, a second small hole (~0.70") for the water pump drive and a third one for the small drive shaft for the distributor. It’s casting number 10128289. See the photo.<br><br> |
| − | The original cover had three holes, one for the crank, a small hole ( | + | The second front cover still had the small hole for the water pump shaft, but it had a much larger hole (~2.63") that sealed on the outside of the distributor housing itself. It’s casting number 10214196.<br><br> |
| − | The second front cover still had the small hole for the water pump shaft, but it had a much larger hole ( | + | The second cover was modified again in 1996 to accommodate the crank position sensor that was located in the lower corner of the cover on the passenger side. This same cover was used for the few engines that were installed in 1997, too. It’s casting number 12550032.<br><br> |
| − | The second cover was modified again in 1996 to accommodate the crank position sensor that was located in the lower corner of the cover on the passenger side. This same cover was used for the few engines that were installed in 1997, too. It’s | + | |
'''HEADS'''<br> | '''HEADS'''<br> | ||
[[File:Lt1 heads2.gif|right]] | [[File:Lt1 heads2.gif|right]] | ||
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'''350 IRON HEADS''' – All of the full-size cars came with iron heads. They were 10125320 or 12554290 castings.<br><br> | '''350 IRON HEADS''' – All of the full-size cars came with iron heads. They were 10125320 or 12554290 castings.<br><br> | ||
'''265 IRON HEADS''' – The 265 had its own unique cast iron head with a 10208890 casting number. The chambers are smaller, so these heads cannot be interchanged with any of the 350 LT1 heads. See the photo.<br><br> | '''265 IRON HEADS''' – The 265 had its own unique cast iron head with a 10208890 casting number. The chambers are smaller, so these heads cannot be interchanged with any of the 350 LT1 heads. See the photo.<br><br> | ||
| − | That’s the story on the parts for the LT1. | + | That’s the story on the parts for the LT1. The chart at the top of the page under "'''''Vehicles that used the LT1'''''" shows how they all fit together year by year, but there are a few more things every rebuilder should know in order to avoid some possible problems.<br><br> |
'''HEAD GASKETS'''<br> | '''HEAD GASKETS'''<br> | ||
The 350 LT1 head gaskets are not interchangeable with regular 350 Chevy head gaskets because they have different water passages due to the reverse cooling.<br><br> | The 350 LT1 head gaskets are not interchangeable with regular 350 Chevy head gaskets because they have different water passages due to the reverse cooling.<br><br> | ||
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When the crank position sensor was added in 1996 for OBD II, the cutback area on the key was shortened so it stuck out far enough (about 0.100") beyond the face of the timing gear to index the notched disc that was used for the crank position sensor. See photo.<br><br> | When the crank position sensor was added in 1996 for OBD II, the cutback area on the key was shortened so it stuck out far enough (about 0.100") beyond the face of the timing gear to index the notched disc that was used for the crank position sensor. See photo.<br><br> | ||
Use the correct key for the year of the engine. Don’t try to get by with a regular 350 key; the hub will hit it before it bottoms on the crank gear and it will cause the balancer and belts to be misaligned.<br><br> | Use the correct key for the year of the engine. Don’t try to get by with a regular 350 key; the hub will hit it before it bottoms on the crank gear and it will cause the balancer and belts to be misaligned.<br><br> | ||
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[[File:Cooling mani.gif|right]] | [[File:Cooling mani.gif|right]] | ||
| + | '''EXTERNAL COOLANT LINES'''<br> | ||
| + | [[File:Lt1 head accbolt.gif|right]] | ||
There is an extra hole that goes into the water jacket on both ends of the heads. See the photo. These should be plugged when they’re in the front but left open when they’re on the back. There’s an external coolant transfer line that connects the holes on the back side to a reservoir that vents the air and steam vapors that would be trapped in the head and cause hot spots.<br><br> | There is an extra hole that goes into the water jacket on both ends of the heads. See the photo. These should be plugged when they’re in the front but left open when they’re on the back. There’s an external coolant transfer line that connects the holes on the back side to a reservoir that vents the air and steam vapors that would be trapped in the head and cause hot spots.<br><br> | ||
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'''FRONT TAPPET CUP PLUGS'''<br> | '''FRONT TAPPET CUP PLUGS'''<br> | ||
Both of the cup plugs in the front of the lifter galleries have a 0.030" hole drilled in them. These prevent air pockets from forming in the front of the galleries and provide added lubrication to the water pump gear drive.<br><br> | Both of the cup plugs in the front of the lifter galleries have a 0.030" hole drilled in them. These prevent air pockets from forming in the front of the galleries and provide added lubrication to the water pump gear drive.<br><br> | ||
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'''WATER PUMP DRIVE SHAFT'''<br> | '''WATER PUMP DRIVE SHAFT'''<br> | ||
Be sure to check the seal surface on the geared shaft that drives the water pump. If it’s grooved, it will leak and it will be your fault. See the photo. New ones are available from GM (p/n 10219554) for around $40. That’s cheap insurance when you consider that the timing cover, chain and gears have to come off to replace it.<br><br> | Be sure to check the seal surface on the geared shaft that drives the water pump. If it’s grooved, it will leak and it will be your fault. See the photo. New ones are available from GM (p/n 10219554) for around $40. That’s cheap insurance when you consider that the timing cover, chain and gears have to come off to replace it.<br><br> | ||
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| + | [[File:Lt1 oil drive.gif|right]] | ||
'''OIL PUMP'''<br> | '''OIL PUMP'''<br> | ||
| − | The LT1 powerplant uses the late model 350 oil pump with the 3/4" pickup tube. This should be fairly easy to identify.<br><br> | + | The LT1 powerplant uses the late model 350 oil pump with the 3/4" pickup tube. This should be fairly easy to identify. The oil pump is driven by a stub shaft that is located where the distributor would be on a Gen 1 SBC, photo right.<br><br> |
'''HUB AND BALANCER'''<br> | '''HUB AND BALANCER'''<br> | ||
[[File:Balancer hub.gif|right]] | [[File:Balancer hub.gif|right]] | ||
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*[http://www.amazon.com/Rebuild-Small-Block-Chevy-Engines-Hp1393/dp/1557883939 ''How to Rebuild Small-Block Chevy Lt1/Lt4 Engines''] by Mike Mavrigian | *[http://www.amazon.com/Rebuild-Small-Block-Chevy-Engines-Hp1393/dp/1557883939 ''How to Rebuild Small-Block Chevy Lt1/Lt4 Engines''] by Mike Mavrigian | ||
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[[Category:Engine]] | [[Category:Engine]] | ||
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