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Timing
What a topic. Much can be discussed on the need of timing, here are some basics. I like to see the use of a GM HEI rebuilt 8-10 degrees idle with no vac line hooked up 20-25 with vacuum line 36 full load no vacuum 40-50 with no load on highway with vac Best to use a adjustable timing light. These cost around 75.00. Your engine will thank You. Torque Plate use
In my mind, a torque plate is a must when honing a block for new or used pistons. Proper ring seal is a must. Why give away the HP and torq from faulty sealing rings? I have performed measurements of the bores in 250 and 292 engines while honing. When torqing the head bolts down to spec, the block will distort by .004 around each head bolt. This distortion will go down into the block 1" deep in the bore. So there will be 4 distortions in each cylinder. The torque plate will do away with this problem. |
Camshaft Break In
Steps must be taken for proper break in of a new camshaft. Most engines are first run in a auto chassis of some kind, so that is what I will discuss. The engine must be run at 2000 RPM for 20 minutes at first start up! Failure of the cam lobes will certainly happen if this is not done. This is a hard task to achieve if you are not prepared. So here are steps to take to get you on your way.
Keep in mind 2000 RPM is a bunch on a new motor for 20 minutes. It will put out plenty of heat and exhaust. 194-230-250 harmonic damper bolt
These engines are not always equiped with a damper bolt. This is important. When the engine is being worked on, always drill and tap the crankshaft snout for a 7/16 fine thread bolt. Drill it 1.5 deep and thread 1.25 deep. This hole will be used to retain the balancer and install the balancer. |
Camshaft Gear Installation
This is a job that is messed up a bunch, so pay attention.
1. Heat your oven to 500 degrees, lay cam gear on one of the racks
2.Install the cam gear retainer plate and ring/spacer. Inside chamfer
of spacer toward camshaft
3.Install camshaft key
4. Place cam in freezer
5. Get your heavy duty oven mitts on, get a helper to hold cam and
a block of wood to go under cam
You will also need a large dead blow hammer.
Pull gear out of over after at least 20 minutes and
insert onto the cam, provide dead blow wacks as needed to seat
the gear down.
Let it cool, you are done.
Do not press gear on, it will certainly walk of later. You will not like it.
This is a job that is messed up a bunch, so pay attention.
1. Heat your oven to 500 degrees, lay cam gear on one of the racks
2.Install the cam gear retainer plate and ring/spacer. Inside chamfer
of spacer toward camshaft
3.Install camshaft key
4. Place cam in freezer
5. Get your heavy duty oven mitts on, get a helper to hold cam and
a block of wood to go under cam
You will also need a large dead blow hammer.
Pull gear out of over after at least 20 minutes and
insert onto the cam, provide dead blow wacks as needed to seat
the gear down.
Let it cool, you are done.
Do not press gear on, it will certainly walk of later. You will not like it.
Cam Bearings
Keep in mind when changing cams to pay attention to the bearings. Here is a abbreviated article from King Bearings on Cam bearing failure.
Structures and Materials of Camshaft Bearings
The typical structures and designs of camshaft bearings are presented. The most traditional design of camshaft bearings is a steel tube with a layer of lead based Babbitt alloy applied onto the inner surface (bush type camshaft bearing). The bearings of this type may be supplied in semi-finished (un-bored) condition. Then the bearings are bored after installation in the engine. However, the precision (bored) finished type is more popular. A relatively thick and soft Babbitt layer provides good conformability of the bearing. The material allows fitting its shape to misalignments. Babbitt also has very good embedability, which is important for bearings operating with contaminated oil. The main disadvantage of Babbitt bearings is their low load carrying capacity. Babbitt alloys are soft; therefore they have low fatigue strength. Also, the fatigue limit of the lining is directly dependent on its thickness: the thicker the layer the lower its fatigue limit. Since the Babbitt lining is relatively thick, its fatigue strength is low (~2,000 psi). Bi-metallic camshaft bearings, with a lining made of aluminum alloy, have a much greater fatigue strength of at least 5,800 psi. The bearings are split shells type, rather than bush. King Engine Bearings manufactures camshaft bearings made of aluminum/silicon alloy: K-788 . Their load capacity reaches 8,000 psi.
A bimetal structure with an aluminum alloy lining is the best solution for camshaft bearings. Aluminum alloy is not too hard, therefore it has good conformability. Also, it is stronger and more wear resistant than Babbitt. In contrast to a tri-metal structure, aluminum alloy bimetal bearings have superior conformability, and can tolerate far greater wear since they do not have a thin overlay. The thickness of the aluminum lining is approximately 0.010”. If the load applied to camshaft bearings exceeds the fatigue strength of aluminum alloys, tri-metal materials having a copper based intermediate layer and very thin (up to 0.0008”) soft Babbitt overlay are used. Tri-metal materials have greater load capacity, but their conformability and maximum wear are limited by the very low thickness of the overlay. Once the overlay is locally worn out and the bronze intermediate layer is exposed, seizure of the bearing by the steel journal becomes very probable. Since misalignment and excessive wear due to oil starvation are typical causes of camshaft bearing failures, tri-metal construction is rarely used in the design of camshaft bearings.
King Bearings are made using the K-788 Aluminum/ Silicon Alloy. These are the bearings I recommend.
Pictures of failed cam bearings. Notice how the soft babbit flows over the oil hole.
Keep in mind when changing cams to pay attention to the bearings. Here is a abbreviated article from King Bearings on Cam bearing failure.
Structures and Materials of Camshaft Bearings
The typical structures and designs of camshaft bearings are presented. The most traditional design of camshaft bearings is a steel tube with a layer of lead based Babbitt alloy applied onto the inner surface (bush type camshaft bearing). The bearings of this type may be supplied in semi-finished (un-bored) condition. Then the bearings are bored after installation in the engine. However, the precision (bored) finished type is more popular. A relatively thick and soft Babbitt layer provides good conformability of the bearing. The material allows fitting its shape to misalignments. Babbitt also has very good embedability, which is important for bearings operating with contaminated oil. The main disadvantage of Babbitt bearings is their low load carrying capacity. Babbitt alloys are soft; therefore they have low fatigue strength. Also, the fatigue limit of the lining is directly dependent on its thickness: the thicker the layer the lower its fatigue limit. Since the Babbitt lining is relatively thick, its fatigue strength is low (~2,000 psi). Bi-metallic camshaft bearings, with a lining made of aluminum alloy, have a much greater fatigue strength of at least 5,800 psi. The bearings are split shells type, rather than bush. King Engine Bearings manufactures camshaft bearings made of aluminum/silicon alloy: K-788 . Their load capacity reaches 8,000 psi.
A bimetal structure with an aluminum alloy lining is the best solution for camshaft bearings. Aluminum alloy is not too hard, therefore it has good conformability. Also, it is stronger and more wear resistant than Babbitt. In contrast to a tri-metal structure, aluminum alloy bimetal bearings have superior conformability, and can tolerate far greater wear since they do not have a thin overlay. The thickness of the aluminum lining is approximately 0.010”. If the load applied to camshaft bearings exceeds the fatigue strength of aluminum alloys, tri-metal materials having a copper based intermediate layer and very thin (up to 0.0008”) soft Babbitt overlay are used. Tri-metal materials have greater load capacity, but their conformability and maximum wear are limited by the very low thickness of the overlay. Once the overlay is locally worn out and the bronze intermediate layer is exposed, seizure of the bearing by the steel journal becomes very probable. Since misalignment and excessive wear due to oil starvation are typical causes of camshaft bearing failures, tri-metal construction is rarely used in the design of camshaft bearings.
King Bearings are made using the K-788 Aluminum/ Silicon Alloy. These are the bearings I recommend.
Pictures of failed cam bearings. Notice how the soft babbit flows over the oil hole.