View Full Version : AMC HD explanation from Off-road.com

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10-13-2004, 02:51 PM
here is my post ont he explanation of why AMC-hd is AMC-hd

each engine has a different torque load on bearings, lifter bores, rocker arms and pushrods and distributor gears

The AMC V8 oil drive system is desinged to hold a cetain load value, when this load value is comprimised the gears break down in order of hardness. Basically when you trash a distributor gear their are many things that can cause this

Please stay with me as my typos become apparent

1. Pins must have been in place to align the timing cover
2. never use a used timing cover on a rebuilt engine
3. the right thickness of gasket must be used on the oil pump or binding may occur
4. flashing on the large timing gear can cause zero oil to get to the gear.
5. flashing anywhere the oil pumps can cause this as well.
6. the wrong oil has been known to cause this
7. using unmatched gear sets
8. Front cam bearing must have oil slot going 360 degree's
9. timing gear must have oil slot at 2:00 position from the keyway
10. fuel pump eccentric must be clear to let oil pass
11. excessive play in the distributor can cause this
12. cam walk caused by flashing inthe oil relief holes in the last bearing area of the camshaft can cause cam walk and destroy a gear.
13. extremely low oil pressure will cause this.
14. a worn oil pump drive gear shaft hole can cause this
15. a piece of bearing material can cause this, as a result from pump binding

Most of what causes this in a running working engine is the shear down rate of the oil at operating and over operating temperatures. Shear down in a engineer term meaning the amount of pressure is takes to evacuate a oil from a surface. The convolute of the gears ating surfaces allow for a certain torque value when maxed out. The composition of these gears has changed now 3 times with Crown automotives distributor gear sets. They at the latest update of 10-12-04 have a material unknown. the previous gears (that are still sold) are a billet type hardened materail which will not allow a presoak condition. When we set up a camshaft and dizzy gear set they are soaked in DTE-14 or DTE-24 (which is considered a neutral ph light spindle oil) This penetrates the cast gears and allows for an easy wear pattern to develope. The wear pattern of the gears is extremely important when longevity or accurate timing is important. the AMC-HD comes into play here as a higher base number that your off the shelf passenger car motor oil but not as high as your 15w40 diesel oil. Oil always starts off with a numbered base and over time and combusiotn and outside road gases entering the crankcase it turns acidic and attacks the molecules of the metals in your engine (bearings ...ect). The problem with a higher base number is that it will attack aluminum. In a AMC V8 or inline 6 the timing cover and other components are made out of cast aluminum with a high silicone rate for fluidity when pouring them into a mold cavity. The base number here is very specific when we are dealing with a v8 because one of the greatest seals between the oil pump and the oil pump drive gear is a static seal between the oil pump drive gears shaft and the timing cover. If you have too much base this would cause caustic results and a leaky oil pump inside the iming cover itself. The base number must be high to allow the oil a longer life. In a diesel the base number is large to allow more ouside air to enter the crank case due to the higher compression leaks. The force applied by a 258 on a rod journal or a 401 on a rod journal is tremendous and can be measured in a spherical load with clearances openeing on the bottom of the bearing after combustion occurs. When we took a look at the force on the surface we found that the tiny grooves from grinding were actually getting larger from oil shearing out of the hot zone with compression. The AMC V8 family is well known for its torque and is close to popular diesels in that area at low rpms. The weight of the oil 15w40 is a two part viscosity. The 15 weight is the highest weight at less than 100 degrees you can run at startup that wont allow the oil fillter bypass to open. Running a 20w50 is fin for a race engine that started ant the high end of the crank to bearing tolerance(most race engines are like this). Esther is added to the oil to replace the natural oils of the rubber seals. This is also seen in lucas and amsoil and in almost every synthetic made. Specific material data and load values were just part of the tech needed to create a blend for an engine. We used the AMC V8 and inline sixes for our data. When the question is asked "hwy are certain types of oil made for certian motors" the answer is always the same. Each motor uses lubrication differently, you wouldnt put 5w30 in your diesel truck would you?

Mfgs reccommended oil weights.

What the mfg reccommends is usually for the term of the warrantee where the clearances are still tight. In almost every vehicle owners guidebook a oil viscosity table and temperature suggestion table is included. After 200,000 miles it would not be more adventageous to use the same oil you used at 20,000 miles. Shock loads cause the issue here, as does slip stick. A shock load is what happens after combustion when the rod fires down on the crank and because the crank is already in motion it comes down causing a round spherical elliptical force (thats the best way I know how to explain it) This causes the oil to be pushed to either the crank case or around teh backside of the bearing. It is a constant fight that the bearings have to conclude with. Slip stick is the amount of energy used to take a part from a non moving stance to the beginning of rotation and is a progressive graph with a very fast curve. Some oils used for racing contain friction modifiers which are slightly larger molecules that aloow for less force to be applied to the rotating parts to start thei rotation. These types of race oil arent reccommended for street motors as the peak rotation occurs the unequal amount of friction modifiers cause the shock load to cause more damage by moving these molecules out of the way and with that move ment causing a unequal lubrication barrier that is easily comprimised. Bearings generally turn like this

average RPM's 1650
odometer reading 150,000
average speed 45 mph
total crank turns 330,000,000

That represents the average life span of a motor with a overdrive.....very average. 330,000,000 turns on the crank with a light duty oil in a high torque situation will cause micro welding of the crank to the cam bearings and wear (this is common wear in all engines). The first array of synthetics to hit the market were a simple blend and cotained zero esther and they would simply leak and/or cause a engine that had no leaks to leak. This isnt true anymore with the advancments in lubrication technology a very minute~ amount of esther is added to synthetic oils to allow the seals to obtain a close to net shape by replacing the natural oils. Esther is a neutral additive. Some additives are simply eshter but be cautious of this as eshter in a 100% additive will not keep the seals swollen as long as thenatural rubber's oils. Onece a additive like this is used as a pure additive or a single bottle additive is may cure leaks but the leaks will return faster and the vehicle will become dependant on the eshter for sealing. This was another consideration that had to go into this oil, we didnt want these engines to be dependant on esther but wanted the right amount that would help a leaky seal and/or maintain a seal. In engine specific oils many many properties are found similar in other oils with the exception of the amount of these additives or properties. Lets take polaris 2 cycle oil for instance. when a snowmobile is sold the value of the sale can be increased by the owner wimply stating that he has always used polaris oil......why? Well the polaris oil has certain additives for the sensors on the valves...what ski-doo called rotax is now common is some form on almost every snowmobile. this was a set-up that artic cat originally came up with and their was some litigation over it, I am usure of the outcome. Using the wrong oil would cause coking and ashing up of the sensors thus causig the engine to run improperly and at close examination the reason would be evident, often this voids warrantee. The amount of breathing a Jeep engine does is another consideration. We needed a oil that can take the breathing and the humid air from the large less than efficient breathers. That is a trademark and I cannot give that up but I will tell you its in there. Their is soo much tech that goes into this oil and into any oil blended for a specific use that it would take notebooks of facts to get up to speed on our winter blend.

hope this helps... I got friggen carpal tunnel now

10-13-2004, 07:32 PM
You forgot to mention the metallurgy of a high nickle block :?


10-13-2004, 08:27 PM
Yes I did and a spell check :oops:

10-13-2004, 08:48 PM
You never did mention anything about having brass balls!! Doesn't that play into it somehow???? 8)


10-13-2004, 08:57 PM
Jack now no more picking on the guys over there... They have forum rules as well. 8)

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