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Cam Gears Ad Nauseum |
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pacerman
Supporter of TheAMCForum Joined: Jul/03/2007 Location: United States Status: Offline Points: 9057 |
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Posted: Nov/15/2018 at 3:05pm |
OK guys, I will keep this short. Below please find three pictures of cam gears. The first is a late nylon toothed gear which cam on a factory 343 short block I took out of the crate (1973 manufacture as a service block). The second is an unbranded set (believed to be Cloyes) from Summit Racing. The third is a Rollmaster gear I received this week. Which is most correct and do you need to see the other side of the gears before you decide?
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Happiness is making something out of nothing.
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Jmerican
AMC Addicted Joined: Mar/29/2016 Location: Seattle, Wa Status: Offline Points: 585 |
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Whew this is allotta earl coming out those slots.
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WesternRed
AMC Addicted Joined: Aug/03/2010 Location: Australia Status: Offline Points: 5799 |
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The factory one is the most correct, the other two have much larger oil slots so less oil will potentially get to the cam gears. The Rollmaster is a shocker, I thought they were going to fix that, but maybe old stock.
Location if the oil slot on the other side is also critical and must be in the same location as the factory gear. It's probably a bit hard to see here, but I had a gear similar to #2 above, I filled three slots with JB Weld, I have seen others weld them up, but this seemed easier. I think the most important one to block is the one that is directly on the oil slot through the gear as that has the most potential to let unnecessary oil out. |
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AlexK
AMC Apprentice Joined: Feb/19/2017 Location: Germany Status: Offline Points: 73 |
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Is it a CS7111 with nitrided sprockets or Standard CS7110?
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ChillyB
AMC Nut Joined: Nov/14/2018 Location: PA Status: Offline Points: 371 |
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The Rollmaster does have two fewer grooves, though. Is it as simple as matching the total cross-sectional area of the grooves? Or has there been observable reliability differences? Not making an argument that it ISN'T a problem, just asking the question.
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RTTComanche17
AMC Apprentice Joined: Apr/19/2009 Location: California Status: Offline Points: 73 |
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While I cannot comment on the reliability issues others may or may not have had, nor am I saying that this is or isn't a problem, however, I can answer the above question from a fluids perspective. It is not as simple as matching total cross-sectional area. If 6 tiny slots and 1 big slot had the same total cross-sectional area, the 1 big slot will flow more than the 6 small ones (given the same source oil pressure). The caveat to this is, while there would still be differences in flow, matching the cross-sectional area is most likely good enough (and should still flow more than factory) due to manufacturing tolerances of factory parts from 45+ years ago. At the low end, you need enough oil pressure and flow to keep parts from metal to metal contact under load in all areas of the engine. At the upper end, you don't want to run the sump dry due to too much flow/not enough oil. As long as you are within these conditional bounds, the engine should be ok. Since all fluids take the path of least resistance, closing up a few of the slots in the aftermarket cam gears as some have done should get you closer to the middle of that range and closer to how the AMC designers intended it to be. There is "wiggle room" in everything. |
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WesternRed
AMC Addicted Joined: Aug/03/2010 Location: Australia Status: Offline Points: 5799 |
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There are some oil holes in the distributor drive gear to let the oil out there and lubricate the distributor gears directly. If the slots in the front of the cam gear are too large, then it can potentially let most of the oil out there and there is nothing left to travel further forward to where it is also needed to lubricate the distributor drive gear, which is a very common area of failure.
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304-dude
AMC Addicted Joined: Sep/29/2008 Location: Central Illinoi Status: Offline Points: 9082 |
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True, though it's all about the high RPM pressures at the gears, between the oil pump being driven by the distributor. The gears being forced against each other requires plenty of oil at the gear, not every where else. Shallow grooves will restrict just enough, like on the nylon gear to be as good as limiting the channels to just 4. I rather have 8 channels of smaller size to allow a more constant flow of oil, though it would require too much experimentation to get it right with depth. Since we all know what works, the experimentation is mute, along with having simpler means of correcting for better oiling of the drive gears. Like the external 1/8" line bypass from pump to cover mod. Not as simple as filling channels, and is very noticeable, since it is not stock. |
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jcisworthy
AMC Addicted Joined: Jul/23/2009 Location: North Carolina Status: Offline Points: 2805 |
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I have primed new engines using a drill with the Rollmaster timing set installed and looking through the fuel pump mounting hole in the timing cover I have seen plenty of oil squirting out the cam gear holes. If a drill rpm and cold oil is enough to squirt a lot of oil out of the cam gear there is nothing to worry about in a running engine. A lot of worry over nothing in my opinion with this topic
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WesternRed
AMC Addicted Joined: Aug/03/2010 Location: Australia Status: Offline Points: 5799 |
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I think you would have ask the question how many distributor drive gears failed with the factory cam gear compared to the number with aftermarket cam gears. Sure there are plenty of other reasons for this but the cam gear oil slots could well be a contributory factor.
I do believe there has also been some design changes with the Rollmaster cam gear over the years so not all gears are equal. |
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