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Rear main Seals Beware |
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401MATCOUPE
AMC Addicted Joined: May/20/2010 Location: Salisbury, MD Status: Offline Points: 5367 |
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Here is my opinion on the rod bearing holes......after talking to an internal combustion engine expert. The half round hole in the bearing half allows a very small amount of oil to continuously flow in the path of the rod swing.....which will not do anything for the cam/lifters, but rather keep this spray in the bottom end of the piston and cylinder......also providing a small amount of lubrication to the wrist pin. He and are both puzzled why parts companies have decided to omit them on current parts........BUT I can tell you that if they are not on bearings that I use, I machine the bearing with my Bridgeport to put the half round in the bearing halves.......with that said, you could do the same with a Dremel or similar tool.....I use the mill because I have it and it is convenient. Engines designers put this feature in for good reason, I am sure some cost cutting genius decided it was something not needed or they made some by mistake without it and didn't want to toss away.....so they internally justified not to put them there any longer,
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Ross K. Peterson
68X,GoPac,343,AT,52A(1stCar) 68X,GoPac,390,4sp,52A 69X,GoPac,390,4sp,64A 70X,GoPac,390,4sp,87A,8 70X,GoPac,390,4sp,BBO,8 70 Jav SST,390,AT,BSO 74MatX,401,AT,Prototype 74MatX,401,AT |
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Steve_P
AMC Addicted Charter Member Joined: Jun/28/2007 Status: Offline Points: 3802 |
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Agree- they are there primarily to spray the bottom of the opposing cylinder and it must have been dropped as a cost savings. |
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Trader
AMC Addicted Joined: May/15/2018 Location: Ontario Status: Offline Points: 6880 |
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The “spray/squirt holes” were dropped for several
reasons: -at low RPM the squirt holes reduce oil system pressure -the spinning crankshaft throws oil exiting the sides of
the rod throws sufficiently to lubricate and cool everything in its wake. Hence
the methods to reduce oil spray with scrapers and windage trays to increase HP. - squirt holes on some engines contributed to excessive
oil usage (don’t know if AMC analyzed this) - the loss of oil wedge on opposing sides on the rod
bearing do to the squirt holes on shared journals caused enough force differential
in some engines to actually be a factor in connecting rod failure, (don’t know
if this was ever analyzed by AMC, but GM and Honda did) Debate is still out with some Classic engines if these
are required, but modern engines do not have these, so hence our aftermarket parts
also do not. Put them in or not, it’s a preference and opinion that’s been debated many times. I don't know of any definitive engine failures in an AMC without them. Only someone doing a full engine analysis on our
classic engines would be able to resolve this – like that is ever going o happen! |
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rang-a-stang
AMC Nut Joined: Sep/25/2018 Location: Camarillo, CA Status: Offline Points: 272 |
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I see the same thing now except it ships 2 weeks out from today. This RMS is elusive!
Whenever I go to this website and try to order, I add it to my cart, I get a popup that says it was added to my cart, but my cart changes over to a Summit Racing cart and the RMS is not in it. If I go to Summit, it has the RMS listed but says it is not available. ggrrr....
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79 Cherokee, 401
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Trader
AMC Addicted Joined: May/15/2018 Location: Ontario Status: Offline Points: 6880 |
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They may have changed their product number to RS 085-5 and not the web page???:
Followed the rabbit hole and it does lead through Summit???, think this is what you need: Edited by Trader - Jan/07/2021 at 11:48am |
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SC397
AMC Addicted Joined: Apr/30/2009 Location: Michigan Status: Offline Points: 5476 |
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I just called them. They don't make the seals, they just rebox a existing brand. The part number is 12905
www.jegs.com/i/SCE-Gaskets/829/12905/10002/-1 |
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DMack
AMC Apprentice Joined: Mar/27/2019 Location: California Status: Offline Points: 227 |
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Just an update here...called SCE. They are no longer producing this seal. 12905 was superseded by RS 085-5, but both numbers are now inactive.
Fel-Pro is most likely going to be your best bet or find an SCE set that someone has tucked away in their garage.
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67 Marlin
AMC Addicted Joined: Feb/21/2015 Location: Minnesota Status: Offline Points: 877 |
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In the first photo, the new model seal (made in Germany with part numbers starting with DPH) is the top one. The old one (part number starting with 318) is the bottom. The reinforcing copper wire in the old seal is smaller and there's more rubber around it (yellow dots to show how much meat is there). The new one doesn't have much meat on that side of the wire. I wonder if that super thin layer is scraped off and then oil pours out. The only other difference I could notice was in that area on the inside of the seals; I used red lines to show a possible difference in geometry. After a couple hours of staring at these things my eyes could have been tricking me, too. I know they weren't tricking me on the copper wire. The second photo is the other side of the pair, two new ones at left and an old school one on the right. The wire is nearly centered in the old one. The two new ones vary a bit, the middle one's real close to the edge. If this is the cause of the problem, then could result in some of the new ones working and some not working. Who knows, just some photos to ponder. |
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JGRANTAMX
AMC Addicted Joined: Jun/02/2017 Location: Maine Status: Offline Points: 1695 |
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I ordered one of the SCE rear seals at the beginning of this month from Jegs it showed a ship date of 1/24/21, yesterday a charge from Jegs posted on my card for the seal amount I will post what I receive.
J
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SC397
AMC Addicted Joined: Apr/30/2009 Location: Michigan Status: Offline Points: 5476 |
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I just picked up 2 more SCE brand seals from my Machine Shop. I have 6 more on order and we were told that they are going to keep supplying the SCE12905 seal with the AM part number on it. There is also the letters "SCI" on the seal, so I assume that this company is making them for SCE.
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