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#7 connecting rod turned a straw color after cam r |
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69kermit
AMC Apprentice Joined: Oct/23/2014 Location: El Cajon, Ca. Status: Offline Points: 37 |
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Posted: Jul/27/2015 at 12:16pm |
I have a 70 390 amc that ran a little warmer than expected during the cam run-in so tore it down and did not notice anything major except that #7 connecting rod has a straw color to it while all of the other rods look to be the same color, the engine did not reach boil over temps as it had a 195 thermostat and the temps reached 212 prior to shut down. Anyone have advice or why only one connecting rod changed?
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401jim
Supporter of TheAMCForum Joined: Jan/07/2012 Location: Brunswick,Ohio Status: Offline Points: 793 |
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Did you prime the engine before lighting it up? Did the oil pressure come up on start up? Sounds like a lube feed to # 7 problem. It is the last one to receive oil pressure. It may have been starved on first time run in. Hope this helps you.
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69kermit
AMC Apprentice Joined: Oct/23/2014 Location: El Cajon, Ca. Status: Offline Points: 37 |
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I had primed the engine and running right about 60 psi hot the real question is the rod bearing look fine with no discolor and no wear upon a visual inspection the piston looks fine and the crank has no signs so the question is should I replace the rod or should be okay as I said it was run for a short time and no other indication of any damage.
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tsanchez
AMC Addicted Joined: Jul/09/2007 Location: Arizona Status: Offline Points: 4303 |
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Did you build it, may just be a rod that was cleaned different
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69kermit
AMC Apprentice Joined: Oct/23/2014 Location: El Cajon, Ca. Status: Offline Points: 37 |
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yes, they were all the same color when installed as the shop had put together the rods and pistons but I did the rest.
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tsanchez
AMC Addicted Joined: Jul/09/2007 Location: Arizona Status: Offline Points: 4303 |
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Well it changed color for a reason and if it wasnt heat from a bearing then it was from piston, that is not good as it would take a ton of piston heat to color the rod
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ScrambledEgg
AMC Nut Joined: Nov/24/2007 Location: Upstate NY Status: Offline Points: 348 |
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If the rod was blue or bluish in color I would think it got to hot. When you say straw, I think of a goldish / tan color. Is that what you mean?
Was the rod wet from oil or dry compared to the other rods? How long did you run it for? Its possible the next stage was to turn blue from lack of lube or being too tight of either the piston in the bore of wrist pin or rod bearing clearance. I would at a minimum check these clearances and inspect all the surfaces and the rod bearings. Plasti gauge it again as well. Was the plug for that cylinder running/burning the same as the others? |
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ScrambledEgg
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Boris Badanov
AMC Addicted Joined: Dec/14/2013 Location: NH USA Status: Offline Points: 4209 |
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Enough heat to turn a rod straw color should show other damage.
bearing, crank or the adjoining #8 rod. Having done a fair amount of heat treating in a Johnson furnace I will say with confidence that the piston would be a puddle of aluminum if it were the source of that heat. My vote is un noticed color before assembly, or, chemical staining by reacting with an oil additive. Check clearances, assemble it and run it. |
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Gremlin Dreams
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Mikel
AMC Apprentice Joined: Jul/15/2014 Location: CT Status: Offline Points: 85 |
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If a rod got hot enough to change color, you would have noticed other very dramatic symptoms, in the form of noises and flying parts.
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SKeown
AMC Addicted Joined: Jul/30/2009 Location: Texas Status: Offline Points: 3085 |
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If you can't find a problem with that rod's bearing or wrist pin I wouldn't be concerned. SKeown
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