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AMX 401 Take 6

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Rebel Machine View Drop Down
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Joined: Jul/03/2007
Location: Western Il
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Rebel Machine Quote  Post ReplyReply Direct Link To This Post Posted: Mar/21/2015 at 5:39am
Originally posted by SKeown SKeown wrote:

Originally posted by Rebel Machine Rebel Machine wrote:

Originally posted by 6PakBee 6PakBee wrote:

Originally posted by Rebel Machine Rebel Machine wrote:


I can do it in three.... Main Bearing Clearance.

-Steve-



I've glad you have it identified and corrected.  Persistence is the secret for solving a lot of problems in life.  Just for the record, what were the clearances when the problem existed and what are they now?


Main bearings were between 0.0035" and 0.0040" when it was having problems. Crank was ground 0.020" under with 0.0017" clearances on mains 1-4 and 0.0025" clearance on main 5 (per AMC tech manual specs). This way they hold back enough oil to feed the cam bearings. Cam bearing failure was the result of the low pressure.

Rod clearances were (and still are) 0.0020".

The reason for the excessive clearance was the bearing manufacturer's information. That's what the engine builder used to set clearance instead of the AMC spec.

The timing gear oil passage issue contributed to the low pressure but I'm thinking it may not have been as large a factor as the bearing clearance. It was still corrected though.

-Steve-


 The problem with making simultaneous changes is it's difficult to determine what did what. Being some drag racers run .004 main clearances without issues leads me to credit the wendage baffle for the improvement. Naturally I could be wrong, but the way you're engine behaved at higher RPM doesn't square with the bearing clearance hypothesis. Besides, remember the impact adding the larger pan had. That to me doesn't indicate a bearing clearance issue either?

 Granted, I can see where the tighter bearing clearance would further enhance the oil pressure. I don't feel that's responsible for the more stable pressure at higher RPM. 

 SKeown  



I think most race engines are also running 15W-50 oil. Remember earlier in this thread when I changed from 10W-30 to 15W-50 the oil pressure returned to normal.

-Steve-
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