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Main bearing clearance question


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6 replies to this topic

#1 Mizac

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Posted 01 February 2013 - 10:29 PM

OK so I'm rebuilding the EJ25 in my 00 Forester. Bearing clearance on the mains is .0004-.0012 in the book. We ran the dial bore gauge down the mains and they read around .0030, which is WAY too loose. My question is, can I throw this thing in the CNC machine and wack a few thousandth off each half; then line hone the mains to the correct size? We are used to American v8's so this is new territory. Thanks for any input!

#2 GeneralDisorder

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Posted 01 February 2013 - 10:32 PM

No the way you fix that is to undersize the crank and install undersized bearing inserts.

The usual way to measure clearance is with plastigauge with the block halves torqued together.

GD

#3 Caboobaroo

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Posted 01 February 2013 - 10:33 PM

You can replace the main bearings with oversized bearings. Shaving the block down can cause bigger headaches.

Damn, GD beat me to it... Heh

#4 Mizac

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Posted 01 February 2013 - 11:12 PM

Ive already bought a regrind crank and undersized bearings and the clearances are just way off for my liking. The main bearing bore is actually bigger than spec. Out of ignorance, what kind of headaches are we talking about if we do the before mentioned work?

#5 Fairtax4me

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Posted 02 February 2013 - 12:27 AM

I'd check it with plasti-gauge before going any further. Buy the next size under bearing if needed. Machining the block is going the opposite direction.

#6 GeneralDisorder

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Posted 02 February 2013 - 11:49 AM

Realistically the mains are not that important on these engines. ACL sells "extra clearance" mains for racing that have an additional .0005" of clearance for example. I have seen plenty of engines run with clearance you measured on the mains and not have any issue at all. The rotating assembly is well balanced and its just not an issue. The rods are where you need to focus.

GD

#7 Mizac

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Posted 02 February 2013 - 02:46 PM

Thanks for all the info and replies. I do appreciate it. Again im a newbie on Subarus. I use plasti-gage when im in a pinch but find a more accurate reading when i use a dial bore gauge to measure the housing, mics for the journals, and a tube mic to measure bearing shell thickness. Anyway, im good on the rods...im running them at .0015. I just thought .0030 was too loose on the mains. Would the case not grow a bit after it got hot, expanding the clearance a bit more? Again just asking because I dont know. I dont want to have to do this again, because the first engine was a disaster when i broke it open. It only had 12,000 miles after a poor rebuild.
Also, is there something going on with the 2.5's where they eat the bearings on the first rod journal? We've got 3 2.5's in the shop and all three have the same prob. Thanks again!




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