Main and Rod Bearing Sizes (Page 1/1)
Kitopher JUN 17, 01:53 AM
I have a 1986 V6 w/140k miles that I am replacing a number of things on due to low oil pressure at warm idle.
I am currently in the process of replacing the main and rod bearings, but have faced some confusion regarding what sizes to order.
I have photos of the upper and lower of one rod bearing, and the lower of a main.




As far as I can tell, both rods say MM100 and have a very faded serial number? on them 18xxxxxx86
They also both say 340xxxx31 (not pictured)
The main bearing has 2 very clear serial numbers, 18011212 and 347 B 532
It also appears as though it may have a very faded marking above the 180... reading 0M 4
I am really just at a loss here as to what sizes I should be ordering to replace these, as any examples of bearing sizing I can find online has much clearer markings.
Everything I can find is also in inches ex:0.03, and I'm assuming the MM stands for milimeters.
Any help is greatly apreciated.

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Kit G

Vintage-Nut JUN 17, 09:45 AM
IMHO (and it is only that, my opinion)

*Measure Your Clearances BEFORE Ordering Bearings*

Years ago, I used plastigage to measure clearances......

But now, look at this link:
How To Check and Set Engine Bearing Clearances
https://motoiq.com/how-to-c...e-bearing-clearances

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Original Owner of a Silver '88 GT
Under 'Production Refurbishment' @ 136k Miles

Patrick JUN 18, 06:05 PM

quote
Originally posted by Vintage-Nut:

Years ago, I used plastigage to measure clearances......

But now, look at this link: How To Check and Set Engine Bearing Clearances



I may be wrong, but I got the impression that the OP was replacing these bearings with the crank still in the engine. I know this is possible with the rod bearings, and I think this is possible with the main journal bearings as well. Anyway, if what I'm assuming is true (and it may not be), using a micrometer to measure the crank journals is probably not possible in this situation... and it would be back to using plastigauge.

[This message has been edited by Patrick (edited 06-18-2024).]

Notorio JUN 18, 11:23 PM
Patrick, yes one CAN replace the main bearing from underneath on the V6 at least.

Kit, you haven't mentioned the condition of the crank surfaces. The old bearings might look like sh-- but it doesn't matter if the crank is still fine. As has been send, Plastiguage will tell you what oversize to purchase. Good luck! You will be thrilled with the increase in oil pressure from replacing the mains and rod bearings.