After driving in a WI blizzard last week on worn tires, overheating once and some hard reving, the oil pressure in my 87 Formula 350 is at about 15 psi at idle (30 psi when moving) and there is a bad metal on metal sound coming from under the hood. I suspect I threw a connecting rod bearing. I have yet to get out and pull the oil pan to see. I'm not driving it anymore in the meantime. My question is: if my guess is right and it is a conn rod bearing, can I get by with just replacing the conn rod bearings or do I need to replace the main bearings and/or recondition the crank as well? I assume I will need to use new conn rod bolts for correct clamp load? Any advice on what is involved (I am guessing remove oil pan and spark plugs and manually turn engine over to access upper bearings) or what else I should check into would be greatly appreciated. Oil pan gasket preferences/techniques and conn rod bolt preferences would be appreciated as well. I have 173K miles on the engine now, & would like to postpone a complete rebuild or replacement crate engine for a year or two. Thanks in advance to all who answer.

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Dave
87 Formula 350/auto, Flowmaster Cat Back, SLP Performance Y-Pipe, 52 mm BBK Throttle Body w/airfoil, SLP Cold Air Induction, Ported Plenum,
March Underdrive Pulleys, Accel 300+ Ignition, Adj. FPR (44 psi), Hypertech PROM, Hotchkiss STB, Global West SFCs, Global West Steering Brace, Jamex Springs

 

if you have a bad bearing you should have the crank measured and replace all the bearings. considering how cheap the bearings are there isn't any reason to not change all of them.

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ICON Motorsports
1st & 3rd

 

Ede is right, you should really replace all the bearings... Also, you SHOULD remove the crank and visually inspect it AT LEAST! Bad/spun bearings can beat a crank pretty bad and you'll be pissed if you repalce all the rod bearings with the engine in the car and have them fail (soon?) again later. My 2 cents, anyway. Plus, a cheapo new crank with GOOD main/rod bearings is probably about 250.00 TOTAL out the door and ready to bolt in, if you need it. Just sell you beat one for 20 bucks, if you need to.

I use the FelPro gasket sets for my rebuilds of the one-pice seal blocks. Nice oil pan gasket...

And if you are looking for hints, replace your oil pump (if high mileage) with a Melling 55 standard volume pump (20 bucks) if you get ALL NEW MAIN/ROD bearings. If you replace just some/all rod bearings, get the Melling 55HV high volume (not high pressure) oil pump, which will help you mask bearing clearance problems in that high mileage motor.

 

It is OK to replace jus the bearings providing that:

A) the crank is not scored
B) the bearing did NOT spin in the rod
C) you check the bearing clearances after installing them and they are in spec.

I have seen many engines go many miles with just bearings, BUT if more damage exists, then don't waste your time, get a crank. and if the bearing spun inside the rod, it would probably be cheaper for another motor.

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ASE Master Tech + L1
Savannah, GA

'87 Trans Am
S/D TPI retrofit including functional PassKey, 22# injectors,
JET AFPR, Ported Plenum,
TB Coolant Bypass,
SSM SFC, Boxed LCAs,
8mm Accel wires,
Flowmaster Exhaust,
16" GTA rims,
Corvette Servo,
KYB Shocks
-->14.97 @ 94.9 MPH<--

'97 Bonneville SSE

 

I agree with GMTech.

Make sure you check all clearances before re-assembly.

My experiance is that if its knocking, its already too late. It doesn't take much to damage a crank.

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ASE Mechanic/Machinist/Smog Tech

1999 NBM Trans Am
1986 Chevy 3/4 ton pick up
1981 corvette
1995 Kawi ZX6R

GO #3

 

Have fun getting that oil pan off. I just replaced the connecting rod bearings in my sister's 96 Jeep Grand Cherokee after she didn't change the oil for 24,000 miles and the oil pump screen plogged up. Changing the acutal bearings was simple, almost fun. Getting the pan off was a little difficult though. On an f-body, MUCH more difficult, obviously.

 

Thanks for the tips, advice and expertise guys. I may have to wait until the snow stops and it warms up a bit before I get the oil pan off and see what happened in there. I'll have the crank measured/replaced if necc. and look into the HV oil pump to. I plan on keeping it for as long as I can. Might as well do it right..or get a crate motor if it looks too bad. Thanks again.


[This message has been edited by formuladave (edited December 18, 2000).]