258 Main and connecting rod bearings

[Basod]

First is it a fools errand to think new lower end bearings with new oil pump will solve hot idle pressure of 12-15psi?

Second FSM states factory bearings are color coded- anyone that can vouch the color is still present after 35yrs. No markings on the block to indicate over/under sized crank or cam. I can mic crank somewhat in place to confirm.

Already confirmed good dry compression 145-150psi and I know at least the the rear main had some scoring from seal replacement last summer journal surface was smooth though. Running 60psi cold idle with 10w-40 and quart of STP blue.
Hot cruising 35-40psi but 800rpm hot idle with cold outside temps 12-15psi.
Water temps running 160 right now 185 in summer- oil viscosity and pressure are only going to get worse.

Plan on doing it engine in and changing timing chain while while I’m at it.


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[Lumpy Grits]

Hope you're not depending on the OEM oil pressure gauge to be 'rite'.
Switch to 20W-50 and add a can of V8 size Restore.
Shake the heck out of the can for 1 minute before pouring into engine.
How many miles on the engine?
Gary

 

[Basod]

Hope you're not depending on the OEM oil pressure gauge to be 'rite'.
Switch to 20W-50 and add a can of V8 size Restore.
Shake the heck out of the can for 1 minute before pouring into engine.
How many miles on the engine?
Gary

Replaced the OEM gauge with an AutoMeter 2421 mechanical gauge not long after purchase and verified calibration prior to install.

No idea on actual mileage of engine as it was swapped in by a PO.
Nothing against the Restore, I know it does work for compression and oil consumption just never heard of it fixing bearing tolerances.

 

[Lumpy Grits]

AMC 258's, didn't have the tightest tolerances to start with.
Give Castrol 20w-50 and Restore a try.
I've used the Restore for years.
Gary

 

[Posi]

Get your engine hot, bring the engine to a steady 2000rpm, look at your oil gauge and post your findings.

Side note: anywhere from 1600-2000rpm will do. Also lower your idle to 600 rpm and post both findings. Both at normal running temps.

 

[Basod]

I don’t have a tach in the dash so used a handheld reflective tape one from work.

My cold choke idle was actually 2200rpm with 58psi it’s around 50f ambient

Warmed up 2000 rpm 18psi ~175 water temp.
Could barely get it dialed down to 850rpm and 13psi oil pressure. Started to hear a lifter tick there as well.

Need to get the new distributor in so I have some vacuum advance it’s stumbling if I try to tune lower plus my carter YAF with custom PO adapter isn’t helping any- keep thinking I’m gonna happen across a mc2100/50 with an adapter cheaper.

I don’t mind dumping $13 worth of restore in it but if I’m just prolonging the inevitable $50 bearings and some labor on my part I’d rather dump a few quarts of K1 to clean out some sludge prior doing bearings, pump and timing set.





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[Posi]

A lot of folks think 13psi is bad however, it’s factory spec at 600rpm.
You do have an oiling problem as you should find 37-75 psi at higher rpm.
If it were me I’d want to drop the pan to inspect the intake tube and screen for restrictions.
Also, an oil pump rebuild.

 

[Kane]

Posi is correct that those pressures are totally normal for this engine. At 160 degree engine temp you will hear some rocker arm rattling. Mine make that noise until the engine is over 180 degrees.

 

[Basod]

Thanks for the info- never would have thought 13psi at idle was good.

Intake screen I verified clear back in July when I did the RMS. Should have rebuilt the pump then but live and learn.
Dropped the rebuilt dizzy in this evening original gear had at least 5 degrees of slop new one dropped in after clocking the oil pump a few degrees.
Can’t really get it to clear up by ear it was smoothish before.

Broke down and ordered a 2100 carb from Gronk so while I’m in the lower end it’s being built.

With the oil pan off for the pump can’t see any reason not to do a bearing roll. Hopefully plastigauge a few of the connecting rods and main with gravity won’t throw me into a full rebuild.


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[Basod]

So pan is off and rolled 3 mains and 2 connecting rods to get an average measurement.
Crank is 2.477-8 which correlated with the 020 stamped on the rear of the bearings 2.498-2.500 stock
Connecting rods 2.077-2.078 with no oversized markings but I was able to cross reference the pn 13310-HDA online. Miced the ID of the connecting rod cap less double the thickness of the bearing and my math puts me with .003 oil clearance.

Going to order .020 oversized bearings for both and an M81-A oil pump kit. Keeping my fingers crossed it all works out.


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[Kane]

If you have the time buy some plastigage and check the clearances of the old vs new bearings. That way you know 100% if the new bearings will tighten up the tolerance otherwise you will be scratch your head if it didn't make a difference.

 

[Basod]

Yes I definitely plan to plastigauge at least a few of each bearing. Going to hit the crank with some 800/1000 grit and a shoe lace has some faint scratches on a couple connecting rods.


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[Basod]

Finally got all the bearings rolled in the thrust bearing was a little tough to start as your trying to axially align the crank to get it started eventually got it to go in smoothly.
All the mains plastigauged at .002-.0015 old bearings were .003. The connecting rods were really worn miced on the bench old ones .062-3 thickness and I could rattle them around by hand torqued down, new were .067 and all plastigauged .002

One thing I didn’t realize after installing the first two connecting rod bearings they had holes at the half’s the rest of the new bearings didn’t- not sure why as old bearings all had a hole at the center joint.
All the oil supply should be coming from the crank internal passages.

Timing chain was really loose so glad to address that at the same time.




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[Basod]

Figured I’d post back with final results.
I did some research and apparently the oil holes in connecting rod bearings are to create a splash mist on adjacent piston skirts but are deemed not necessary now...

With 10w-40 and no STP I’m running a steady 15psi at 650rpm. It took some adjusting on the initial timing and a little tweaking on the idle air screws to get it smoothed out. My random misfire at idle is gone and I can connect the vacuum advance.


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