Compression test while engine (4.0) out

Hi,

in effort to replace the engine in my Tacoma (2014, 4.0 V6), I have purchased a replacement engine that will be coming in tomorrow. Before I install it I would like to verify the compression readings provided by the seller.

Assuming it has sat for some time I am concerned about inducing damage during the test without adequately preparing it—I believe it will come without oil.

What can I do to prevent damage to any of the bearings and internals? It will be out of the truck when I test so I will be hooking up the started to conduct the test.

Ideally, I would appreciate a sequence of steps in order of what I should be doing. I’ve been getting inconsistent information online and this will be the best place for an appropriate answer. Thank you for any help!

 

Drain old oil and inspect for metal shavings. Turn crank bolt with wrench and make sure it turns smoothly.

Spark plugs all out. Can spray in a little WD-40 or other thin lubricant into the cylinders. Not a lot.
You don't want to add so much as to mask any compression problems. Just enough to lunlbricate things, until the oil can get squirted there.

Pull the valve covers and inspect. Clean a little while there if necessary. All things looking good, add a thin coat of oil to all of the moving components.

Add in a few quarts of oil.

Jump start with bolted on starter and battery.

https://youtu.be/CXxddyaRr5c?si=nl7iwyAls6nxgZ9u

 

Turning it for a compression test without oil isn’t going to hurt anything.

 

Thank you Torspd! This is super helpful

 

Alright, looks like my compression test and engine replacement will have to wait. The freight carrier came today and the pallet arrived damaged so I couldn’t accept delivery.

good thing insurance was included but now I’ll have to wait for that to process ‍

 

That's a bold recommendation for a unknown motor that uses plain bearings. Sure it might appear to be fine afterwards but that doesn't mean it didn't hurt the motor. Plain bearings require a layer of oil to prevent metal to metal contact. Since a Tacoma uses 0~10W oil which is way on the thin side you have no idea how much of that thin oil remains on those bearings to provide that clearance and if it's drained dry the oil pump isnt picking up the slack. It's naive to assume it couldn't cause damage, not saying it will but it might be as simple as reduced oil pressure because the plan bearings just got hammered by the engine's compression while they were dry, that can can increase their clearances which affects oil pressure not to mention bearing condition. It might not be enough to cause a low OP warning but it's sure not good for the motor.

 

Smart move.