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Hagerty
Hagerty Employee

Piston Slap: Primed for success, or does it even matter?

To prime or not to prime? This is a discussion that is still not settled among even the best engine builders. We use much assembly lube to protect the engine upon start-up. What happens to the lube when we prime the engine?
https://www.hagerty.com/media/maintenance-and-tech/piston-slap-primed-for-success-or-does-it-even-ma...
8 REPLIES 8
Swamibob
Technician

Hello Sajeev:

I am not currently a professional engine builder, but I was for many years. Now I do it for fun or the odd customer that understands and is willing to pay for that level of Quality.
When I build engines, not only do I always, prime the oiling system, I always hand crank the engine and make double sure every bit of oil passage had full oil flow and pressure before starting the engine the first time. I also test ran and did proper cam break in on every engine. Later in my career, roller cams became common, so the break in became a simpler affair.
In some cases, after doing the break in, on my run stand we'd also take the engine to one of the local engine dyno shops and do a full cycle of running and testing before handing it over to the end user. No it's not inexpensive, to do it that way, but I never had a problem and always had happy customers in the end.
Sajeev
Community Manager

I wish I had someone like you to do that to my engine the first time it got built! If I did, it woulda never needed a second rebuild! 

Swamibob
Technician

Feel free to touch base; if you get into that situation again Sajeev.
Sajeev
Community Manager

Hopefully not, but I will do so if it happens! The guy who un-screwed my motor is a great guy with a fantastic shop. Now that I think about it, I've been meaning to visit it and see his dyno in action...

Swamibob
Technician

Ya! Dyno Day is always fun. 😉
Oldroad1
Technician

I assemble with STP and nondetergent 30wt. Cam and lifters get a whole jug of STP. On the stand I turn the pump till I see pressure and valve train oiling using 30wt break in oil. In the car, start up at high idle, 1200 rpm, shortly after If I don't hear any funny noises I adjust to low 2k rpm for 20 min with a good fan in front of the radiator and my eyes and ears open, looking and listening for anything. If your engine has open headers I would suggest muffling them before start up because if there is any clatter you won't be able to hear it. If your a success drain the break in oil with the oil of your choice. For high performance and flat tappets I use 15w40 diesel engine oil. I leave the filter on. A little extra ZDDP never hurts.
Sajeev
Community Manager

I like this regiment. Makes a lot of sense to me. 

DUB6
Specialist

   Me too.  In my view, assembly lube (generic term that can be STP or any number of other products, based on personal preference) is just that: a lubricant for assembling parts and keeping them protective and protected during assembly.  They are not part of running lubrication.  So "what happens to the assembly lube upon priming?" isn't the issue, because if you've primed and established full oiling circuit filling and pressure, your engine will be lubed upon firing, regardless of whether or not there is any "assembly lube" left.

   Now, on my Pontiac, getting the oil filter in past the headers and bellhousing necessitates turning it completely upside down and sideways - so pre-filling it at oil change time isn't practical.  However, I run the motor a bit before an oil change, so my sense is that it still has a coating of lubricant on critical parts and I am confident that I have a good oil pump, so that my relatively small filter (again, due to clearance restrictions) will fill quickly upon start-up.  Draining the oil pan doesn't drain every drop of oil from the oil galleys all over the engine - it isn't dry in there.

   So count me in the column of "prime it" believers.