how to break in rebuilt motor???

[Dj Buttchug]

I heard once from a master tech that you cant run fully synthetic oils in new engines. specifically GM stuff. The idea was that the synthetic oil creates to much lubrication and prevents the engine from breaking in properly... totally ot but ya. weird

[318isbmw]

The nice thing about this subject is that there are lots of "authoritative sources" with different opinions.

I learned the procedure I described from a NASCAR engine builder. He said that they ran the engine like that mounted on a water brake dyno, then tuned engine and tested it. From there it went straight to a race car and was raced. If there was a better way, you can be real sure that they'd use it. As he told me, "10hp is the difference between 1st and last at Daytona.". They'll do anything that they can to wring the last fraction of a horse power out of the engine.

Seating the rings or breaking in the cam is essentially a polishing operation. You want to do it with the parts under the least load. Running the engine at 2500rpm with the car stationary is a minimum load situation.

I learned the same technique for breaking in a rebuilt motor. From a drag racer/ engine builder here locally. He's been doing it for years and I've got a couple motors that he bored and balanced for us that we used the technique on when we did first start up. Also several family members he's built motors for that have lots of miles over the course of 20 or so years with no ring failures as mentioned by nando as a possible issue.

[Dagamus(NM)]

they are likely breaking in a cam at the same time though. that's the exact method you use to break in a cam. And then, they basically race the motor. So you're really not disagreeing with me. :)

This is where it gets confusing. Breaking in the motor as though it is brand new. All head parts brand new, all bottom end parts brand new except reconditioned rods and crank.

Some talk about breaking in the cam, others about the rings. What is the es way to do these simultaneously?

I figure that I will heat up my Torco oil in a large roasting pan in the oven to about 325 degrees then pump it into the motor. Prime the system with the little socket thing I made to spin the pump with my cordless drill for a couple minutes. Bolt the pump hatch shut and start the motor.

Then most likely a mix of freeway loads, wot/ct and again.

Clutch is also new. Should be fun.

[Irish1]

Who's building your M20s? I need a shortblock done to replace a bad one from a previous build.

i've only done 4 m20 break ins. so far from expert but i do follow the same steps as nando.
warm up the engine (the gaskets will smoke) at this point i bleed out the coolant system.
then drive her up and down the street for about 30min. take it for a short drive come home and check for leaks. finish driving her like a grandma till i hit 100 miles. change the oil and proceed to drive her like i stole it.

[brianao34]

Bumping this, I would like to try the website method as it makes more sense, but what about the clutch?
Obviously I'll have a new clutch that'll need to get broken in as well and I've always heard not to get on it hard with a new clutch for the first 500 miles.
Or is it if I just don't drop the clutch?

[nando]

I dunno, I "broke in" my clutch at the same time I was still learning to drive stick and with a brand new motor. It never had a problem.

[catuned]

All valid points. There is brake in oil additives available made by redline and most imports (ie Honda, Acura, etc) say to use Straight 30 oil for brake in. That is for the 1st oil fill. Then after oil change going to multi level oil.