Breaking In Bearings

[poolboy]

I figured with having just seen 99999 on the odo,the least I could do was to replace the main and rod bearings along with the thrust washers.
Finished that up this morning, put in 10w-30 oil and took a 30 mile test drive.
So now I'm wanting some ideas about what I should do for a breakin.
Suggestions?

 

[Guest]

You make it sound so easy.

 

[poolboy]

What is it they say "the devil is in the details"? Sliding that upper half of the main bearing into place WAS the devil.

 

[DrEntropy]

Ummm... if ya chimed it up without using a zinc laden oil, it's already too late to make th' recommendation.


:shocked:

 

[poolboy]

Yeah, just plain oil. With all the talk about the ZDDP stuff, I gathered that it was a benefit for the tappets alright, but I didn't make a connection for new inserts.

 

[AltaKnight]

When I did mine last year I just used good 'ol Quaker State 20W 50.
I had to pull one rod bearing apart this year, don't ask why, and the bearing surface looked just like new so I think that oil and some gentle'ish driving for the first few hundred miles seems to have worked.

 

[poolboy]

I gotta ask, sorry. Why?

 

[foxtrapper]

Break-in really has nothing to do with the bearings you replaced. It's about cylinder walls and piston rings, and tappets and cam lobe faces. Things that have microscopically rough surfaces that have to wear on each other, getting friendly and neighborly. You don't have that with soft metal bearings against a polished smooth hard surface.

 

[Hasbeen]

I'm with Foxtrapper. With a bottom end rebuild, as you describe, we reckoned that the bearings were run in, by the time the oil was up to operating temperature.

In fact, with racing engines, where we lapped the rings to the cylinder walls with braso, [silver polish] it was the same. Warm the thing properly, so the oil was warm, then go race.

Hasbeen

 

[Guest]

How did the old bearings look? How did the crank look at 99999 miles? Did it look like it was necessary after all or was everything still good?

.

 

[vettedog72]

Congratulations on the 100,000 miles. The thin oil you used sounds right. I would change it at 500 or 1000 just for good measure and if you are in a warm climate you might switch over the the 20W??. Are you using the OEM oil filter? I bet the oil pressure is up a bit after the redo; did you make a comparison?

 

[TR6oldtimer]

The only time the bearings and crankshaft have a chance to touch is during startup. Once pressure is up and the crank is rotating, the crank rides on a wedge of oil, separating it from the bearing.

So, if only the bearings were replaced, drive the car and have fun. No break in for the bottom end needed.

 

[poolboy]

Thanks for the info from all you guys. So I'm good to go.
The journals were bright and shinny and slick.
The old rod bearings showed patches of copper exposed.
The main bearings were showing quite a bit of copper, all except for 1 set that still had at least 90% babbit.
The old Thrust Washer was about.002 thinner than the new ones. The end float with the old ones was only .006.
I'd say for 100k, the wear was less than I expected for the rods, and the right time for the Mains.

 

[poolboy]

Vettedog. I have the spin on conversion. I've been using 20w-50, but put the 10w-30 in for "break-in".
I kept an eye on the Oil Pressure gauge during my first outing, just to see if was holding.
When I get the 10w out and the 20w back I can compare.
I've always had good oil pressure. With engine and oil fully heated, I estimate about 65 at 3k.

 

[poolboy]

Vettedog, Since I was convinced that I didn't need to do anything too special, I put my usual concoction of 20w-50 Castrol with about 20 oz of Lubra-Moly.
The oil pressure with a fully warmed up engine and oil is about 80# at 3k. So that's a 10 to 15# increase in pressure.
I've noticed in the past that once the oil gets about 500 miles on it the pressure may drop a few #'s but I think it will still be higher.