Intrepid

Hugh? What do you mean?

Enforcer

<sigh>

Trying to avoid this highly controversial topic and brings back a lot of memories. Sorry for the long post and sorry it's taking me so long to write it.

When my father was young he worked in a garage (~50's era) and had experience with everything automotive including racing until mother threatened to divorce him (she was pregnant with me). As my brother and I grew up we naturally were into cars and built up a couple Dodge Superbees. We hatched the bores and used chrome rings. And followed our fathers instructions on how to break them in. But the rings would not seal (you check this by wet and dry compression testing). At fathers urging we pulled the 383 heads, rehatched the bores, roughed up the ring edges put it back together and this time used Rislone by pouring it right down the carb throat varying engine spead from idle to WOT (hard to do pouring oil down a carb and you can't believe the smoke!) and then performed the father recommended break in. It worked.

In my 20's I rebuilt several engines for friends (never used chrome rings again) and the one that got me into Z's was the last one, a 280Z. My friend claimed that he had driven other 280's and this one just didn't have the power and since it had nearly 200,000 miles on it and the compression wasn't in spec, assumed it needed an engine rebuild. Well, I couldn't believe my eyes. I could still see hatch marks in the cylinder bores and there was no ring-wear lip. It looked as if the engine was never broke in. It's sometimes hard to tell but I believe the headbolts were original, could not see any marks on them (but the manual says the bolts are one time use, so if it was pulled before me they might have replaced the bolts as required by the manual). Well I couldn't believe my eyes and called my father for an explanation. He said to ask around and see if they had nitrided the cylinder bores. I talked to the local dealer and they claimed the 280's came with nitrided cylinder bores. I don't know if that is true to this day. Suspected it was urban legend but still cannot explain the lack of ring wear with that mileage. Anyhow, rehatched it and rebuilt it (replaced all rings seals bearings gaskets) and broke it in and compression test was good.

On every engine I have rebuilt, I broke the car in myself following what my father had taught me and in every case the compression checks in the end were good. But times have changed, manufactuers are using materials today that were not used in the past. Like molybdenum. And could be nitriding cylinder bores or something even more esoteric. So I'm not going to recommend this until I read the manual. Here at long last is my fathers and now my tried and true break in procedure:

Immediately take the car and accelerate normally from a stand still to highway speed but don't "hone it" (fathers terms) going through the rpm range (idle to less than redline). Repeat this many times (about an hours worth). Then for the first 1000 miles avoid driving at single speeds (rpm+load) for long distances and make a point to do the stand still to highway speed a few more times during that first 1000 miles. Mix it up. And don't redline it.

I've been looking at the HP and torque graph and believe the rpm limit would be 5500.

The point is, take it through the rpm range with good load many times right up front. I would define "good" load to be 70-90% power from idle to 5500rpm. Do not go past redline, do not drive at one speed. My father swears that if you drive at one speed, if you do not load it, and if you overload it or you redline it during this procedure and the first 1000 miles, it will not break in properly. And I say that you can't break in an engine without load. It's the load over the entire power rpm range that really matters. Only you can have too much load and too much rpm. Now to describe what I mean by that...

The discription on that website about how rings form a seal to the engine wall is correct to my understanding as well as the scrapping/cutting/seating of the rings. It's the roughness of the rings and the hatch marks that make it all work. That is why there are two or three sets of compression rings and a bottom oiler ring. The compression rings are staggered so the slots don't all line up and the oiler scrapes the oil off of the cylinder wall ahead of the rings. Which is why you have carbon deposits behind the rings in the piston ring groves but not on the cylinder walls. The spring tension of the ring does not form the seal. The reason you don't want to exceed redline or go to max load is because of "blow by" and vibration. Since the rings are just cutting into the cylinder walls and "seating" themselves the exhaust gases can blow by the rings between the cylinder wall and the ring...thereby preventing them from cutting/seating to the cylinder wall. Same with vibration at excessive (above redline) rpms. At excessive rpms the piston vibrates in the bore causing piston slap and is where the psiton actually slaps into the side of the bore with amazing force and thereby causing the piston and rings to vibrate (like tapping a lead glass goblet). This vibration causes very quick damage.

Breaking it down into what is going on in terms of pressure and seating/cutting and vibration is the best way to describe the break-in. And is why it is so hard for manufacturers to describe it.

But I agree with everyone that has said, RTFM (Read The Fine Manual) and follow it. Now that you understand the process better, and have heard some experiences and opinions, hopefully the vague words in the manuals make more sense.


Enforcer

Intrepid

Thank Enforcer. Very interesting.

z350z

Thanks very much, Enforcer. Information like this from first-hand experience is worth a hundred messages with info based on "I heard" this and "I assume" that. (Like my previous message!)