Break in run for nailhead 264

[Guest btate]

Not being a very knowledgeable car person, I just had a question. My re build mechanic said we need to run the car at 2000 rpm's for 20 minutes to break in the cam properly. I asked if it should warm up for a couple minutes and said a couple minutes warm up is ok but then run at 2000rpm for 20 mins. Just doesn't sound right to me, to run a newly re built engine that fast and that long. Hope to start the engine this coming Wed. 26th. Also what transmission fluid should I use? Thanks. merry Christmas

[60FlatTop]

I think Crane and Isky cams made that recommendation a long time ago. This is from when I was a kid and if Ed Iskenderian said "Do it." you did it. Here is a modern version:

As I remember it has to do with the balance of the cam action against the valve spring tension. At the elevated RPM inertia comes into play and relieves the high pressure contact at the cam nose and the lifter surface when it goes over center.

Bernie

[old-tank]

Bill

That's a pretty standard break-in procedure. Also follow the builder's recommendations on oil and additives.

For the tranny use DEXRON III/Mercon automatic transmission fluid; install 4 quarts before starting and add during the run-in until full (do not run a dry transmission). Get some helpers and a supply of beer ( after the break-in )...this for me is always a fun time, although nerve racking....enjoy!

Willie

[NTX5467]

The other main reason is that the camshaft lobes have NO pressure oiling to them . . . unless you might use some lifters with very small holes drilled into them to bleed a certain amount of motor oil on their lobe contact surface (a recent invention, it seems). Therefore, the mantra for flat tappet camshaft motors is do an initial adjustment on the valves (on engines which have adjustable rocker arms for hydraulic lifters OR non-hydraulic "mechanical" lifters), ensure the engine will start the first time, and when it does start (hopefully very quickly!!!), then you run it at about 2000rpm for 20 minutes to "break-in" the camshaft. The reason for the higher rpm is that with no dedicated lubrication for the camshaft lobes, they rely on "splash" from oil thrown off from the crankshaft main bearings as their main oil supply.

When the new camshaft is prepped for installation, the lobes should be smeared with a moly-paste cam lobe lube (designed just for this purpose) or, if the engine will be fired very soon, some of the oily "cam pre-lube" viscous liquid lube. Naturally, the lifters will have been dipped in oil just prior to their installation in their respective bores. So, the more the "non-splash lube" time can be minimized, the better! This is why the distributor will physically be "approximately timed" in its location, the oil pump will have been turned with a drill motor to pressurize the oiling system, the carburetor will have gas in it . . . all done just prior to initial start-up.

In a V-type motor, there can be some "liberties" taken which an inline-type motor can't really benefit from (without some additional "labor operations"). For example, on a V-type engine with adjustable rocker arms, you'll need to do an initial valve adjustment, which will necessitate the engine being "roller over", cylinder by cylinder, to set each cylinder's valve clearance (or hydraulic lifter pre-load). So, with the moly paste on the cam lobes, it can be smeared somewhat as this happens. Which is why ANOTHER recommendation was to pour some of the old GM Engine Oil Supplement (pint size, "thick and viscous" version) into the lifter valley so it would drip onto the camshaft lobes before the intake manifold items were installed. You could probably do similar on an inline engine, if you waited to put the side covers back on until the last thing, but it WOULD be messy and inconvenient, I suspect, compared to the V-type engine.

The OTHER consideration in engine "break-in", which is more or a concern on a new engine (with a somewhat "uncured" engine block) than on a used,rebuilt engine (with a very cured engine block) is that you need to let the various "sliding items" learn to live with each other before putting a heavy and extended load on the engine. This is where the "wear-in" orientation comes from, as the block cures (with hot and cold cycles), the machining stabilizes with time and use. Such stabilization is NOT a real issue when you start with a cured/used block which is machined during the rebuild. As it was assembled, the various things (bearings, pushrod ends, piston skirts, piston rings, valve stems, etc.) should have been oiled prior to assembly such that they are not "dry" upon initial pre-lubed start-up . . . and can live for the few seconds until oil flow happens.

I learned about the "cured block" issue in Bill "Grumpy" Jenkins' book on drag racing (circa mid-1980s). He said they used, exclusively, salvage yard engines to build their drag race motors with. Once the used blocks were machined for new pistons and the main bearings saddles were line-honed, those dimensions didn't move as the engine was further aged. Just like using a "deck plate" to simulate the cylinder heads being bolted to the block, as the block's cylinders are finish "power honed". He also stated that when they needed to purchase new blocks from Chevrolet, they'd leave them out on his patio for six months or so . . . to cure . . . from which they'd vat and clean them up and build a race motor.

Back in the middle 1960s or so, I read that when you did a rebuild on an engine, you didn't need to "baby" it as you might if it was a new engine in a new vehicle, but to drive it a little harder than you might normally do. One highly intense old-line mechanic once told me that when he rebuilt the engine in his daughter's '60 Fairlane, he did the rebuild, put new oil in it, didn't do the cam stuff as he reused the original cam, but then took it out and drove it hard until it got good and hot. Then about 30 minutes later, he brought it back into the shop and did an oil/filter change on it. Then he handed his daughter the keys. I was kind of surprised at what he said, but later it made better sense. PLUS the fact that he was doing everything to it that she might be capable of doing to it, one way or another. So, if it didn't break with him driving it, it would be fine for her. In later times, I knew of him to do customer's cars the same way. He had peace of mind that he wouldn't be getting a call, after hours, about an engine issue.

Be aware, too, that before the engine in a new car gets to the assembly plant, it's already been run-in at the engine plant for about 30 minutes. First, it must past the "cold test" by starting. Then the run-time is done on a dyno stand. After the prescribed running time, the various "hot tests" are done. If it passed those final tests, it was readied for shippment to the vehicle assembly plant.

IF you live in a totally flat area of the country, then the dedicated "variable-speed" cruise technique can be good to do. Moreso with a new engine, but it can also be good to do (for fewer cycles) on a rebuild. This is where you very the cruising speed by starting at about 30mph, then lightly accelerate to about 45mph, decel back to 30 and repeat a few times, then more progressively higher until you cover the speed ranges available in your area. The light load acceleration puts stress/load on one side of things with the decel putting load/stress on the other side of things. Chrysler used to recommend "passing gear" accelerations from about 50-70mph a few times in the first 500 miles (on a new car) for good measure.

Many GM Crate Motor installation instructions mention a specified number of 1/2 throttle 1/4 mile "passes", then progressively more throttle as the specified procedure progresses. Kind of the same "variable speed/load" situation as the return road time will be at idle, or thereabouts, due to local track regulations.

After mentioning these things . . . I highly recommend that you follow your engine builder's recommendations as HE's the one whose going to have to live with the longevity and reliability of the engine rebuild items. I suspect he's got his OWN way and orientations of doing things . . . which might seem a little suspect to some . . . but HE's got his reasons for requesting they be done, too, from his own experiences. Do things as he requests they be done--period. If he might determine that some problem was due to "installation errors", any possible warranties of what's been done might be null and void . . . at HIS discretion. ALSO, HIS choice of motor oil for the rebuild and initial miles, too.

Just some thoughts and observations . . .

HAPPY HOLIDAYS !!!

NTX5467