Few questions

[slo87]

95 4.0 block 95 7120 head 88 4.2 crank and rods comp cam cannot recall part # right now bored .030 overbore flat top Pistons and for now planning to go forward with the 4 barrel Holley.

What spark plugs (HEI dizzy) and fuel grade do you all recommend? And do I really need to run in the camshaft like they say? 2500rpm for 15 minutes at very first start up sounds slightly rough on all new components (mains rods cam bearings rings etc) just don't want to fuckup a year or so in the savings

[Russ Pottenger]

Do you know what your static compression ratio is?
You said you're running a flat top piston. At TDC how far below the deck is your piston?

The initial fire up is important for properly breaking in the camshaft. The camshaft has a slight taper on its lobes and the corresponding lifters have a crown on its bottom base. Along with the camshaft lobe being offset in the lifter bore this all helps to ensure that the lifter turns as it's cycling up and down and it's bore. If at any time the lifter doesn't spin it will cause the camshaft lobe to go flat.

This leads us back to the camshaft break-in procedure.
The initial increased RPM helps to ensure that the lifter gets adequate splash lubrication that helps to promote the lifter to spin. Also keep in mind it's not necessary to run the full 15 to 20 minutes at one time. I'll typically run it for about five minutes and shut it down so I can do a quick inspection to check for oil leaks and verifying that the cooling system is still topped off.

[slo87]

Not sure on SCR machinist did all of this a while back. I am using slp-677ap30 piston set and comp cam 68-239-4 and using Matched springs the ones in the kit wouldn't work for the 4.0 head. The cyl head was also shaved .010 for flatness.

[Russ Pottenger]

Ok. That makes little more sense.
The 677 isn't a flat top piston and was concerned that you're gonna have to much compression.

[slo87]

So any real reason to run other than stock plugs for the 4.2 and 87 octane and just guess on the gap.

[Russ Pottenger]

Stock plugs stock gap is fine.

Increasing the gap just puts more strain on your ignition system. The lifespan of your cap, rotor, and wires will be
reduced and won't make any significant if any difference in a stock ignition.

[SkylinesSuck]

Would it be helpful to add an extra quart of oil during break in to get the crank splashing more oil all over the cam?

[jsawduste]

No, just adds more foam.

[Cheromaniac]

Would it be helpful to add an extra quart of oil during break in to get the crank splashing more oil all over the cam?

That's unnecessary. Just add the required amount of oil (6 quarts with new oil filter) to bring the dipstick up to the MAX mark.