What is the best way to break-in a rebuilt slant six?

There seem to be many competing opinions...

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1963 Dodge Dart, motor by Doug Dutra, Offenhauser two carb intake, Pertronix, Clifford 6x2, Flowmaster 40's, Erson RV15/295 RDP, head work. Addco anti-sway bar, urethane suspension bushings, KYB's, racing leafs, SSBC discs. Need ZDDP? Get STP.

and i quote, straight from the Haynes Repair Manual

"Drive the vehicle to an area with minimum traffix, accelerate at full throttle from 30mph to 50mph, then allow the vehicle to slow to 30mph with the throttle closed. Repeat the procedure 10 or 12 times. This will load the piston rings and cause them to seat properly against cylinder walls. Check again for oil and coolant leaks.
Drive the vehicle gently for the first 500 miles (no sustained high speeds) and keep a constant check on the oil level.
Change oil at 500 miles
For the next hundred miles, drive normally, don't pamper or abuse it"


that's what i did, after 1,000 i took it on a trip to from los angeles to san diego back in one day. car didn't fail me...

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70 Plymouth Valiant 4dr

That sounds consistant with what I've also read on the web. I'll have to also check my Dart shop manual, 'cause I bet it says the same thing.

The real trick will be to find a place where I can do that without too much interference.

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1963 Dodge Dart, motor by Doug Dutra, Offenhauser two carb intake, Pertronix, Clifford 6x2, Flowmaster 40's, Erson RV15/295 RDP, head work. Addco anti-sway bar, urethane suspension bushings, KYB's, racing leafs, SSBC discs. Need ZDDP? Get STP.

i did my break in on the freeway at about 3am.. no traffic

just turn on your emergency lights

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70 Plymouth Valiant 4dr

Is that after initial cam break in?

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1966 Dart GT
4 spd. OD conversion
8 3/4 - 3.55 SG (Sold)

62 Lancer GT
B Body 8 3/4

Yes, most initial cam breakin advice is "run engine at 2500 rpms for 20 minutes".

rough bore finish or honed? I rebuilt mine the old way, rough bore, and it took a li'l bit longer for breaking it in, but now, with 4k miles on it it's like a purring kitten (except for when I WOT it, my 2" duals like to scream )

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Juan Ignacio Caino

Please use e-mail button istead of PM'ing. I do log in sometimes but I'll be answering quicker thru e-mail.

This is V8 cam break-in thinking, where the cam is up high and gets limited oil splash, the high RPMs helps to keep oil on it.
With the SL6, we don't have to worry as far as getting oil on the cam, it's right next to the carnk so it gets lots of splash.

The key to a successful cam break-in is to be sure that you maintain a "hydro-dynamic wedge", a fancy name for keeping things spinning fast enough so the valve springs don't have time to squeeze the oil film out of the lobe to lifter contact zone.
With reasonable valve spring pressures, this does not take a lot of RPMs, I tend to keep the start-up idle on a new engine in the 1000-1500 RPM zone for the first few minutes and quickly check the engine for oil pressure, leaks and to be sure that all the pushrods are spinning. Shut-off the engine and correct if anything does not look right.

If all is well, I let the engine warm so it runs with-out the choke, then bring the idle down under 1000 to "listen" for any signs of trouble. I give the engine some throttle "blips" during that step, not real high on RPM, may-be up to 2000 or so just to hear how it responds to throttle opening.

By now, 5- 10 minutes has gone by and the engine is hot, I idle it down and go into a final valve adjustment. Button it up and go for a test drive, using the "run it up and then let the engine decellerate" method needed to suck lots of oil up into the ring packs.

After a few miles of that, I drive it like normal. ( and that is not "baby in the car" driving, closer to "got to get to distination now" driving style)
Do the first oil change in 300-500 miles then "put the hammer down" on the thing.

This has always worked for me, I have never had a cam lobe fail and I have lot's of "data points".
DD