Breaking in a rebuilt engine by mostly idling?
 

I was wondering how feasible it would be to break in a rebuilt engine by using a throttle pedal depressor and idling the engine (say 4K rpm for 4 tanks of gas worth, then maybe 5K or 6K for another 4 tanks) rather than putting actual street miles on it?

no

to properly break-in an engine, the engine has to see different loads. set speed idling is bad for engine break-in.

So just drive it regularly, and dont rev it high for the first couple hundred miles. then slowly go up the RPM range for about 1000 miles. then u will have a longer lasting happy engine.

^+1

or you can go an beat on it a bit and drive it normally. its debated as to which is better, just go with what you are more comfortable with.

This would be best. IMO

This is how I drove my engine after about 500 miles. It was hard for me to stay off the gas that long. I'll bet a lot of people have that problem.:)

yeah, i know a few people who just drive them like normal after a rebuild and they are still going strong, good compression on both housings.

No problems here after 3 years. I don't drive mine much at all, so I tend to "clean the carbon out" when I do.

I'm about done with the breakin cycle on my motor after 400 miles. Most of its early running was it just sitting there with me messing with the idle tuning and such. Then I drove it around giving it maybe 1/4 throttle max. I think I first hit a little boost at about 80 miles. I just ramped up the amount of boost and the amount of throttle I gave it as the car put miles on.

But I think a lot depends on the condition of the housings and the clearances in the engine. Engines with more worn parts take a longer time to break in and build compression. I never once flooded my car or had trouble starting it once I got some electrical bugs worked out. But most of the parts in the engine were brand new or low mileage.

A lot of engine builders actually are of a mind that running the engine hard early is important to break in. Mind you, that's for piston engines, I don't know is the same applies for a rotary. The thinking is, seating the rings to the bores is best done while the honing is still fresh, and under load - most of the wear-in is done in the first 20 miles or so of driving.

My experience years ago with a rebuilt inline 6 was that babying it (no steady engine speeds, but avoiding both high rpms and high throttle), gave me an engine that used too much oil and was down on power from what it should have been - the rings never seated properly. I don't know if they still do, but Porsche used to test/break-in/QA their motors by running them for an hour (or maybe 2?), at both max rpms and varying load, including WOT. And I know some engine builders/racers who build their engines, and run them hard right away for break-in, with good, long-lasting results.

^^^^ ya all the V8 old school guys do this method of BREAKING IN the motors. it would suck to have a fresh rebuilt motor and try this method and something go wrong.:(

IMO if everything is Done to Spec Nothing should break if you drive it hard...
I think its more of a safety net..
What about when a brand new rotary car comes from the Factory? Do they say don't drive over 5k RPM for the first 500 miles. I don't think they Do..

Well I'd guess that any fresh brand new engine for a new car goes through some sort of break-in/shake-down at the factory on an engine dyno before even being placed in a car. But might be putting too much faith in manufacturer quality assurance. =P

Either way I was curious about using the throttle pedal hold and idle to put break-in miles on the engine because its a bit difficult to do so on the road. Freeways are packed from 9am-9pm basically and since I take my gf to work in the mornings I can't do freeway loops all night as I would like to ...

The proper way to break it in is to gradually increase the maximum rpms and throttle over the course of X miles (e.g., 1500) until you're up to full throttle & rpms. Anything else is BS.

Use conventional oil only since synthetic won't give enough wear to break in the seals. Change the oil at the end of the break in period to get rid of all the worn metal & what not produced during break-in.

Improperly breaking in an engine leads to reduced power and gas mileage from worsened sealing.

for sports cars, most factory engines off the showroom floor were never "properly" broken in, in the sense that most of the cars were driven hard by a salesman, a potential buyer, or a technician.

I'm still relatively new to rotaries, and most of my knowledge pertains to piston engines, I'm certain that changing your oil several times during the first 1500-2000 miles is a good idea just to get all the assembly lube out of the system and all the moving parts properly lubricated by the oil before pushing it hard. Last thing anyone wants is a thirsty rotary engine.

the last 4 or 5 motors i've build for various rx-7s held up find after a 40-50 mile break-in of no wot. and then going balls to the wall for a 30 min trip around the city. it's really how well the engines are built... but i wouldn't go full boost or rpm after an engine has been running only 15 mins.

for n/a's as long as the specs are to factory, beat it.