Running in a rebuilt engine.

Just wondering how many miles/hours running in, you guys that have had engine rebuilds do?

None just nail it

[Red Herring]

I've always been told that running in an engine gently is good for the bottom end, it allows the crankshaft journals to bed in and in the long run last longer. Problem is running in also tends to glaze the bores so the pistons don't seal as well, so potentially give less power. In the perfect world you would run it in nicely, then whip the pistons out, hone the bores and thrash it straight away. Given that as racers we don't live in the perfect world and will probably be rebuilding the engine before the journals need it anyway do what he said...thrash it straight out of the box and enjoy!

LOL I like your way of thinking lads, I'd be cacking myself incase I did it harm after the money I spent!

take it easy for the first 5 minutes then you can take the revs right up but never full throttle. you need to heat the parts internally and cool them, heat them, cool them etc etc. a couple of hunderd miles or 3 hours of this and all will be well, if you rebuilt it ok
use semi synthetic, never synthetic.

[yorkie_chris]

Crank should not need any running in, they are plain bearings so no actual contact.

Original running in you are bedding in gears and all sorts which depend on a bit of gentle use to work harden them.

Answer is a big 'it depends'.

Bike had new carillo rods, shell bearings and wiseco pistons, bores honed and heads ported.

[yorkie_chris]

So basically all you're running in is the new ring/bore interface. Let it rev IMO.


Rotax, what parts inside an engine are hot enough to affect the metallurgy?

Originally Posted by yorkie_chris

So basically all you're running in is the new ring/bore interface. Let it rev IMO.


Rotax, what parts inside an engine are hot enough to affect the metallurgy?

the main part is the rings/bore that need treating right.
if they are run in too carefully then they are never seated as intended.
too harsh and you risk it picking up which ruins it all in seconds.
in short/simple terms the rings need to cut the high spots before they are polished.
its how i always do it. my kart engines took 20 minutes of 'careful' abuse and that was it. high revs with a stab to full throttle every 10 or 15 seconds. that turned out powerful motors but bear in mind they needed rebuilding every 15 hours (soft components)
the rest of the motor needs no running in with modern tolerances and oils.
i never use fully synthetic but if i did it would be after 10,000 miles use and only in 2 strokes after the run in

everyone has their own idea of running in and that is my way after talking to many tuners and testing back to back in the past
one or two mates do it by the book and wont listen

[Red Herring]

I know on the one occasion I had a brand new race bike the tuner wanted me to put a few road miles on it before he pulled it apart. After that we never ran it in again after rebuilds, in fact the first thing we did before I even rode it was stick it on the dyno to see what it could make.