Running in an engine....again? Needed?

[Chr15py]

Ok, I have a question for all you engine builders in the know. I did put this in the "Guru" section but wasn't allowed to reply to a question on my post so really....the forum just doesnt work!

Why do you not need to re-run in an engine in if it has been taken apart and put back together? I can understand the need to bed in the piston rings into the block when new (2000 miles with various levels of tune etc) but why not if you have taken the pistons out and put them back in? Surely the rings will move and not settle back in perfectly to the “grooves” they made the first time?
It confuses me lol.

Any answers would be appreciated.

Cheers
Chris

[Rogue]

The purpose of running in an engine is to bed the rings in against the cylinder walls. The edges of the rings wear against the cylinder wall, matching themselves perfectly to the surface and provided a final hone. There are no grooves - the rings rotate within the pistons as they cycle.

Provided the original pistons and rings are replaced in the same cylinder and everything was fine beforehand then there is no need to run it in again.

[steve b]

So then, thrash it from the off or gently, gently?

Thinking about it the warm it up, then thrash it should do a better job.

[Mike 'MR2' McHugh]

Just do what i do and drive it round changing gear at 3000rpm because your scared of breaking it !!!!

[Lauren]

Just do what i do and drive it round changing gear at 3000rpm because your scared of breaking it !!!!

Well you could do that. There are a few school of thought on how to run in. The important thing is to get the rings under enough pressure to seal them effectively to the bores.

I tend to go for the warm it up and drive it reasonably hard. I don't thrash it, but will give a bit of full throttle in say second up to 5000 odd rpm then lift off that kind of thing. Don't labour it but don't baby it.

Then once i've got a few hundred miles on the clock I bring the revs up closer to the redline. I did this with my last two (brand) new cars. I seem to have lower oil consumption than some who took the traditional method of babying it (not going over 3000rpm) for a 1000miles.

At the end of the day if it's going to break it's going to anyway.

[Rogue]

In Chr15py's case we're talking about an engine with a failed headgasket that's been completely stripped, checked and re-assembled. It's already run-in, so there's no need to do it again - nothing's changed (except the headgasket!).

You'll be able to give it full duty straight away.

[Mike 'MR2' McHugh]

Just do what i do and drive it round changing gear at 3000rpm because your scared of breaking it !!!!

Well you could do that. There are a few school of thought on how to run in. The important thing is to get the rings under enough pressure to seal them effectively to the bores.

I tend to go for the warm it up and drive it reasonably hard. I don't thrash it, but will give a bit of full throttle in say second up to 5000 odd rpm then lift off that kind of thing. Don't labour it but don't baby it.

Then once i've got a few hundred miles on the clock I bring the revs up closer to the redline. I did this with my last two (brand) new cars. I seem to have lower oil consumption than some who took the traditional method of babying it (not going over 3000rpm) for a 1000miles.

At the end of the day if it's going to break it's going to anyway.

No thats how i drive it all the time.....