# Bad break-in and blow-by

**URL:** <https://community.cartalk.com/t/bad-break-in-and-blow-by/166972>\
**Category:** General Discussion\
**Created:** [July 8, 2020, 1:16pm UTC](https://community.cartalk.com/t/bad-break-in-and-blow-by/166972 "2020-07-08T13:16:33Z")\
**Posts on this page:** 3\
**Page:** 1

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**Author:** ![arwcca\_166186](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/arwcca_166186/32/20285_2.png) [@arwcca\_166186](https://community.cartalk.com/u/arwcca_166186)\
**Post date:** [July 8, 2020, 1:16pm UTC](https://community.cartalk.com/t/bad-break-in-and-blow-by/166972/1 "2020-07-08T13:16:33Z")

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Hello,

I would like to ask a simple question about blow-by in a brand new engine.  
Ok so, if an engine is flogged during its break-in period, does it cause piston ring damage?  
And also, if the piston rings are damaged, will that cause excessive blowby?

Thanks!

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<div class="post-metadata">

**Author:** ![Cavell](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/cavell/32/43396_2.png) [@Cavell](https://community.cartalk.com/u/Cavell)\
**Post date:** [July 8, 2020, 1:27pm UTC](https://community.cartalk.com/t/bad-break-in-and-blow-by/166972/2 "2020-07-08T13:27:33Z")

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Why are you flogging a new car? Or is that an assumption? Is it your car you are asking about?

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**Author:** ![Mustangman](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/mustangman/32/44130_2.png) [@Mustangman](https://community.cartalk.com/u/Mustangman)\
**Post date:** [July 8, 2020, 1:27pm UTC](https://community.cartalk.com/t/bad-break-in-and-blow-by/166972/3 "2020-07-08T13:27:50Z")

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> [@arwcca\_166186](#):
>
> if an engine is flogged during its break-in period, does it cause piston ring damage?

It can, depending on how hard it was flogged. I’ve built race engines that didn’t get more than 1/2 hour of run-in sitting in my driveway and 1/2 hour on the track before being raced at high RPM with 240 degree water and 290 degree oil temps that didn’t have excessive blowby afterwards.  
But I usually broke the engine in on non-detergent conventional oil for the first 1/2 hour blipping the throttle in the driveway (I was the favorite neighbor!) but switching to synthetic for the first track session.

> [@arwcca\_166186](#):
>
> if the piston rings are damaged, will that cause excessive blowby?

Absolutely it will.

If the piston ring end gap was too tight when the engine was built, they can butt ends and break. That will cause excessive blow-by. Too great an end gap when built can cause that as well. Installing the rings upside down also causes that. All this takes a tear-down to identify.