Blow by pictures?

[Ozzie Seadoo]

Hi all,

Here is a piston out of a Seadoo XP with a 720 Rotax Engine. From what i can deduce myself, i think this piston has blow-by, meaning that the motor was not run in properly (ie: Was reved to high during the break in period). Is this correct and if so, i'm guessing that i should baby the engine for the first 10-15 hours on the new engine??? Thanks.

NOTE: Please click on the photos for better detail!

[Technical Support]

Re: Blow by pictures?

5-10 hours is good for break-in, read our tech article. Yes that blow-by is from a lack of ring-seating, most likely due to improper break-in.

[Bill O'Neal2]

Re: Blow by pictures?

That doesn't necessarily mean it was not broken in properly. It may have many hours on it. Look at the top ring. Does that thing look like it was seated ? No. It looks like it was leaking badly. It should be shiney all around, not covered with carbon.

When watercraft sit all winter unfogged, they rust the clyinder walls. When you bring them back out in the spring, the rings have to ride on those rusty clyinder walls. No so good on the ring surfaces.

[chris w]

Re: Blow by pictures?

I like to break em in hard. Others will vary and have varying opinions, but if you want good ring seal, run it in hard IMO. That dosent mean to keep it pinned at full throttle, after about 1 hour of normal easy break-in / heat cycle to run in the bearings, I give it full thtottle stabs, then let off to cool, .

The heat and pressure from the full throttle stab wont build up, it is cooled by the over rich low speed setting I like to use for break in.