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Talk about engine building here. New products, tricky questions or showcase your work - If it's engine building related it's welcome here.
= Resolved threads
Hello all,
Uncommon to rebuild: skyactiv 2.5L out of a 2015 Mazda CX5. Purchased and drove 2 hours running on a couple cylinders.
Leak down: Cyl 1,3,4 exhaust/intake valve leaks.
Teardown revealed "blunt force trauma" inside engine, which is likely what bent the valves, see pictures. Cylinder walls okay.
Deck had 0.008" gap between cyl 2/3 when checked with straight edge.
Machine shop found 5 slightly bent valves, decked head, faced valves and refinished valve seats.
Concerns:
- Service manual specs: deck warp limits: 0.002", no machining allowed!
- Machinist could not "remember" how much he machined off the head. But said he did not remove an alarming amount.
- This engine is running over 13:1 compression ratio from factory on 87 octane.
Questions:
1. Should i run OEM headgasket or get Cometic to make me one with 0.008" added material?
2. Why is there no machining allowed? How can I confirm what I have will not be a problem?
Attached Files
Damaged-head.jpeg
- Machined-remnants-of-damage.jpeg
- Piston-damage.jpeg
Because of the extremely high compression and the fact that Mazda use wide variations in valve timing to effect final compression and internal EGR there is likely close to interference with the piston under normal operation, if you skim the head or deck you will likely have valve to piston contact unless you are running a custom calibration, clearance the pistons or run aftermarket pistons or recover the height with a gasket or combination of some or all.
Thank you for your input, Slides.
I Don't think the early generation of these engines had EGR control.
What would be the best method for me to identify gasket thickness that I need to order? Clay method?
That would probably be the safest. You would need to work out the worst case intake and exhaust cam variable timing positions in operation.
It looks like im stuck with limited gasket options, Cometic does not have the tooling for this.
Regarding gasket thicknesses, I see various manufacturers online (MAHLE, Victor Reinz, ENGINETECH, etc.) list the gasket at various thicknesses. Not sure if they are referring to crushed or uncrushed dimension. (0.0110"-0.023")
What are your experiences with these basic OE replacement options such as those from rockauto? Are they all the same OE size?
