Broken DASA Power Valve
- Thread starter Ken23
- Start date
Big Kahuna
Administrator
- Location
- Tuscaloosa, AL
uh, looks like something was hitting the face of the Guillotine ......
Was definately hitting the piston at some point?? Probably what ultimately broke the stem?
Looking at sides of the blade shows signifigant wear? Hard to tell how bad by the pics?
Measure cyl slide path (ways) width in both #1&2 and compare? Guessing they are different?
Also compare blade withs # 1&2? Guessing you will more than likely find inconsistencies?
Looking at sides of the blade shows signifigant wear? Hard to tell how bad by the pics?
Measure cyl slide path (ways) width in both #1&2 and compare? Guessing they are different?
Also compare blade withs # 1&2? Guessing you will more than likely find inconsistencies?
Big Kahuna
Administrator
- Location
- Tuscaloosa, AL
Think Jr is saying compare both blades. Measure up and down on both side. Believe he is wanting to see if one blade is longer than the other which could be causing it to strike the piston. dont believe he is asking about the thickness.
- Location
- Here
Don't do that stuff over the stator section. If a chunk fell in, and you didn't see it.....
Pump lives matter.
Pump lives matter.
- Location
- Redondo Beach, CA
Only one of those pictures is clear enough to really tell anything...but my nerdy bored on a Saturday morning over engineered 2 cents...
Assumptions:
1) There is an obvious stress riser where the small stem diameter meets the larger boss/spring locator. A larger fillet radius here would help alleviate that stress riser.
2) The PV is 6061-T6 aluminum. Why? It's common, readily available, versatile, lightweight, easy to machine, and CHEAP...also...most jet ski folks aren't in the market of making parts from exotic alloys. 95% of your "billet" aluminum parts in any aftermarket are manufactured from 6061-T6.
This looks like pretty textbook fatigue failure. You can very clearly see the point of initiation, crack propagation, and finally the fast fatigue fracture. (meaning it starts to crack, the crack spreads, and it finally breaks suddenly). I suspect it was accelerated by 1 of 3 things, or a combination of the 3.
1) Over torquing of the PV cap bolt damaging the stem at the stress riser.
2) Excessive clearance between the PV and the cylinder causing it to rock (and fatigue).
3) Piston contact of the guillotine, although this likely happened after the stem failure.
Why do I say excessive clearance? Because if the clearance was too tight causing galling and stiction, the PV would stay stationary, or stick. Then, the only forces acting on the stem would be the spring force, and the force created through exhaust pressure filling the bellow. Both of these are very small forces that in no way could cause tensile failure. Now, if it were excessive clearance causing rocking; this *could* cause small shock loads in the PV and over time accelerate a fatigue failure at an already weak point (the stress riser).
As to water causing the failure due to hardening or making the material brittle? Not likely. Actually...I'd say no way, no how. First, 6061 is not very quench sensitive compared to say... a high alloy steel (where brittle failures are more likely in heat treated specimens). Second, in order to heat treat and quench and temper aluminum alloys, you need to get the material to ~900*F or higher. These PV's are held within the cylinder, which is a giant heat sink. So while they are exposed to small amounts of hot exhaust gas, I'd feel safe to assume their temperature is equivalent to that of the cylinder under operation...ie... nowhere near the 900*F it takes to heat treat aluminum. If it were that hot, the rubber PV bellows which are filled with exhaust gas would melt very quickly.
My recommendation? Call Dasa (I know, "call your engine builder" is becoming the most popular response around here) and get the proper clearances and tolerances of the PV to cylinder, the PV to piston when installed, and while you're at it, ask about the acceptable piston to bore clearance. Measure your cylinder and your new PV's to make sure you're within the specified range. Measure your bore and pistons, you may need to bore the cylinder after the rings made contact with the PV's. Once all that is OK, make sure you have proper clearance between the new PV's and the pistons when installed. Finally, when installing the PV caps, just snug the bolts with a drop of red loctite.
Good luck and let us know what you find!!
Assumptions:
1) There is an obvious stress riser where the small stem diameter meets the larger boss/spring locator. A larger fillet radius here would help alleviate that stress riser.
2) The PV is 6061-T6 aluminum. Why? It's common, readily available, versatile, lightweight, easy to machine, and CHEAP...also...most jet ski folks aren't in the market of making parts from exotic alloys. 95% of your "billet" aluminum parts in any aftermarket are manufactured from 6061-T6.
This looks like pretty textbook fatigue failure. You can very clearly see the point of initiation, crack propagation, and finally the fast fatigue fracture. (meaning it starts to crack, the crack spreads, and it finally breaks suddenly). I suspect it was accelerated by 1 of 3 things, or a combination of the 3.
1) Over torquing of the PV cap bolt damaging the stem at the stress riser.
2) Excessive clearance between the PV and the cylinder causing it to rock (and fatigue).
3) Piston contact of the guillotine, although this likely happened after the stem failure.
Why do I say excessive clearance? Because if the clearance was too tight causing galling and stiction, the PV would stay stationary, or stick. Then, the only forces acting on the stem would be the spring force, and the force created through exhaust pressure filling the bellow. Both of these are very small forces that in no way could cause tensile failure. Now, if it were excessive clearance causing rocking; this *could* cause small shock loads in the PV and over time accelerate a fatigue failure at an already weak point (the stress riser).
As to water causing the failure due to hardening or making the material brittle? Not likely. Actually...I'd say no way, no how. First, 6061 is not very quench sensitive compared to say... a high alloy steel (where brittle failures are more likely in heat treated specimens). Second, in order to heat treat and quench and temper aluminum alloys, you need to get the material to ~900*F or higher. These PV's are held within the cylinder, which is a giant heat sink. So while they are exposed to small amounts of hot exhaust gas, I'd feel safe to assume their temperature is equivalent to that of the cylinder under operation...ie... nowhere near the 900*F it takes to heat treat aluminum. If it were that hot, the rubber PV bellows which are filled with exhaust gas would melt very quickly.
My recommendation? Call Dasa (I know, "call your engine builder" is becoming the most popular response around here) and get the proper clearances and tolerances of the PV to cylinder, the PV to piston when installed, and while you're at it, ask about the acceptable piston to bore clearance. Measure your cylinder and your new PV's to make sure you're within the specified range. Measure your bore and pistons, you may need to bore the cylinder after the rings made contact with the PV's. Once all that is OK, make sure you have proper clearance between the new PV's and the pistons when installed. Finally, when installing the PV caps, just snug the bolts with a drop of red loctite.
Good luck and let us know what you find!!
- Location
- Here
A lot of good points and opinions. I'd still like to see better photos of the fracture point.
With the supplied pics, I'm still seeing porous casting with aeration in the pour. But hey, I'm side saddling on the internet.
With the supplied pics, I'm still seeing porous casting with aeration in the pour. But hey, I'm side saddling on the internet.
- Location
- Here
Ahem...... I may have noted same, in previous post.
Again, I'm just a mudslinger, slinging mud for a practice pond. But, take a good long think about, the "obvious stress riser where the small stem diameter meets the larger boss/spring location." and go back and read what I posted. But hey, I just make parts for fun, or fix the poop that I have to install. I mean, any machinist that knows there a$$ from a hole in the wall knows you need a radius on a shoulder to reduce stress.
Anyway, I'm going back to hauling item 4, for the dam in the pond. BBQ is fired up, chicken, beef, and pork are going on, while I cut and section trees, cut out clay, and mix the cement.
Dumb, fat, and happy. Well, o.k. At least I'm happy.
And not for nothing, but engineers don't always have a clue. That's the best part. Y'all can spout specs, but in the real world, well. I get it, gotta make up for that 'spensive edu-ma-cation, right. I just wish part of that poop involved actually working with the garbage you designed.
Burgers, dogs, pork loin, and a huge rump roast are on the fire. If you are near me, swing on by. Just bring something to get mudy in.
Again, I'm just a mudslinger, slinging mud for a practice pond. But, take a good long think about, the "obvious stress riser where the small stem diameter meets the larger boss/spring location." and go back and read what I posted. But hey, I just make parts for fun, or fix the poop that I have to install. I mean, any machinist that knows there a$$ from a hole in the wall knows you need a radius on a shoulder to reduce stress.
Anyway, I'm going back to hauling item 4, for the dam in the pond. BBQ is fired up, chicken, beef, and pork are going on, while I cut and section trees, cut out clay, and mix the cement.
Dumb, fat, and happy. Well, o.k. At least I'm happy.
And not for nothing, but engineers don't always have a clue. That's the best part. Y'all can spout specs, but in the real world, well. I get it, gotta make up for that 'spensive edu-ma-cation, right. I just wish part of that poop involved actually working with the garbage you designed.
Burgers, dogs, pork loin, and a huge rump roast are on the fire. If you are near me, swing on by. Just bring something to get mudy in.
- Location
- Here
.....he said textbook.
- Location
- Redondo Beach, CA
Hahaha. Too funny. And good points. Friggin' engineers...
Btw, the pv's are not castings. They're machined from billet. So it's highly unlikely theres an inclusion.
DAG
Yes, my balls tickled from that landing
- Location
- Charlotte, NC
How are the billet Ingents made K-lee.... At a foundry perhaps
- Location
- Redondo Beach, CA
DAG
Yes, my balls tickled from that landing
- Location
- Charlotte, NC
But whats forged? The casting?
- Location
- Redondo Beach, CA
Pretty sure by definition a forging isnt a casting. Crashby. Read a book.