Hussein's 1998 V70 Xr : The Force Awakens


lookforjoe
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i am not sure i would rule piston design flaw out just yet...many opinions expressed which there is nothing wrong with that , but that's all they are, opinions ... bottom line ,  this is a hard ache that happen to someone that poured a lot of time, sweat and $ that has utmost respect here and it ended this way. 

 

haw many total miles on this engine/pistons ? 

 

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Hi Hussein, just wanted to drop in and thank you for all the well documented live R&D you've done on your car and shared here.  This forum lives off user generated content, so hopefully you will revisit the platform (C30 or possibly a future 850 or something ;) ).  We will always need some more of the hand drawn legal pad sketches showing how you will braze something the way Volvo should have done it from day 1.

The issue I think we run into with these cars is that you can really only go so far with X displacement.  If you are satisfied at 400-500bhp it is feasible, but much beyond that and you end up with a number of points of high levels of stress.  Maybe an S60 T6 bears some consideration for those looking to go beyond those levels...

My guess on failure is that somehow Wiseco overlooked something.  In any case, certainly took the car past where most would or could.  I wish we had a a final trap speed on it though!

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As there were more reports of the same cracking, all 5 of the pistons where cracked in much the same way, and by the nature of the cracks, I regard them as equally likely at least.
Also I can't think of a reason why all 5 would crack like that, unless the rods were touching them. I'm not sure if that's even possible that high up in the piston.
The location of the cracks make detonation very unlikely, as the tops of the pistons were undamaged.
A weak spot giving way due to going through many heat cycles could very well have caused this to happen.
Without the hardware in hand it's hard to say, but just because Wiseco is a big, well known company doesn't mean they cannot make mistakes, or produce bad batches.

We may never know what happened, and I'm not pointing a finger here, but not even seriously considering a design flaw at all isn't the right mindset imo.

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Well that's a bummer, Dude. That's a bummer.

Understand the point to move on. I've regretted parting out my green 854 off and on over the years, but it's easy to be nostalgic about the good times and forget how much shit goes wrong when you're pushing the limits. I'm with Eric here that putting this much power through the given displacement just isn't going to be ultimately reliable. Yeah yeah I know there's a lot of strong stuff out there but whenever I see those EVOs or GTRs with a bunch of extra power shit breaks all the time just the same.

Best of luck with the new car!

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what's more likely to be the case

 

weisco design flaw OR something somewhere in his setup was causing an issue

It could well be that the shortskirt-piston/longer-conrod combination didn't agree that well with this block after all - for this type of forged pistons that is. Increased sideways pressure in combination with piston-rock due to the shortskirts may have loaded the skirts in such a way that it fatigued the alloy relatively quickly. Whether the essential flaw then lies in the piston design or the custom conrod/shortskirts design remains to be investigated.

Both the bores and skirts seem to show these vertical markings as signs of excessive sideways loading

Edited by Boxman
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I touched base with my Wiseco contact:

 

Hi Trent,

 

The skirt breaking off like that is really strange.

Excessive piston to cylinder wall clearance could cause that. The piston would be rocking in the cylinder.

If the piston came into contact with something, that could also cause the skirt to break off.

 

If you’d like to send them to us, Harvey here could take a look at them. We could send them down to the lab at the factory for review.

 

Best regards,

Adam Silverthorn

PMI Canada / Wiseco Piston Canada

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Those are the only things I can really think of as well.   It either was contacting something.... unlikely if there weren't marks found anywhere...  or perhaps the clearances were off and it was allowing the piston to rock in the bore.        Or..... the skirts of the pistons were too short for the rod length and stroke and it was side loading the piston excessively.    With the longer rod it tends to reduce the side loading but the skirts on these are shorter from what i know.   

 

 

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