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Cast pistons and boost

 
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clay
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1972 Chevrolet Nova

PostPosted: Fri Jul 18, 2014 6:42 pm    Post subject: Cast pistons and boost Reply with quote

Guy at work brought something interesting to work. He has a BMW 335 twin turbo. He's an electrical / electronic engineer and has made several upgrades to the car. He's upped the boost of course and has it setup to measure the ethanol content and tune accordingly. When he turns the key on the speedometer will display actual ethanol content. This is just one of the neat electronic things he's done. Stock boost was around 6 lbs and he's running 18 with E85. Now comes the not so good part.




Now it looks like he just burned a piston but the piston top doesn't show any of the classic signs of detonation. Next few pics are where it gets interesting.




I told him you don't think you're lucky but you are. He drove it about 50 miles after this happened. I don't know why it didn't completely fail and try to shove the rod out the side. This last pic is curious to me. Even though it's cast it is a really good looking piston. I'm wondering what the brown colored band is above and below the top ring land. It's uniform so it's not leakage and I'm thinking this piston has a coated top ring land.


He has the engine out and it didn't hurt the bore and he's trying to decide what to do - replace with stock, upgrade, etc. Thought everybody might find this interesting. Clay

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clay
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1972 Chevrolet Nova

PostPosted: Fri Jul 18, 2014 7:51 pm    Post subject: Reply with quote

Forgot to add - take a guess how much a BMW dealer wanted to fix it. Don't just think stupid - think reeaally stupid......Clay
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10sec.et
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1969 Oldsmobile Cutlass

PostPosted: Fri Jul 18, 2014 10:18 pm    Post subject: Reply with quote

i wonder if maybe he got a bit of crappy fuel that last time. we all know how hard it is to watch all the gauges at WFO. probably didnt take much to blow that top part of the piston off. it actually looks like a fat nitrous tune that detonated.
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It seems we can look at our magical Balls and come up with a fix?

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10sec.et
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1969 Oldsmobile Cutlass

PostPosted: Fri Jul 18, 2014 10:18 pm    Post subject: Reply with quote

oh, my guess on the dealer cost is $15K
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SMOKEmUP
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1979 Chevrolet Camaro

PostPosted: Sat Jul 19, 2014 12:03 pm    Post subject: Reply with quote

Clay...are you building a BMW motor? (With forged pistons)

My guess on the dealer quote is $20K.

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Big Dave
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PostPosted: Sat Jul 19, 2014 7:45 pm    Post subject: Reply with quote

I don't know if BMW sells crate engines (I know they ship them to dealers that are not qualified to work on them as a warranty replacement as we had a few when I was working twenty years ago for testing in marine applications). But I would think $20K would buy a new six or four banger motor making it cheaper to replace than rebuild.

Did you explain how lucky he was to survive that incident with out blowing it up? That is an incredibly unusual event for a cast piston. I don't know whether to praise German engineering or to trust just dumb luck.

Big Dave
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clay
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1972 Chevrolet Nova

PostPosted: Sat Jul 19, 2014 9:26 pm    Post subject: Reply with quote

No I'm not working on it I just thought this was one heck of a failure. I told him he didn't know how lucky he was. I still can't believe he drove it about 50 miles after it happened. He knew he had a problem and the drive was to get it looked at with a bore scope. I talked to him a little bit about forged pistons. Basically told him they would still fail with the wrong tuneup but they would stay in one piece. Rebalancing would be an extra cost for him plus buying all 6 pistons of course. I don't know what he's going to do yet. Some of you almost got stupid enough - dealer wanted $23,000 to fix it. I did ride in it and it was VERY impressive. What really got me is no noticeable turbo lag - very responsive. As far as power it was originally rated around 300 hp but I'd guess his is making 500 by the butt dyno. Not bad for 181 c.i. Clay
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af2
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PostPosted: Sun Jul 20, 2014 9:18 pm    Post subject: Reply with quote

Considering JE and everyone else makes forged pistons for around $1200 I don't see the parts costing more than $4000.
Man that is a lot of labor....
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10sec.et
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PostPosted: Sun Jul 20, 2014 9:29 pm    Post subject: Reply with quote

BMW thinks they are special. its stupid and so are the people that pay full price for that stuff . you're absolutely correct. technically theres nothing special about that engine.
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Paul P
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1971 Chevrolet Chevelle

PostPosted: Sun Jul 20, 2014 9:47 pm    Post subject: Reply with quote

The only BMW motor feature I saw that was different was the Main oiling was fed into the cap so he oil hole for the bearing was there right at the load point bottom middle of the cap. The main cap was really beefy too likely because there was a hole in it that took strength away.
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clay
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PostPosted: Sun Jul 20, 2014 10:04 pm    Post subject: Reply with quote

Yeah I don't get that price either. I don't know what year he has but looking on Craigslist there is a 2011 for $24,500 and I'm sure they'd take $23,000 - FOR THE WHOLE CAR! I'll update on what he finally winds up doing. Clay
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PostPosted: Mon Jul 21, 2014 10:41 am    Post subject: Reply with quote

I'd say do it for half the dealer cost.

$12K Price
$4k Parts
$2K machine work

$6K Profit.

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Paul P
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PostPosted: Mon Jul 21, 2014 10:41 am    Post subject: Reply with quote

Oh yeah that pricing is way stupid... Most BMW owners I know buy newer so that they have a warranty because of all the small problems that can cost big $$$.
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