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Author Topic:   Damaged pistons - pics - opinions?
fairlaniac
Dirt Maniac

Total posts: 110
posted October 17, 2003 09:37 PM  
Our last race out we encountered the damage shown in these pictures (see links). Can anyone offer some ideas on what may have happened? It's a .040 Chevy 350 with 11.5:1 lightened Wiseco pistons, 2.02 heads, Brzezinski 4bbl intake with a Carter AFB. If there is any more info you need, I can supply best to my knowledge. I notice how the damage occurs near the piston ring end gap? We're looking on correcting this for next year. Oh yeah, we're running 1/2 Sunoco 94 and 1/2 Cam2 racing gas.

Pic links: http://home.dejazzd.com/thebenders/images/cyc2-2003.jpg http://home.dejazzd.com/thebenders/images/cyc3-2003.jpg http://home.dejazzd.com/thebenders/images/cyc4a-2003.jpg http://home.dejazzd.com/thebenders/images/cyc4b-2003.jpg

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Doug
"Lift for a second, that's where you'll finish!"

outlawstock17
Dirt Forum Champ
Total posts: 1363
posted October 17, 2003 09:47 PM  
looks like detonation to me. stop mixing your fuel. racing engines need racing fuel. how much timing advance are you running?

Rookieracer76
Dirt Freak

Total posts: 289
posted October 17, 2003 10:01 PM  
fairlaniac, had the same thing happen to me. running a very similar engine combo and did the same thing with the mixing fuel. I only had about 10 races on my engine. Curious to know why this happend too...

dilbert
Dirt Full Roller

Total posts: 38
posted October 17, 2003 11:17 PM  
I don't know, could be detonation that just did its damage at the weakest point and then the ring lined itself up there, but I'd be suspicious of the ring gap relationship too if it occurred on 3 cylinders. What kind of rings? Are they moly or cast? Also, are you sure they were gapped correctly when the thing was put together?
You might try posting this question in the Engine Tech section. May have more pro engine builders surfing there.

rocket36
Dirt Freak

Total posts: 209
posted October 18, 2003 02:07 AM  
detonation.
with 11:1 cr you'll need to run racing gas.
personnally i would run minimum 100 octane and set correct ignition timing.
plenty of people retard the timing to overcome detonation but you won't stop it and you'll end up with a slug of an engine.
correct ignition advance is way better than compression.

Trapper
Dirt Full Roller

Total posts: 64
posted October 18, 2003 07:49 AM  
I would suspect that the bore and ring gap were not correct. A forged piston requires a little more clearance. If it is too tight it will create a detonation problem.

TRAP

rico 08
Dirt Forum Champ
Total posts: 1139
posted October 18, 2003 01:12 PM  
I would look into the carb.I'm not a big fan of carter carbs,the side by side float bowls tend to dump fuel on the drivers side and lean out on the passenger side when in the corner.Are you sure those are 11-1? they look like flattops to me,so the fuel mixing would be fine except if you we're running a really small chamber head(49cc).

fairlaniac
Dirt Maniac

Total posts: 110
posted October 20, 2003 09:34 PM  
Thanks for the input! We're running 36 degrees total, the pistons are 11.5:1 but the engine probably is not. The head and block have been decked. We've actually paid a reputable engine builder to do the engine. We're still unsure what we've got. We definately need to be more involved with the inards of the engine. We're sure we are at the bottom of the totem pole as far the best customer. The guys shop is a proven winner in the NE DIRT Modified series.

------------------
Doug
"Lift for a second, that's where you'll finish!"

Raz_900
Dirt Forum Champ
Total posts: 635
posted October 22, 2003 08:33 AM  
Those pics all look like a ring butting problem. It could be from excessive heat (either coolant or comb. chamber) or incorrect end gap. Take a non-broken piston out and check the top ring gap. I'd like about .020"-.022" for a race motor minimum. But if you have the spec sheet from the pistons, that's the best thing to go by. They might call for more (I use Keith Black's and run the top rings around .032"-.033")

What heads are on it? That'll help determine the actual compression ratio. What octane was the Cam2? That's a generic name and could be anything from 110 to 116. 50/50 94 and 110 will be 102 and 94 and 116 would be 105. I'd be fine with the 105 and 11.5 compression.

hollywoods62
Dirt Roller

Total posts: 22
posted October 22, 2003 07:23 PM  
Sa thing happend to me last year , talked to mach. shop and it was ring gap. Had him gap rings this yer and no prob , Talk to your shop for advice hollywoods62

77k
Dirt Maniac

Total posts: 174
posted January 03, 2004 09:25 PM  
keith black sends pics that look like that and says not enough ring gap will cause it,I had same proplem untill i started .022 plus on top ring

thirty2rocksu
Dirt Roller

Total posts: 18
posted January 04, 2004 08:32 PM  
quote:
Originally posted by 77k:
keith black sends pics that look like that and says not enough ring gap will cause it,I had same proplem untill i started .022 plus on top ring

if you will notice all your pictures show damage right around the end gap on the rings..looks like a combination of two things to me, first one being a little too lean which in turn used up all the available end gap. if it would have had a little more end gap it might have run a little longer but i still think air fuel ratio is where it started.

fairlaniac
Dirt Maniac

Total posts: 110
posted January 05, 2004 08:10 PM  
quote:
Originally posted by 77k:
keith black sends pics that look like that and says not enough ring gap will cause it,I had same proplem untill i started .022 plus on top ring

77K,
Do you happen to have any copies of the pictures from KB?

------------------
Doug
"Lift for a second, that's where you'll finish!"

nascar_krazy
Dirt Roller

Total posts: 6
posted January 11, 2004 11:39 PM  
I spent some time in a local machine shop and I have three words for you....WAY TOO LEAN! Those pistons melted because those cylinders lean out big time.

77k
Dirt Maniac

Total posts: 174
posted January 26, 2004 12:59 AM  

 
here are pics

77k
Dirt Maniac

Total posts: 174
posted January 26, 2004 01:40 AM  


 
Here are more pics[only took me about 3 hours]Have pistons like them.I started gaping at least ,022 and have not burnt any since.I have used same parts,same carb,same tracks, same gas and same timing.I am not a rookie,I have won 3 championships and about 15 top ten.

Raz_900
Dirt Forum Champ
Total posts: 635
posted January 26, 2004 01:23 PM  
.022" or .032"?

I'm hoping .022" was a typo.

77k
Dirt Maniac

Total posts: 174
posted January 26, 2004 06:25 PM  
nope. Paper says circle track gas unrestricted ,bore x .008. A .030 over, 400 is 4.155 bore x .008 = .033 ring gap..003 to .0045 side clearance. These pistons had shorter skirts so the wall clearence is tighter. I will gap from .022 to.028, useing cast rings and i have not burnt anymore pistons up. I know it sounds like a lot but i have seen the facts with my own eyes and engine. P.S do the pistons in pics look like yours?

towmandan
Dirt Freak

Total posts: 370
posted January 27, 2004 07:13 AM  
Way to lean..Also a little wider ring gap might help but It wouldnt have saved your engine do yourself a favor and talk to KP on hear and get you a good carb...In this case I think it would have saved your engine...good luck...towman

Raz_900
Dirt Forum Champ
Total posts: 635
posted January 27, 2004 09:26 AM  
No... my pistons look perfect. I've used the same set of 350 KB231's in 3 motors that have been run virtually without water at times and at 270+ degrees. After 3 years they still look virtually new minus the 1 piston that had a hole burnt through it from bad gas 2 1/2 years ago. (Gotta love $4/gallon gas with water in it :\ ) I also have 2 350's with KB260's in them and they're running fine with the same clearance specs as the 5.7" rod motor. Not counting the 50 or so motors I machined while working in the engine shop with KBs.

I run about .003"-.0035" piston-wall clearance and top ring gap is .032"-.033" with Sealed Power moly's. That's why I was wondering why .022"? That's typical ring gap for a normal hypereutectic piston in a performance application. I could see where running .022" or less on a KB would snap the tops off.

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