Detonated piston & blew head gasket. Now what?
 

First, how should I proceed with this?

Second, how do I prevent it from happening again?

It was pointed out to me that I overloaded the motor with a bigger prop (23p mirage +) and was running too lean so it blew a chunk off of the #6 piston and blew the gasket between 4 & 6. I'm running a lightly modified 350 vortec (guessing around 350 HP) on an alpha 1 with 1.65 gears.

http://i191.photobucket.com/albums/z...ps9hkmadi2.jpg

#4 and # 8 also have some very light scoring. #4...

http://i191.photobucket.com/albums/z...psb5o1fawm.jpg

Scoring is so light that I can't catch a nail on any of it. I'm getting 4.031-4.0325 on the mikes.

So, what should I do next? Probably a very dumb question but any chance I can just put a new head gasket on and go (after getting it tuned right so it's not running lean)? Is that piston trashed and just waiting to explode more? Can I get another month out of her without doing any more damage if I just cruise around below 4000 RPM with a mild prop? Boating season is almost over so one more month would be nice then I can pull the motor. But, I've already torn half of it apart so it's close to being ready to pull now.

I really don't think I need to bore it with those numbers I'm getting and such light scoring. But, I'm obviously not a pro or I probably wouldn't have blown it up in the first place. LOL. So I'm thinking just a light honing and at least one new piston. Or, do I need to replace all of them? Pretty sure they're Silv-o-lite Hypereutectic if that matters. Also pretty sure they're not a balanced set.

Hone it myself or take it to a shop? It should only be about $100-125 to take it to a shop. Does it even need honing since the scoring is so light and the tolerances tight? Do I need to re ring all pistons or just that one? Or just the ones that light scoring on the cylinder walls? I've read a little about moly rings for making a better seal and preventing blow by. With the light scoring, should I go with a set of new moly rings? Pretty sure the cylinder needs to be honed with the right grit for molys?

Considered stroking it but the rebuild is only 2 years old and the damage is very minor IMO. I'm probably looking at $1500 minimum for parts and machine work for about 35 more HP? I'm also on an Alpha and I'm afraid of tearing it up with what I have now.

As far as what caused it... I was running an edelbrock 1409 600 cfm. It was recommended I go with a Holley double pumper 750 because a SBC with my mods will run lean. Is that damage something that builds over time and finally breaks or is it just based on the current conditions? What I'm getting at, did I cause it by running lean on the edlebrock for 1.5 seasons or not tuning the holly right for 2 weeks? Or is the holly messed up? It is a factory refurb & still under warranty so I don't want to keep it if it's just going to keep blowing stuff up. I though I had it dialed in right as far as the fuel/air but it seemed awful lean to me. When it came to me from the factory after being flow tested the mixture screws were only backed off about 1/2 a turn. When I tuned it, I could only back off the mixture screws about 3/8 of a turn or it would sputter and stall and not want to start again. With the flame arrestor off I could back em off 1/2 turn so I'm assuming they flow tested it w/o a flame arrestor.

When I was taking off the heads, I also noticed that 4 of my intake manifold bolts were loose. All 4 on the opposite side of the detonation if that matters. It still had a tight seal (had to encourage the intake to come off) and I had just had a vacuum gauge on it about a week ago and it didn't show a low or slow dropping reading.

And, I confess I didn't check the fuel pressure or secondary accelerator pump but I had no stumble on acceleration or at WOT.

You have a lot of questions, but for one, you can't reuse that piston. A 600 marine edelbrock isn't too small, and a 23 pitch prop isn't too big as long as you are turning correct rpms. I have a modified vortec 350 and have run both of those with no issue.
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What was the total timing you were running? How are the heads? Damage looks to be from severe detonation.

I said it was a dumb question. LOL. Just wishful thinking that I could get a few more days on the lake this year.

I was only turning 4700 RPM when it happened.

32 degrees total timing.

After brass brush & kerosene...

http://i191.photobucket.com/albums/z...ps35zrsc1f.jpg

After a couple of light passes with surfacing stone...

http://i191.photobucket.com/albums/z...pspw6b6wjn.jpg

32 total is to much for a vortec head,usually 28 is tops,that with a lean mixture was the issue.take the engine to a experianced machine shop,just changing one piston would not be the correct path to a happy engine.do it right and you will enjoy next year,s boating.

You will want to have that head checked with a straight edge to see if it needs to be resurfaced. Good chance it does having blown between cylinders.

X 2. Time to tear down and do it right. I am surprised all your valves are still in tac. I hear what your wanting to do but look at it like your thankful. I'm afraid if you replace a piston quick to get in a few more runs you will regret it. Have your heads gone through and spare no expense on your exh valves when you rebuild. Just curious what your spark plugs look like?

Please post a pick of hottest one.

No coloring/carbon on heads and pistons.

Hard to see from here, but one piston (1st photo) looks like it has had material removed (detonation) and looks like ring lifted.

^^^^^^ 100 % agree.i think the water from the blown head gasket steam cleened a few cylinders.

Ooops...I didn't catch that. Doh.

You were lean, you had a loose intake manifold, your timing was too far advanced, you ran it hard, consider yourself lucky thats all you tore up..... Time to pay the nice man holding the shiny wrench who is shaking his head and thanking you for your business.

I see a 383 stroker assembly in store. Smile smile.

I don't agree with the 32* being too advanced, unless the stock Vortec dinky cam and decent compression.

Experiences may vary.

I ran a 355 with flat top 4 valve relief Pistons, vortec heads, comp xtreme marine 262h cam. I ran it at 31* all in. I got a ton of hours on it.

Detonation is caused by
lean, lack of fuel for some reason
too much timing
octane to low and or too high of compression
hot water temp
hot intake air temp

pick three,lol.i will go with 1 2 and a little of 4 caused from the detonation.

I've come across articles in the past I read for some reason or another and most articles/forum post seem to be btwn 30/32 total. I never dug into why however those total advance numbers would always seem to pop up. Does it make sense to me without researching it. NO. Are the combustion chamber on those designed differently that makes some magic prespark or something? Only vortec heads I've run were/are on gm trucks with 89 octane. I'm not agreeing or disagreeing with anyone on the subject rather curious.

I ran a 350 with a hot cam and forged flat tops. Had a 650 demon on it. 32* total timing and it was all in by 2500 rpm. Ran a 21 mirage on a 1.65 ratio drive. Turned around 5600 rpm. Never had a minutes trouble except for the occasional broken Alpha. Same engine is still running in my buddies boat today.

Yeah, think I pretty much copied your build when I was researching what to do when my 305 bit the dust. You and a couple others on here were running similar setups. Dual plane intake also.

Previous photos of the heads were after a little cleaning and a couple passes with a surfacing stone to knock the carbon off. Here's one untouched except for a quick wipe with a rag. Didn't do anything but stick to the carbon and make it whitish.

http://i191.photobucket.com/albums/z...psqk7tbuiw.jpg

Here are plugs 2, 4 6, & 8, in order...

http://i191.photobucket.com/albums/z...psdpa9xfsn.jpg

And 7, 5, 3, 1 in that order...

http://i191.photobucket.com/albums/z...psgcf7luzg.jpg

And here are the piston tops, untouched...

http://i191.photobucket.com/albums/z...psefljti12.jpg
http://i191.photobucket.com/albums/z...psg1vtfxrd.jpg

And, yes, I will check the head surface. Just need to track down my straight edge and feelers.

Just the exhaust valves or all valves? I thought the #1 thing to do was make sure the valve guides and stems haven't worn out. I'll measure for deflection and pull em and measure for wear. Just need to track down my dial indicator...

Both intakes and exhaust are important. The exhaust just needs a better valve (alloy) A good quality inconel Exhaust valve Is just more resistant to heat and made from a nimonic alloy. Much more resistant to heat than stainless. Every one of my marine engines gets those and even muscle car builds. That doesn't mean to use blue light specials for intakes. Not really many areas to cut corners on marine engines unless you idle back and forth through a channel all day.

assuming OP would have heads brought to speed shop. Btw unless I'm seeing things from iPad it appears to much timing by looking at plugs. Certainly not starving for fuel that's for sure.

How about the pistons and rings? Those Silv-o-lite hypereutectic flat top, 4 valve relief good enough for what I have or is there something better in the $150-200 range? I did research it before the build and I think those got me where I needed to be to have a safe compression ratio and still be able to run 87. I was going to do a forged D dish and a thinner head gasket to get an optimal quench but then most people told me it was a waste of money because it's not a race engine.

Rings? Cast, Ductile, or steel? Moly coated or no?

I'll take the heads to a shop if they need resurfaced or the guides are worn or they need seat work. All of that was just done/checked two seasons ago so I'm trying to stay optimistic. LOL

Any recommendations on some reasonably priced valves for what I have? I'm down for spending money where/if it's needed but this is also a mild build and I really don't run it hard. Not looking to squeeze every ounce of performance out of it and using the absolute best parts if they're not going to make much difference. I rarely run for more than 20 minutes at a time. From dock to our favorite beach or island is under 20 minutes. And when we're tubing it only takes me about 5 minutes to flip the kids off the tube. LOL I rarely run WOT either. Was just doing it to test a new prop.

you cannot cheat a build because you don't really beat on it, spend the money, do it right and it will be ok, you don't need the BEST top of the line parts, but don't cheap out, that never helps...

Once it is together I suggest a wideband for tuning, I went years without it, the last 2 seasons I have had it full time and I will say it's priceless to tune and then keep eye on things, may be overkill but I recently was able to resolve a very annoying issue because I had a wideband....

couple of things, those pistons are pretty much junk from the start, vortec heads have a higher compression that std heads, you can run the 600 cfm carb, but once you start changing anything without a 02 to see where you are, the pin has been removed, the factory merc carb 350 use a 750 weber(same as edelbrock), and yes to me 32 deg is high with vortec's, again with out knowing AFR's its russian ruliet, damage is from running lean...

Ok. I'll get a wideband. Any recommendations for which brand/model?

Same for the pistons. Not opposed to getting better components if what I have is not good enough. Just need to know which ones to get. Any recommendations?

I like AEM wideband, easy to set-up and see in the sun. Sensor seem to be more forgiving to water then others, can be found for about 200 bucks as well.

I'm going to guess that head is junk, or they will be taking to much off and will raise compression to much. it doenst look good between those two cylinders.

IMO 87 is a craps shoot. I always ran 93 in mine, especially if the gas I was buying had ethanol in it

You have to make the ultimate decision regarding parts etc however on Pistons if you can find a deal on a set of forged go for it. There's cp, je, wesico, auto tek, etc. Proper clearance and build as far as I'm concerned you'd have no issues with a mild NA build. If you go cast is lean towards the KB performance Pistons. They run for ever. In regards to rings you could just use a speed pro moly coated cast. Yes there are numerous different routes you can go there as well. If you so choose to save a little money on cast Pistons and rings in my opinion that's fine but just remember to not scrimp on the exhaust valves.

Just do your research and you'll be fine. If you have a machine/speed shop nearby have them ck block, rods etc before reassembly. Over time rods stretch and may need resizing. It's relatively inexpensive.

I always use this on every fill up. Snake oil?

http://www.homedepot.com/catalog/pro...db0a28_400.jpg

It keeps the alcohol from separating but can't imagine it does much as far bringing the BTU's back up. I ran the Lucas branded treatment just to keep the carb from gunking up

I'd get a head gasket and piston combination that nets you a .040 quench. Proper quench, fuel, timing, loading and temp go along way to staving off detonation. Then when it's together run the shorter prop first. If it makes the engine over speed go up, but not til you know you won't torque load the engine.
I have a 9.85:1 iron head forged flat top 383 that does fine that way.
I do not have a wideband either, but I just checked my plugs and they are lean, so I'm jetting up before my next run. I'm probably a little lucky/safe because my ignition has knock retard.
If your compression will end up much over 9.6:1 perhaps get some spark plugs that are one range colder. The colder plugs resist detonation.

Pre-ignition.

And I agree with what you said above.

the question........Detonated piston & blew head gasket. Now what?

simple

4l whippled efi bb,say in the 580ci range.:D end of story.go big or go home.

really should used forged pistons, marine engines hard on them as under a load all the time..

I did get the quench as close as I could with the original build. That was a few years ago and I don't recall for sure but I couldn't get it to the ideal .040 without zero decking the block and/or using expensive D dished forged pistons and/or a thinner head gasket and/or raising the compression too high. I think the thinner head gasket would have done the trick or gotten me very close but they don't make them for a marine application. I remember seeing a few references of one company making them in the past but they don't anymore. And, most people told me it wouldn't make that much of a difference since I wasn't building a high performance race engine.

Sounds good. Wanna trade? :)

All valve stems are .342 to .3425 (.343 is new)

Valve stem clearance is .002 to .0025

Heads are flat. Can’t fit a .002 feeler between a machined straight edge. Can’t even fit a .0015.

I hit the intake seats with a brass wheel on the dremel but it disintegrated before I could get to the exhausts. First pic is the one that blew up.

http://i191.photobucket.com/albums/z...pscrvdczlh.jpg
http://i191.photobucket.com/albums/z...psoj8nms5j.jpg
http://i191.photobucket.com/albums/z...psoo5ms88m.jpg

I stuck a flashlight into the ports with the valves seated and there was some light that came though. Not much but there was some. So, I'm thinking I just finish cleaning everything up and lap the valves and heads/valves are done. Also, since I'm running a bigger cam, going to pull the pressed in studs and replace with screw in's while heads are off.