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Engine Guru's - Need help-Take a look
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My rat started knocking after coming off full throttle and this is what I found.
-Engine is GenIV 460 ci. Decked .010 -TRW L2465 pistons .226 dome -Stock Peanut heads with some grind work, also milled .010 -Comp cam ,magnum #11-306-4 with .222 and .226 duration @.05, and .525 lift for both, and 110LSA -Stock valve train except stronger springs -Performer intake with 750edelbrock carb -EMI exhaust -Stock TBIV ignition As I understand , these heads average about 119cc I estimate it has around 9.7:1 compression, without accounting for head mill. (maybe someone can help here) As for quench, I estimate about .050 as is with stock gasket, but will verify this build. Built with a budget at the time, and built for grunt, not top speed. Will still get me close to 65 in my 23fter at 5200rpm or so. Motor has maybe 150 hrs total. Surprisingly still had over 160 psi in that cylinder.Rings are still intact. Nothing went down below. Heads are still fine, but will verify. Runs on 93 octane. Trying to get back in water and save some summer. What do you guys think caused this? I am no expert and could use some advice. Reversion? detonation? Other cylinders look fine, but this area seems washed on all of them. As for rebuild, I'm thinking I may be ok down below. Will I be able to find this piston for replacement? I realize TRW has been absorbed by SpeedPro? Will a replacement piston be the same? I read somewhere about oilers being changed, etc. Not sure which way to proceed with this. I will remove that rod and check for straightness, and check bearing clearance. Anything else I should be doing? Thinking about checking all clearances while I am there. Not sure yet. Maybe re-bearing while open? Oil pressure is good. 65 at idle cold. I see some of my lifters have started to lose their crown. I will replace as well. Maybe time for a better cam? I wouldn't mind changing heads if price was right, or maybe open these up with bigger valves? Always happy to get an extra mph or two. But have to stay somewhat reasonable with money. Thanks for your insight. Rich |
That's some serious detonation. How did the plugs look when you were tuning? Did anything cause the carb to go lean? Low fuel pressure ect? Not sure if it had anything to with it, but a 750cfm carb seems on the small side for a 460ci motor. With all of the pounding the motor took, make sure to double check the crank and all bearings surfaces for damage.
Darrell. |
Looks to me like the valve tagged the piston. Isn't that a little half circle indentation in the valve relief? Did you check valve to piston clearance during assembly? They must be close beings they all show that washed area right there.
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Hi Guys,
Plugs looked fine, and actually appear on the richer side of life. As for valve contact, I saw that as well. I am thinking it happened when cyclinder was trying to eject the debris and some got caught in the seat. . Top side of other pistons are smooth and look good except for the washed area. Trying to upload another pic. Server issues here at work now, will try again shortly. |
Originally Posted by rich allen
(Post 3462396)
My rat started knocking after coming off full throttle and this is what I found.
-Engine is GenIV 460 ci. Decked .010 -TRW L2465 pistons .226 dome -Stock Peanut heads with some grind work, also milled .010 -Comp cam ,magnum #11-306-4 with .222 and .226 duration @.05, and .525 lift for both, and 110LSA -Stock valve train except stronger springs -Performer intake with 750edelbrock carb -EMI exhaust -Stock TBIV ignition As I understand , these heads average about 119cc I estimate it has around 9.7:1 compression, without accounting for head mill. (maybe someone can help here) As for quench, I estimate about .050 as is with stock gasket, but will verify this build. Built with a budget at the time, and built for grunt, not top speed. Will still get me close to 65 in my 23fter at 5200rpm or so. Motor has maybe 150 hrs total. Surprisingly still had over 160 psi in that cylinder.Rings are still intact. Nothing went down below. Heads are still fine, but will verify. Runs on 93 octane. Trying to get back in water and save some summer. What do you guys think caused this? I am no expert and could use some advice. Reversion? detonation? Other cylinders look fine, but this area seems washed on all of them. As for rebuild, I'm thinking I may be ok down below. Will I be able to find this piston for replacement? I realize TRW has been absorbed by SpeedPro? Will a replacement piston be the same? I read somewhere about oilers being changed, etc. Not sure which way to proceed with this. I will remove that rod and check for straightness, and check bearing clearance. Anything else I should be doing? Thinking about checking all clearances while I am there. Not sure yet. Maybe re-bearing while open? Oil pressure is good. 65 at idle cold. I see some of my lifters have started to lose their crown. I will replace as well. Maybe time for a better cam? I wouldn't mind changing heads if price was right, or maybe open these up with bigger valves? Always happy to get an extra mph or two. But have to stay somewhat reasonable with money. Thanks for your insight. Rich |
Personally...I don't like the cam being a 110 LSA.
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Originally Posted by tinman565
(Post 3462486)
Personally...I don't like the cam being a 110 LSA.
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Breaking the top ring land can be caused by a combination of too rich and detonation, fuel actually puddles on top of the ring and burns there, seen it several times on drag cars that were setup "safe",
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Those look like pretty big domes on those pistons and I agree with others on the 110 lsa. 112 or 114 would be better.
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9.7 is fairly stout compression with an iron cylinder head in a boat, although the 110* cam actually helps that situation slightly as the increased overlap bleeds some cylinder pressure. Nonetheless... definitely detonation related.
Obviously, the combination worked for 150 hours... yet you're more suceptible to issues such as fuel quality, or a stack-up of minor detonation-creating factors when you've got alot of static compression. Less safety margin. |
Originally Posted by lil red
(Post 3462500)
Breaking the top ring land can be caused by a combination of too rich and detonation, fuel actually puddles on top of the ring and burns there, seen it several times on drag cars that were setup "safe",
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It would help to know the exact cc's of that piston dome. Doing the math with accurate numbers would be the first thing to do. If it is 9.7, you're getting up there to the point of detonation with iron heads. One bad tank of gas is all it would take to melt it. Take a look at the undersides of the other pistons. If they are dark to black, you're making too much heat in the combustion chambers. The first change I'd make is a 120 degree thermostat from Arizona Speed and Marine. Keeping those heads cool is important! Then I would ditch the Edelbrock carb and get a Holley 800 or 850DP. The Holley is easier to tune and the Edelbrock tends to go lean just before the secondaries open, right where we always want to cruise.
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I doubt if being too rich caused this. Usually it's too lean that causes this kind of heat. Look at the way Mercruiser sets up their carb engines. Plugs from them are always dark. Does this engine burn any oil? A little in the chamber can promote detonation and make it look like the engine is running rich.
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Originally Posted by PatriYacht
(Post 3462540)
I doubt if being too rich caused this. Usually it's too lean that causes this kind of heat. Look at the way Mercruiser sets up their carb engines. Plugs from them are always dark. Does this engine burn any oil? A little in the chamber can promote detonation and make it look like the engine is running rich.
I really appreciate all the comments people. Helps me to feel like I'm not going through this alone.. in the dark.. LOL |
Originally Posted by rich allen
(Post 3462552)
Funny you mention the oil. I found 3 or 4 torn umbrella seals when I popped the valve covers off. Haven't even started down that road yet towards root cause. Not sure if this was one of the cylinders. I'll check tonight. I'll also be pulling pan and looking at all this from underside as well.
I really appreciate all the comments people. Helps me to feel like I'm not going through this alone.. in the dark.. LOL |
Originally Posted by PatriYacht
(Post 3462540)
I doubt if being too rich caused this. Usually it's too lean that causes this kind of heat. Look at the way Mercruiser sets up their carb engines. Plugs from them are always dark. Does this engine burn any oil? A little in the chamber can promote detonation and make it look like the engine is running rich.
Oil in the chamber is exactly one of those stack-up conditions I was referring to earlier, when combined with other unfavorable conditions sets you up for a bad day. The dome volume on the L2465F piston at .030 is 25.7cc. I'd say his math on the 9.7 is pretty close. |
Question?
Originally Posted by rich allen
(Post 3462396)
My rat started knocking after coming off full throttle and this is what I found.
-Engine is GenIV 460 ci. Decked .010 -TRW L2465 pistons .226 dome -Stock Peanut heads with some grind work, also milled .010 -Comp cam ,magnum #11-306-4 with .222 and .226 duration @.05, and .525 lift for both, and 110LSA -Stock valve train except stronger springs -Performer intake with 750edelbrock carb -EMI exhaust -Stock TBIV ignition As I understand , these heads average about 119cc I estimate it has around 9.7:1 compression, without accounting for head mill. (maybe someone can help here) As for quench, I estimate about .050 as is with stock gasket, but will verify this build. Built with a budget at the time, and built for grunt, not top speed. Will still get me close to 65 in my 23fter at 5200rpm or so. Motor has maybe 150 hrs total. Surprisingly still had over 160 psi in that cylinder.Rings are still intact. Nothing went down below. Heads are still fine, but will verify. Runs on 93 octane. Trying to get back in water and save some summer. What do you guys think caused this? I am no expert and could use some advice. Reversion? detonation? Other cylinders look fine, but this area seems washed on all of them. As for rebuild, I'm thinking I may be ok down below. Will I be able to find this piston for replacement? I realize TRW has been absorbed by SpeedPro? Will a replacement piston be the same? I read somewhere about oilers being changed, etc. Not sure which way to proceed with this. I will remove that rod and check for straightness, and check bearing clearance. Anything else I should be doing? Thinking about checking all clearances while I am there. Not sure yet. Maybe re-bearing while open? Oil pressure is good. 65 at idle cold. I see some of my lifters have started to lose their crown. I will replace as well. Maybe time for a better cam? I wouldn't mind changing heads if price was right, or maybe open these up with bigger valves? Always happy to get an extra mph or two. But have to stay somewhat reasonable with money. Thanks for your insight. Rich |
i had a set of cast dome pistons do the same thing im my mustang. i tried to go cheap and it cost me, broke in the same spot. right where the valve relief is real close to the ring gland. the casting is week right there and under the pressure it didn't hold, plus they had the large reliefs for a big cam and 2.02 valves. i talked to a rebutable engine builder and he told me i should have never went to a dome cast piston. i think your marks on the top of the piston is the aftermath of the failure.
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Make sure both valve seats are still in the head. (Big blocks drop valve seats) There is no real detonation damage there, look for a source of debris.
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Rich,
It looks like the pistons have been flycut for valve clearance. You just cannot do that with those pistons. They get real thin right at the back edge of the ring groove, then they burn through and then you get the "death and destruction" that you have here. That was just the first one to go :( The others will be right behind it, have seen it too many times. I cant post a picture but if you want I can e-mail you a doctored up one to show you exactly where I am talking about. Bill Koustenis Advanced Automotive Machine Waldorf Md |
Also wanted to add that those do not look like the correct head gaskets. They are awful close to the bore and are probably hitting the chamfer at the top of the bore. Might be whay they are getting pushed out in a couple of spots. Could also be from detonation, but the gaskets do not look correct.
Bill Koustenis Advanced Automotive Machine Waldorf Md |
Afr Ratios
Have you ever measured the AFR ratios?
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Appreciate the comments
Some answers to questions: -Gaskets are Felpro 17040 -Valve seats are intact -No fly cuts on pistons. These have not been touched. In that pic of damaged piston it may have looked like it but no. -No I have never measured AFR I have attached another pic of different cylinder. This one is cylinder #8. It appears detonation is at work here as well? The previous one I posted was #4 Oh, and since I'm already attaching scary pics, thought you might enjoy another one of damaged piston. |
Looks like your valve floated and hit the piston. Did you over rev?
Somehow your pics posted before my post, looks like a meltdown. Must have went lean...... |
I would double check the entire fuel system before you put the motor back in. After all of the time running the motor as is, something had to change to cause such a major problem. There's no way you were getting detonation for all of the hours running and she didn't blow earlier. Also just to be sure, I'd drain the fuel and run it in the family wagon...... just to be sure.
Darrell. |
Everything you've got there is positively detonation related damage. Broken/lifted ring lands are a text book sign of detonation.
Here's a link to some good reading on the dynamics of normal combustion. For a much better understanding of detonation, how it is caused, and what it's effects are... Check the section which specifically explains detonation, it starts on page 6. http://www.jcmmachine.com/PDF%20file...port%20ch3.pdf |
The 17040 gasket is fine, but the signs of heat on the gasket, and the fire ring squirming around are just more evidence of detonation.
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Very interesting artical you posted there cubicinches!
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Originally Posted by rich allen
(Post 3462995)
Appreciate the comments
Some answers to questions: -Gaskets are Felpro 17040 -Valve seats are intact -No fly cuts on pistons. These have not been touched. In that pic of damaged piston it may have looked like it but no. -No I have never measured AFR I have attached another pic of different cylinder. This one is cylinder #8. It appears detonation is at work here as well? The previous one I posted was #4 Oh, and since I'm already attaching scary pics, thought you might enjoy another one of damaged piston. no magic to any of that. as for what caused the detonation that killed your motor, that's going to come down to fundementally understanding the final operational set up... the fuel system , cooling system and timing. if it was me, i would make a trip to the dyno and dyno the thing with a dry set of headers with EGT's in them and make sure i understood what was really happening. that would be the best 500 bucks you ever spent. and i offer the same advice that i offer to everyone. get a handle on what your own skills and knowledge are and don't treat this as a trial and error deal. don't put anything back in that you are not absolutely certain of as a matter of fact. if you aren't certain, trot it off and show it to someone that knows more than you do. you don't have to actually make the mistake in order to learn from it. |
I'm on board with everyone else on the detonation. I also think the engine was lean. It think the ring land lifting could have been either detonation or it being lean, or a combo of both. Definitely have a look at the fuel system. Make sure you have a fuel pressure gauge the next time you run it to be sure it is holding pressure at WOT. Just because the plugs are black, that doesn't mean it isn't lean at some point. All it takes is a few minutes of rich idleing to blacken the plugs and you would never know it was lean at some point.
If your quench is correct at .050, then that means the piston is about .010 in the hole. Using that, the 26 cc dome, and 11 cc gasket, I come up with a touch over 9.8:1. That's really pushing it with today's crappy fuel and cast iron heads. Lose the cast pistons. Get some O2 bungs put in the exhaust. Might also want to invest in an add on knock meter to dial in the timing. With that setup, you will need to run as much timing as possible to keep the egt's in check. However, a little to much and you end up right back where you are. As mentioned, a dyno is invaluable. You can monitor the egts and afr. Feed it timing until it stops responding with power and lower egt's. Every engine is different. Don't pay any attention to what the actual timing number is.....it doesn't matter. If the engine wants more timing, then give it to it. And vice versa. If it doesn't make any more power with say 36 deg. then it did with 34 deg, then leave it at 34 deg. If it keeps responding up to 38 deg, then give it to it. Don't worry about the number. It is what it is. One last thing....pay close attention to the combustion chambers. Remove any and all sharp edges or points that can collect heat. Not only that, a good chamber will help with lowering the timing. Good luck. Eddie |
Well, I think I made it past Stage 3 of Grieving process, which was depression. I almost threw in the towel for this season and was ready to move on to other projects. But I think I made it to stage 4, which is acceptance and hope.. I guess I am ready to give it a shot, and "hope" I can do this within reasonable budget.
-I'm tired of throwing good money after bad, so this will be it for those peanut heads. I would need to open them up for inspection, probably need to replace a valve or two that got smacked, rework some damaged seats, etc.. and I am not feelin it. It was a nice experiment, but these heads have their limits. That being said, I would like to be in the water again this summer. I will fully disassemble to inspect bottom end. So far, I only pulled a couple of caps for a look,including the damaged piston, and bearings still look damn good, with most of surface coating still there, and no scratches.. Hopefully a good sign. Everything will get mic'd. I will still probably install a fresh set of bearings throughout lower end. Any opinions on this? Beyond that, I am open to suggestions for this rebuild. i will replace: -Heads (off the shelf variety from World products, etc..) -Cam,rockers, pushrods -pistons I have performer intake, 750 edelbrock carb, EMI exhaust. Block is decked .010, and bored .030, (assuming I won't see anything in the bores that forces me to go .060) Looking to probably lower compression a bit to gain some margin of reliability, but would like to keep some nut as well. I love the mid range torque, and don't expect to go much over 5200 rpm Let's here what you have for ideas/combo's, with consideration for quench, etc. without breaking my wallet and my marriage. This is a river runner, not an offshore poker runner. I am ready to get this going in the opposite direction. Thanks guys |
Personally, I wouldn't use a World Products head. Not that they won't perform, but their castings are terrible... at best. If you've got your heart set on an iron head, I'd use a Dart Iron Eagle... Much nicer piece than the World Products Merlin. If you're open to spending just a few more bucks, consider Edelbrock's Performer aluminum marine head... They're reasonably priced, and the aluminum head has several advantages over iron.
Also, as was stated earlier, I would ditch the Edelbrock carb in lieu of a Holley, or check out a Quick Fuel carb... Nice stuff for little more than a stock Holley. I use alot of their stuff. |
Originally Posted by cubicinches
(Post 3463499)
Personally, I wouldn't use a World Products head. Not that they won't perform, but their castings are terrible... at best. If you've got your heart set on an iron head, I'd use a Dart Iron Eagle... Much nicer piece than the World Products Merlin. If you're open to spending just a few more bucks, consider Edelbrock's Performer aluminum marine head... They're reasonably priced, and the aluminum head has several advantages over iron.
Also, as was stated earlier, I would ditch the Edelbrock carb in lieu of a Holley, or check out a Quick Fuel carb... Nice stuff for little more than a stock Holley. I use alot of their stuff. |
Originally Posted by cubicinches
(Post 3463499)
Personally, I wouldn't use a World Products head. Not that they won't perform, but their castings are terrible... at best. If you've got your heart set on an iron head, I'd use a Dart Iron Eagle... Much nicer piece than the World Products Merlin. If you're open to spending just a few more bucks, consider Edelbrock's Performer aluminum marine head... They're reasonably priced, and the aluminum head has several advantages over iron.
Also, as was stated earlier, I would ditch the Edelbrock carb in lieu of a Holley, or check out a Quick Fuel carb... Nice stuff for little more than a stock Holley. I use alot of their stuff. |
Keep in mind that if you replace the pistons with a different part number or brand, there will probably be a pretty big difference in weight and you should rebalance the crankshaft to compensate.
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This is a picture of a detonated piston. Note all the little melted sections. There really is none of that on the parts you have posted. You have numerous hit marks from the ring and piston pieces bouncing around in there but there really is no detonation damage. Also note that detonation will almost always eat away at the sharp edges of the piston and do a fairly uniform job, once again none on your piston ledges or edges.
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Timming
Have you ever check the full advance on your timming? For good fuel 10 degrees initial and about 38 Degrees total with your advance. If your going into 40 Degrees plus on pump gas then that would cause your detenation problem. If you was running race fuel then you can get away with 40 plus degree full advance. Timming would definatlly run cause this on low octain fuel. If the advance was too much. Just my two sents
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Originally Posted by Ted G
(Post 3463972)
This is a picture of a detonated piston. Note all the little melted sections. There really is none of that on the parts you have posted. You have numerous hit marks from the ring and piston pieces bouncing around in there but there really is no detonation damage. Also note that detonation will almost always eat away at the sharp edges of the piston and do a fairly uniform job, once again none on your piston ledges or edges.
I've seen many engine failures (Valves, valve seats, pistons, head gaskets, rod bearings) that were dismissed as a simple part failure by the owner or builder, when the real cause was detonation to some extent. Especially in a marine application. A perfect example is your blanket statement that valve seats fall out of big block heads... which is innately untrue. There's millions of big block pickups and street cars running around out there with their valve seats intact. The truth is that the valve seats fall out of ANY engine which is experiencing cylinder temps high enough to cause the seats to lose their press fit in the cylinder head... cylinder temps which are either caused by, or contributing to... you guessed it... detonation. :drink: |
Originally Posted by cubicinches
(Post 3464022)
No two detonated pistons are going to look the same. The damage varies and presents itself in different forms, typically dependent upon the severety of the detonation, and exactly what the conditions were that caused it. The pistons from an engine that was operated for a long period of time, while being continuously pushed just to, or just past, the point of detonation will look much different than pistons from an engine which experienced severe detonation for only a short period of time. An engine will typically make it's best power when tuned right at the ragged edge of detonating. That being said, many "perfectly tuned" engines are operated daily, over long periods of time, while being pushed just into short periods of detonation... every time this occurs, parts are fatigued... until the point in time that one or more conditions become unfavorable, and something fails. An engine whose tune-up is completely missed, due to fuel mixture, spark timing, etc. may be pushed into such a severe state of detonation that it only lasts one trip across the lake. The result is the same... broken parts. Yet the broken parts will likely look different from one engine to the other, due to the difference in conditions and the severety of them.
I've seen many engine failures (Valves, valve seats, pistons, head gaskets, rod bearings) that were dismissed as a simple part failure by the owner or builder, when the real cause was detonation to some extent. Especially in a marine application. A perfect example is your blanket statement that valve seats fall out of big block heads... which is innately untrue. There's millions of big block pickups and street cars running around out there with their valve seats intact. The truth is that the valve seats fall out of ANY engine which is experiencing cylinder temps high enough to cause the seats to lose their press fit in the cylinder head... cylinder temps which are either caused by, or contributing to... you guessed it... detonation. :drink: the motor burned a piston because of detonation. fix the motor with a correct combination of cr, afr ,cooling and set up, dyno it and get the egts correct and go home early. that's the only answer here. |
I have a set of JE forged 4.560 flat top pistons on a set of GMPP 6.135" rods with ARP fasteners for sale. I have less than 100 hours on them and they are in mint condition. They gave me 9.01:1 compression with 117cc chambers. I bought the boat with 50 hours on it and it had been stored for years and the cylinders were rusted. Had to go .005" to clean it up. I can give you the number to the speed shop doing the work and you can get the straight scoop from them.
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