rich allen

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

DMOORE

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.

picklenjim

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.

rich allen

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.

stevesxm

for me when you lose a piece of the top ring land its generally detonation...

tinman565

Personally...I don't like the cam being a 110 LSA.

rich allen

My understanding is this was done to aid in fuel charge due to poor breathing heads. Is that right? I always wondered about that LSA

Unlimited jd

iTrader: (5)

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",

kvogt

Those look like pretty big domes on those pistons and I agree with others on the 110 lsa. 112 or 114 would be better.

cubicinches

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.