Maverik

Some of you may remember my post regarding the sudden mis-fire my lt4 developed from a few months back. To refresh your minds and enlighten those who don't know, I ended up getting zero compression on cylinder #7... further digging revealed this:



That would be a valve seat which dropped, bound the valve open and resulted in the piston looking like this after hitting said valve:



So, the heads went off to rebuild and get upgraded while I was it:
2.02/1.6 valves installed with medium porting/bowl work, new seals, etc... courtesy of Golen.

The intake was worked on a bit to freshen it up, but nothing major. I picked up a custom cam from comp cams, again nothing too crazy:
214/224 duration @ .050" Lift
565/595 on a 114 LSA

From the initial troubleshooting, I have a new opti/injectors/plugs/wires/etc... so those will go on nicely. Since I live in SoCal, I need to remain smog legal so I will likely pick up some hooker shorty headers. Otherwise, I just need the rest of the install goodies, bolts, gaskets, (new lifters, these have 130k miles). I'll be chronicling the rebuild for those interested.

Today I cleaned up the piston crowns and block to help make a decision; Pull the motor and do a proper rebuild with the bottom end completely taken apart / machined / bored / honed or leaving the relatively fresh ~18k miles bottom end together. There is some light scoring you can see in the pictures below, but nothing I'm extremely worried about. I had great power with little to no oil consumption... though the piston crowns carbon build-up don't quite say the same story... The only concern I really have is the smack in the top of the #7 piston in the picture above. To give you an idea of why I'm not all gung-ho to pull the motor, heres my garage space:



While there's some room forward and aft, it's a royal pain to do an engine swap... I recently did one in a mustang in there and was not too happy about it. That being said, it isn't impossible so I'm torn... In the following pictures, I only cleaned the head deck/piston crowns.

Block before cleaning:


Block after cleaning:


The weird marks in the cylinders you see aren't actual marks, but reflections of the valve clearance in the top of the pistons. As I left her:



Re-worked heads:

RichS

My one concern would be if the bearing got damaged from the impact. It would suck to go through all that work, then spin a bearing.

The Green Rocket

I dropped a valve on mine, redid the head and its been going strong for a long time now. That said, I didn't have but just a nick on the piston top - yours is dented, which would make me want to replace the con rod bearing for that one cylinder. Removing the pan with the engine in car to replace that bearing is very doable. I wouldn't rebuild the whole engine unless I found signs of bearing material in the oil.

Thomas

Muffin

What Green Rocket said.

aboatguy

+1


I'm wonder what else is going on with your engine. I've had numerous LT1s apart and even one with 150,000 miles on it and it did not have 1/20th of the build up that's on your pistons.

MIke

The Green Rocket

Whenyou pull the piston to replace the con rod bearing - tell me how many pieces the piston rings are broken into. To me that looks like burned oil deposits. My next guess is a fractured, cracked, or broken piston ring.

Thomas

mtwoolford

replaced all the lower end bearings on my LT4 with the engine in the car; not that hard.

judging by the amount, and eveness of the oil carbon build up I doubt its rings...all pistons would have to have bad rings; would suspect oil coming in through the intake....bad intake manifold gasket or bad pcv system.

i'd maybe replace the number 7 piston and ring pack...replace the lower end bearings, and oil pump and get that puppy back on the road.

good luck.

Maverik

Thank you for the comments so far. My belief is the previous rebuild didn't have a proper break-in or possibly honed surface for the rings to seat leading to the abnormally high oil deposits on the piston crowns. The only solution in my book is to pull the motor, have the block re-bored/honed and do a proper break-in this time around. I'm sticking with the stock crank and rods (pending #7 being ok, not too concerned) but will update the pistons to some nice JEs.

I leave this week for a month of travel so it will be a while before I have anything definitive for you guys. Thanks again!

Maverik

Whew, six months and change later... finally running again! Here's what I ended up doing because a full on rebuild was going to cost too much for me to do it right:

Rebuilt heads by Golen with minor clean-up, nothing fancy, really just cleaning them up and fixing the #7 intake valve seat. In the process, he swapped out all of the valve springs for a triple spring setup (two control, one damper) and slightly bigger valves. I had to buy one roller rocker due to damage when the valve bound. The rest was a top end rebuild... all the gaskets, bolts, etc... Since I initially thought the problem was ignition or injection, I have a brand new ignition/injection system as a bonus. The compression across the board with the reworked heads on is 215 psi... good to have like-new compression.

The car didn't fire right up, in fact it felt like it was firing on one cylinder. After troubleshooting it for a day, I finally reasoned the only thing that wasn't working was the spark... I dug back into the front end and pulled the opti and took it apart to find I made a mistake assembling it the first time around. The encoder wheel was slightly misaligned resulting in it touching the sensor throughout the entire rotation. I don't have a code reader, but I would imagine it was giving me a DTC related to the optical sensor. Anyway, I reassembled it correctly, put it in and the car fired right up within one revolution.

I took her out for the first drive in ten months or so and she runs smoother then ever! I'm going for a longer drive tomorrow to make sure no gremlins are going to surface. I can honestly say it felt fantastic to be back behind the wheel after such a long time driving my daily driver.

ch@0s

Nice to be back in the driver seat huh?

CTillman

how much did that cost you? im in the same boat with my LT4 right now but cyl 5 instead of 7.