Triple-locked LX470 blew plug out of cylinder 7 at 270k. New engine advice?

[ikellymo]

Awesome. I didn’t even notice that lighter strip on the wall. Yes, I attributed the tick to exhaust manifold. Only myself to blame, but I had no idea.

But if I have the head pulled right now, wouldn’t it be much easier (almost guaranteed??) to remove any metal between piston and wall? Just reach in with a wood toothpick? Otherwise, I like the thread insert and test approach, but as noted, risky to get metal in.

I’ve never pulled an engine apart, just an engineer trying to learn all this quickly. I don’t have a good idea how much space between piston and cylinder wall.

 

[2001LC]

Awesome. I didn’t even notice that lighter strip on the wall. Yes, I attributed the tick to exhaust manifold. Only myself to blame, but I had no idea.

But if I have the head pulled right now, wouldn’t it be much easier (almost guaranteed??) to remove any metal between piston and wall? Just reach in with a wood toothpick? Otherwise, I like the thread insert and test approach, but as noted, risky to get metal in.

I’ve never pulled an engine apart, just an engineer trying to learn all this quickly. I don’t have a good idea how much space between piston and cylinder wall.

It is why I put out the Spark alert, and beat the drum loudly. So many experienced 4.7L pro shop mechanic and most of mud members, don't know either.

If head pulled now, would be easier to clean. But cost much more. But, still no guaranty, any more or all metal removed. The concern and reason to move piston down & up. First dry than wet. It to try and get any now down at side piston, sitting on ring. But no assurance it will stick to cylinder wall as piston lowered. If metal in piston ring grove, it will likely not come out.

We look for clues, to gauge risk and out-come. Than, weight that against present and future cost vs benefit. For one, if a replacement engine, is in the plan. Do the time-sert now. Vehicle on road in a day, gives you time to find a GOOD engine.


Do the math.

 

[ikellymo]

Had no idea those dims were available in the FSM. So only 50um of clearance between piston and cylinder wall. Given the noticeable imprints, I bet my chunk of metal wasn't turned into many little pieces and was only a chunk. AND it's definitely bigger than 50um.

I'm actually really questioning if I know the condition of the threads in the head. The best photo I have is here, but I didn't take a comparison shot of different cylinder as a control. Guessing there should be a flat sealing surface. Maybe I'll go over next week with some Dykem blue, a spark plug and a tap and try to check thread engagement before we make a more drastic call.

Nobody seems to think there is any chance that metal piece is hanging out in the head above the valves. There is some concern that valves could have been bent or sealing surface scratched, but that can be verified with leakdown check.

 

[2001LC]

That is a very good idea, to see if a spark plug will hold in head. Since, what happens is they rotate out as heads & spark plugs heat and cool, expanding and contracting. At first the gasses escape past the threads, only a little while engine warming. But with each heating and cooling cycle, they continue their walking out. Loosening more and more. To the point, we hear tick even after operating temp reached. Then they blow out the head.

Plug sometime look like yours (plug melted), other like @Bomar posted (electrode intact). Where some portion at base melted, takes a lot of heat for sure. Possible the threads kind of soften and folded inward, loosing grip.

I would not clean threads, with a thread tap. A tap would likely cut into threads. You just want threads cleaned. A thread chase is designed for cleaning and restoring thread. But even those can cut away some thread metal.

JIS:
Choose wisely! 100 series are made in Japan, which size are based on JIS (Japanese Industrial Standard). JIS varies just a bit from metric. My chase kit, is mix of standard Metric & SAE, so are my spark plug chases. I've never used any on a spark plugs/heads threads. In threads I have used on. They seems to enlarge cut away some threads (Increasing OD & ID). Which we don't want.

You'll also want to inspect valve seats, for damage.

With luck all metal particles, blew out with plug or out exhaust valve ports cleanly. The line, I pointed out on cylinder wall. Could be carbon sitting on ring, which shouldn't be and issue if.

I've tested the compression of a few cylinders, after time-sert done in place. The compression in each, was lower than other cylinders in same engine. They failed either by below 145PSI or more than 14PSI differential. But engine still runs fine. Again most will never ever notice, low compression. Provided, compression does not get so bad, it results in fouling CATs.

If you choose Time-sert in place. Do no Harm! It must be done with the utmost care, not dropping in metal. Clean as you go and after the best you (shop) can.

How do we clean cylinders before or after. With a lot of imagination, creativity and patient.

 

[ikellymo]

Here's an update. I visited my car today and tried chasing the threads with a chase - not a tap. Used some marine grease to hold onto any chips, but there weren't any. After chasing the threads, I grabbed a brand new spark plug and tried threading it in. No-go. It spins and spins but won't bite.

I put dykem blue on the end of a socket extension and drop into hole to verify that there is a flat washer surface inside. Dykem blue is a machinist tool to transfer from one surface to another to indicate high spots. Just an indicator ink. Verified with scope, and you can now see that the internal ledge is flat.

Next I put a bit of Blue on the end of the spark-plug and dropped it back in. Note the ink is on the tip.

Threads are so warn that the new sparkplug just drops through the hole. The only thing that the chase was biting on was the very last lip. There is nothing there to start a time-sert or helicoil thread saver type of tool to get the enlarged cutters positioned properly. The only way I could imagine fixing this is to drill it out and tap from scratch. But drill must be aligned perfectly, and so would the tap to follow. This would be very tricky on cylinder #7, which has tight clearances for just changing the plug.

Here's a scope of a good one for anyone who is interested.

 

[ikellymo]

With all that data, I guess the plan now is to rebuild the top end of the engine. Remove both heads, replace drivers side with a used head, and do a standard rebuild on both so that they match. Install headers to eliminate exhaust leak if there is a real one (not just the spark plugs).

My only concern is if the electrode impact caused the piston to pinch the ring and that's whats actually causing the stripe that we're seeing above. Looks like there is quite a bit of meat on the piston though (1/4 atleast?) so I'm not convinced. This is all speculation.

 

[MechE30]

Good investigative work. If you’re planning to scrap the head anyways, my plan would be to try a helicoil tap anyways. If it works it would save a lot of time, if not you are still scrapping it.

 

[ikellymo]

Good investigative work. If you’re planning to scrap the head anyways, my plan would be to try a helicoil tap anyways. If it works it would save a lot of time, if not you are still scrapping it.

I've tapped many a hole .... I just can't imagine that going well ... and lots of time cleaning up any metal that fell in. But I'm all ears for a technique that might work.

 

[awesomeissquid]

With all that data, I guess the plan now is to rebuild the top end of the engine. Remove both heads, replace drivers side with a used head, and do a standard rebuild on both so that they match. Install headers to eliminate exhaust leak if there is a real one (not just the spark plugs).

My only concern is if the electrode impact caused the piston to pinch the ring and that's whats actually causing the stripe that we're seeing above. Looks like there is quite a bit of meat on the piston though (1/4 atleast?) so I'm not convinced. This is all speculation.

View attachment 3517814

Great investigation. How long after the issue did the engine get run? The reason I ask is because when I purchased my LC I found some metal sitting on top of the piston. From the records it had been banging around in the head for ~3 years. As part of my baseline I remove the metal pieces and ran the engine assuming the worst. It lasted another 3 years until the piston destroyed itself. If you only ran the engine for a short while it might be safe.

That said, still the issue of installing a timesert with the head in. I would probably want to pull it to ensure it could be installed correctly on a bench. At that point why not just do the new head like you suggested.

 

[ikellymo]

Great investigation. How long after the issue did the engine get run? The reason I ask is because when I purchased my LC I found some metal sitting on top of the piston. From the records it had been banging around in the head for ~3 years. As part of my baseline I remove the metal pieces and ran the engine assuming the worst. It lasted another 3 years until the piston destroyed itself. If you only ran the engine for a short while it might be safe.

That said, still the issue of installing a timesert with the head in. I would probably want to pull it to ensure it could be installed correctly on a bench. At that point why not just do the new head like you suggested.

Ya know, I think I probably ran the engine about 10 minutes "in that condition". If you look at the marks on the piston, looks like about 5 taps between the electrode falling in and getting ejected.

 

[Somebodyelse5]

Time sert. I did one with the head still installed.

 

[ikellymo]

Time sert. I did one with the head still installed.

Does it use the existing threads to pull the tap in and cut the new threads? Threads at bottom of tap chase existing threads ...

 

[shtbrwn86]

just buy a used engine off ebay (one with a warranty) and call it a day. its surprisingly easy to pull the motor in the 100 ( i did it in my garage with no help from anyone whatsoever)
View attachment 3512285

That was when you did the valve covers right?

 

[Somebodyelse5]

Here's an update. I visited my car today and tried chasing the threads with a chase - not a tap. Used some marine grease to hold onto any chips, but there weren't any. After chasing the threads, I grabbed a brand new spark plug and tried threading it in. No-go. It spins and spins but won't bite.

I put dykem blue on the end of a socket extension and drop into hole to verify that there is a flat washer surface inside. Dykem blue is a machinist tool to transfer from one surface to another to indicate high spots. Just an indicator ink. Verified with scope, and you can now see that the internal ledge is flat.
View attachment 3517798View attachment 3517799

Next I put a bit of Blue on the end of the spark-plug and dropped it back in. Note the ink is on the tip.

View attachment 3517801View attachment 3517802

Threads are so warn that the new sparkplug just drops through the hole. The only thing that the chase was biting on was the very last lip. There is nothing there to start a time-sert or helicoil thread saver type of tool to get the enlarged cutters positioned properly. The only way I could imagine fixing this is to drill it out and tap from scratch. But drill must be aligned perfectly, and so would the tap to follow. This would be very tricky on cylinder #7, which has tight clearances for just changing the plug.

Here's a scope of a good one for anyone who is interested.
View attachment 3517805

Take the head off, give it to a machine shop. they can do this for you no problem.

 

[Bomar]

A ford shop or RV shop have the tools to do it since they do it all the time....

An RV shop did mine.

 

[ikellymo]

Great investigation. How long after the issue did the engine get run? The reason I ask is because when I purchased my LC I found some metal sitting on top of the piston. From the records it had been banging around in the head for ~3 years. As part of my baseline I remove the metal pieces and ran the engine assuming the worst. It lasted another 3 years until the piston destroyed itself. If you only ran the engine for a short while it might be safe.

That said, still the issue of installing a timesert with the head in. I would probably want to pull it to ensure it could be installed correctly on a bench. At that point why not just do the new head like you suggested.

How did your piston destroy itself? Any early signs?

 

[awesomeissquid]

During the investigative disassembly of the blown engine my best guess was fatigue near the top most piston ring.

There really weren’t any early warning signs (aside from finding chunks of metal on top of the piston when I bought the truck). When it all happened we were on hour 7 of a 12 hour road trip. Had just gotten gas maybe 20 minutes before and it started making weird noises. Thought it might have been some poor gas quality so we kept driving until we started getting smoke, misfires and found 3 quarts of oil in the air intake pipe.

 

[ikellymo]

Ugh sorry about that. Lol, I hope it doesn’t happen to my engine after we rebuild the top end.

 

[awesomeissquid]

Ugh sorry about that. Lol, I hope it doesn’t happen to my engine after we rebuild the top end.

I think these engines are very strong and would bet you will be okay. From my LCs previous owner records, the pieces of metal were in the cylinder making a mess for a number of years from when a timesert was installed.

You can read about my issues in this thread. On one of the last pages I have pictures of the destroyed piston. Would have loved to have fully pulled the piston but there was a time crunch on getting the new engine in.

Misfire on Cylinder 8 and Oil in Intake Pipe -Investigation and Engine Swap

forum.ih8mud.com

 

[caci]

3 weeks ago. 2001 LX, 362,000 miles. #6…
Coil tip came out with loose plug. Threads in head all but gone. I used Helicoil brand with sleeve (not wire insert). Reamer/tap is premium quality, compared to Chinese mfg kits. Engine seems to be no worse for wear (pun intended).
We are replacing LX with 200k 2006 LC.