Toasted 3.4 cylinder head

[Gary Blake]

Not having much luck with the 3.4 in my 2000 T4R. First motor made it to about 200,000 miles and totally lost compression in one cylinder due to a suspected bad injector spraying too much fuel and causing a gas wash which takes all the oil off the cylinder wall and kills the rings.

Replaced the motor with a 3.4 from a wrecked 2004 Tacoma with about 80,000 miles and when that engine hit around 200,000 miles it blew a spark plug out while on an extended road trip. Had a heli-coil insert installed and that only lasted about 10,000 miles and the insert blew out.

This time I bought a spare motor and had two heads rebuilt and installed along with a bunch of other stuff while the runner was laid up. (This was only a little more expensive than buying just a head and now I have some spare parts)

Some pics of the toasted head. You can see how much the spark plug hole is enlarged for the heli-coil and the stripped threads when it blew out….

Good thing I am really fond of the old girl…

Oh well, my mechanic tells me there are worse addictions….

 

[jgue467]

My current near 305k motor blew a plug (and destroyed the coil on the way too) about 125k ago - luckily fine since. Do you suppose Poor metallurgy causes this? mechanic said he saw it from time to time, 'not unheard of'. I do see lots of carbon buildup, how did the plugs look? marine startron helps with that. :cowboy:

 

[vipergrhd]

Heads

Besides the carbon build up any other issues that your mechanic told you? I would send it out to a reputable machine shop and have them fully inspect it.

Replace all the injectors and upstream O2 sensor.

 

[Stick Figure]

Heli coils work okay, but for something critical like that a Time Sert kit would be the way to go.

 

[Gary Blake]

My current near 305k motor blew a plug (and destroyed the coil on the way too) about 125k ago - luckily fine since. Do you suppose Poor metallurgy causes this? mechanic said he saw it from time to time, 'not unheard of'. I do see lots of carbon buildup, how did the plugs look? marine startron helps with that. :cowboy:

125k is doing really good then, you can see here that there is not much original metal left between the bored out plug hole and the bottom two valves.

Yep, lost the coil pack both times with this one as well. I am putting it down to a bad casting in the head (metallurgy) for this to have happened twice in the same cylinder. Most mechanics I have talked to say this engines are very good for not throwing plugs (unlike Fords). Cross threading and over or under torquing the plug are about the only mistakes to cause this. The long thread section on the plug usually holds pretty well. After looking at the head when it was removed the insert appeared to have been installed properly. Diagnosis looks like weak metal around the plug bore hole.

Carbon is not as bad as it looks in the photos (these were taken with a very sharp macro lens), mostly light fluffy stuff, you can see on the good cylinder most of it just brushed off the one valve with one pass of a gloved hand.

Usually treat the engine to one Seafoam dose per year, the motor was running very strong prior to blowing the plug.

 

[Gary Blake]

Besides the carbon build up any other issues that your mechanic told you? I would send it out to a reputable machine shop and have them fully inspect it.

Replace all the injectors and upstream O2 sensor.

No other issues, my one good head and a donor head were both sent to a machine shop and fully rebuilt.

Plan on using the injectors from the donor motor as cores for a rebuild set from LCE performance or similar company.

o2 sensor has been done not too long ago

 

[Gary Blake]

Heli coils work okay, but for something critical like that a Time Sert kit would be the way to go.

May be that I just used the wrong term, never heard of the Time Sert kit but after looking it up that looks exactly like the kit the mechanic used for the repair. The repair was done in Whitehorse, Yukon Territory on an extended road trip. The mechanic spoke with a local engine rebuilder before he did the repair, and went with the rebuilder's recommendation