3.4L T100 Diagnosis

[placelast]

My mechanic called me and said one of the heads is cracked; he ordered one, while the remaining good one went off to the machine shop. New valves are a-comin'.

I went in to see it and he showed me where it goes from the intake to the exhaust seat; suprisingly the head gasket held as best it could. Forgot to ask him what caused this failure to begin with, and will when it's done in a week or so.

He said the bottom (block, pistons, compression and therefore the rings) looked good and I can expect many more miles out of it. Just reached 274k so I did get my money's worth, though am a bit bummed as I was going to replace it with something newer before it went south.

[mustang67408]

Originally Posted by placelast

My mechanic called me and said one of the heads is cracked; he ordered one, while the remaining good one went off to the machine shop. New valves are a-comin'.

I went in to see it and he showed me where it goes from the intake to the exhaust seat; suprisingly the head gasket held as best it could. Forgot to ask him what caused this failure to begin with, and will when it's done in a week or so.

He said the bottom (block, pistons, compression and therefore the rings) looked good and I can expect many more miles out of it. Just reached 274k so I did get my money's worth, though am a bit bummed as I was going to replace it with something newer before it went south.

Can you get a picture of the crack and head?
That would be interesting to see.
Thanks

[placelast]

Sorry; have no camera. If he hasn't thowned out the parts then I could have someone take a pix later.

[mustang67408]

Originally Posted by placelast

Sorry; have no camera. If he hasn't thowned out the parts then I could have someone take a pix later.

Sounds like a plan

[placelast]

Mechanic said he'd take pix and I could try to place them on photobucket.

Also said other head ha$ $maller crack, found at the head-machine $hop after an initial wa$h. Now the estimate is up beyond the vehicle's street value if running well!

So it's off to ebay for engines.

[placelast]

Got my pickup back today. Both heads were cracked at the valve seat, middle cylinders. $1k for labor and $1.6k parts. He said it should go at least to 400k or more before needing full rebuild the way I baby it (grandpaw driving habits and no loads other than occasional dirt bike hauling).

He took pix of the heads before sending them to Clearwater Cylinder Heads, Inc., but said the quality of them is marginal. I'll post them if the crack is detectable.

I asked if the machine shop or he had any idea why this happened as valve clearances were fine. He suspects the material the seats are made of (?) vs. the head (Al) are not compatible, and I proposed coefficient of expansion differentals and breakdown between the two. No one knows for sure but he has seen this happen before a few times to a small trend.