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2005 SRX 3.6
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48 Posts
Discussion Starter #1
Well, I posted a note a couple weeks ago about needing to find good doc for an LY7 teardown subsequent to a primary timing chain failure at 50,500 miles.

Got that. Did that. Found this.

So clearly I've got no issues with moving parts around. And unless I drop the exhaust and tranny and am prepared to reinstall from below, the book says I can't even install a complete engine -- build-up should be in-place, starting with a replacement short block.

So my question is ... are all LY7 3.6 blocks and heads the same -- VIN 7, 8th digit, option LY7? Sure, intake, accessories, and engine management change... but are the major castings, crank, pistons, and valve trains the same? I can find a late model low miles engine a heck of a lot cheaper than a matching high miles engine. I can find a G8 engine with the transmission with less miles than mine had for $1200 to $1600.

Yeah, there are some threads. One even commented "all LY7s are the same [except the computer and fuel management]". But there's no confirmation. No one ever comes back from the effort and says, "Yeah, it worked great! The 2008/2009 STS/Olds/Chevy block and heads worked great! Here are the photos!"

True? Can I find a low miles wreck dropout from a G8? Vue? Aura? I think I'm still gonna pull it apart to put a good Cloyes chain set in... but will all the doohickeys and whatchamacallits bolt on in the right places? Will the compression be right?

Thankee in advance.

- ep
 

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Registered
2005 SRX 3.6
Joined
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48 Posts
Discussion Starter #3
Short answer: 2004-2006 Cadillac castings are unique: Right Head Cast # 12581596; Left Head Cast # 12581597; Block Cast # 12586559.

2007 through 2009 Cadillac castings are different: Right Head Cast # 12591206; Left Head Cast # 12591207; Block Cast # 12600129. Accessory idler belt and water pump arrangements seem to have changed. No word yet on whether an earlier Caddy timing cover can bolt up to a later block and heads, but I wouldn't count on it. The crankshaft is also different.

The engine rebuild kit and gaskets are the same, so the diameter of the crank snout might be the same... but length might be different and keying definitely is different. Also, Cadillac changed from the 9.5 mm pitch timing chain of earlier models to the 7.7 mm pitch in mid-year 2007, which explains finally why the customer satisfaction program includes the secret 10/120 timing chain warranty from mid-year 2007 forward, depending on the specific VIN. All the sprockets are different. The finer pitch chain is apparently significantly lower noise. Basic engineering precept: lower noise means lower energy lost means lower wear. Mystery at least partly solved.

Note that this implies that the second version ( as opposed to the early 2004 model year ) timing chain system fits into the 2007-2009 model year block and heads, which implies that key hard points for tensioners and guides must be identical, but it still doesn't tell us about the external differences.

Early versions of the LY7 simply don't exist for other marques. They started to appear in 2008 and 2009 on the G8, Vue, others. Those castings are not the same as the Cadillac castings, and some are transverse, so while the internals might be at least partly compatible, the exterior fit and bolt-up is going to be different.

We blow a 2004-2006 LY7, we need to replace the mechanicals with 2004-2006 LY7 metal. Which is why they're more costly used.

- ep
 
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