243/799 Heads On Lm7 Factory Rotating Assm.

Proud2235 · March 5, 2011

Hey GuysIm a newbie on this site and I got some technical questions that im hoping to get answered. I got a '04 1500 with the LM7 and Im blowing smoke out the Tailpipes and consumingbout a quart of anti-freeze a month. Pulled the valve covers Last night found wonderful oil/antifreeze white goo on the bottom of the valve covers. did some research found the GM TSB on Castech heads. went out popped the hood Low and behold the Numbers 706 stamped on my heads. Now heres My question what would I be getting into to replace my 706 heads with 243/799 heads Im not really looking at making big power changes at the moment I just want to get started in the right direction for later down the road. Ive read the 243/799 heads need machined down anywhere between 0.35-0.45 to keep a decent compression ratio. Any help would be greatly appreciated Im not afraid of doing the work just there is so much to the technical aspects of it .

Slabi · March 5, 2011

If you have been going through that much anti-freeze I would be looking at a full rebuild. THAT much coolant must have already started to affect the bearings...unless the DEXCOOL does not like to eat the zinc in the bearings like the good old green stuff did.

I'll defer to one of the Official GM tech's on that one..

beave84 · March 5, 2011

I think I'd look into a complete rebuild too.Thats alot of antifreeze to lose and if its in your heads you'd think its got to be in the botton end too. It would suck to put new heads on then spin a bearing and have a piston kiss one of those new heads. Just a thought.

Also I'd change or at least have your cats checked and make sure they didn't get plugged with all the burnt antifreeze flowing through them.IMO

DwayneJ · March 6, 2011

I suspect the beginnings of this problem on my truck and right away I called the guy that did the heads and cam for my street/strip car. He said he didn't have a CNC program for the little 3.78" bore but was interested in making one.

With needing to do a prototype though he might not be able to give you the turnaround you need but you could take a look at his site and maybe email to inquire.

Advanced Induction

I should say too this would be a competition level ported head, again maybe not your cup of tea. This guy helped me make a street/strip Caprice with an LT1 run 11s on a junkyard shortblock naturally aspirated. Makes me anxious to try his LS stuff.

Proud2235 · March 6, 2011

As far as the bottom end Ive been keeping and eye on my oil and there dosent seem to be any antifreeze contamination, the level hasnt increased theres no goo on the dipstick and the oil seems fine. Plus I regularly change the oil. Though there was more sludge that I would have expected.

beave84 · March 6, 2011

As far as the bottom end Ive been keeping and eye on my oil and there dosent seem to be any antifreeze contamination, the level hasnt increased theres no goo on the dipstick and the oil seems fine. Plus I regularly change the oil. Though there was more sludge that I would have expected.

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Thank God for that. I'd do something quick then before there are any bottom end problems. I'd post in the ask a tech area,there are alot of good techs here that can tell you exactly what should be done, before this gets outta hand here and you get alot of bad advice.My $.02 worth

[email protected] · March 6, 2011

799/243 heads(milled of course or you'll lose all your compression and power) would be a great step in the right direction, those flow plenty enough for a 5.3, they(799) even come stock on the newer 5.3s.