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LM7 5.3 Iron block 2003 LM7 had not been started since owner past away in 2013
I was giving a 2003 Silverado 1500 4X4 with 136,000 on the engine and drive train 4L60e, Took the motor out and now I
am into the motor and it turned with ease, but the internal parts are a bronze color, is this normal wear or is it because it sat so long? everything was solid.
ummm, now i am wondering if i should just go ahead leave the bottom end and just concentrate on the top end , it came with 706 heads and i plan to add a cam and springs and put a TBSS intake and see what she has to offer! thoughts? or what would you do??
The bottom end SHOULD be OK, so don't disturb.
If the heads come off, treat them to a good multiangle valve job and bowl blend (aka pocket port). 706 heads are perfect for stock and near stock 5.3's.
Then replace the lifters, plastic trays (w/ gennie GM ONLY), timing chain (sprockets should be OK), and maybe a new oil pump.
If the cam comes out, get a new retainer plate and screws. Check for bent pushrods (roll on glass).
If the 706s are Castech (look for a casting mark that looks sorta like a D cell battery under the rocker pivot rails near the right end of them as viewed from the exhaust side) then either get them welded up BEFORE they crack and leak coolant into the oil, or replace them with 862s or non-Castech 706. They tend to crack at around the 140 - 175k mile range. Cracks will be right above one or more of the 3 center bolts in the upper row of large ones, the ones kinda in the center of the head; and will make the bolt head and area around it look like it's been steam-cleaned. (for some odd reason...)
Whatever heads you put on it, follow Gary's advice and get a good quality valve job and do some mild porting. Be aware that the bottom of the intake rocker bolt holes is VERY CLOSE to the surface of the intake ports; if that becomes exposed, the engine WILL burn oil shamelessly from oil getting sucked in past the threads. They will require some gasoline-resistant sealer (NOT RTV) on the threads.
FWIW, do NOT buy the GM flat head screws retainer plate. Make sure the Mahle B31822 plate works for your motor before ordering. If it does, I recommend going with that. It uses the early hex head screws for attaching to the block, instead of the PITA flat heads. If your motor has the hex heads now, the B31822 will be perfect. You'll thank me later, trust me!!
FWIW, do NOT buy the GM flat head screws retainer plate. Make sure the Mahle B31822 plate works for your motor before ordering. If it does, I recommend going with that. It uses the early hex head screws for attaching to the block, instead of the PITA flat heads. If your motor has the hex heads now, the B31822 will be perfect. You'll thank me later, trust me!!
Yeah, we sure don't want a repeat of THAT thread...... LOL!
What do you guys think? I purchased some gen 4 rods
If it was mine, as suggested above, I would leave the bottom end alone and run it. At 136,000 miles its barely broken in. But if you bought rods, you're obviously wanting to go all in on this thing.
The stock bottom end is pretty tough. Not like the old small block. If at all possible, I'd leave it ALONE.
The difference between gen 3 and gen 4 rods is, the piston pins float. Pretty sure you have to also change pistons out to use them, as the ones in press-fit motors don't have the groove for circlips. There might be other ways to retain them butt I don't know about that. Meaning, it's a COMPLETE teardown, changeout, and rebuild, to switch to them. Yeah, sure they're "better", butt considering how little difference they make in most applications, it's AHELLUVALOTTA maze to run, with very little cheeeeeze at the end. The kind of thing that if you were already there anyway (motor destroyed and has to be rebuilt, no choice in the matter) or if you were going all-out max-effort, you might do; butt to tear down an apparently otherwise perfectly good short block, when all you're gonna use it for is a daily or a weekend cruiser, makes little sense. There's no "there" there.
Of course, you haven't told us what you're going to use it for, so that advice may or may not apply.
One of the things I do on my LS swaps using used engines that have sat for awhile I send the injectors out to be cleaned and flowed. Some will do it themselves but there is a company somewhat local I use and trust. Just reduces the issues that can come up on first start up.
Thanks for all the excellent advice and to answer some question pertaining to this engine, It came out of a perfectly running 2003 Chevy silverado LT 4X4, a family member owned the truck and when he passed the truck just sat in a field and mice took over the truck and when they tried to move the truck it would not turn over (electrical) it was last inspected in 2013, so it sat until May of this year, I inquired about the tail lights, I have a 99 GMC with a 4.8 LS in it and i am wanting to build up this truck, so my nephew became owner of the property and he reached out and asked if i still wanted the tail lights or just take the whole truck, I took the whole truck, no title and the truck became my parts truck. Now I have this nice truck with a few very small (2) dents and some rusty bumpers, but everything under the hood was in excellent shape once cleaned and power washed. Now I am trying to figure out this convertor that came with it, If anyone can help with it I will post a pic in the reply. came out of 4l60e
yes the plan is to put the motor into the 99 GMC, with built heads and cam,springs, lifters,rocker arms and bolts with a trunion kit, I bought some gen 4 rods because I read that they were stronger and would last longer, I still am thinking about just breaking down the 5.3 and replace the bearings and having a machine shop clean it up and check it out for me, nothing wrong with the GMC motor that is in it, but when i was giving this i made my mind up i wanted this 5.3L to be strong and reliable street and strip if you will, I am not sure what I am going to do with the rest of the 2003 Chevy (parts truck) I did remove the leather interior and the carpet which was in excellent shape, also the accelerator pedal and wiring, also took out all the wiring from the 2003, the back glass and side windows are all in excellent shape beside the rear passenger window, I broke it when we were loading it on to the roll back, frame is excellent and the front suspension is in tack and steering everything is in good working order
For a head/cam 5.3 there is absolutely NO WAY I would even touch the bottom end of that low mile of a engine that is clean like that one.
If you just want to rebuild an engine I would find one that doesn't have 200,000+ miles of life left in it.
I have taken 300,000 mile engine's out of trucks and slapped a cam in them, spin 7,000rpm with no issues.
Gen 4 rods are no better than a gen 3 rod for your application unless you plan on boosting the engine and pushing 600+ rwhp, and even then its not necessary.
As soon as you untorque those rods you have now opened yourself up to potential problems that where never there otherwise.
09-20-2024, 02:24 PM
LM7 5.3 Iron block 2003 LM7 had not been started since owner past away in 2013 
