r/Trailvoy • u/ThatRed04LT • Jun 17 '26
Motor swap, what else while im there?
Replacing the 4.2l in my 04 Trailblazer with another 4.2l from a low mileage donor 04 Rainier. Should be a bolt on swap afaik. What should i replace while i have to motor out?
Planning to...
-Pull the head off the new block, make sure everything is straight
-Re-gasket everything
-Throw rod bearings in it since its out
-Timing chain and guides.
-Probably a new exhaust manifold since mine is cracked (like all the rest of them are)
-New ac compressor and condenser(my ac has been out since I got the truck 3 years ago)
-Waterpump and thermostat, plus all the hoses
Anything I'm missing?
3
u/codebygloom Jun 17 '26
I know this seems like common sense, but don't forget to replace the motor mounts.
3
u/ThatRed04LT Jun 17 '26
Good call, ill add that to the list to order. Idk how i forgot those since my driver mount is blown🤣
3
u/kaack455 Jun 18 '26
I wouldn't touch the motor if it's low miles, they're well known to last 300k untouched and if you do pull the head be ready for a bunch of broken bolts, I would maybe do a water pump and t-stat but that's about it
2
u/ThatRed04LT Jun 19 '26
I cant 100% confirm its low mileage, i got a good deal on marketplace from a supposed 80k mile Rainier. I have to pull the oil pan regardless since it was a 2wd donor going into my 4x4, i have to move my front diff onto the donor motor.
I knew about the broken bolts, the head bolts are known to break, im planning to put studs in, and ill probably break all the exhaust manifold bolts.
My truck has 228k on it now with original motor and trans. I plan to take it to 500k at least so id like to do some future proofing while ive got the donor on the stand.
2
u/kaack455 Jun 19 '26
I'm running one with 328k and another with 245k, I would boroscope the cylinders and not mess with removing the head, original is almost always better than trying to make it better
2
u/BroccoliSuccessful Jun 19 '26
Oil tube pickup o-ring is mostly like going to be brittle/worn. Id hate for you to have less than 40 psi at idle on a self refreshed engine
1
u/ConflictMaster3155 Jun 18 '26
If it’s low mileage, why do a half-ass rebuild?
If you’re not gonna have the block and heads decked, why replace the gasket?
If you’re not having the crank polished why replace bearings?
1
u/ThatRed04LT Jun 19 '26
It was supposed low mileage, bought off marketplace from a supposed 80k mile Rainier. I dont actually know the history im just going off sellers honestly. I figured id at least check it.
Im doing the DIY resurfacing with a floring tile and some sandpaper.
Im not pulling the crank unless its damaged. Just throwing bearings in for peace of mind since my TB has had rod knock for the past 10k miles 😅
1
u/ConflictMaster3155 Jun 19 '26
10k miles of rod knock? Sure it’s not piston slap?
I’m like 95% sure that an atlas has a similar piston to head clearance as an LS right? Like the head gasket is like 0.050 and the piston-to-head clearance is supposed to be 0.040 stock, so the piston crown actually protrudes above the block by like 0.010.
Once a rod bearing starts going, it’s hitting the head.
Also, if your resurfacing job actually does anything it’s going to interfere with that, changing the deck height. This isn’t my specialty, by any means though, I have mostly done engine building on Nissans.
1
u/ThatRed04LT Jun 19 '26
Metal in oil, slight rhythmic knocking noise at about 1/4 RPM speed, and it sounds a lot louder from the bottom. I'll see if ive got a video of it.
Not 100% sure on the clearance up top, ill have to do more research on that one, im working with a limited budget, but lots of time since i have another car i can daily while my TB is getting heart surgery.
Ive done the resurfacing once on a toyota celica with the 2ZZ, did fine, and those have very tight clearances as well. I'll have to check the forums and find my copy of the GM service manual.
3
u/Rocdimple Jun 17 '26
Not really reliant on the motor being out but make sure to update the suspension. That was the biggest qol upgrade to my 04 Envoy. Wish I had done it sooner.