naf

iTrader: (7)

350 in shop and found three of the piston skirts cracked. The shop manager says he's seen it before and maybe it was over-revved. This is a 70's 350 and I have no knowledge of the prior history. When I got it, it would idle and run fine til it warmed up then go to crap. Took it apart and all of the cylinders had a fresh hone but the bearings were all worn. 030 over pistons, but two of them were a different make (with obviously much less run time on them).

Anyway if I save it, the cranks gone, pistons in the trash: I'd be re-using the rods and caps. Shop wants to re-bore and hone with a flush/cam bearings. Maybe $2-300 in shop work (he's getting me a quote together). Anything I need to worry about if I re-use the rods/etc.?

Yeah I know it's a two-piece flat tappet block, but it'll end up in my nephew's car with some low mileage swirl port heads I've got. He doesn't need much now.

Damon

If the rods aren't bent or cracked and are properly machined, yes, you can resue them (I shy away from "mix-n-match" rod sets, however, if I find they are not an original matched set). I remachine stock rods all the time and use them in my mild street buildups. Aftermarket rods are getting awfully cheap these days, however. Compare the cost of new to the cost of redoing your current ones.

Have them check the bores before you pop them over to the next size. If there's no ridge at the top and they are not worn tapered or ovaled out or have big vertical scratches, you can get by with just a quick hone job (I do that quite a bit with throw-together motors as well).

None of this is stuff you consider for a race engine or something you have your soul invested in, but for your neighbor's kid or your second cousin who has no money to spend, I consider this acceptable practice. Fix only what needs fixing. Got quite a few "throw together" motors still our running strong on the street 2 or 3 owners later.

sofakingdom

iTrader: (1)

I agree, cracked skirts is almost always the result of too much revs.

Thing is, if the pistons were over-revved, so were the rods. And even worse, the rod bolts. Those have a bad habit of breaking suddenly catastrophically unexpectedly, even if they look good now. And THAT tends to scrap the whole block, the cam, and lots of other stuff.

Same for the crank. Cast cranks don't crack, like forged ones do; they fatigue, like aluminum does. In other words, everything "looks" and "checks out" just fine, until one day, you're drivign down the road, and out of the clear blue, it breaks in half. Revs is what does that to cast cranks. It will break between the #1 main journal and the #1 rod: either where the throw connects to the main, or where the rod pin connects to the throw. But at least, if the crank breaks, it usually doesn't scrap the motor.

What Damon said about a tear-down and slap-back-together is true; however, when the parts you want to re-use have ALREADY been stressed like that, it might not be the best idea. Works OK when it's been grandma's motor all its life, or in a phone company van, or something relatively low-violence like that; but tends to cause a calamity when it's already been hot-rodded to the end of its useful life, as cracked pistons show that it has. Not a good candidate any more for re-use of ANY of the parts, without significant service.

naf

iTrader: (7)

Thanks. I'll see what the quote from the shop says and meanwhile I'll look around locally for a later model 350. By the time I pay for a crank kit and new rods I might be close to the cost for an assembly that has parts I can re-use.

Supervisor42

Could you post some pics of the cracked pistons?
I don't run into that much...

naf

iTrader: (7)

I'm going by the shop today at lunch. Only one of them was very noticeable, prompting closer inspection of the remaining. We suspect that the two odd-ball replacement pistons were installed recently to replace two cracked pistons and they failed to replace the complete set. I mean, who buys just TWO pistons?

naf

iTrader: (7)

Spoke to the shop manager today. He's not happy with the current bore size as it's nearly out of tolerance for 30 over pistons. It was near 40 over and he suspects this contributed to the cracked pistons. He says the rods are OK but will include new bolts.

He can provide me an assembled short-block for just under $800. However his charge for pistons w/rings is $100 and crank kit at $140. He's got no problem with me providing my own. I can pick up a kit for around $100 at AZ. Any recommendations on a piston/ring set? Worth it to buy my own or not?

I know I could get a new 2-piece short block for around $1200 and probably would if it were for me, but a couple hundred is a lot more money for a sixteen year old. By the time I'm done with gaskets, etc and considering the parts I've already got on-hand I expect to have a running motor for around $1000.

Sorry, camera was locked up in my guy's office when I left for lunch. Pics will have to wait.

400 hp

iTrader: (19)

the 350 motor i bought had 3 broke pistons in it. stock pistons dont like hight rpm. i went with new rods.. it was cheaper. then rebuilding the old ones..

gmtofd

iTrader: (2)

My 350 tale of woe is buying a used ZZ3 crate mtr that had 4 bad pistons, (cracked ring lands) all on the left odd number bank. Located a set of std bore TRW forged pistons, new rings/ rod bearings and back together it goes.

Piston weight can vary no more than 20/30 grams, otherwise it 's rebalance time.

As far as your situation, if the rods are going to be reused, consider magnfluxing for cracks. and check the rod big end for roundness. The crank should probably also be magged.

Good luck with your repair.

naf

iTrader: (7)

After all was quoted, I was looking at near $1000 for a short block assembly. I picked it back up and will use it as a core towards a rebuilt long block that will run me ~$1200 (with a warranty for what it's worth). 'Course this will be a mid-70's smogger motor but I can save the heads in my garage for another project. I just wasn't that comfortable with a .060 bore and the time to assemble it is getting scarce.

Had a fire next door that burned one side of the house and we've been relocated to an apartment for the last six weeks. By the time I'm back in my garage it'll be the heat of July.

I attached a pic of the worst piston. Sorry 'bout the delay getting it posted.