Hi,

Tearing down my 72 350, found some play between the piston rods and crank, there's some minor front to back slop which seems normal but there's side to side and up/down play too. It feels like 1/16" to 1/8" tops.

Is this normal or indication of excess wear?

Thanks, Will

 

1/16" of play in the big-ends of the connecting rods is a rod knock, and a loud one.

Are you really sure? ⅛"? Really?

- Eric

 

The specs on allowable bearing clearance and rod side clearance are published in the Chassis Service Manual. Rather than guessing, get the appropriate measuring equipment and MEASURE the clearances.

 

Thanks,

I was trying to avoid unnecessarily pulling the piston rod ends to make measurements. More looking for go/no-go advice. It seems that #5 is markedly worse than the others, also there's some evidence of over-travel on the pistons themselves.

I'm going to go ahead and tear the bottom end down all the way. I have a Haynes that give acceptable journal diameters.

One more question...this is a 72 350, I think, casting 395558 with 2009674 on the oil filler, but it has #7 heads not 7A could this be a stock engine?

I'm turning up 4 different cranks for the 72 350, is there any more information out there beside the 442.com olds faq?

Thanks for being there.

-Will

 

If you can feel any play at all with oil on the bearings (if you are very sensitive, you might feels a tiny bit with the bearings perfectly dry), it is too much, and it has to come apart.

You're doing the right thing.

- Eric

 

Get the Chassis service manual for the right specs and procedures and throw the haynes manual far far away. You can also check clearance with plasti-guage but micrometers are in order if you tear it down.

 

Check the VIN pad on the block. The heads could have been replaced sometime in the last 40+ years but the block stamping will tell you what you want to know.

Head_ID.jpg

 

pretty much any 350 crank will do.

If your crank is toast, and it probably is, then ask the machine shop about getting a crank kit- reground crank with bearings to match. Last ime I was doing this it was about 200 for a grind plus 100 for bearings, or $200 for the crank kit, delivered. Of course, you may get a smogger crank with a PN in the 5xxxxxx range, but for the driver, who cares? If you really care, spend the $ on a 330 crank and flexplate and a rebalance and have a forged crank.

 

Fun71 - VIN derivative is 32Z100184, head stamp is definitely 7 not 7A. This has a 'N' on the first lobe of the crank which indicates nodular iron, right? Yet another item that should not be in a stock 72 from what I've read.

Octania, crank looks ok, no visible wear or scoring. The rod bearings are crazed and look like they could use replacement. It felt like when I was removing the pistons, the looser rod ends weren't torqued as tight as the others.

This si the furthest I've ever tron down a motor so I can promise many more dumb questions.

Thanks All,
Will

 

Speaking of dumb questions, how do I decide what size connecting rod bearings to buy?

Rockauto has .001, .010, .020, .030, and .040 undersized.

Thanks,

Will

 

thats a machinists job

 

Yeah, don't buy bearings until you know how much the machine shop needs to grind the crank.

As for the N on the crank, I have no idea what that era crank has for numbers, but ALL cranks are either modular cast iron or forged. Since the only small block Olds with a forged crank is the 330, by default your 350 has a nodular iron crank.

 

i want a factory manual no haynes crap.... M Dchanicwhat brand book would recomend.