I have a 1985 z28 camaro with a 1980-85 half ton pick up motor in it. A chevy 350. The cylinders are bored 40 over and i was doing a rebuild becuase i was loosing oil pressure in cylinder 1 i noticed a scratch but that shhould beable to be honed out its not bad. My problem is that on that piston for cylinder 1. The pistons are fairly new and theirs not really any miles on them. Anyways the skirt was good at the base by the head but as you bring the mic up to the top of the skirt it was collasped about 2 thousandths of a inch and thier was some un smooth area on the piston where all the others were smooth. is it a bad isea to put that piston back in?? I have heard mixed reviews from multiple people the guy at the machine shop said i need to buy new ones and the mechaincs i work with say it should be fine after re ringing them. what do you think?

 

jacborn,

I'm not quite sure what you mean by loosing "oil" pressure in that Cylinder!
Could you be talking about "Cranking pressure", or Blow By ?

Anyway, you have the Piston out of the block (no doubt) and as long as you do, I'd go ahead and replace (just) it if there was any question about it. I'd take it by the Shop, and make sure that the new one, weighed the same as the other, AND, that it was the same type.

As far as clearing (honing) that scratch on the Cylinder Wall, I suppose you don't have much choice about that, IF if was very deep. Given the type Piston's you have, clearances vary, and as long as you don't hone out over the maximum clearance for that type, then that's ok.

I'd be real interested in finding our just why that scratch occurred though !
Make sure you wash things off real good after the honing, that debris can really cause you problems if there's any left on the components.

 

Honestly I can not answer why their is a scratch but ill be taking the block into to have it looked over to see if i can hone it. Im sorry for the bad grammer i was in a hurry i didnt meant I was loosing oil pressure in cylinder one i meant i was loosing oil pressure so i decided to do a rebuild end of sentence. than I went to go on about cylinder 1. Yeah the problem is im only a senior in highschool and im tight on money so what its going to come down to is if the block and heads dont need a rediculous amount of machine work ill probably just buy new heads im just kinda out of luck if the blocked is SOL. I really want to do a rebuild on a motor because its my first time by myself but if that block is out than i will not have a enough money to buy a new block and what ill end up doing is just buy a used running motor throw it back in and once i get done with basic trainging and tech school build a motor that i want. I should be taking the block in soon so ill find out if im lucky or not. The guy that owned it before me ran the **** out of it and caused the damage. I got a nice kit lined up on summit that i want its just a matter of money hahaha . gotta love life
Jacborn

 

Ok, I understand now. Loss of Oil Pressure comes from several things.
Crankshaft Main Bearings, Rod Bearings, Camshaft Bearings or worn Rocker Arms, if they're Shafted. You need to take all that with you when you have them look at the Block. They can tell you if any of the Journals on the Crank or Camshaft are worn excessively.

You can buy "undersized" Main and Rod bearings, in an attempt to not have to turn your Crank. You GOT to be careful on the selection, have that pro make a suggestion on that.

I'd go ahead and foot the bill for new Cam Bearings anyway, and again, it depends on what kind of Pistons you have, as to how much you can hone that #1 Cylinder.

I got a suggestion though............
I think I'd slap this engine back together as cheep as possible, and get you some wheels under you asap. Then, after you catch up on the bucks a little, go and buy you another basic used Engine, just from the Air Cleaner down to the Oil Pan. THEN, you can take your time and do a first class overhaul on it, turn the crank, maybe a good balance with some good new Pistons, and after you get it together, stick it in, and sell the old engine for some spare cash.

 

The effect of what you are talking about is someone who didn't know what they where doing and not check the ring gap during the assembly.The compression ring butts together scoring the bore.The other thing to be checked is the amount of taper in the bores.Being that it is a .040 over bore engine,I suggest you don't invest much in to it because it has not much a future for any other rebuilds.Maybe just a slam bam thank you mam rebuild.

 

Neff is SO right on that part !

And remember, you're going to need to do the Ring End Gap adjust for EACH of the Cylinders. Specially since you're only honing out the #1.

The Pistons should be marked 1-8, if not, mark them before you pull them out. That includes the orientation of the Piston in it's Cylinder. Put the #ID at the top (toward the Intake Manifold) of the Piston Face, and make sure that it goes back the same way. You don't have to stamp them, just use a Black Sharpie or something like that.

Once you set the Gaps set on the Rings for a given Cylinder, put those rings on that Piston right then, and make sure that Piston gets back in the Cylinder it was marked for !!!

If you don't know the proper way to set the Gaps in the Rings, just say so, and we'll talk about that.

Just a little explanation about Boring out Cylinders...
You really don't know just how careful the Machinist was about this.
Each Cylinder is done individually, and there are coarse and fine cuts on them. If he was interrupted, or not all that careful on the finals, the Cylinder size may vary some to quite a bit.

This shouldn't happen with a good Machine Shop...
But, ya never know.