Pulled the motor guys and had a piston slap smh. Only one piston was damaged but instead of replacing that one piston which is a Sealed Power 332AP .060 piston...was thinking of upgrading to flat tops but from my research I see the pin diameters are slightly different. The current pin is .9804 and the flat tops I see are .981. I really would like some flat tops without having to buy new rods and pins. Are there any out there I haven't found or would these work? Helppp lol thanks guys
Ruined piston in top<br/>Good on the bottom

 

Are the flat tops full floating pins? That might explain the difference and require the rod to be opened up accordingly.

That is some bad skirt damage and suggests to me that either the bore is too large or the piston is small. I suppose it could have been tight also but that is a lot of aluminum that has been displaced.

 

Chris, first glance that appears to be a case of not enough skirt clearance on the piston, causing the severe scuffing. The machine shop that will press the pistons on and off the rods, should be able to hone out the rods to get a proper fit with out any difficulty.....if they know what they are doing. The S/P flat tops are press in pins.
Using the Sealed Power flat top piston that have a 1.612 comp height , with the 66cc heads you bought, a 4.087 bore, a .041 head gasket and .025 deck clearance will get you approximately 10 to 1 give or take......
Harold

 

Yeah but my concern is that I have a cylinder bore now of 4.057 and not 4.087. That's the size of the current pistons I have now but I wanted to change them all to flat tops because these are not flat tops that I have. I found some flat tops with the same exact bore of 4.057 but I noticed the pin diameters are different. Iowa's wondering if they make flatops for this engine of a 4.057 bore with the exact pin diameters without having to change rods as well. Or I may be misunderstanding something bc I'm no machinist, leading as I go through this problem. Are you suggesting that I increase my current bore of 4.057 to 4.087 by boring it or honing it? Thanks appreciate it.

 

I guess that's something I should check because I can't recall if the flat tops I found online are full floating. They're also made by Sealed Power

 

And I currently have. 060 oversize inch pistons. What's that mean or the difference between the .030, .040, or .060?

 

4.057 is the standard bore from the factory. If you have .060 thousands oversize piston the bore is no longer 4.057. Your bore now would be 4.117. I thought since the piston is scored pretty badly, the cylinder would also be damaged requiring an over bore on all cylinders to clean up the damage on the one cylinder. Checking Summit, I see the flat S/P pistons are not available in .060 oversize. Can you post a pic of the cylinder wall from the scuffed piston?

 

The bore on a stock 350 is 4.057 inches across (diameter). If you now have a .060 oversize piston the hole is now 4.117, 4.057 + .060 = 4.117.
.980 is the standard wrist pin size on an Olds 350. Most pins are not full floating as they have to be pushed on and off the rod.
I'm a little confused by the whole thread. Do you have just one hole that's .060 over or are all the holes .060 over?

If your concern is can a .060 over piston fit in a .030 over hole the answer is no. The other way around is possible but is absurd from a machinists point of view to even consider. That would no doubt give you severe piston slap.

Your best bet is to have everything checked for accuracy. There is no doubt some machining is off on that engine. Whether it is the piston or the cylinder one or both are off. Out of curiosity what does the cylinder look like?

 

Lol, thinking alike?

 

No, I'm aware that .060 will not fit in .030. I just didn't understand what the different sizes meant but now I understand. All my pistons currently have .060 on them so now I know that my cylinder bore is 4.117. This definitely helps understanding things now. I will post a pic as soon as I get home here shortly.

 

Will take a pic as soon as I get home shortly. I was told that I could probably hone it out myself at home with the right tools. And still keep the same size cylinder bore.

 

Any type of honing is going to enlarge the hole. That's why we wanted to see the cylinder wall to see how badly scored it is.
Piston slap is how you described the problem which is why I went with too large a bore. Piston slap sounds like a diesel engine at start up until the engine reaches operating temperature and the pistons expands enough to fill the bore correctly. All pistons have a recommended piston to wall clearance to allow for thermal expansion.
You have severe galling on that one piston. You can see the aluminum gathering on the edge of the skirt as it was dragged into place. I might have to change my opinion and go with too tight a bore until you know more.

 

Best pic I got but someone told me that that you hone it out without boring it bc it's not that bad. So I'm not sure. And question, does a. 060 piston means my engine was bored .060 over bc it didn't drive like it.

 

What do you think Mr Harold? My father has built 3 engines in his life (not this one) but he said we could hone it out. He said it looks as if it was too tight and lacked oil due to my mechanic dry starting the engine. He said he has gone cylinders before and this one wasn't that bad

 

You can hone that cylinder and hope for the best.

The evidence suggests that something wasn't correct-machined,when the rebuild was done. Either debris and junk got in there, or it wasn't measured properly to begin with.

 

Couple things to consider, your current pistons sit down in the hole farther then the stock ones did, they have a rather large dish so your compression is probably pretty low the way things are now. You could invest in one piston and see how much you would have to hone to clean up the bore and still end up with the right piston skirt to cylinder clearance. Do that before you have the piston/rod assembled. Just punching out the bore .060 thousand does not make for a significant power increase. Low compression on the other hand does make a big difference.

 

You picked up 5 inches in engine size which probably doesn't even equate to 5 horsepower on your build. You won't notice that.

Did this engine blow a head gasket? I see stains on the deck right where the scoring is and the crankshaft is rusty.

 

No a head gasket wasn't blown. It was the thin metal ones and seem fine upon removal. Oil pressure seemed to read fine on start ups around 60. And dropped to normal readings when idled. Didn't run hot any after radiator swap, highest ever hit was 220. Took a chance one day to drive an HR to the beach and on the way home heard a slight ticking or slap. Pulled motor and this is the results. Never dogged it out and always putted around town here and there..until the beach trip. Do have a leak in between the intake manifold and the intake manifold gasket that rests on the head. Aluminum intake was either torqued too much and warped it or it was done on the lowering of the engine bc I saw he had the carb off and a plate was mounted in place of it to be hooked with a chain for lowering the engine. Too much weight on an aluminum intake in my opinion, cast iron would of been different. So no blown head gasket.

 

Hmm, a lot going on here, check the piston to wall clearance on all the cylinders, you may have more issues. Has the block been decked, or heads milled, I ask because of your intake sealing problem. I wouldn't plan on new pistons until I miced everything.
I've used an intake lift plate with an aluminum manifold many times with no issues.

 

I agree. Thanks Don

 

Oh OK. Well it was a suggestion from someone so I wasn't sure. But the heads are supposed to be stock. Key word "supposed" to be but for info, they're not matching heads. On the drive side is a 7a and the passenger side is a 8. Found this out a month ago after my own inspection. So I now have some #5's on the way now that are milled down .010. So now I'm curious to how the intake is going to sit on the new heads. And if milled heads will interfere with flat top pistons, if I can find the correct flat tops.
P. S. And no the block is supposed to be stock with no decking

 

Shouldn't be any issue with the heads milled .010 and flat top pistons. Factory piston-to-deck clearance is reported to be ~.020" or so. Locating flat tops in .060 overbore may be interesting.

Seems I remember a while back someone was looking at having some 4.125" forged flat tops made and was asking how much interest there was in them.

 

So you're saying I could have my engine bored out to a 4.125 even if the stock was 4.057? And use forged flat tops that are 4.125 in diameter? Just asking because I didn't want to overbore anything because I always heard boring anything over .060 was pushing it. Not insulting your knowledge just trying to be careful bc I'm tired of spending money and continuously having problems lok

 

Mr Harold I noticed you suggested here a 4.087 bore of flat top pistons, and I assumed that's with you already knowing I have a bore of 4.117. Are you suggesting that I could replace the current pistons I have with some flat tops 4.087 with a .030 difference and I should be fine? Do the piston rings help manage that .030 gap clearance?

 

No, I posted that before I knew you were already .060 over. You are now committed to using 4.117 (.060 oversize) pistons. There is a company called Egge Pistons that does make a .060 or 4.117 oversize flat top piston. The part number is L2320 on page 13 of their down loadable catalog.
But I have to caution you, make sure that before you spend more money on pistons, first find out if that bad cylinder can be honed out and still stay within the max limit in regards to piston skirt to cylinder wall clearance. For a cast piston like yours, maybe somebody more knowledgeable then me can tell you what the safe maximum clearance could be.

 

Thanks I appreciate it

 

Be aware that those cast pistons form Egge are short on compression height so your final compression ratio will not be as high as you think.