Yes I have posted on here a few weeks ago about getting a repair manual which I bought online thanks for the help with that. Now a little about my problem I have a 2012 f250 gas/flex fuel 6.2 engine. I bought it knowing the piston was bad and the dealership would not just fix the piston they would only put in a new motor if he bought one. So he sold it they said he had a hole in the piston. Well I got the motor apart this weekend (its still in the truck just took head and oil pan off to get it out). Its the #8 piston when I got it out there is a crack across the top, the side of the skirt has a peace busted off the side, and the valve was burn up. Got a guy to check the head today he said it was good ordering the valve tomorrow. But my problem is the piston, I went to the dealership and they couldnt help me at all. They just told me they dont do much work on engines and printed on a page which i have in the online book I bought. Prob is the piston comes in 3 grades 1,2 and 3. 1 being 101.960 mm (4.0141 in) 2 being 101.970 mm (4.0145 in) 3 being 102 mm (4.0157 in). Now I dont have a mic (i am going tomorrow to a shop to get the piston mic) I do have a set of calipers and the bore on the cylinder which i could only get a measurement on the top (also getting a tool tomorrow to put down inside to get a better measurement) but it was 4.008. Not the piston which it said in the book to measure down 42 mm and then measure at a right angle from the pin so I did this and I get 101.80 or 4.008 (now the top of the piston was like 3.989 or something close to that ) but the 4.008 does not match the piston list at all I have to choose from with the smallest being 4.0141. Any ideas here why the piston would be so different I will post the pic of the chart on here as well that the ford place printed for me.0

 

Your piston diameter plus piston to cylinder wall clearance should equal your cylinder bore.

 

The gap between your piston and cylinder wall is taken up by the piston rings. If you're ordering a new piston, order new rings with it. Go off of your actual cylinder bore diameter and subtract the recommended cyl wall clearance to equal what piston diameter you need.

Also, when you get the old piston out, make sure you measure the bore diameter of the cylinder at least at the top, middle, and bottom of the stroke, to make sure there's not too much wall taper.

When you get the new rings, carefully place them in the cylinder one at a time, use the new piston to push them in straight, and then measure the ring gap, which is the distance between the ends of the ring while it's in the cylinder. Often times these rings will need to be trimmed for correct ring gap. Be careful with them while handling them, rings are very brittle and easily broken by mishandling.

 

Also, I'm guessing that it is assumed your bore will require some clean up milling, which is why the pistons are oversized?

 

You're going to have to have the cylinder milled, aren't you? Have it milled to the grade you want. Probably grade 1 if its in good shape. If you don't mill it you won't get a rough surface to break in/seat the new rings.


Another issue though is getting your rotating assembly balanced with one different piston. Not going to happen. There must be a way to just order a stock piston, no?

 

If your a newbie at fitting rings order yourself extras. Be sure to use a high quality compressor when fitting the slug into the jug. Oil it up good too. Put stud protectors on the rod studs(if equipped) so you don't ding the crank journal on the way down. Yes a bore gauge is critical and you need to take at least 9 measurements down the bore to verify concentricity (a tolerance zone for the median points of a cylinder). If you don't have significant glazing or a top ridge or an out-of-spec (out-of-tolerance) hole your repair should be a success. Id lightly hone it at minimum. wash the hone with dawn and water then dry and oil the bore immediately. If you dont wash out the hone material it will take the rings out in short order.
However I would ask myself why did said piston crack? Fix that too. If it was me I rip the whole thing down to inspect all of it which in my world is a re-ring re-bearing job at min.... but I'm somewhat retentive and it is a sickness!

 

Well my cylinder wall is in good shape very very minor wear on it. only 114k on it and the piston didnt hit the side of it. So I prob just hone it and let it be good. I did get to measure the bore on the block it was 4.015 to 4.016 which falls in the grade 1 section so that's what piston I ordered. but there is only 4 thousands of a difference between one and two seems the ring would fix that much gap which is only like 3 sheets of paper. Also for anyone else doing this says to order new head bolts because they are tighten to yield or something and cant be used again. One other thing it keep saying was to use gasket remover which I ordered and also metal surface prep which I didn't order because it was over $200 or a small tube anyone know what this does and can i get by without it if i clean it good?

 

I have done rings in older motors but nothing on these new ones. I am mainly worried about the timing. I had everything marked on the head and motor which is gone now because i had a bad valve and had to send it off to get fixed. So this is my main worry I have he workshop manual maybe I can get it in time but the duel overhead cam really got me worried lol.

 

I have done many piston replacements. and yes...different size piston offerings account for anticipated honing and if needed ridge cutting. factor milelage and the work needed to round out an oval piston hole (leading and trailing wear more than sides) and the ridge from where the rings do not reach. end result is a bigger piston hole.

so you need to recondition the hole and determine piston and ring sizes. more of an art than a science. also need to put the rings in the hole and measure the gap and file it down if it's not within spec. need to dry install the piston with the rings and measure side gaps to make sure the piston is correct size....piston needs to expand when hot so it can not be a tight bang it in place fit. also need to make sure the piston sits with in the correct extension point and does not extend too much into cumbstion chamber or into crank case...deck height...etc.

make sure you lube everything with at least assembly lube. correct torques and wrist pin clips. ring gap spacing of 120 degrees apart is theroetical and obviusly moves around during operation.

the rings go in a particular sequence and particular direction as does the piston.

before start, skirt some oil in the hole and do a crank run with out the plugs and ignition hot to make sure there is no binding.

on something like what you are doing which is the result of engine damage, I would use clay to measure valve to piston clearence incase there is valve binding.

drain the oil and change the filter to try to get metal fragments out from the incident that cuased the damage.

also, keep in mind this is all a crap shoot...since the oil pump is designed to protect the oil filter....you could have some oil pump damage so watch your oil pressure.

other problem is stuff like one new piston running with others that have carbon build up....odds are your going to get some harmonic vibrations until you decarb the other pistons.

sorry if this all sounds basic but I know many folks who blew and engine becuase assumptions were made.

 

I would also stop and do a careful analysis of this engine. Why did the #8 piston crack, the piston skirt chunk break off and a valve get "burned up"?

Fixing the damage without addressing the cause of the damage is just an invitation for more damage. Are the other cylinders about to repeat this act?

 

well just for future ref the top of pistons have grade numbers 1,2 or 3 at top, mid, and bottom. Wish I would have seen it before I ordered. I could see the number after I knew where to look. I ordered grade 1 and it was suppose to be 2 but there was only a difference of 4.0141 for grade 1 and 4.0415 for grade 2 . the ford dealership said it wouldn't be a difference really like a 1/10 of a sheet of paper. and to be honest the skirts have been rubbing on the sides. as far as how the prob started i am hoping the guy just over rev it and the valve burn a hole in it and made it hit the piston. not sure what else it could be unless the injector messed up and the air fuel lean out.