Does this mean my engine was bored .030 over?

[Anonymous]

I'm checking my reciepts from all the PO's of my car. One of the rebuild reciepts says the guy who owned the car bought "219x + .030 Rings" and "1120 + .030 pistons". : The other odd thing is that he only bought 3 of the new pistons and had 3 cleaned and pressed. : Can anyone figure out(or just take a wild guess) what went on here?
I'm just hoping this block is still useable for the rebuild. Guess I won't know 'til we pull it though.

 

[Anonymous]

well it could mean that it was already bored when he rebuilt it, and ya its still useable you can bore to .60 over. if my memory serves me right

 

[Anonymous]

Paul,

You can tell for sure when you tear it apart by measuring, or a lot of the replacement pistons will have the over bore punched in the top. Mine say .060 on the top of the piston.

Yours might need to be bored more our maybe just honed....Youre machinist will be making that decision

If you plan on using the 2.3 litre HSC piston I believe they only go up to .060 overbore.

According to various Ford manuals in my possesion, the max reccomended overbore on a 200 is .080.

Later,

Doug

 

[addo]

80 thou!

At that point, you'd have bores splitting on a serious engine. Unless it was sentimental, I'd bail after 40.

 

[Anonymous]

Yup, Federal Mogul makes .080" oversized pistons for the falcon six...

 

[Falcon62]

I'm with Addo here. These blocks were cast using thinwall technique, so I'd prefer not to take any block past .030 if I could help it. If you are building for serious power, have the block sonic checked to verify cylinder wall thickness.

I was displeased to find my block punched all the way to .060, and don't know if it would have cleaned up at anything less than that. Not that it mattered after the fact.

 

[Anlushac11]

8)

Im not an expert but wouldnt there be problems trying to balance an engine using standard and oversize pistons on half the cylinders?

The weights should definately be different.

 

[CZLN6]

Howdy All:

Dissassembly is the only real answer to this mystery. And, yes, it was/is not uncommon to fix, ei, bore and replace any number of cylinders, as a cheap alternative. And, Yes, it will not be a well balanced engine.

The reason for not boring beyond .030" or .040" is related to cylinder wall rigidity and integrity. The thinner the walls, the more easily they are distorted due to torque and stress. As they distort they lose contact with the rings and/or become too tight. Distortion is caused by head bolts and torqueing, water pump tightening, Main bearing cap tightening and torqueing, heat and stress. What happens is a perfectly round cylinder, after boring and honing, becomes distorted from round to a some what square-ish shape as the four head bolts and other fasteners are torqued down.

This is critical when you realize that 80% of the power output in a 4 stroke engine occurs in the top 20% of the power stroke ("Torque Plates: Do you Need Them", Marlen Davis, Car Craft, March 2001).

So, what can you do?
*Only bore enough to achieve clean, true cylinders,
*Bore and hone with as many fasteners as possible in place and torqued to specs; bell housing, water pump, main caps, and most important, if at all possible, bore and hone with a torque plate and gasket. Torque plates are very expensive and few shops have one for our six. Don't be surprised or undaunted if you have to give up on this one.

And, be sure to use hardened washers on the head bolts on reassembly to help spread the load. Torqueing the head into place in timed stages may help to lessen distrotion. For example, torque the head to half of the final ft lbs and let it "set" for a few hours. Then add another 10 to 15 lbs and let it "set" over night if at all possible. Then loosen and tighten to specs each bolt in the proper sequence.

The farther you overbore past stock, the more important these details become.

Keep us posted on disassembly Paul. Every mystery needs a climax and solution. Thanks for sharing.

Adios, David

 

[Anonymous]

OK. It just seemed kind of odd to me that they would bore 3 of the cylinders.
I'm just not going to worry about it until the machinist looks at it. There's enough junked Fairmonts and Granadas around here, that it shouldn't cause me too much of a headache either way.
I'll be sure to fill you all in when we get started. Prolly with some pics too if I can find a good webserver.

 

[addo]

To further David's comments about causes of bore flex, a turbo or other forced motor will experience bore flex on the power stroke. This is where the wall thickness becomes critical. 40 to 80 thou may not sound much, but as a proportion, it's huge. Especially, this is because when you consider a cross-section of the wall, the stiffness is not simply a fractional relationship from one thickness to another.

 

[mugsy]

To all,

Just a general note. I have heard (never verified) that oversize pistons dimensions are changed very slightly to "match" stock pistons. If all dimensions were held except the diameter on an oversized piston, the static compression ratio would increase. The reason: by oversizing the bore there would be more swept volume, but keeping the combustion chamber the same size would result in a (slightly) higher static CR. So the piston mfg try to maintain the CR by lowering the compression height. I also heard (never verified) that oversized pistons are the same weight as stockers. So the 3 old/3 new pistons might not be as bad as it sounds . I just want to know why only three cylinders wore that much more than the others!!!! Or maybe there was some "value engineering" going on .

 

[addo]

Mugsy - Ford pistons were within the same weight tolerances, regardless of oversizing. They make a point of this in the manuals. Plenty of "old-time" shop work just used to turn one bearing, or hone one bore to repair. (For that matter, I have heard of precision hardwood pistons being used in WW2, but it's another story...).

Regards, Adam.