When pistons are pressed off rods, are they usually damaged such that they cannot be used again? The KB pistions I am using in my rebuild are not all the same - the valve reliefs are different depending on whether the exhaust valve is on the left or right of the bore. The machine shop got two sets reversed. Very discouraging. Can they be safely pressed off the rods and then pressed back on the correct rods? Or do I need 4 new pistons?
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Re: Pistons
Mark,
You might want to double check to make sure that the machine shop messed up. They should be oriented from the front of the block on each side in the following order....#1-Exhaust/Intake #3-Intake/Exhaust #5-Exhaust/Intake #7-Intake/exhaust.....same order for the even bank. You should have four pistons set up one way, and four set up the other. If you have all pistons with intake reliefs oriented first, then you have got to have them reheated and pressed off, and corrected. It should not hurt the pistons. They just heat the rods and press the pins out of the pistons....Hope this helps -
Re: Pistons
The rods are numbered, and four were installed incorrectly. (for example, #5 is oriented intake/exhaust). Just goes to show, I should have checked them before I left the shop (and paid the man). What gets me is when I asked him for the old pistons back, he said sure, but pushing the pistons off the rods would probably damage them and render them unusable. Hope he was wrong.Comment
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Alternative Piston Fix?
The four incorrectly mounted pistons are only "incorrect" because of the number stamped on the rod and rod cap. The rod cap end of each rod was rebored and obviously new pistons will be used. Setting aside the wrong-number-in-the-hole issue, is there any risk of damage if I reuse a rod in a different bore upon reassembly (i.e., rod from #2 gets used in #4)? That would create a mis-numbered set of rods, but avoid the need to press the pistons on and off the rods again.Comment
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Re: Alternative Piston Fix?
Mark------
First of all, "pressing" the piston pins out will not harm the pistons, at all. For one thing, the pins are NOT a press fit in the pistons; they are a press fit only in the rods. If they were a press fit in both, you would not be able to move the piston on the rod and the piston/rod assembly would not "work" in the engine. The piston must be free to rotate on the piston pin. In a pressed fit rod, the piston, alone, pivots on the pin. In a full floating rod, both the piston and rod can pivot on the pin.
As far as the rod numbering goes, that is primarily done to index the rod cap to the rod. You ABSOLUTELY CANNOT interchange rod caps on rods. If you had the engine rotating assembly precision balanced, then it might be wise to keep the rods in the proper cylinders, as marked. For the most part, though, it probably wouldn't make any difference since, even in a precision engine balance, the rod/piston assemblies are weight-matched as part of the balancing operation. If the engine was not precision-balanced, then it really makes no difference, at all, what cylinders that the rods go in.In Appreciation of John HinckleyComment
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Re: Alternative Piston Fix?
I thought the issue was the stress placed on the piston when the pin is pressed out - that it can cause the piston to deform. Any risk of harm to the rod when it is pressed out?
The pistons and rods were weight balanced.
Caps are all where they belong.Comment
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Re: Alternative Piston Fix?
Mark-----
There is no stress placed on the piston when the pins are pressed out. Also, there is no harm which comes to the rods when the pins are pressed out, regardless of how many times that it's done.In Appreciation of John HinckleyComment
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Re: Alternative Piston Fix?
Mark - as Joe mentions, no harm at all. They should have a special piston fixture to support the pin boss area when the pressing is done...CraigComment
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rehone the piston pin bore because
it may get distorted and you want to make sure it is roundComment
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