Removing Pistons from Rods 383

[condor74]

I have a 383 shortblock I built some years ago and I never installed it. When I had the machine work done I requested rods resized and assembly balanced. I found out after I assembled the motor that the assembly was not balanced. Currently the short block is together. I am going to remove the pistone, rods, and crank to have them balanced. I have to press the pistons back off the rods and I don't want to damage them. The pistons are a set of NOS direct connection 11.5 to 1 forged pistons. They are not available anymore so I am screwed if I damage one. Anyone have any experience removing pistons for reuse?

 

[bm02tj]

A shop with the proper equipment can press them of with no damage

 

[miller]

You'd be alot better off, if you had one of the stock piston pin tool sets, that both remove and installs the pins.

 

[dvw]

I'd weigh them assembled first. They may not be off as you think. May just have to get the bobweight and spin the crank. Talk to someone who knows balancing. You would be surprised what you can get away with.
Doug

 

[miller]

Agree. Even with the pistons still mounted on the rods, weighing the rods end to end, will give you the story. Just a matter of getting the same combined weight on the tops...with the pins and pistons.
(Last set of rods I weighed were spot on, both ends, and total.)

 

[Cranky]

Why are these pistons not full floating? If you've never pressed off old used pistons without damaging them, I sure wouldn't start learning with these! And if you do not have a small machine shop (or access to one) with at least a small lathe and a milling machine to make the tools that are needed for this (instead of buying them), forget doing it yourself. Pressing pistons isn't all that difficult if you know what you are doing and have the proper tools to do it with and even then, it's not that hard to mess up a piston either.

 

[condor74]

I have pressed off many pistons before but never had the intention of putting them back on. The block is 1969 383hp block I believe. The connecting rods were press fit. I am not sure of the year break down on what had press vs full floaters.

 

[Lionized]

Wouldn't you (or a machine shop) weigh the assembled rod and pistons to find the lightest anyway? I may be wrong but I believe that's how it works.
How did you find out it isn't balanced?

 

[Cranky]

Not all forged pistons were machined for full floating pins but a good machine shop can do it if they were not grooved for keepers. Sure makes life easier at rebuild time too. I've had good success with supporting the piston at the pin boss area and pressing out the pin. First time I tried using a V block setup and it didn't support the piston at the boss and the force required distorted the piston. Heating the small end of the rod didn't help enough either.....and I hate it when some shop uses too much heat an assembly and turns the little end blue or worse. On assembly, I'll heat them some but never enough to change the color of the metal. Also Keep in mind that any time you heat up a hole, it gets smaller before it gets bigger.

 

[condor74]

I was looking through my receipts and didn't see the charge for it. That is how I found out it wasn't balanced. Initially I was going to just go ahead and run it but have thought better of it. I called the machine shop yesterday and they said the need to have the pistons off the rods so they can weigh the ends of the rods .

If the pistons were stock replacements I may have just left it alone.

The pistons are machined for floaters but rods would have to have small end bushings installed. I don't have the locks anymore but I could get them I am sure. I am on a budget so not sure I will do that but I do want it assembled correctly.

 

[PurpleBeeper]

Yep, even if it slows down the build, get it right. If a machine shop is good enough to balance an engine, they're certainly capable of pressing pistons on/off.

 

[condor74]

Oh they said they can remove the pistons. It will cost 60 dollars though

 

[mopar 3 B]

You can not replace a damaged piston for 60 dollars. But personally I have never had that problem.

 

[condor74]

If they damage the pistons I can't replace them either. If it was a modern piston that was still currently available I would not worry about it as much. Another headache that I worry about is say worst case scenario happens and one piston gets damaged. I can't just slide a modern set of pistons into the engine as modern technology has tightened up the pistons to cylinder wall clearance. These are old forged slugs that are expected to grow. They have .010 skirt clearance already honed into the engine. If one breaks I basically have a good set of rods and crank with nothing else. Sorry not trying to be a stress case but just looking at it from all angles.

 

[Lionized]

If they damage the pistons I can't replace them either. If it was a modern piston that was still currently available I would not worry about it as much. Another headache that I worry about is say worst case scenario happens and one piston gets damaged. I can't just slide a modern set of pistons into the engine as modern technology has tightened up the pistons to cylinder wall clearance. These are old forged slugs that are expected to grow. They have .010 skirt clearance already honed into the engine. If one breaks I basically have a good set of rods and crank with nothing else. Sorry not trying to be a stress case but just looking at it from all angles.

To reiterate my previous post; balancing the reciprocating assembly means finding the lightest rod and piston "assembly" and matching the rest. I'm finding it hard to understand why you should have to disassemble the rods and pistons. Most, if not every machine shop, will assemble the rods and pistons to balance them prior to assembly.
I find it very hard to believe that an engine building machine shop would NOT go with the lightest connecting rod/piston combo and build/balance from that. It's textbook. Period.

 

[condor74]

To reiterate my previous post; balancing the reciprocating assembly means finding the lightest rod and piston "assembly" and matching the rest. I'm finding it hard to understand why you should have to disassemble the rods and pistons. Most, if not every machine shop, will assemble the rods and pistons to balance them prior to assembly.
I find it very hard to believe that an engine building machine shop would NOT go with the lightest connecting rod/piston combo and build/balance from that. It's textbook. Period.

I understand what you are saying. I am going with what the machine shop told me. I am no expert on balancing. For what it is worth i did watch a video on what is done when an engine is balanced (for my own curiosity). They did show the small end of the rod being weighed individually from the big end so when I called the local machine shop and they confirmed this I did not question it.

 

[69Bee]

Not all forged pistons were machined for full floating pins but a good machine shop can do it if they were not grooved for keepers. Sure makes life easier at rebuild time too. I've had good success with supporting the piston at the pin boss area and pressing out the pin. First time I tried using a V block setup and it didn't support the piston at the boss and the force required distorted the piston. Heating the small end of the rod didn't help enough either.....and I hate it when some shop uses too much heat an assembly and turns the little end blue or worse. On assembly, I'll heat them some but never enough to change the color of the metal. Also Keep in mind that any time you heat up a hole, it gets smaller before it gets bigger.

It is normal to heat the small end to just past blue (straw), to install the piston pin. I heat to this range, and do not go to cherry red. You will damage the rod at this level. If you do not heat it enough, it will cool and contract too fast, and possibly not get the pin installed properly.

 

[69Bee]

To reiterate my previous post; balancing the reciprocating assembly means finding the lightest rod and piston "assembly" and matching the rest. I'm finding it hard to understand why you should have to disassemble the rods and pistons. Most, if not every machine shop, will assemble the rods and pistons to balance them prior to assembly.
I find it very hard to believe that an engine building machine shop would NOT go with the lightest connecting rod/piston combo and build/balance from that. It's textbook. Period.

I do not know of anyone who does this. The pistons are matched to the lightest one, the rod big ends are weight matched, then the overall rod weight is matched by grinding the small end. Piston pins are usually assigned to a piston to get the lightest piston/pin combo. One set of rings, and one set of rod bearings are weighed for bobweight computation, and the last is about 4 grams of oil weight is added. You will NEVER get everything exactly the same weight, so why split hairs over it. A half gram spread is pretty damn good considering stock specs are 2 grams.

 

[Lionized]

I do not know of anyone who does this. The pistons are matched to the lightest one, the rod big ends are weight matched, then the overall rod weight is matched by grinding the small end. Piston pins are usually assigned to a piston to get the lightest piston/pin combo. One set of rings, and one set of rod bearings are weighed for bobweight computation, and the last is about 4 grams of oil weight is added. You will NEVER get everything exactly the same weight, so why split hairs over it. A half gram spread is pretty damn good considering stock specs are 2 grams.

You're correct. It's the pistons that are weighed. Then the rods. Then connective components.
I was certain it was the assembly to the lightest then weight matched.

 

[bm02tj]

Engine balancing is an art the bob wts are a % of rotating weight and expected operating RPM needs to be known
A proper shop has the equipment to safely press pistons off
as rods need to be matched per end not total weight