Shortening rods with heat?

[Dirk37]

Had an odd idea this morning. So a while back I bought some custom forged pistons that were made incorrectly and have a compression height that's too tall. Consequently to use them, I would need shorter rods. 0.221 inches shorter to be exact.

Now I've asked everywhere and done a bunch of research, and I can't find custom rods for under $2000. There's only one rod from another engine that's close enough to work, but it would require removing too much material from the crank bore to be safe. Also it would require boring out the piston wrist pin bore. The cost of the machine work would probably be as much as getting custom rods, assuming I could find someone to do it.

So the idea I had is shortening a set of stock rods. I was going to get an induction heater and heat the center of the rod, the use a press and a jig to press the rod 0.221 inches shorter. The rod should theoretically just balloon out in the heated section.

Now I have a few questions. Are the rods heat treated and is this going to mess it up? How can I check that the bores stayed parallel?

 

[sperold]

i think grain structure is very important in rods, and squishing the rod lengthwise might be harmful to the grain structure.

A quarter of an inch is an awful lot of change in length in something that is not too long to begin with.

Could a wafer of steel material in the head bolt area with a head gasket on both sides be of any use in making up that quarter inch you need? It will have its own set of issues (like head bolt thread analysis to make sure there is lots of factor of safety in the thread engagement length in the standard engine), but unless the top ring is too close to the original block deck, it could be worth looking at.

 

[Dirk37]

That's actually a great idea. Just checked and the top of the piston to the ringland is 8.5 mm. The other pistons are 5.6 mm too tall. So with a 5.6 mm spacer the first ringland would still be 2.9 mm below the original deck. Know of anyone that makes spacers?

 

[TimboSHO]

If you move the heads up that much, the intake will not bolt up anymore, as the bolt pattern will be spread out too far.....

 

[Dirk37]

I think I should be able to space the intake apart a bit with longer couplers. Good catch though

 

[rubydist]

1. There is zero chance you could shorten a rod by .221" by heating the center and putting it in a press and smooshing it. If you were able to do this, you would not have a straight rod, nor would you get the 6 rods smooshed in the same exact location so you would have a terrible balance problem, and you would destroy the heat treat on the rod. All of which means you would blow the motor up in short order. So you really need to forget that idea.
2. Moving up the heads by .221" will (in addition to the problem that TimboSHO points out) cause you significant issues with timing belts and cam timing. The tooth pitch on the timing belt is approx .315", so you would move the heads up 70% of one tooth, and you would increase the spacing between heads by 70% of one tooth, and that means you have to add an idler pulley between the two heads to get the cam timing right. And then you likely need a custom belt that is 2-3 teeth longer. That plan seems destined for trouble as well. (Plus, I would not want to run the top ring that close to the top of the block.)
3. I think you need to accept that the incorrectly made pistons are really paperweights and move on to something else.

 

[Dirk37]

Wouldn't adjustable cam sprockets solve the cam timing issue?

 

[rubydist]

No, I don't think they adjust enough to make that work. You still have the belt length problem to deal with.

 

[luigisho]

I think your first sentence is correct. You can try a bunch of stuff but you and we all know that custom rods is the surest way to get this done. I'd like to see something crazy work but I wouldn't throw effort into that stuff myself

 

[Dirk37]

I know the proper way to to get rods or the correct pistons, but as you've all seen I like doing things unconventionally. If I really wanted a fast car I'd sell all my ******** fords and buy a Corvette, but whats the fun in that?

 

[luigisho]

I get it. I'm in the other camp -- thinking about getting away from the older SHO and getting a faster platform. We'll see. I really enjoy my truck these days

 

[Toolman]

Get rods.

 

[kevinspann]

I'd like to see you try, but even if you could shorten them, rapid unintended disassembly would very likely be in that engine's future.