Seized piston

[Millwork]

About three years or four years ago l had a terrible engine knock and found a piston all but seized on on the wrist pin. I hat put new aluminum pistons and new connecting rods in the engine back in 09 all standard size. Fast forward to last weekend l am about 90 miles into a pleasure cruise and the engine starts banging, dies and l coast off the road. Engine was locked up tight. So l am checking everything out after hauling it home and decide to pull the pistons then l discover number one piston is practically welded on the pin. Luckily the cylinder wall is fine with a quick home. Easy enough to fix and get back on the road but wondering if this is a common occurrence that l have never heard of happening to anyone but me?
Dave

[Scott_Conger]

It happens

need to ensure freedom of the wrist pin...stiff like in bronze bushing and cast iron piston is simply too tight. Aluminum should not be stiff on wrist pin and most are as they come out of the box. A quick kiss with a ball hone and cross drilling the bearing bosses is pretty much mandatory. The cross-drill will supply oil to the wrist pin and does nothing to compromise strength.

this link details your exact problem, with some good dalogue and a few good links to boot: http://www.mtfca.com/discus/messages/33 ... 1370521617

[Les Schubert]

Unfortunately it happened to me also many years ago when I believed the manufacturers recommended piston clearance. Now I fit for.005” clearance minimum!!
Another thing that can get you is when you check your oil using the Ford test cocks. ALWAYS be sure you actually have a bit of flow. Just the appearance of oil at the valve is not good enough. Another I learned the HARD way!! It caused me to seize a wrist pin like you did from inadequate oiling

[Millwork]

Thanks for the input guys and thanks for posting the link Scott guess l’m not the only one with such luck
Dave

[Scott_Conger]

You're welcome David

I think you'll have it on the road in no time.

[Adam]

All the repro pistons need to have their pin bores line-honed before assembly. THEY ARE NOT USABLE right out of the box with any certainty. The bores need to be honed a little larger than normal for that type of piston. Most times I set them up at .0008”. This is generally the size that will also bring the bores in line with each other too.

The seized up wrist pin in aluminum pistons has been a “known issue” for decades. Properly honing the pin bores before assembling, and very slightly oversize, is the advance remedy.

[Jem]

Yes, I posted about this not long ago. 2 engines, piston pins seized after a couple of thousand miles, even though they seemed loose on assembly. Seems the old test of letting the rod drop when holding piston horizontal does not work. Honed them out, we'll see how the next few thousand miles go.

[Art Wilson]

I have seen a piston pin become slightly tight in a piston after the pin clamping bolt was tightened in the connecting rod. The pin fit was fine before the bolt was tightened and fine when the bolt was loosened.
I think it is because the rod does not clamp the pin with even force around the perimeter of the pin due to the way the upper end of the rod is designed. The uneven force results in uneven compression stresses around the perimeter of the pin which can cause the pin to bend slightly.

[Jem]

Good point Art. I made sure that the pin felt free once clamped up in case the clamp caused distortion.

[Les Schubert]

Art
A very interesting and plausible theory.
Further to that, I would suspect that the amount the bolt is tightened would have a effect.
I personally don’t tighten those particular bolts very much and of course I rely on high temp Loktite to keep them in place. Perhaps this is why I have never experienced this problem.
Just a thought

[Adam]

Art hit on something I almost forgot about because I haven’t dealt with in several years! I started babbitting and machining my own rods several years ago. I developed a procedure for blueprinting, re-machining, pre-straightening, and pre-matching rotating and reciprocating weights before babbitting and machining. It is a process of over 20 steps. One of the steps is to hone the pin ends of the connecting rod on a Sunnen honing machine. I only remove enough material to effectively de-burr it and make it absolutely cylindrical again. The result is that the rod, when clamped to the wrist pin, precisely holds its alignment regardless of torque, AND that high spots in the pin bore are not bearing on the pin and affecting its straightness.

Many rod cores and many of the rebabbited rods I’ve seen from the major vendors are really rough in the pin bore. If your piston pins are a nice fit, then are noticeably stiffer when the rod is assembled to them, then you have burrs or unevenness inside the small end of the rod affecting alignment of the pin. This can certainly be one of the causes of seized pins.