No 1 piston has tightened up and dug into the cylinder wall. Quite why this didn't happen during running-in but waited for several thousand miles, I can't say but I'm just an amateur. The pros will probably know why.
Interesting that the expansion is neither along the line of the pin or at rightangles to it.
Jem,Hopefully the block was not damaged beyond repair? Bud.
No, just needs a light hone
Your not the first and I suspect you won't be the last. Happened to me back in '89
I have honed out several blocks for others since
Interesting that it was #1. Usually it's #4!!
It's from climbing mount Snowdon Jem ;~)
What you have is scuffing, that's a different scenario from seizing from a too tight, ie, incorrect bore clearances at rebuild.
Like you said you had the run-in miles well up on this engine.
Scuffing on the piston in the wider clearance of the cam grind on the piston is from high pressure areas, ie, tight wrist pin, which we know has been a problem on new pistons before, hot spot- water or oil.
Uneven head bolt tensions will likewise cause distortion of cylinder bores.
My friend's T engine seized after a rebuild and aluminum pistons in 1966. I later bought the engine and used it even though all 4 pistons showed scoring as yours has. After 50 some years and several thousand miles it got too hot and seized again. After cooling down it started and ran fine. I have driven it many more miles without problem. It holds compression and gives "free starts" more often than my other 4 T engines. I conclude it was bored too tight and that the scoring has no noticeable effect .
Just my experience.
Richard, does that engine smoke (burn oil) at all ?
An ex of mine had a 57 Hudson Metropolitan (Hudson-badged Nash). She seized that
engine several times, where I was able to free it up and it kept on going. Never did break
it down to see what was going on. But it didn't smoke or burn any noticeable amount of
Is there any taper on the pistons? They should be cam ground and have taper so only the bottom of the piston skirt is measured for boring to size. The rest of the piston has more mass and will expand more than the bottom. If there is no taper it will seize. It looks like the piston is rubbing for most of the body. I would think about changing the pistons. Scott
Burger, no, this engine doesn't smoke. It is somewhat balanced and is the sweetest running engine I have despite the ugly scars on the pistons. I am surprised it has run well for this long.
I have seen this twice on local cars with about 2 thousand miles on fresh rebuilds. What was wrong on both the wrist pin siezed putting the pressure on the skirt.Ever since I have the pin hole loosened up on new pistons. Steve
Some may be skeptical of a wrist pin seizing an engine. I would have been. This happened on a different engine of mine. It locked the engine completely. The aluminum bonded completely to the pin. I had to saw the piston to get the rod out.
P.S. Don't get me wrong. I have traveled thousands of trouble free miles but occasionally things do happen.
I had a motor for a model A built and within 600 miles it broke a wrist pin due to the bore being to small/ not enough clearance. It was a total loss block was cracked when the crank broke. Very few parts were usable. I use a reputable engine builder who has done my other motors for years. I wont say his name because this doesn't represent his work fairly. He paid shipping both ways and sold me all needed parts at a very low price. The other motor i sent to him and had built is still running and driving weekly and has 16k miles. Tim
Can Herm, Mike or other experts please comment on the pin fit that normally exists with off the shelf parts, and whether they routinely remachine the piston pin bores to achive a slightly looser fit? What is the "optimum" pin fit for standard vendor replacement aluminum pistons?
I always check the pin fit on the vendor supplied aluminium pistons. Most are not correct and are too tight. I have found that if you grasp the skirt of the new pistons the pin will slide easily out. Release and it binds. I believed that when the pistons are factory bored for the pins the clamping action has distorted the piston and allowed an incorrect bore to be produced. I was burned once by defective piston pin fit and have since always checked the pin bores. Of the several hundred engines I have rebuilt since then I have never had a problem. Always verify the fit. JP
Steven wins joint first prize. The wristpin IS tight, not seized, but tight. Problem solved. Thanks for all the input.
Sorry, everyone gets joint first, you all chimed in with the wrist pin while I was working on my one-finger typing.
Jack - I can't find anything specific ref "pin fit" for Model "T", but what I found for Model A is interesting, and, I would think be similar to Model "T", and, tends to verify what you just said about "clamping action" and "incorrect bore":
This is a quote from a well known and respected Model A parts catalog table of Model A "specs",.....
"Rod wrist pin bushing - Machine shop must expand ID of bushing in rod before honing to - .0003 or 4."
For what it's worth,.....harold
P.S. That's not a "typo" on my part,....that's what it says, - .0003 or 4. Less than half a thou'?
Jem, tell Neil T I said hi. Steve
Mike mentions the need to check and likely hone out the pin bore in the pistons here (no numbers mentioned that I saw):
What percentage of aluminum pistons are having issues with the wrist pins being too tight? And from what vendors? I used aluminum high compression pistons from Snyders in rebuilding my 16 engine and did not have the pin bores honed to give more clearance.
I did check them and they seemed ok to me.
I had a little different experience. Due to a blocked breather hole in an oil sight glass, I ran my van low on oil, enough to cause the same scoring of the no 1 piston. At the same time the piston pin fit was compromised, not siezed, but very tight.
This was after the van had done some 20 000km.
I honed the bore to clean it up, and filed the piston down. The pin bore was honed and the original pin reused. That was some 4 years ago, and all is well.
Allan from down under.
Philip, I think Snyder's pistons has improved in recent years, so it depends on when you bought them. I first bought a set of 0.030" OD alu pistons like four years ago - they had a very tight fit to the wrist pins and had to be freed up with timesaver compound and lots of elbow grease.. Then I bought a second set like two years ago and they were better. No high compression pistons though, might be a different producer for them and different issues with the fit to the pins?
If I were to buy pistons I'd buy them from EGGE.
I installed aluminum pistons from Bob's Antique Auto Parts 25 years ago, I don't know the brand. When the engine was disassembled a couple years ago the pins were extremely tight. After some polishing they slide easily now. The pistons did not have lubrication holes so I drilled some like the original iron pistons have. Hopefully that will help the pins stay free.
After honing the cylinders some shallow scratches were detected in the number 4 cylinder on the front face in the middle of the cylinder (3 inches from the top / 4 inches from the bottom). Don't know if this could be attributable to the stiff pins. It looks more like something metallic got in between the rings and burrowed itself out along the cylinder wall.
Stain marks on the oil ring coincide with the scratching.
BTW the piston looks fine. No galling marks.
Erik Sole's scoring in the cylinder wall looks like a wrist-pin score caused by either a too-long or off-center wrist pin (too-long and off-center wrist pins are often aggravated by bent rods). I have seen several such blocks and even run a couple myself. If the damage is not severe, usually they will work fine. I do not know the why or how, but most I have seen have had the three marks exactly like his shows.
Nothing at this moment to add to Jem B's other than I am very pleased that the damage was not worse for such a wonderful car!
Drive carefully, and enjoy, W2
The why and how is answered by the fact that the engine was not set up right in the first place, cast iron piston bush is pressed in to eliminate the pin from ever touching the bore, Ford service book page 105 p 417. Jahns aluminium pistons had a very good boss also so it would never happen when a big end completely come apart, today's new pistons as a rule are good too but should always check, just in case, some times the pin can do with a few thou shortening.
I had a new rebuild seize, caused by a tight rear cam bearing. That showed me how tough the camshaft is. RPM was at idle and it happened several times at about 1 minute into the run (on an engine stand).
Thanks for the insight Frank. I will measure how close the pins come to the piston edge and rework as necessary.
Frank, you're spot on. The rear boss on all the pistons is shorter than the front one and allows the piston pins to protrude from .012 to .028" into the cylinder bore IF the big end allows them that much fore-aft movement. The strange part is that it's the front side of the cylinder that is scored...? The pistons were installed right side forward so... who knows. I'm going to have the pins cut down a bit just in case and have the machine shop run the hone through the pistons. I've tried with fine sandpaper and Timesaver but there is some misalignment between the two sides which I hope the hone will smooth out.
The lubrication holes in the pin bosses (last picture) were added recently. I hope they will prevent the pins from getting so tight again.