damaged piston what? why?
 

I am posting these questions for my friend and fellow Model A'er and FB'er? Hope he doesn't get mad at me.
Couple months ago we tore his engine down to find out why there was a major oil leak - front and rear. Turned out to be bad gaskets and seals. While into the engine we check all the clearances and they were sopt on .0015 to .00175. Replaced all gaskets and reinstalled his engine and adjusted the valves while we were into it. good news NO LEAKS.

Next chapter. On his way home in his A - about 15 miles, His engine started a loud clikcking noise. Like a loud chirping criket. Noise was coming from the center of the block as in # 2 or 3 cyl. Again, his engine came out of the car yesterday and we started tearing it apart to fine the cause of the chirping.

Discovery. Severe scraping on the side of #3 piston. See picture below. Two pictures showing each side of the piston. Also the Oil Ring was stuck - as in it would not rotate in its groove - and had to be puled out with pliers. The scraping had damaged the goove to the point it had wedged the oil ring in its groove.

Question to you engine gurus? What would have caused this damage? The engine was making no unessary noises before the first tear down.

Inquiring minds need to know. ken

Re: damaged piston what? why?
 

I would expect the cylinder walls to have scratches as well. Material / debris broken off of that stuck oil control ring is a likely culprit. I have seen this type of failure in an engine that sat idle for a long time, and was started with dry cylinder walls.

Re: damaged piston what? why?
 

My guess is that something sneaked in through a plug hole and did the damage. I bet the head has some witness marks.

Re: damaged piston what? why?
 

It could have been many things incld a radiator issue. Take everything to a knowledgable place to determine the cause.

Re: damaged piston what? why?
 

I would say to close of a fit in the cylinder or to much slug around bore in the block. It was caused by to much heat. Maybe slow timing.

Re: damaged piston what? why?
 

Re: damaged piston what? why?
 

I agree with George Miller. Ford said .002" max clearance, today's pistons and higher speed driving need more. I bore to .003" and hone another .0005" as minimums, more on performance engines.

Re: damaged piston what? why?
 

I bore the same as Jim Says

Re: damaged piston what? why?
 

Was it just gasket replacement or did you pop in a fresh set or rings while you were in there?

Re: damaged piston what? why?
 

Per part of comment in reply #6:

"Did you ensure the pistons were re-installed in the same hole they came out of?"

Whether this was the primary cause or not, in re-installing pistons and connecting rods, we are involved with measurements in thousandths of an inch; former engine cylinder/ring wear; and human beings performing the initial re-bore of the block where all cylinders may not be 100% "exactly" alike.

FWIW: Always a good idea to provide small marks on tops of pistons and sides of connecting rods, e.g., from I thru IV on piston tops, and small l, ll, lll, llll, vee marks on sides of connecting rods.

Mechanical failures always occur for a definite reason:

If you would have had several "shop" spy cameras rigged up in your shop, you could re-play the video and possibly "see" the actual cause of the wear ..... maybe not enough water replaced in radiator or whatever ..... "hint", "hint" .... we might have to wait until next year for Model A parts suppliers to offer "shop" spy cameras for after-the-fact mechanical investigation.

Re: damaged piston what? why?
 

As Mitch said, it could be any number of things.
I've seen identical damage from timing too advanced, and causing the engine to ping.
Of course the ping caused the piston to overheat and do the damage.

Re: damaged piston what? why?
 

Jim and George are right. The only time you get piston galling like that is to tight of fit.

Never go by the instructions that come with the set of pistons !

Never under a .001 per inch. Just like main and rod bearings when new.

Herm.

Re: damaged piston what? why?
 

Engine is mine.

There is NO cylinder wall damage. Pictures below.

No damage above oil ring. no damage on top of piston. No damage in head.

I suspect Ken is sufficiently "knowledgable". :)

This engine was built by Berts in 1986. It has just under 6,000 miles. It has been hot in the past, but that has been solved for the past couple of years I have owned it. The other three pistons are perfect, and all four cylinders as well. No apparent problems before this showed up on my drive home from Ken's. The engine ran well and was at normal temperature all of that time.


No, it did not get hot. No, the piston was not dry when removed. The first tear-down that Ken mentioned was only to replace gaskets and main bearing seals. The pistons were not removed at any time, hence could not have been put back improperly. As noted above, there is NO damage to the cylinder walls.

Quote:

Originally Posted by Y-Blockhead (Post 1445024) I can't see anything going down the spark plug hole and getting past the compression rings to do that on both sides of the skirt but who knows??

Agreed.

Only gaskets.

One suggestion from another of my local knowledgeable friends was a possible stuck wrist pin. We were looking closely at that when we removed the pistons and found no indication that that was the cause. The rod moved easily on the pin as well as the pin moving in the piston, completely equivalent to the other three pistons. There was no excess movement.

Regards,

Bill Lee

Photos show one of the other pistons, and the #3 cylinder. Very hard to get a decent picture of the cylinder, and it does not show well that there is NO damage in that cylinder.

Re: damaged piston what? why?
 

Quote--It has been hot in the past, but that has been solved for the past couple of years I have owned it---quote


A hot running engine is a slow death.... very possibly it was not corrected soon enough:)

Re: damaged piston what? why?
 

Agreed.

What is puzzling Ken and me is the COMPLETE lack of any damage to the cylinder itself. I would think that if this piston damage had been going on for a longer time than the last 15 miles I would have 1) heard it long before now, and 2)had significant evidence in the cylinder.

Really strange.

Re: damaged piston what? why?
 

Ken & Bill,

If you try a very accurate bore gauge to measure the top and bottom diameters of each of the four (4) individual cylinders, and accurately measure the external diameters of the four (4) pistons, these measurements may give a clue as to what happened.

Aluminum pistons will wear quicker than cylinder walls.

Takes a tight fit to cause wear like this whether caused by heat expansion or not.

Re: damaged piston what? why?
 

It was caused by heat, but that does not mean it was hot on the temp gauge. It means it was hot on that cylinder wall. I have seen it many times. Number 3 runs hotter than 1,2 any way. It could happen if you were running it faster than normal on a hot day, or pulling a long hill, spark retarded to much, or to lean which will make it run hot inside the engine. Or all of the above.

Re: damaged piston what? why?
 

That kind piston damage does not hurt the cylinder wall most of the time. Some times a little of alum from the piston sticks on the cylinder wall, but you can hone it off. This is a common problem with the model a now days.

Re: damaged piston what? why?
 

I think Miller and Blockhead have it. Just suppose there was no water in it by mistake? The temp gage would not show hot. Just hot air in there if no water. Then it ran for 15 min. Sounds possible.

Re: damaged piston what? why?
 

It would be coincidental, but maybe the dipper tray developed a hole. The oil would just run out of the tray as fast as the pump replaced it.

Just a thought...