Help identifying Model T pistons, please!

Discuss all things Model T related.
Forum rules
If you need help logging in, or have question about how something works, use the Support forum located here Support Forum
Complete set of Forum Rules Forum Rules

Topic author
Marshall V. Daut
Posts: 104
Joined: Wed Jan 16, 2019 2:57 pm
First Name: Marshall
Last Name: Daut
Location: Davenport, Iowa

Help identifying Model T pistons, please!

Post by Marshall V. Daut » Thu Aug 29, 2019 4:27 pm

I have redone only about five Model T engines completely, but dozens of Model A's. So, I guess I am still a neophyte in the Model T world. Yesterday I encountered something in a friend's Model T that I hadn't seen before. 'Probably old hat to most of you, but I am stumped and need to know what to do in order to correct what I perceive as a problem.
Some of you may recall the 1924 Coupe my friend bought in late 2017 to match the one his parents owned in the 1930's. Here is the link to refresh your memory: http://www.mtfca.com/discus/messages/70 ... 1513295186. The car is a so-so amateur "restoration" , whose shortcomings have become evident since my friend can now drive the car more confidently. I have always felt the engine was more sluggish and under-powered than even a stock Model T with standard cylinder head should be. It does run smoothly, but just not much oomph. Yesterday we intended to install a new Z head his wife gave him for his birthday (We should ALL have wives like that!). Before removing the old head, I ran a compression check. The car is more than an hour away, so I really haven't had much chance to perform such tests on the engine before now. The readings were 30#, 42#, 25# and 47#. That explains why the car was so doggy with two such weak cylinders. We pulled the head and at least three piston tops were thickly coated with oily grundge. Clearly, a telltale sign that the oil was getting past the piston rings. Rather than just slapping on the new Z head and calling it a day, my friend agreed that we should remove the pistons and re-ring them.
O.K. so far. Problem identified, solution at hand. Right? Maybe. When I pulled out the rods with cast iron pistons, the attached photos show what I found. Are these original Model T pistons? They don't match anything I have pulled out Model T engines. Three top rings (1/4") width) AND one ring almost at the bottom of the piston skirt with a groove beneath that full of holes? The markings on the piston tops are also a mystery to me, as no typical Ford size stamp appears that I am familiar with. Could the "031" be the oversize? Kind of odd, if that's the case. .031"??? All four pistons have this same odd number. The other stampings on each piston top are "SS" and "174". I don't have a clue what that means. Some kind of secret society code? The pistons are secured to the rods with usual bolt.
Can anyone tell me, please:
(1) What are these pistons, if not original Model T?
(2) Do any of the stampings indicate the oversize number?
(3) Are new rings available if not Model T pistons?
(4) Should I replace them with new aluminum pistons?
Thanks in advance for your advice. 'Sorry for showing my ignorance. I am still learning about these "T-Model" critters.
Marshall
Attachments
IMG_2463_resized.jpg
IMG_2462_resized.jpg
IMG_2461_resized.jpg
IMG_2460_resized.jpg


Les Schubert
Posts: 526
Joined: Thu Jan 10, 2019 5:47 pm
First Name: Les
Last Name: Schubert
Location: Calgary

Re: Help identifying Model T pistons, please!

Post by Les Schubert » Thu Aug 29, 2019 5:03 pm

1. Aluminum pistons so not original T
2. Numbers; I have no idea. Stock T bore is 3.750”(or darn close to this)
3. Rings should be available although with only 2 compression rings is more common
4.Low compression, I would have suspected exhaust valves first (especially #4 cylinder)
Hopefully this helps a bit


Wayne Sheldon
Posts: 1591
Joined: Sun Jan 06, 2019 3:13 pm
First Name: Wayne
Last Name: Sheldon
Location: Grass Valley Califunny, USA
Board Member Since: 2005

Re: Help identifying Model T pistons, please!

Post by Wayne Sheldon » Thu Aug 29, 2019 5:22 pm

Are you sure those are quarter inch rings? They don't look that large. Cast iron pistons you say?
.031 used to be a common standard oversize for engines. I have a couple nearly new sets of cast iron pistons that size, and I may use a set one day. Why that uneven size was chosen as a standard I don't know. .015 was also a common standard. However, the common standard .031 cast iron pistons used three rings at a quarter inch thick apiece. I have seen four ring aluminum pistons for model Ts, but few and far between, and I don't know if they were made specifically for the T or not (although the tapered top looks like it?).
.030 oversize rings have been available (in the standard quarter inch thick for cast iron piston's size) for many years, and may still be. Again, in the photo, those rings do not look that thick.
Interested in what others say, and Good Luck!


Jim Sims
Posts: 113
Joined: Sun Jan 06, 2019 12:38 pm
First Name: Jim
Last Name: Sims
Location: Reed City,Mi.
MTFCI Number: 13377

Re: Help identifying Model T pistons, please!

Post by Jim Sims » Thu Aug 29, 2019 5:47 pm

I see wrist pin bushings, aluminum pistons do not use separate bushings. Every thing else looks like normal iron pistons.


Les Schubert
Posts: 526
Joined: Thu Jan 10, 2019 5:47 pm
First Name: Les
Last Name: Schubert
Location: Calgary

Re: Help identifying Model T pistons, please!

Post by Les Schubert » Thu Aug 29, 2019 6:09 pm

Easy to find out if aluminum or cast iron. Aluminum is DEFINITELY not magnetic. Cast iron has some magnetic attachment.
Every cast iron piston I have seen had 1/4” wide compression rings.
My guess is that these are early aluminum pistons for the T (‘50’s-‘60’s?). By the ‘70’s when I got into the hobby I did see some aluminum pistons with 2 oil rings for the first A crank engine I built. One up high and one at the bottom.


Topic author
Marshall V. Daut
Posts: 104
Joined: Wed Jan 16, 2019 2:57 pm
First Name: Marshall
Last Name: Daut
Location: Davenport, Iowa

Re: Help identifying Model T pistons, please!

Post by Marshall V. Daut » Thu Aug 29, 2019 6:15 pm

Les -
A magnet sticks to the pistons, so they are not aluminum. The compression readings were taken from #1 through #4. So, #4 had the highest reading and also had the cleanest piston top, as well as cleanest spark plug electrode. That cylinder is doing what it's supposed to do. The other three are not. The other three piston tops are covered in an oily crud, telling me the rings are either undersized or never seated.
We'll examine the valve seats and heads and if o.k., we'll lap them in. I didn't have my spring compressor tool yesterday to remove the springs and examine the seats and valves. Next time.

Wayne -
You are correct: I misread the ruler. The rings are 1/8". Where are you going to get .031" rings for your pistons? Or do you have an extra set available for sale. :lol:

Jim Sims -
You are correct about the pistons being cast iron, not aluminum. Sharp eye!

'Still would like to know if these aftermarket cast iron pistons made for a Model T or some other make made to fit, as Ford didn't seem to offer this kind of ring pattern and odd oversize. Because of the size, that eliminates changing to new aluminum pistons unless the block is bored to go 0.040", right?

Marshall


autoneer
Posts: 18
Joined: Fri Jul 26, 2019 12:46 pm
First Name: Jeff
Last Name: Beaumont
Location: Gardnerville NV 89460
Contact:

Re: Help identifying Model T pistons, please!

Post by autoneer » Thu Aug 29, 2019 6:36 pm

Back in the old days, standard over-sizes were 1/64" (.016") and 1/32" (.032") and they are still that for valve guides & stems. Hence the .015" and .031" oversize pistons. I would run a hone in the bores and mike them. IF they are round and plus .034" over or less, you could go to a .030" Aluminum piston set. The extra couple thou won't kill you, the max tolerance for new pistons in an old bore is +.004" on the bore size, or 3.784" in your case. Might be a little noisy on starting cold, but noise will vanish in a couple minutes, I had a 27 Tudor with this same situation. One of the best running T's I ever had though.
If its over that, you can hone to .040" over and go up one size, but that probably entails pulling the engine, which opens up another whole can of worms. Good luck! Best Jeff


Les Schubert
Posts: 526
Joined: Thu Jan 10, 2019 5:47 pm
First Name: Les
Last Name: Schubert
Location: Calgary

Re: Help identifying Model T pistons, please!

Post by Les Schubert » Thu Aug 29, 2019 7:31 pm

Valves
IF the valves are of 2 piece construction, then it is strongly recommend that they be replaced, as the valve heads have a reputation for coming loose and doing nasty things!!
Rings
As they appear to be “ordinary “ widths, then replace with.040 and spend a little time filing the ends to get good fit. EASY PEASY!!
Piston fit
If the clearance is in the.005-.007 range I would be HAPPY
All the best


Wayne Sheldon
Posts: 1591
Joined: Sun Jan 06, 2019 3:13 pm
First Name: Wayne
Last Name: Sheldon
Location: Grass Valley Califunny, USA
Board Member Since: 2005

Re: Help identifying Model T pistons, please!

Post by Wayne Sheldon » Fri Aug 30, 2019 5:21 am

FYI, I do have a set of .030 oversize rings for my .031 oversize pistons, however, the pistons are cast iron and take quarter inch rings, which mine are so they won't do you any good anyway. You may need to special order rings, but they should be available to fit those pistons. Changing to aluminum pistons would be a good idea (although some crazies like myself do like cast iron pistons?!). One used to be able to buy .030 oversize pistons, but I don't know if they are available "off the shelf" anymore or not. Larger oversize pistons can be turned down, even cam ground by good shops, and even"blank" oversize are usually available to be custom fit.
Always, carefully check the measurements before ordering any pistons. Not simply the bore size, but taper and oval wear. I personally like using a ridged hone to straighten a slightly worn bore. However, one must be careful that the wear has not drifted off center too much with a ridged hone because the hone will self-center to the wear. If a cylinder is worn off center too much (they ALL wear off center somewhat), it must be cleaned up with a properly setup boring jig in order to regain proper center alignment.

Les S mentions the two-piece valves. I think that bears repeating. I consider two-piece valves second ONLY to Babbitt thrust washers in the MUST BE UPDATED list. Such an easy fix. Even for a broke fellow like me? Not that expensive. And SO much damage can be done by a valve breaking at speed. (Thank you Les S for bringing it up!)


Topic author
Marshall V. Daut
Posts: 104
Joined: Wed Jan 16, 2019 2:57 pm
First Name: Marshall
Last Name: Daut
Location: Davenport, Iowa

Re: Help identifying Model T pistons, please!

Post by Marshall V. Daut » Fri Aug 30, 2019 10:45 am

Thank you all for your replies so far. Barring any subsequent expert opinions and advice to the contrary posted over the weekend, it would appear that these are aftermarket cast iron pistons that were intended to be used in a Model T, not pistons from some other engine forced to do duty in a Model T engine. Because of the odd size (0.031"), I would be hesitant to swap to 0.030" aluminum pistons, although 0.001" difference is virtually negligible. Good rings should make up that difference, assuming the cylinder bores are o.k. I am not ruling out changing to aluminum pistons, but that would be our last preference.
So, assuming we keep these cast iron pistons, where am I going to find a set of 0.031" rings in the number needed, i.e., FOUR rings per piston? I have looked through the Internet and Model T vendor catalogs, but cannot find any such animal in captivity. Unless I can find a set of four rings per piston with 1/8" grooves, there are only a couple possibilities open to us:
(1) Replace with 0.040" aluminum pistons with new rings; as mentioned, though, this is not our 1st choice;
(2) Order a 0.040" three-ring set for cast iron Model T pistons from a vendor and file the rings ends to fit the cylinder walls with correct end gaps. If we do that, which of the top three grooves should be left without a new ring? Or should the bottom groove be left empty? We'd rather not buy two sets of rings, just to get that missing fourth ring. Do we really need THREE compression rings? Why FOUR rings on these pistons, when all other Model T pistons have only three?
(3) If we do the above, could I select the best four used rings presently on the pistons to fill the empty groove caused by purchasing a three-ring set? If so, which groove should the used (and presumably undersized) rings go into? In other words, which of top three grooves are the most important to fill with new rings? I assume these top three grooves are all for compression rings?
Look at the lowest groove in my first posting photo. This does not look like an oil scraper ring to me. It appears to be just another compression ring. Maybe that's why oil has worked its way onto the top of the pistons + four compression rings, no dedicated oil scraper ring. Were the wrong rings installed in this groove? This lowest groove is for the oil scraper ring, isn't it? Isn't the lowest groove in a piston always reserved for the oil scraper?
Why is nothing simple on these cars, as everyone says it is? :lol:
Marshall


Wayne Sheldon
Posts: 1591
Joined: Sun Jan 06, 2019 3:13 pm
First Name: Wayne
Last Name: Sheldon
Location: Grass Valley Califunny, USA
Board Member Since: 2005

Re: Help identifying Model T pistons, please!

Post by Wayne Sheldon » Fri Aug 30, 2019 5:50 pm

Piston/ring/cylinder debates have been ongoing for well over a hundred years! Any full discussion would fill hundreds of pages in a book. In short, several major factors must be considered. Piston material, piston design (Cam grind? Slotted side?), oiling system, water jacket design and water flow characteristics, are all high on the list. Even ambient conditions and the radiator quality and design sometimes need to be considered. My opinion, and the opinion of many long-time model T people, is that a model T piston NEEDS to be more loose than almost anything manufactured in the past half century.
Pistons should be checked for fit and clearances. The needed clearances vary greatly based upon piston material and design. Cast iron pistons can be MUCH tighter than aluminum pistons due to the differences in the coefficient of expansion characteristics. Some model T cast iron pistons can be set up with only about .002 clearance (the Chevrolet "cast iron wonder" was recommended .0015!) (all measurements given are of course decimals of a USA inch). They can usually be run safely all the way up to a rattling .010 (many years ago I ran a Chevy cast iron wonder for many tens of thousands of miles with a quick freshen of a badly worn .019 tapered bore!), however, that is not recommended.
The point of some of that, is that a .001 difference in old versus new standard oversize is not something to be concerned about.
Aluminum pistons in a model T fit depends a lot on piston design. I get tired of seeing "fit measurements" given without piston specifics. Roughly speaking, round (not cam ground) pistons without a skirt slot, need to be pretty loose. .006 minimum feeler gauge between one side piston and cylinder. I prefer .007 myself, that design piston tends to have thermal expansion and seizing issues. Cam ground varies based on the degree of grind, but generally reduces the needed clearance slightly. A slotted skirt also reduces the needed clearance slightly. MY opinion, a model T even with cam ground and slotted skirt aluminum pistons should have a feeler gauge one side clearance never less than .005, and I prefer about .006. Again, like the cast iron pistons, a .010 clearance may rattle on cold startup, but can often run for many trouble free miles.
On a model T, a bit loose is better than a bit tight.

Running one good condition used ring amongst a set of otherwise new is not a bad thing (as long as you KNOW the old ring was carefully removed and not fractured in the process. Which groove should get the used ring? Is debatable. I tend to believe the top ring should be a new one. As far as holding compression is concerned, each successive ring holds against less and less compression as the rings above keep reducing it. But whether a worn ring above reducing the compression somewhat for the new ring below is better than the new ring doing a better job reducing the compression for the weaker worn ring below is an interesting debate that can go on for hours. (Non-engineers have NO clue what it is like to be an engineer and get into such debates!)

Ring design is another huge subject. Some rings do not have an "up" or "down" side. Many other rings that distinction is CRITICAL! "Scraper rings" generally (not always) have a square cut on the bottom side of the ring. These MUST be put in the correct way because if they are upside down, they will push the oil up instead of down. I have taken apart a few engines that previous people had installed some or all such rings the wrong way. This nearly always results in an excessive oil burning issue.
SOME oil rings also have no up or down. Many do, and many are not well marked. I picked up a new-old-stock set of rings awhile back, and the instructions are missing. (Ah, the joys?) I tried to find something online to identify the specifics for installation, but found nothing helpful. I do hope I can figure them out? I know I will be using a magnifying glass when I look them over.
Some compression rings have an angled cut (chamfer) on the inner edge of the ring. These, the chamfer must be on the TOP side. The theory is, that some compression flows down from above and around the back side of the rings, the chamfer is supposed to capture the expanding gasses which in turn push the ring outward helping to create a tighter seal against the cylinder walls. Many engineers cry hogwash to that theory, but that is the theory. (Personally, I tend to think the theory is hogwash.)


Topic author
Marshall V. Daut
Posts: 104
Joined: Wed Jan 16, 2019 2:57 pm
First Name: Marshall
Last Name: Daut
Location: Davenport, Iowa

Re: Help identifying Model T pistons, please!

Post by Marshall V. Daut » Tue Sep 03, 2019 2:22 pm

Thanks to all responders with their excellent information and advice. I have checked with a couple Model T vendors and inquired about the availability of new rings for these cast iron pistons with FOUR grooves and 1/8" thick and 1/8" wide rings. No luck. It appears that my only option is to install new aluminum pistons and rings. I will be driving to the town where the car is stored tomorrow and measuring the cylinder walls for wear and taper. No ridges are present at the top of the cylinders, so my guess is the engine was rebuilt sometime in the past and these pistons installed. The rod Babbitt looks almost new. Hopefully we can just swap 0.030" pistons and rings. If there is some wear on the cylinder walls, but not enough to need boring, I guess we'll order 0.040" rings and file to fit.
More updates in the next few days. Am I the only one in the history of the world to face this four-ring dilemma? Surely others reading here have encountered this kind of oddball 0.031" piston? I wonder if it is from some other make of car and was pressed into doing duty in this Model T engine? Just my luck!
Marshall


tdumas
Posts: 72
Joined: Mon Jan 07, 2019 9:45 pm
First Name: Ted
Last Name: Dumas
Location: Dallas, TX
MTFCI Number: 20999

Re: Help identifying Model T pistons, please!

Post by tdumas » Tue Sep 03, 2019 4:45 pm

You could just use 2 new one eighth compression rings and one new oil ring in the top 3 grooves and reuse the bottom skirt ring. Or buy 2 sets of rings and have 3 new compression rings and a new oil ring on each piston. In any case you should the cylinder walls so your rings will break in correctly.

Aluminum pistons are 3 ring, two compression and one oil control.


Topic author
Marshall V. Daut
Posts: 104
Joined: Wed Jan 16, 2019 2:57 pm
First Name: Marshall
Last Name: Daut
Location: Davenport, Iowa

Re: Help identifying Model T pistons, please!

Post by Marshall V. Daut » Tue Sep 03, 2019 5:24 pm

Aren't new rings for cast iron pistons 1/4" thick? The ones on my friend's pistons are only 1/8".
Marshall


Kerry
Posts: 392
Joined: Mon Jan 07, 2019 2:42 pm
First Name: Frank
Last Name: van Ekeren
Location: Rosedale Vic Australia

Re: Help identifying Model T pistons, please!

Post by Kerry » Tue Sep 03, 2019 5:41 pm

Ted is saying to use the 1/8" aluminium piston rings on those cast iron pistons.


Topic author
Marshall V. Daut
Posts: 104
Joined: Wed Jan 16, 2019 2:57 pm
First Name: Marshall
Last Name: Daut
Location: Davenport, Iowa

Re: Help identifying Model T pistons, please!

Post by Marshall V. Daut » Tue Sep 03, 2019 7:58 pm

Aha! The light bulb finally turns on! THAT was the missing piece of the puzzle = the rings from aluminum pistons will fit the grooves in these cast iron aftermarket pistons. My mindset was focused on cast iron pistons needing rings made for cast iron. But you are saying I can mix and match? I dug out some old aluminum pistons that I had replaced in an engine a couple years ago and compared the grooves in them and the rings to what those aluminum pistons used. Sure enough! They are a match! 1/8" thick, 1/8" wide. Once I measure the wear in the supposed 0.030" over cylinders tomorrow, that will determine whether we can use 0.030" or 0.040" rings on these cast iron pistons. Thanks, Kerry and Ted. Those were the answers I needed!
So, let me see if I have this straight before spending my friend's money: you're suggesting the new ring set be placed in the top three grooves of the cast iron pistons, oil ring in the bottom of those three, and re-use the bottom ring in the fourth groove below the wrist pin. Correct? What was the purpose of that lowest 4th ring. If it was to serve as an oil scraper, it didn't do its job, if the oily grundge on top of the three pistons is any indication.
Yes, our plan is to hone the cylinder walls prior to re-insertion of the pistons with new rings.
Marshall

Post Reply Previous topicNext topic