What is the maximum piston to wall clearance for a stock engine with aluminum pistons? I'm honing an existing engine for a piston / ring job in the car. The engine was not excessively worn, but I have corrosion on one piston and need to replace it so I'm replacing the set. I do not expect to have 'new engine' tolerances, but I do want to be comfortable that the engine will run well and last.
I don't really think there is a maximum in my opinion, I did the same on my 24 6 years ago and it's still running strong. I get some piston slap at low idle when cold but goes away as engine warms up. I can live with it as I know the cause. I have put over forty k on this engine since the overhaul and enjoy driving it. Close budget at the time. I am working on A 23 pickup project now which will be my new truck. Don't want to be without a T to drive, so the 24 will be ok till this project is done. I drive 30 to 35. KGB
It will run with excessive clearance, but will knock and also the rings will wear out faster due to moving in and out of the groove when the piston "slaps".Actually, the groove wears out leaving excess room for compression to escape and oil to enter. So the result is the engine will keep on running, but not as long or as well as it would with better clearance.
I would attempt to keep it within the .004 - .005 range.
You probably already know this, but the general rule is to re ring if clearance is less than 10 thou, if over, rebore. Of course you won't have even wear, most will probably be in the center of the bore and you may well have taper or oval. Still I would go by the general rule. Some of the smoothest running engines have the most clearance.
Ok, this gives me something to work with. Keep in mind this is not a rebuild and I'm not looking for the desired numbers...... Lots of info on that....... And I do understand the problems that can occur when the gap is excessive. I don't have the engine torn down for evaluation of sending to a machine shop. This was a good performing engine, I'm doing what should be a routine repair in the car.
So what I am looking for are measurements that are red flags during this type of maintenance. 4-5 thousands is great for a new rebuild but that's not what I am doing. Engines loosen up as they are driven, guys re-ring them all the time, and they run fine. I would think when that is done many people measure the cylinders and decide if the gap is acceptable. Lots probably just re-ring and run.... I probably have 10,000 miles tops on it since it had rings and pistons installed 25 years ago. I don't expect a problem..... I am just looking for a generally accepted maximum clearance for a basically stock T motor being re-ringed.
Gary, In answer to your question, mine had about 9thou. wear at the worst and as Richard says that was at center of bore. Your mileage may vary. Also I have for forty years used Hasting rings as they seem to have the best oil control ring. My engine does not use an excessive amount of oil either, like most T's mostly leaks. KGB
Thanks!!! Good to know what you had and the results, and Richard's suggestion fits that as well. I will measure and record, then post results after a few months of driving.
Gary, the rule usually was .001 clearance per inch of cylinder bore dia. (street engine) cast aluminum pistons. .0015 if your running them in a race situation. that's on a new bore situation. No out of roundness. Old cylinders that are egg shaped or bell shape vertically I've seen AS MUCH AS .008 RUN! But I would not run one that way ever. Rebore or solid hone with wipers to the next size increments of .010". Be sure to do a 6 way mike job on each cylinder!
Have fun and good luck.
Like everything the are a few opinions. Check out this recent 2013 thread for a long discussion on the subject:
I remember a machine shop owner that put new rings in his OHV Rambler with .011" taper and it pumped oil so bad he couldn't drive it.
but I too have seen 'em get by with .008"
I went .008 for years and no I did not knowingly have any piston slap. I was told that was the best clearance. I do believe that it helped top speed. I have decreased slowly down to .004 the last few years. I had my own boring machine and measured the piston clearance the way Herm says to do with the Piston against the wall on one side and measure on the other side. I have 40,000 miles on my Center Door that was bored to .008 with not piston slap and does not burn oil. I have run the Center Door HARD for 25 years and climbed a lot of tough hills. I even ran it in the Montana 500 one year. So I really don't know which clearance is best but would say anything between .004 and .008 is OK.
Aaron - I'd say that perhaps that would be a machine shop to avoid!
Dave - Would that "Center Door" have had iron pistons or aluminum?
I have never run anything but aluminum pistons. I also have dips on all the rods, I assume that the pistons get some lubrication
Anyone know what the whatzit is above and NO, its nothing to do with tires and tubes.
I just finished the hone and measuring..... Worst case is .0005 out of round and .0005 taper. Cylinders were bored .040 over, so target measurement was 3.790 and all bottoms measured exactly that. It's about as good as it gets!
If you only show half a thou wear, that is fantastic. That is probably how it was bored.
Its amazing what a ring and valve job will do for a tired engine.
Could you mystery tool be some kind of bearing oiler or greaser ?
Please excuse my STUPID information I did last night on your Thread!!!! I mean STUPID. I answered your thread about 2:30 am and was definitely not coherent! I awoke this morning at 7:15 am and realized what I had said as I was entering the shower. Damn I said that was stupid! I am sorry. What I gave you was how to figure ring end gap on 1/8" thick piston rings. The Ford T has either 3/16 or 1/4 inch thick (top to bottom) rings and I am NOT sure what to tell you on those! It has been 30 years since I built any T engines! I usually have them bored out on a Sunnen honing machine that bores to the center line of the mains. I had to make a mounting bar for the T engines as the ones that my machinist had were to big for the T mains. Once you bolt the block in this machine it bores all 4 cylinders to the same dia and square to the crank. Providing your mains are line bored first. And before you pour in any babbit. The pistons spacing (clearance) you asked for!!! in the first place (again MY MISTAKE) would vary acording to the piston material you are using. When going over size with the pistons we usually hone out that clearance after the bore job. Your pistons will have that specification in the box on a data sheet. I used Mark Auto and Gaslight years ago when I was doing engines.
I have been so embarassed ALL DAY and I had to be gone until just a minute ago (11:45 pm). I wanted nothing more than to write you this morning but could not. So I know that everyone read the dumb statement I made last night. I want to apologize for that And NO I have NOT read what everyone said but reluctantly I will! After I shoot this apology off to you. The iron pistons that I use are the original if I can find a set of four and gram weigh them out for a matched set. Usually if you have an original engine that was never torn apart then you can use the whole set as Ford matched these when new. That usually does not happen in my book as too many people messed with these engines over the years. You will also have to have any steel pistons tin coated (Linolit) if you are close to a plater with this ability. This will also enlarge the dia. about 1 to 1.5 thousandths. I have re-sleeved several of my old blocks back to std. Then we hone to fit the pistons clearances. A lot of work. When using the aluminum pistons the correct way is to mike them about 1-2 inch from the bottom of the piston. The skirts are the larger dia at that point. Hone out for the clearance set forth in the piston literature that comes with the pistons. Place the piston upside down in each correct hole and down into the bore about 1/2" and using a round feeler or if using a flat one radius it to the wall circumferance and slide it without pressure in between the piston and the cylinder wall on one side only to check it before any attempted assy. I am NOT going to try and remember but I think it is around .002 and on some I have seen .003" if my memory serves me right. It also will be in the old recopies of the Ford Service Bulletins available and you SHOULD have and get a copy for your referencing. I call it the T bible! LOL. I am really embarrassed to read what I brought forth but in all honesty I DESERVE it! One thing about having taught for 27 years is no one wants to give out false information nor appear stupid especially in front of the WHOLE WORLD!!! I have done such during my teaching career. It is highly embarrassing to an instructor to find out that he or she gave out the WRONG information.
That is one good thing about this forum! People DO read it!!! And other's in the know will steer you correctly. That is a beautiful thing that goes on here. Also some of us mean well enough but at some of our ages Dementia is setting in and when it happens we do not even know or recognize it until it is too late. Gary sorry again.
Change 1-2 to 1/2"
Well I just read everone's statements after my first post. Thanks everyone for not blowing me out of the saddle. "I am old and cranky" was a sign I use to put on my T's at shows and Mall displays in florida. In front of that was a picture of an old man with a can and a scowl on his face and it said "Please don't touch me..." That sign when I was 30 years old... Has became me!!!!!! The 6 way miking of the cylinder was correct.
That is unbelievable Gary. That is practically no wear! Ford use to roll harden the walls on the T blocks to tighten up the grain of the metal. 3 rollers inserted into the 4 cylinders. Wish I knew how to accomplish that today as boring leaves a non-hardened cylinder wall to wear. Other engines use to flame harden their cylinder walls.
Thanks again everyone for being understanding.
Change can to cane!
Joe; it's funny, I knew what you meant and didn't count the 0s! Thanks so much for your reply.
The cylinders were bored .040 over a few thousand miles ago, so I did not expect much wear on them. I still wanted to measure them though and to compare them to the new pistons when they arrive back from balancing, before installation, to avoid making an expensive mistake. I did use a engine cylinder bore gauge, set zero with a caliper at 3.790 to allow for the .040 over, and was careful when making and recording all of my measurements.... I measured about 1" from the top of the bore, 3/4" from the bottom, and made measurements at approximately 120 degrees apart. There is no ridge at the top of the bores. I'm very comfortable with the results. I did take one measurement mid-bore in each cylinder to look for any flags and all was well.
I am returning to my original cast iron low head and will use it with high compression (domed) pistons; this is in place of my aluminum high compression low head (WITH the Ford script!!! Those are hard to find!). The reason I'm going through all of this is I found a pinhole leak in the combustion chamber of the head on #1 cylinder. I've sent the head out for professional inspection and repairs, will have it cleaned and surfaced, then stick it on the shelf.... it doesn't eat much.. I've had 2 welding shops say it's an easy repair and they do them often on modern aluminum heads, but I don't drive this car much and I'll feel better if it sits around with a cast iron head. There are a couple of corrosion spots on the mating surface of the head near the bolts that extend into the water jacket and I'll have them taken care of at the same time. I've got the same aluminum head (with script) on my '11 but I drive and attend to it regularly, and the '15 just didn't get the same amount of attention as it was kept at a friends house. That may change now that I'm bringing the car back home, we'll see; it sure is faster to polish the brass on the '15!
I'll go ahead and lap the valves while it's open, those are only a few thousand miles old also, but may as well while the head is off. I should have it back together in 2 weeks, I only have Saturday's to play 'T'.
You are doing the right thing it sounds like. Wow, You own an aluminum head! I never had one. I know that they are a replacement and are suppose to give the T engine more power. I found the low heads thru the years which are correct for my cars 09 thru 15. The newer models naturally have the tall heads.
I was a teacher mostly in life and a gen class C contractor doing repairs to aid in my affording my addiction to building my cars. Corvettes, hot rods, muscle, and T's and A's. It was a long ongoing lifetime process. Work first, paying bills, kids, church! You know the score I'm sure. I never could BUY what I needed and always had to rebuild all of my (extra stuff) car parts. Usually, other club members and NEW-to-the-sport types would like what I owned (built)and would either buy it or have me do the same job on their cars. Got to meet and know a lot of interesting people that I would have NEVER met in life without my doing such.
On another note... it is 5:15 am and I awoke an hour ago and found more confused formulas were rolling around in my mind and I find that being it is so long since I have done any of this stuff I am really confused!!! On ALL of my formulas that I use to teach and use!!! Was it .001" per inch of bore or .004"? I cannot give any more advice, it seems, because every time I open my mouth junk falls out. Yes, I really have done those things in my history and back then I had mentors who were really good at what they did both on the racetrack and in restorations. Some were REALLY good and some just so-so. Naturally, one tries to get as close as possible to the hot dogs (winners)and to shut-up and listen. Once in awhile I could sneak in a question and get a REAL answer or they would tell me to bring it over and we look at it or take care of it. I learned a lot from them. I never went pro nor went in business for myself as that took money away from needed things at home. So you learn to do a lot of this stuff yourself out of necessity. Except for some in the old car clubs that have big pockets. You envy those guys but I cannot run with them. You instead concentrate on getting the facts as exact as possible and quietly getting things done on my cars. Early on in the T meets I would show up at shows and the BIG guys would nod and say nice old Ford. Or this or that is not right for your car. That hurt as I was proud of my work and parts that I had found and rebuilt for my car. So you start studying what do I need to be correct. High prices for items I needed did not help! They would tell me what they were going to get at Hershey for the parts that I needed to make my car right. That made me MAD but I lived with it. Then you learned what was needed and you learned to make fast trips around the swap meets. Get there early and BUY what ever you could. Sometimes getting me in trouble with the big guys in the sport. But I was finding the parts I needed! Not fun really. As I admired those guys. So several times I would quit the hobby and go on with the Corvettes or back to hot rods as the people were not as cut throat nor opinionated. And...I had fun shifting gears and feeling that torque again. Especially after a hard day at teaching high school. It felt good to see the tach. go upwards of 7000 r's and shift to second, then on to 3rd or 4th! Leaving all of the hassles and minutia at the work place behind me. So I enjoyed my times away from the T's and A's groups and the hassles of "GETTING IT RIGHT"! Or not having the $$ to purchase that wooden coilbox with the 4 brass-topped coils at $700.00!! that I needed for my 1911 car. I sold all of my cars about as fast as I finish one. And, like you, I found that some of the Calif., Utah, also Oklahoma big guys were making their own repo parts and they did a pretty good job on early parts. We would visit at the end of the day at shows and swap meets where I would be STILL looking for affordable parts for my cars. Those guys taught me a lot! Earnie Brown and his carburetors! We became friends. Those guys taught me that it takes just as much effort to repo an exact (as close as possible) part as it does to do a kind-of close part. You just have to start by having an original to go by. There were many more that taught me how to accomplish this. So I started to collect the parts I needed to, someday, put my stuff together but we finally find ourselves getting to old to maybe do this. And that's where I may be today. ???
Gary, I think I goofed on the formulas that I tried to tell you here on your thread. And I am sorry. I was laying there tonight after my frantic posting and things started racing thru my feeble mind and "Was this right that I said tonight?" "Or was I confused again? ??? I thought about all those rings that I bought (.005" oversized) and cut with my ring grinder machine (hand operated) and was it .004 ( Pi), times every inch of diameter of bore or .001"????? I have everything I usually do and would do in my file cabnet. But I would have to find it. I do have a really good and full 4 drawer file cabinet where I keep all of my notes, patterns, drawings, and articles. Except for the full pattern dwgs rolled up in tubes that I did over the years for my cars... tracing the real original parts to make new parts for the big guys. So many interests I had. So many cars. It can get confusing. That is why I always taught everyone (else) to NOT rely on memory and to make notes! All three of my boys do this religiously. And they all each own their own businesses. Which vasselate according to the economy and the trends. I feel for them sometimes and wonder if I have done the right thing by them.
Gary, Nice to meet you sir! Good luck and God speed with your car! Maybe I'll see you at Chickasha. You all have seen me, and I you, you just never knew me nor I you at swap meets. A few of you we delt with one another years ago thru Hemmings or the rear pages of our MTFCI and MTFCA magazines. Take care and thanks for NOT paying me any attention. You are better off! It's 6:00 am and today is Sunday. Got to get ready for Church.
Joe in Mo.
Oh, and I was an engineer for 9 years in 4 different industries off and on through out my career employment. Engineers get laid off a lot in Mil Spec industries. Contracts filled, and no other back up commercial products and also thur politics! I would go grab another school when that happened. They always loved having me back in house it seemed. Lucky I did that as it finally allowed me to retire.