I'm new to T engines, or any other engine for that matter so please bear with me. After seeing the thread on clearances on aluminum pistons I started to wonder. I've recently had my cylinders bored to .030 oversize and I had planned on buying domed aluminum pistons sometime in the very near future.
My Dad and brother each bought theirs from Egge a number of years ago and seem good so far, but they really haven't put many miles on their cars yet. Anybody dare make specific recommendations of who I should or should not purchase them from?
I haven't heard anything bad about any of the pistons available. If you set them up correctly I seriously doubt if you'll have a problem with any of them. I have used Egge brand as well as different ones, probably imports, from Langs, Chaffins and Sacramento Vintage Ford. I have also used cast iron pistons. No problems I can recall.
It's usually good practice to buy your pistons first, (from whomever you decide), and THEN have your cylinders bored & honed to fit.
In the interest of preventing piston seizures when you first start your engine, IMO, do the following:
Use light motor oil like 5W-20 or 5W-30 and add 1/2 to 1 whole quart of Dexron III/Mercon ATF to your "break-in" oil. Fill the cooling system with your coolant of choice.
When the engine starts and runs, don't run it any faster than fast idle and use plenty of spark advance (at least 1/2 way down).
Run it no longer than 30 seconds and shut it off and let it sit for at least 5 minutes before cranking it again.
The second time you start it, do as above but run it no longer than a minute.
Run it a minimum of 10 minutes this way before you run it continuously.
That's what I did and it worked for me. Necessary? Maybe not, but it made me feel better.
I have to agree with Jerry - you need to give the pistons to the machinist prior to boring & fitting.
I've no argument with the practice of buying pistons and then boring/honing to fit. But how do you determine what it's going to clean up at? I'd hate to buy .060 over pistons and find out the block only needed .040's.
To be specific, I'm talking about a block that's been sitting around for 50+ years with no pistons in it so you'll be boring through .XXX" of rust before hitting clean metal (the bores look about the same as the outside of the motor block).
My standard approach has been to use a "sacrificial" cutting bit to remove the worst of the pits then make the final passes with a good carbide tipped bit.
I've purchased many sets of replacement pistons and have never found the skirt diameter to vary more than 0.0002". The low-compression pistons that I bought for my T varied only 0.0001" and would have given me 0.0035" clearance in 3.770" (0.020" over) bores.
Since 0.005" clearance looks like the good number, honing 0.0015" of diameter would have been no big deal. It wasn't needed though since I installed them in "used" bores "honed" with oiled 220 grit Wet-and-Dry sandpaper.
Had the skirt measurements varied 0.001", then I would have to agree with Jerry and Steve, but as close as they were and the fact that a little more clearance is desirable, I have to disagree.
Thanks for your thoughts so far on this. Sounds like it doesn't really matter where I buy my pistons as they all should be fine. I don't mind saving a few dollars when it makes sense.
Lowell Spicer bored and honed my block so maybe what I'll do is order my pistons and take the whole thing back to him and ask him to check clearances. He's a top notch engine guy so I'm sure he accounted for adequate clearances, but it's a lot easier to double check now rather than after towing it home after a problem. Please let me know though if I'm missing something.
Thanks for your help.
Sounds like a great plan Mike. Enjoy your T.
I don't think there's any hard and fast rules when it comes to cylinder boring a T block. With the top ring going right to the top and then no ridge to tell you the amount of wear so a cylinder bore gauge or inside mike is needed to determine the wear correctly. It's been my experience when boring an engine that was still running and still had standard pistons that .020 over pistons would be required in 90% of the cases to remove all the taper and low spots in the cylinders. In a few cases .010 over would have worked but it usually ends up that one cylinder won't clean up and then you have to go back and redo the others up to .020 over anyway.
When it comes to a damaged cylinder caused by broken rings, a loose pin or a spark plug left out and rusted I elect to bore and sleeve that cylinder first. I then bore the block to the smallest diameter needed to recondition the block. That way you are not over boring the other cylinders unnecessary to match the extra material needed to be removed from the damaged cylinder.
Whenever I recondition a block that has heavy rust or pits in the bores I will bore and sleeve and fit it back with std. pistons again.
When re-ringing an engine in which the same pistons are being reused I use a ridged hone so all or most of the taper is removed along with any low spots. I then will also knurl the skirts of the pistons the get the required clearance back.
Finally I have to go with those saying to have the pistons in hand before you bore. It was taught to me that way so I have to go with this SOP when starting a "boring" job. Not all pistons are created equal so it's best to have the ones you are going to use to determine what the manufacturer wants for a clearance since cast, forged, piston with full shirts, some with expansion slots, and some without and will all have a slightly different clearance spec. Maybe not a lot but it's a real job adding that .001 of metal back to a block once it's been removed. Bob
Wow, you guys make it so complicated. On the advice of my machinist, I always bring him the block so he can bore it it close to the smallest oversize that it will claen up at. Then, he tells me which size pistons to order. When he has my new pistons in hand, he does the final honing to fit. It seems the only logical way to approach the situation.
Eric, Thats the way we do it. Our guy won't do it any other way. Then we have him bore for one or two extra thou. for clearance. Never a problem.
You have him hone the extra "couple of thou" so his boring machine wouldn't have been tied up with your set-up block waiting until you got your pistons. :-)
Seth, You do it your way and we'll do it ours.
Sleeve it and put Henrys pistons back in there,no worrys!:>)Just had to throw that in the mix,and chances are that is what I would do!
But whoever does the boreing work,and whatever piston you use,PLEASE give it the exspansion room it needs.
I aint trying to disaggree with anyone here to make fuss.But I have overhauled alot of different air cooled small engines over the years and the 1's that needed boreing,the machinst would look at me like I crawled from under a rock if I ask him about boreing a engine without the pistons and their specs handy.I will be overhauling a 390 v8 later this year,and if it needs boreing,the pistons will be in hand before hand.
From what I understand each company gives the specs it feels is right for thier product.And I would think if you were to need them to back their product under a warrenty,they would want to do some measureing for themselves to insure the work was done to suit them.IF companys that make the pistons back thier products to begin with.
And I think it also makes sense to do the final fit with the hone,not the boreing bar.