Clearance for Cast Iron Piston

[dhidaka]

I know this is not SpeedTalk, per se, but there is a lot of previous experience from others outside of HP engines. I have a Fairbanks Morse low RPM hit-or-miss cylinder (1500 RPM) that needs an oversize piston fitted. Piston measures about 2.375" This is 1 1/2 HP and we are boring about .100 to 2 HP. The 4-ring piston I have is not new, but looks good. This a vintage deal so there are no engine building specifications available. Question is: What clearances would be acceptable for a cast iron piston to cast iron block? Machine work quality 100 years ago is not what it is today. So, a range of clearances would probably work. Customer says .005. I don't know. I just don't want any lock up problems.

[ProPower engines]

I have done several of those engines for a local historical outdoor museum that do run them as they were intended in farming displays of yesteryear and all the engines use between .005-.007 depending on the HP rating given.
Mostly they have is 2HP versions and .005 to .006 is what they run.

I got some new rings last year from Hastings for the last engine project the same as the originals if you need any.
You can give Dawn a call directly at hastings. Her extension is 1359. Give her you rind size info and she can get you fixed up.

Hope that helps

Dave

[modok]

My guess would be .002" per inch of bore if the piston is mainly round
.001" per inch of bore if it has some taper and cam.

[Schurkey]

I've never worked with cast iron pistons.

Gotta say I'm VERY surprised at the clearance recommendations. I'd have guessed that they fit T-I-G-H-T, as the piston wouldn't expand much compared to aluminum--the piston and the cylinder would expand at about the same rate except of course that the piston would be hotter than the cylinder. (Compared to aluminum, where the piston is still hotter than the cylinder, but expands much more from heat as well.)

I learn something new every day.

[PackardV8]

Most are 125-year-old technology.

[Sparksalot]

These old engines use just a drip oiler to lubricate the cylinder/piston system. Close clearances are the last thing they want. Also the bottom of the bore is open to the atmosphere and all the crap and crud associated with whatever circumstance they are used in.

The pistons are always longer than the bore diameter and operate at very low piston speed so plenty of clearance is not a drawback, it's necessary. The pistons are always round, no cam shape ever.

I love the history of internal combustion engines and technology. I have and have had more than a few of these old pieces. It's fun to run a current high HP piece and in the same day fire up a century old hit and miss to hear it wheezing, sucking and popping away.

[modok]

Iron pistons do run tighter than aluminum. If you made an aluminum piston the same design it would have to run looser yet!!

[Kevin Johnson]

Model T iron piston fitment circa 1925; paragraph 404:

1925_Ford_Model_T_Service_Manual.gif

http://www.cimorelli.com/mtdl/servicema ... mcolor.pdf

Cylinder Specifications
Cylinder Bores 3.750" diameter 6.752" long

[cjperformance]

Bore x .0015" on that type of piston and an open crankcase engine doesn't mind a little more to stop airbore crud from jamming up the bottom of the cylinder.
Cool old engines, on a side note the hit/miss engines run cooler than a throttle governed engine due to the miss cycle pumping air only in/out of the cylinder unless they are fully loaded for long periods and fire every firing stroke.

[autogear]

I love hit-n-miss engines, steam engines...all that cool cutting edge stuff from the late 1800/early 1900s; Im sure most of us do TBH.
I find it interesting in the Ford Service that Kevin supplied; it says to use a leather mallet to address any minor out of round (Paragraph 404).

When my nephew was about 11 or 12, We took him to an Antique Engine/Tractor show. Watching him try to process what was going on when I set a model Stirling engine on the palm of his hand and it ran, was pretty cool. He was fascinated by the huge flywheels on some engines, and all the polished brass and exposed mechanicals. It really made me remember those same things when I was a kid with my great grandfather (Who worked for Franklin Motors).

[Kevin Johnson]

In a pinch you can use bacon rind or belt leather for replacement rod bearing babbit in your Model T -- per an old car buddy (an Okie who moved to California in the late 1930s) who sadly passed away back in 1994.