MTFCA Forum

#1 Given .003 and .005 OS pistons are not available, what is the maximum allowable cylinder wall wear before cylinders must be bored and .010 or larger pistons, installed? #2 What is the maximum allowable wear between crank journals and main and rod bearings, with all shims removed, before crank must be turned and new main and rod bearings, poured? I acquired a new to me, short block and just wondering.

Bearings will begin to knock at .003 clearance .

Hey Terry,

I don't have an answer before me, and sorry for a smart Alec/hijack answer...but I chuckled at the mere thought, and thats a good thing.

Answer to 1- When you blow oil or lose compression.

Answer to 2- when you run out of shims and don't take kindly to filing the caps.

Sorry, and to make up for it, no promises because while I will go look, I may not have it here, there is a Ford shops advice page somewhere, been circulated forever, that says at what point rebuilds should occur on a feature by feature basis. Someone else will probably find it and post it before me.

I’ve got some original Ford .0025 iron pistons.

Just measured crankshaft with micrometer. All main and rod journals measure 1.240 and I know with no wear they should be 1.248. Cylinder bores at top of cylinders, measure 3.74, which is .010 wear and measured at the top. Cylinder wear measured at the bottom should be even more because of taper, but the block still had Standard Ford cast iron pistons in it. Pistons had a lot of carbon on top of them, but NO scoring or visual damage or wear. Vaporizer block 1927, 15,000,000 + number. EE crank, lightweight rods. Block does not have the late 'tin can pistons' or cast in dippers on the rod caps, which I thought was strange.

Mains & rods. Measure @ @ least 90 degrees also. The important thing is are they each the same diameter +/- .001" & smooth, not 1.240 & 1.246 etc.

speedytinc wrote: ↑

Sun Apr 21, 2024 5:25 pm

Mains & rods. Measure @ @ least 90 degrees also. The important thing is are they each the same diameter +/- .001" & smooth, not 1.240 & 1.246 etc.

John, I measured each rod and main journal by making an initial measurement and then holding the mic jaws firmly against the crank journal as I rotated the mic's jaws around the journal. In every case, the measurement never varied. I was amazed.

max cylinder wear that I have gone with is 60 over.

dinosbunny wrote: ↑

Sun Apr 21, 2024 6:25 pm

max cylinder wear that I have gone with is 60 over.

Dino, I know that cylinders can be bored that much. They even make .080 pistons, but I'm talking about piston to cylinder wall wear that occurs naturally from operation. As I said above. The short block that I acquired yesterday has .010 or more wear in each cylinder, but still had standard size cast iron pistons. I never heard the motor run when it was still assembled, but I bet it had a lot of piston slap.

I've bored many a T block and never order pistons until I do a test clean up bore, they can be so far out that even a STD piston block can take up to .060" to clean up.

Kerry wrote: ↑

Sun Apr 21, 2024 8:18 pm

I've bored many a T block and never order pistons until I do a test clean up bore, they can be so far out that even a STD piston block can take up to .060" to clean up.

Frank, I agree with you. When I first made this post, I had made no attempt to measure the bore of this block or the crank. All I knew was it had standard pistons and I was expecting the bore to be worn no more than .005 wear. I was amazed when I measured .010 wear at the top of each cylinder. As I said previously, the engine must have had a bad piston slap (unless the pistons that came with the block were not original to it). I cannot guarantee that they did, although the seller I bought it from said he dissembled the block. At any case, I would always bore the block until a true bore from top to bottom was achieved and then order pistons (unless a bore of over .080 was needed and then it is sleeve time). This block MUST have been a service or replacement block as the last Model T had #15007032 and this block is neatly stamped with factory type numbers, 15030503 (August of 1927).

What is the standard factory bore? The encyclopedia says 3.750".

Mark Nunn wrote: ↑

Mon Apr 22, 2024 1:22 pm

What is the standard factory bore? The encyclopedia says 3.750".

Mark, Remeasuring tomorrow.

Terry, if you had wear present wouldn't the bore be greater than 3.750"? So if your diameter at the top of the bore is actually less than 3.750" could you maybe have a ridge forming? I don't recall if Model T engines form a "ridge" over time like other engines, but maybe. If that's the case then your measurements should be taken using a bore gauge rather than relying on a caliper reading or such at the top of the cylinder.

Jones in Aiken SC wrote: ↑

Mon Apr 22, 2024 7:27 pm

Terry, if you had wear present wouldn't the bore be greater than 3.750"? So if your diameter at the top of the bore is actually less than 3.750" could you maybe have a ridge forming? I don't recall if Model T engines form a "ridge" over time like other engines, but maybe. If that's the case then your measurements should be taken using a bore gauge rather than relying on a caliper reading or such at the top of the cylinder.

James, you're absolutely correct. I'm going to remeasure the cylinders tomorrow. Meanwhile, I'm going to delete my last post and chalk it up to a senior moment.

Noo worries, Terry. I had to calculate it in my fuzzy brain a few times. Really, I was wondering about if maybe there was a ridge forming at the top of the cylinder.

The 1/4" wide top ring on a standard Ford engine comes so close to the top of the bore there is little chance of a ridge forming. I have never seen one. That does not rule out the same occurring with non standard pistons and rings.

My local machine shop had an interesting experience around bore ridges. An owner had used a Ridge Remover on a later model V8 and went a little too deep with the cut and too far down the bore. On start up the top ring on two pistons went into the removed ridge land, and two new pistons lost their tops! Rather than call the Ridge Remover just that, they call it a Bore Butcher!

Allan from down under.

Terry, Your Ford factory numbered August of 1927 block could very well have come in a new TT truck. Ford continued selling some new TT trucks into the fall harvest season in 1927, built from parts on hand at some branch assembly plants.

kmatt2 wrote: ↑

Wed Apr 24, 2024 3:14 am

Terry, Your Ford factory numbered August of 1927 block could very well have come in a new TT truck. Ford continued selling some new TT trucks into the fall harvest season in 1927, built from parts on hand at some branch assembly plants.

Thanks, Matt, I was wondering the same thing, as the numbers are stamped so straight and uniformly as most T engine numbers are.

Wouldn't they be numbered until the end of production? the last one listed was in 1941 No 15176888

In the 50s and 60s, I successfully used a ridge reamer on engines that were getting new piston rings but not being rebored. There is no point in removing the ridge if reboring the block. The machine shop would most likely prefer the ridge to be left alone before they received it

I have recently seen where the ridge on a model t engine where the ridge is much greater on one side than the other side. The greater side was on the passenger side. This condition would be difficult to deal with on block that is not being rebored.

Art Mirtes