Big Fifteen bore size/liners

[tailseat15]

*Update on post #12*

Ok, need help with an engine rebuild. I have a little research going on here, and I am not a machinist. Just want to be clear up front about that. I pulled the pan and head off the engine, to start measuring the engine for wear. Found a few things I had questions about. Also in case it changes things, this isn't a matching #'s tractor. The engine I've been told is a replacement engine, as it doesn't have a serial number, and has a rectangle boss cast into the side of the block just above the carburetor mount, that is machined flat.

1. This engine has sleeved bores. I didn't think the fifteens came with sleeves, so maybe was this done during rebuilding? Or did they come this way? The rods and pistons have been stamped before with numbers, which to me indicated its been rebuilt before. I'm just trying to figure out what we're working with here since I have no paperwork or anything telling me what was done on this engine.

2. Manual says 3-3/4" bore. So my thinking is the bore in decimal equivalent would be 3.750" brand new bore. I measured mine with a dial caliper at the top of the bore (no significant ridge at top of bore present) and got measurements of 3.764 to 3.765". The bores look to be in good shape, no crosshatch left but also no large scratches. Definitely good enough to touch with a hone and re-use, at least in terms of cylinder wall finish. One of the pistons has STD stamped in the top of it. Here's where I need help. I thought this meant these bores were .015" oversize. I thought this was equal to fifteen thousandths overbore. I was told by another fellow much more experienced than I that its really just standard bore, only half a thousandth over. I think we're (me) having trouble getting our decimal place moved one spot over. Please help.

3. Parts book lists pistons available as std., then jumps to .020" over. But it shows rings available in Std., then .010" over, then .020 over. So my question is, if you were to bore a Std. bore to ten thousandths over, what piston do you use? Can you use standard piston with .010" over rings? I haven't pulled the pistons out yet, so I don't know what their O.D. is. The service manual doesn't list a clearance spec for the pistons that I could find, for acceptable piston wear. It doesn't even list the standard piston O.D. for new pistons.

4. I'm hoping to as I said just hone the cylinders and put new rings in, assuming the pistons look good. Do these rings need to be special ordered/made, or does anyone know if they are available from anywhere that stocks them.

Sorry for the long post, but thanks for the help.

[JasonPayneCrawlers]

This were I have bought rings for my machines. They are a nice place to deal with. Think the fellow that I have talked to name is Dave. http://www.pistonrings.net/

[tailseat15]

Thanks for the suggestion Jason. I'll give that guy a try if it looks like I need some rings. I'm going to check the main and rod bearing clearances today, and then pull the pistons so we'll see what it looks like once this engine is apart. The service manual says acceptable main & rod clearances are from .003" to .012". I'll probably set it up a little on the tighter side of that range.

[zootownjeepguy]

Hi, Not only should you check the bore at the top but it should also be checked with a Bore Gauge or telescoping gauge for "out-of roundness" and straightness. Measure the bore at 3 or 4 different levels at 0, 45, 90 and 135 degrees from the crankshaft. Cylinders tend to wear on the sides about halfway down the bore from the side load of the pistons. If the bore is bigger in the middle or out of round a new set of rings will not seat very well. Most good auto parts stores will have a bore gauge that you can rent or borrow (not so much with the big "chain" stores such as Auto Zone or Pep Boys, they only want to sell you parts and floor mats).

A typical spring-type hone or "dingle ball" hone will only break the glaze and finish the surface. A good "micrometer adjustable hone" will actually true up the bore and make it straight & round again if used properly.

3.764" is 14 thousandths over 3-3/4", not 1-1/2 thousandths ( .014" is almost 1/64", 1/64" = .015625").

Good Luck, and c'mon back if you have any more questions

[tailseat15]

Thanks Zootown that helps. I pulled the pistons today, and I will measure the bores and pistons like you said. That will tell me quite a bit about the bores. Oh and as a side note I have a flatfender habit as well.

I plasti-gauged the rod bearings today and it seemed that whoever rebuilt this engine last set it up too tight. There was only .001-.0015" clearance in all 4 of the rod bearings. I didn't even check the main bearings, figured I'd do that later after cleaning everything up. The reason why is because all the bearings and journals looked to be in good shape (except I have to come up with some shims to get the bearings back to spec!)

This engine/tractor sat outside for some time and got some water in the exhaust. Two of the exhaust valves were stuck open. When I removed one of them, the top part of the valve stem guide was broken off. I tried to show this in the photo. How can this be repaired?

I'll throw in a photo of the casting block I was talking about above the carburetor, which is different than the original/matching engines I have in other fifteens.TaIlseat 15 Restoration 082.jpgTaIlseat 15 Restoration 077.jpgTaIlseat 15 Restoration 080.jpg

Also shown is the sleeves in the engine block. This is what I'm not sure about, if they are original or if the engine was sleeved during overhaul. The sleeves have two holes in each of them, towards the bottom of the bore, where the bolt holes for the lifter guides go. It appears to me that the sleeves are factory because of the corresponding holes. It seems that if the engine was sleeved later during a rebuild, there would be no reason to put these holes in the sleeves. But again I don't know, so I'm hoping someone else does and shares!

Thanks again for the help everyone.

[zootownjeepguy]

The Valve guides can be replaced, they are just pressed into the block. Your valve Seats look pretty rusty and probably will need to be inserted with new seats. This can all be done at your local automotive machine shop. They can also bore or hone your cylinders too. I'd take the block to them and have them give you an estimate.

[8C 361]

Otto's Gas Engine works.

www.pistonrings.net/

[tailseat15]

Thanks for the lead! Looks like the right place. I'm trying to get ahold of him right now.

[Steve A]

or open the grove in the piston to use 3/16 rings or some will run 2-3/32 in the same grove