Boring 883 Cylinders to 1200

[John Harper]

Originally Posted by bweever

Just wondering if there is machinist who has actually done the machining of 883 to 1200 cylinders themselves that can answer my questions. Thanks

You might contact Hammer Performance. They used to do cylinder boring, and can probably tell you all you ever thought you needed to know, and more, about the process. I don't believe they bore them anymore, but I think they offered a 1212cc bore kit.

John

[aswracing]

Originally Posted by bweever

I am aware of the cylinder liner thickness has changed over the years, all the cylinders that I am boring out are pre 2007, I am not interested in purchasing any 1200 cylinder kits as I have acquired several 883 cylinders that I will be boring to 1200 so I can get the exact piston to cylinder clearance that I want for the engine builds that I am doing.
The 883 cylinder skirt end has a much more pronounce chamfer which is closer to the cylinder base than a stock 1200 cylinder skirt, so when the ID of an 883 cylinder is bored out some of this chamfer is cut away due to the boring process which will cause the skirt to become shorter by about .100" so my question is how short of a cylinder skirt is still considered acceptable?
I have noticed a lot of suggestions of using torque plates while boring, I have measured both 883 & 1200 cylinders with torque plates and without torque plates and I do not see any change in dimensions.
Just wondering if there is machinist who has actually done the machining of 883 to 1200 cylinders themselves that can answer my questions. Thanks

I've personally bored several hundred of them, and the amount the spigot gets shortened in the process has never been an issue. FYI, after boring I always put the cylinder on the lathe and put a chamfer on the inside of the spigot.

If you're not seeing a difference between in and out of the torque plates, well, I can only tell you that I see the shape change to the tune of .0010-.0020. Hopefully you know this, but you need a tenth-reading bore gauge (.0001) to make these measurements accurately. Zero it with a tenth reading micrometer.

Another thing I noticed a long time ago is that I can get a cylinder straight and round top to bottom to within a tenth or two, take it out of the plates and it'll move as I described, and then put it back in the plates and measure again and it won't be exactly the same. Close, but it'll be a tenth or two bigger here and a tenth or two smaller there. Others who bore and hone cylinders have confirmed to me that they see the same thing.

[aswracing]

Originally Posted by John Harper

You might contact Hammer Performance. They used to do cylinder boring, and can probably tell you all you ever thought you needed to know, and more, about the process. I don't believe they bore them anymore, but I think they offered a 1212cc bore kit.

John

We still bore and hone a lot of Twin Cams, but only a handful of XL cylinders.

As you may know, the two common Twin Cam bore sizes are 3.750" (used on 88 & 96ci) and 3.875" (used on 95ci & 103ci). It's real common to punch those out to 3.938 (3-15/16), which gets you to 97.4ci on the 4 inch stroke motors and 106.6ci on the 4-3/8 stroke motors. We call those 98 and 107 inch kits respectively.

3.938 is about the safe limit on the factory Twin Cam cylinder. Both S&S and HD offer a steel liner cylinder that allows a thinner spigot and a full 4" bore. Similar to our 1275 cylinder. But the introduction of those products doesn't seem to have slowed demand for boring the stock pieces. The price difference probably has something to do with that.

[Iron Mike]

I have bored 883-1200 before. I too have seen discrepancies with/without torque plates.
To expedite the boring process prior to the Van Norman bar, majority of material is removed in the lathe, then the remainder removed with torque plates in the bar. Then of course finish honed with plates.

Just my $.02

[bweever]

Thanks aswracing for your info regarding the spigot, I have notice the cylinder shape float around a bit by a tenth or two when taking the jug out of torque plates and putting it back in the plates just like you have described, but I have not seen the huge change of ,001 to .002 yet, but then also I am just starting these projects and discovering something different everyday.
I am retired machinist from the aerospace industry and I really don't know how to use a measuring tool if it does not have a resolution of .0001"