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Okay. A little update. I have the motor and swingarm back from the machine shop, but I'm not sure everything is ready for prime time. The bored out cases don't allow the swingarm pivot to slide through easily. It needs a bit of pounding to get it through. Then, once I pound it through with the swingarm on as well, there is a lot of resistance to the swingarm moving up and down. I think the pivot is having to bend slightly to get through both case bushings because they most likely were not bored straight through with a long drill--probably bored from each side. Bugger.

So I'm going to run a drill through it on my drill press. The only drill I can find locally that might work is a 3/4", i.e. 19.1mm as per the package. Think the extra 0.1 mm will allow too much slop? Should I just order a 19mm over the interweb?

I think you want it as close to spec as humanly possible.

Yeah, what's another $25 for a special 19.0mm drill bit in the broad scheme of things? Sucks that I have to order it. I am chomping at the bit (ha!) to get this project rolling along!!

FWIW, the machine shop that did my cases used a reamer. I'm not sure why you'd use a reamer over a drill bit, but I'm sure there is some benefit.

Just throwing that out there before you buy the drill bit.

The ream is designed to make a perfectly sized hole that is clean and straight. They cut from the sides. A drill is designed to cut only from the tip with the flutes (the curly sides) made to remove the debris from the cutting head. In my work it's very common to use a drill to make the hole then a ream to make the size exact.

Sometimes I use a reamer because it will do a better job of removing a small amount of material leaving the hole more round. In soft metals the drill will want to pull its self into the work unless you give it some negative rake (dull it). This tends to make the hole somewhat eggshaped. It just depends on the job and how precise it needs to be. Always make sure to account for clearances or talk to the machinist about it. I would take the pivot bolt with me and let the machinist match the bore to the bolt.

dfeckel wrote:Yeah, what's another $25 for a special 19.0mm drill bit in the broad scheme of things? Sucks that I have to order it. I am chomping at the bit (ha!) to get this project rolling along!!

19 mm? I measured the bolt and it was 17, why 19 for the drill?

scheckaet wrote:

dfeckel wrote:Yeah, what's another $25 for a special 19.0mm drill bit in the broad scheme of things? Sucks that I have to order it. I am chomping at the bit (ha!) to get this project rolling along!!

19 mm? I measured the bolt and it was 17, why 19 for the drill?

Don't the case halves have bushings? Not sure about the size. I read where you left the pivot bolt with the shop for sizing. Was it tight when you picked it up? Have you tried to polish it a little to see if that helps? Does it bind when not in the frame? It would probably not hurt anything to have up to .008 oversize on the bore.

When I picked it up, I was curious about why it needed to be tapped through, but I figured since it went through and the swingarm fit that all was good. Once I got it home and realized how much effort was required to move the swingarm up and down compared to stock, I knew something was up.

I'd rather not take it back to the shop if I can avoid it. I think just a few passes with the drill press, going all the way through from one side, will open it up enough.

dfeckel wrote:Once I got it home and realized how much effort was required to move the swingarm up and down compared to stock, I knew something was up.

Is the swingarm not moving freely with just the bolt in place or is it not moving freely when the pivot bolt is torqued to spec?

Brian wrote:The ream is designed to make a perfectly sized hole that is clean and straight. They cut from the sides. A drill is designed to cut only from the tip with the flutes (the curly sides) made to remove the debris from the cutting head. In my work it's very common to use a drill to make the hole then a ream to make the size exact.

That make sense, thanks for the info. The shop charged me for the reamer and I got to take it with me when I do another engine. I was looking at the reamer wondering how they would 'drill' with it and make a 17mm hole into a 19mm. Your explanation clears that up.

The resistance to movement was with just the swingarm and pivot bolt attached to the cases on the workbench. I still have the 125 motor, so I fit everything up on it, and the swingarm moved very smoothly. Also, the pivot bolt slid right through the cases without any persuasion at all.

Wow. So you are thinking that the hole through the cases isn't straight and the pivot bolt is bending? Even though it is hollow, that is big bolt, I would have thought the aluminum cases would give before that bolt would bend.

I'm all for doing things yourself, I try to do that as often as possible. But is there another machine shop you could take the cases to? Might be worth it to pay some more money and make sure the hole is straight and the right size before you try it on a drill press. If you screw up the cases, that isn't going to be cheap.

no way you'd bend the bolt on the engine case.

Well, the bolt isn't BENT, it's just flexed a bit from having to go through two SLIGHTLY misaligned holes. The flex puts enough pressure on the swingarm bearings to bind them up. Remember, I took the exact same swingarm pivot bolt and the exact same swingarm with bearings and assembled it in the back of the 125's cases and the swingarm moved smoothly. Crazy, huh?

If you use a drill press, and the holes are misaligned like you think they are, then the result will be larger misaligned holes. The fix for this would be to remove the bushings (drill, mill, press, etc.) and install new ones (made by machine shop from material of choice) with properly sized bores.

A drill will most likely follow the bore (especially considering the distance apart) and just overbore the holes. If you overbore the holes enough to align the bolt then you will have a sloppy fit on you hands.

If the machine shop bored them off center then they should fix. This is an easy fix. Machinist 101.

Yep... should have been line bored.

Alright, alright. I'm convinced. I'll take it back. Thanks for all the info, guys!

You may want to bring the kx engine along so you can show them how it is supposed to fit together.

Good luck.