Suggestions for flywheel machining setup

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charkmandler
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Suggestions for flywheel machining setup

Post by charkmandler »

I have some classic motorcycle flywheels that were put together a few years ago. Unfortunately the small end bush is too small for the std piston as the bush was originally for a piston with a smaller pin. So the little end bush needs to be opened out from 17mm to 3/4”.

Originally the small end bush was machined true to the big end sleeve so there is no guarantee that the small end eye of the con rod is true; if I replace the bush with one just undersize and ream it, it may not be square to the big end sleeve.

The flywheels run amazingly true, zero on one side and .0003” on the other so I don’t want to take them apart as they may not go together so well.

The plan is to set the flywheels on the mill, bore the bush and then hone with a split hone that has been sized in the mill spindle so it runs true. I use Timesaver as ‘grit’ as it disappears and does not embed in the material.

Setup is the difficulty as the X axis tram is true but the Y axis is out by .002” over 6”, most of this is in the quill to mill body error. I can level the flywheels on machinists jacks so a mandrel in the small end bush is true to the spindle axis when using quill but this makes it difficult to support the small end of the con rod without twisting on the big end.
A rough set up as seen in the photo is with a round block with a deep hole for the overhang of the bush and the eye of the rod to sit on (deep hole for chips and provide room for honing). If this is the way to do it I will make a jack to go under the block. I would then clamp over the con rod to hold it down on to the block. An angle plate on each side would resist any possible rotation of the con rod round the big end rather than clamping to one angle plate with possible distortion squeezing the little end eye.

The problem with this setup is that when a mandrel in the small end bush is true to the spindle / quill axis there is a gap on the back side between the con rod eye and the block. How to shim this so there is no tension on the rod or big end - or is there a better way to do this?

Hope the makes sense. Thanks for any suggestions.
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whateg0
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Re: Suggestions for flywheel machining setup

Post by whateg0 »

I would worry less about the flywheel and more about holding the connecting rod. I know that's easier said than done. But am adjustable parallel with brass or aluminum sheet. Or maybe a piece of copper wire to take up the gap. Lightly clamp the flywheel. I know you don't want to put too much force of the Conn rod, but that's the part that needs to be held. I would think that even the tenths gap in the bearing could cause chatter or an out of round condition.
charkmandler
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Re: Suggestions for flywheel machining setup

Post by charkmandler »

The flywheel is the easy bit and sorted out. Its clamping the rod and not imposing any twist. Any twist or out of true with the big end will can cause the big end to push to one side, run hot etc. Also cause more friction between the piston and the bore.
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Bill Shields
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Re: Suggestions for flywheel machining setup

Post by Bill Shields »

I would clamp the big end bearing (vertically between two cylindrical bits) and not touch the flywheel at all.

Once the big end bearing is anchored, shim up under the con rod (as you appear to be doing) and clamp it down...

I would make a clamp with a hollow opening that will hold the small end in place -> through which you can enlarge the hole...
Too many things going on to bother listing them.
charkmandler
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Re: Suggestions for flywheel machining setup

Post by charkmandler »

As I mentioned holding the flywheel is not the problem. I got them held and with a mandrel in the little end its true to the mill spindle but off with the table. The only thing I can think of is putting shims under the block that supports the little end and a gauge to measure if there is any twist when tightening down the rod to the block. Just wondering if there is a better way.
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rmac
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Re: Suggestions for flywheel machining setup

Post by rmac »

In case it doesn't become obvious very shortly, I'll say up front that I have no clue what I'm talking about. I did have an idea, though, that might at least trigger some thought, so here goes ...

Could you get everything all set up exactly the way you want it except for the hold down clamp on the con rod itself, with a gob of slow-setting epoxy (JB Weld???) between the con rod and the round support block?

And maybe a piece of saran wrap or similar to keep the epoxy from sticking to the con rod?

The epoxy would then cure into the exact shape and thickness of the shim you need and you could clamp the con rod down against it.

Maybe?????

-- Russell Mac

epoxy_shim.png
Last edited by rmac on Tue Nov 09, 2021 4:45 pm, edited 1 time in total.
charkmandler
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Re: Suggestions for flywheel machining setup

Post by charkmandler »

Worth thinking about, thanks
charkmandler
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Re: Suggestions for flywheel machining setup

Post by charkmandler »

Thanks Russel I will use epoxy as you suggested. I have a rough setup with the spindle in the little end parallel to the mill spindle to just under .0015". Next step is to get as near to zero as possible. For anyone interested I've detailed the setup below.

In photos 1 and 2 you can see the little end of the con rod supported, the bottom section of the support is a screw jack made for the job. I put the dial gauge on top of the spindle thats in the little end (fairly tight so wont move) and measured the up and down movement of the rod (moving on the big end - very small as new), then adjusted the jack so that movement was in the middle - This is purely to take any loading off of the big end, it has nothing to do with squareness as the whole assembly is being tilted with the jacks under the flywheels so that the spindle in the little end is parallel with the mill spindle.
This will have no doubt moved the setting of the initial up / down central location of the rod so I will then measure that again and then start again getting the little end spindle parallel with the mill spindle. Back and forth a few times and then clamp the flywheels down making sure nothing moves.
I will then pull away the jack supporting the rod and put some epoxy under the little end (with cling film - or may do a test to see if grease stops the epoxy sticking to the little end) this will take up any possible tilt in the support.
Once dry I'll check the settings again and clamp the rod down on to the support with two dial gauges on the spindle to make sure there is no movement.
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whateg0
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Re: Suggestions for flywheel machining setup

Post by whateg0 »

Maybe I missed it, but are you planning to move the quill to bite this? Or are you moving the head?

That's supposed to be b o r e but I'm leaving it because bite is more fun to read. Stupid phone
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rmac
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Re: Suggestions for flywheel machining setup

Post by rmac »

charkmandler wrote: Thanks Russel I will use epoxy as you suggested.
Hope it works! As I tried to make clear, I have never tried anything similar and have no clue what might happen. Having said that, it sounds like you have thought through the whole process enough that you will probably discover any problems before they bite you.

-- Russell Mac
charkmandler
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Re: Suggestions for flywheel machining setup

Post by charkmandler »

Hi Whateg0, ideally I could move the head as I spent a time shimming it and the tramming but its not very smooth - one day I will motorise a ball screw which will be better for boring. Thats why I'm gauging the setup to be true with the movement of the quill which is slightly out to the head.
Russell, as I mentioned I've got the setup, but rather than finish it the same day I will sleep on it for a couple of days and see it with fresh eyes. Hopefully it's there.
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GlennW
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Re: Suggestions for flywheel machining setup

Post by GlennW »

What does the clearance between the piston pin and bushing need to be?
Glenn

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