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Crank Assembly


alan_nc
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Split my TY250 crank (bearings were bad). Marked it good for re-assembly but would really like to have any suggestions on "Tricks" to ease the re-assembly process. I'm still concerned about getting it aligned correctly.

Thanks in advance.

Alan

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Split my TY250 crank (bearings were bad). Marked it good for re-assembly but would really like to have any suggestions on "Tricks" to ease the re-assembly process. I'm still concerned about getting it aligned correctly.

Thanks in advance.

Alan

Alan,

I usually install the main bearings/seals in the cases (use a little anti-seize in the case bearing bores to ease the bearings in) and then lightly press the crank into the case side that i'm starting with to assemble the trans components. I like to use a light coating of anti-seize or assembly lube on all shaft ends and a light coat of grease on the journals that will have seals on them. When installing the case together I use a hard rubber mallet to ease things together and if you run into any unusual resistance, pull the case off again and see where the problem is-never force the cases together. Things will be a little stiff but the anti-seize will help.

After the cases are together, set the engine upright and turn the crank slowly. It will seem like something is wrong as it will be a little hard to turn, no worry. Take a soft metal mallet (so the ends of the crank are not damaged, I like to use a copper mallet) and lightly tap each end of the crank ends to "center" the crank in the case and it should free up and turn easily. Take two large, heavy rubber bands and stretch them diagonally (to form an "X") on the cylinder studs, passing them through the top hole of the connecting rod. That way you'll be able to turn the crank to check things and not have the connecting rod flop around.

Jon

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JSE,

Thanks, that will help.

Do you have anything special you do to align the halves of the crank prior or during assembly? I have a good press (used to take it apart), that will press it together fine, but what do you do to maintain the shaft alignment?

Alan

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I sit a set square up the side of the flywheel at 90 degrees to the crank pin for initial alignment then press it together. I weld up a pair of vee's to sit the crank in then run a dial gauge on the shafts to test run out.To correct it I hold the crank in one hand and hit the outer corner of the flywheel with a copper mallet.Sounds horrible but works well - you sort of get a feel for it.

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For re-assembling a crank you will need obviously a decent press, some decent parallels. and a truing fixture (Knife edge type) with DTI to test for runout. and a copper/hide hammer of the Thor variety.

Press the halves only partially together to start with (Just a few mm) You can get the thing quite close with a decent engineers square by checking at several points around the flywheels. You really need to get the whole thing having minimal runout at this early stage as it's very difficult to make the flywheels budge when fully pressed home.

Just take your time.

Wayne...

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JSE,

Thanks, that will help.

Do you have anything special you do to align the halves of the crank prior or during assembly? I have a good press (used to take it apart), that will press it together fine, but what do you do to maintain the shaft alignment?

Alan

Doh! I'm sorry, for some reason (besides senility) I thought you needed case assembly advice.

jon and wayne have good suggestions and the main thing is to take your time as it's like tightening spokes (adjust-check, adjust-check etc.).

I'm fairly sure the Mono 250 is like the 350, crankwise, and here's the spec's for the 85' TY350N (I don't remember what year yours was, but a twin shock is probably a little different) if they are of any help:

Crank width (outer flywheel surface to outer flywheel surface-65.95-66.00mm

Runout (crank on roller v-block, measured on the center of the journals where the bearings go-.03mm

Rod side clearance-.25-.75mm

Small end play (wiggling the top of the rod side to side)-.4-1.00mm

You also may need a "wedge", which looks like what you use to split logs with and it's used to spread out the flywheels.

If you've ever watched a master crank aligner work, it's scarey. They look like they are beating the thing to death but their movements are remarkably precise. The older cranks are fairly easy to work with. Most of the new cranks require special fixtures to get them right and the older Honda cranks with the sheet metal covering are nearly impossible to get spot on.

Jon

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I have a lathe available and plan to chuck it on the bearing surface and check runout with a dial indicator. Does anyone have any idea what the runout would be on the tip end (flywheel side) if I chuck on the clutch end?

Well, I guess, what would allowable runout be on one bearing journal if I chuck on the other?

Thanks for the help - I think I have the idea...... proceed sloooooowly.

Alan

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I have a lathe available and plan to chuck it on the bearing surface and check runout with a dial indicator. Does anyone have any idea what the runout would be on the tip end (flywheel side) if I chuck on the clutch end?

Well, I guess, what would allowable runout be on one bearing journal if I chuck on the other?

Thanks for the help - I think I have the idea...... proceed sloooooowly.

Alan

Alan,

I also use my lathe for checking crank journal runout, but be aware that you will need two live centers, one at each end. You can't chuck one end in and use only one live center (or worse yet, just take a reading from the unsupported end) or your readings will not be accurate. The .03mm listed is probably a good baseline to use. The lathe actually works very well as you also have a good, solid base for the dial indicator.

Jon

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I tend not to use the lathe,just grind a deep vee into 2 pieces of flat steel then sharpen the vee's.Weld them onto a third piece of flat big enough to clamp the DTI onto,or for its magnetic base to stick too.If you weld the two vee's on so the crank fits nice and tight into them its much easier to work out which end is not true.

Hand scraping timing side main bearings is next weeks job !

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  • 2 weeks later...

An update:

Re-assembled the crank yesterday. New bearing and pin (same rod). Put pin in one half first. Then put bearing, shims, rod on and used a square to line up halves as best I could. Pressed 2nd side on pin 1/16 to 1/8" then put it in a lathe we had set up ahead of time. I was about .060 thou out the first time. Used lead hammer and after about 6 or 7 "adjustments" I had it +- about .0005. From then on I would press it in about 1/8" take it out and measure....repeat. Actually once I started it didn't move much at all.

Just a note: I started with a 5 ton manual press. Gave up and went to a 15 ton hydraulic, Worked much better and I was able to press much more carefully.

I had taken all of the measurements before I took it apart and I actually have it closer now than when I started. The proof will be when I start her up.

Alan

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