TRUING b25 FLYWHEEL

Here you can talk about all kind of TECH for the B50 B44 B25 And Other BSA unit Singles

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richardreade
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TRUING b25 FLYWHEEL

Post by richardreade »

Evening all, hope you are all well, I had to take the flywheels off a B25 crank to have the big end journal ground, I marked them up including the bolts, so I could assemble them the same as they came off. My question is, how do I make sure the flywheels are running true, I have set it up in the lathe between centres and put a dial gauge on the edge, but the flywheels have a section that is machined narrower each side and very difficult to clock it, do I just bolt it up and hope for the best?
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kommando
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Re: TRUING b25 FLYWHEEL

Post by kommando »

Bolt it up and call it done.
mlb50
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Re: TRUING b25 FLYWHEEL

Post by mlb50 »

I haven't done a B25 flywheel but B50 yes and a few others.
If the crank seperates into drive side and timing side then its important to set these as close to zero run out as possible. If its a one piece crank with removable flywheel then its just refit it and bolt it up - use new high tensile bolts.

For a crank that seperates - Its not the edge of a fywheel that matters - its the mainshafts. These need to have minimal run-out up n down.
Set the drive side into the lathe chuck and assume that as the datum. Fit the conrod and put on the timing side. Have the big end lock nut nipped up firmly. Its now about truing the timing side main shaft. Use a dial indicator on the shaft section that fits into the bearing. Rotate the crank slowly and observe any rise and fall on the dial indicator.

Use a soft face dead blow hammer to tap the timing side crank flywheel until the dial indicator shows not more than .001" run out. Run a dead centre tool on from the tail stock to pin the timing side shaft and progressively tighten the flywheel lock nut. It pays to check the consistency of the inside gap between the flywheels. I generally machine 2 alumnium spacer blocks and fit these inbetween opposite to each other with a bit of tape to hold them in place to prevent any angling in when the timing side flywheel is being fitted on and tightend up.

Anyway, if you get a B50 one day then that's the way to do it.
B50 @ 10:1 - what's a leg between friends?
richardreade
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Re: TRUING b25 FLYWHEEL

Post by richardreade »

Thank you all, it is a one piece crank with bolt on flywheels, thank goodness it is not a B50, which I could not afford anyway, even if I could find one, so its a bolt it together and go I guess :ban <216
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madsundaysurvivor
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Re: TRUING b25 FLYWHEEL

Post by madsundaysurvivor »

richardreade wrote: Thu Apr 09, 2020 8:31 pm do I just bolt it up and hope for the best?
Yes. You can check to the seal around sludge trap conexion crank/flywheel, with your finger block the holes in main journal,
then infiltrate oil with an oil gun through the right hole until it is full and you have pressure and check for leaks between flywheel and crank. is better to improve this use loctite sealant in this place.
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