9 replies to this topic

[edi57]

Hi All,

A friend of mine was trying to remove his flywheel. Using the flywheel puller, he screwed the three bolts into the flywheel and then tightened the main centre bolt. Instead of the flywheel coming off, he has stripped the threads of the flywheel where the three "pulling" bolts where screwed into.

He's away for about a month and I'd like to help him out with this.

What are my options?

Thanks,

Ed

[GraemeC]

Helicoil the holes.
Or tap them to the next size up (making sure you can get bolts of the right length and grade and that the bolts will fit through the puller).

[mini13]

drill and retap the threads to 7/16 unf and get some socket head screws (as they are high grade)

make sure you dril/tap/screw them in far enough that they go all the way through the flywheel so you get maximum thread engagement.

Actually it may be easier for you to source M10 taps and socket head bolts, so that may be a better option.

[Dan]

If I did that I would stamp the puller locations to show they had been re-tapped to a different thread.

I often wonder when it becomes necessary to do this how much it affects the flywheel balance.

[edi57]

Ok, helicoiling gets a bit expensive...

This is a spare engine which we want just for the gearbox (as it's good).

Can the flywheel be cut off without too much difficulty?

[mljb59]

easiest option is definately to drill and tap a size bigger

[MRA]

drill and retap the threads to 7/16 unf and get some socket head screws (as they are high grade)

make sure you dril/tap/screw them in far enough that they go all the way through the flywheel so you get maximum thread engagement.

Actually it may be easier for you to source M10 taps and socket head bolts, so that may be a better option.

Not all socket head screws have a higher tensile rating, and some hex head have a higher or at least as high tensile rating..... it is all about grade not necessarily type

from 3/8"UNF to M10 will only give you approximately 0.55mm of radial engagement on the diameter

Cutting off the flywheel will almost certainly damage your crank (if it isn't already damaged)

More than likely you have a crank and flywheel assembly that has welded itself together by micro fretting This is nearly always the result of the flywheel NOT being lapped on to the crankshaft

[samsfern]

whats meant by "not being lapped on to the crankshaft"?

[bmcecosse]

Drill and tap to M12 - M 10 will be too close to the original size. Balance won't be affected - it's a tiny amount of metal - and all 3 holes are on the same pcd anyway!

[MRA]

You get the flywheel and a thin layer of very fine grinding paste on the crank tail fit the two parts together and rotate as if lapping in an engine valve

The reason for balncing stems from the casting of the flywheel, during the process you can get harder more dense regions, these heavier sections / nodules will cause an out of balance force, now drilling out to a larger size is unlikely to disturb this effect to any great amount and can for nearly all eventualities be ignored

Higher revs....... and you should be using a steel flywheel for safety anyway

Edited by mra-minis.co.uk, 28 October 2009 - 11:02 PM.