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Collection, Preservation and Display of Old Lawn Mowers

Suffolk punch aluminium engine flywheel removal

I notice on the 98cc engine, it says to use 1/4UNC bolts as a flywheel puller.

Having removed the starter basket, I put a small screwdriver in the holes to check the length of bolts required.

depending on the position of the flywheel, the length of bolt required changes. There are clearly some structures behind the flywheel that the bolts could hit.

what are they hitting, but more importantly, should I only seat the bolts onto the deepest part - although one bolt always seems to be on something.


i don't want to damage anything behind there in getting the flywheel off.


any guidance most welcome




wristpin Tue, 07/06/2016

Think that you may be misunderstanding the purpose of the bolts . They are not to force the flywheel off but to attach a puller which will bear on the end of the crank (protected by the nut) to pull it off.  One and a half to twice the bolt diameter is a useful rule of thumb for how far to screw them in but obviously stop if you think that they are touching something.



JohnWillmott Tue, 07/06/2016



that makes a lot of sense.

will make a puller with a bit of steel bar



hillsider Wed, 08/06/2016

Quite agree re the length of thread as quoted by wristpin but I would recommend that you do not use the flywheel bolts to do the pulling but make the puller beam heavy enough to allow you to drill for a center bolt  of a slightly larger diameter to the flywheel bolts. You can either drill and tap a thread in the puller or use a nut and bolt to apply tension to the puller.

Lastly wind the flywheel nut off until it is flush with the end of the crank, this helps to protect the thread and to restrain the flywheel when it lets go of the taper.

JohnWillmott Wed, 08/06/2016

Thanks for the suggestion.

One the tension is on the puller, does the centre nut need a tap to break the taper - and if so how hard? Not sure if the crank bearings can take that type of lateral load.


advice most welcome



hillsider Thu, 09/06/2016

A short sharp tap from a hammer will normally be enough to release the taper, if it still refuses to let go try gently warming the flywheel with a heat gun or a blow lamp.


wristpin Thu, 09/06/2016

If you are worried about tapping the centre bolt of your puller and the engine Is off the chassis , hold / suspend it by the flywheel just enough  to take it's weight. That way the shock load is confined to the interface between the crank and the flywheel and not transmitted to the block and bearings.