Flywheel bolts

[ndevans]

Morning.
Stripping the engine ready for a rebore.
I've got 5 of the 6 flywheel bolts off (it's a Marina 1275), but the last is stubborn and won't shift. Will I do any damage if I use a blow torch to heat it up?
Cheers N

[philthehill]

Heating the flywheel mounting boss of the crankshaft to allow for the removal of that last stubborn bolt will be perfectly alright.

Keep the pressure on the bolt head whilst you heat the boss so that at the ideal moment the bolt will become loose.

Of course it goes without saying do not get the boss red hot.

Were the bolts previously secured with Loctite or similar? They usually come undone without difficulty.

I would suggest that you do not use an impact spanner or rattle gun as the threads in the rear of the crankshaft could be damaged.

To clean up the threads do not use a tap but a bolt with a flat filed on its side to below the root of the thread - then you will not be removing thread only crud.

[oliver90owner]

I’ve never had to heat anything to remove flywheel bolts. Perhaps I have been lucky? Doubtless not removed as many as PTH!

However, I always tighten and loosen bolts across the centre line - I have seen so many who are trying to turn a road wheel when attempting to remove wheel nuts, for instance. Stationary engines are often more of a problem!

A good rigid breaker bar (not a long bendy one), and a good thump with a lump hammer, is usually sufficient to break the grip. Preferably using a 6-point socket, of course.

[philthehill]

Under normal circumstances the flywheel bolts on the 'A' Series are easily removed but the OP appears to be having problems with one bolt.

I have never had to use heat to remove the flywheel bolts but the OP has asked the question and I have replied with no concerns.

The crankshaft needs to be stopped from rotating before attempting to undo the flywheel bolts. It also needs to be stopped from rotating when tightening the bolts.

I would clean the threads and refit the other five bolts, secure the crankshaft and start again with the seized bolt being tackled first.

Care must be undertaken with the flywheel securing bolts as it is easy to strip the threads especially those in the crankshaft boss.

I have had the flywheel locking washer jam under the bolt head which has made it harder to remove the bolt.

Flywheel bolts with the 12 point heads are best.

Phil

[ndevans]

Thanks for the tips gents.

I put the flywheel bolts in, 3 years ago. Can't remember for sure, but I think I would have tightened them in pairs across the centerline, to whatever torque setting is recommended (if any), with no loctite. I think the remaining one is just a stubborn one.
I have been using a 12 point socket, but the bolt head has rounded a little, which isn't helping.
I'll try a little heat and see if that helps.

Cheers N

[philthehill]

The correct torque setting for 1275cc Marina/Ital flywheel bolts is 40 lbf ft.

[ndevans]

The correct torque setting for 1275cc Marina/Ital flywheel bolts is 40 lbf ft.

Thanks. I'm pretty sure I would have done them up to that, I'm pretty fastidious about things like that!