Crank Thread Problems

[Lamaddict]

Drive side. I started to put the bolt in and it wasn't having it, I stopped, bought another bolt and tried that, same problem. I gentley tried an 8MM tap but it wasn't a success, threads seem hard. Anyone know the pitch or anyother suggestions. The problem made me feel sick.

[Grumpy225]

those are fine thread, so a common coarse tap won't work. Assuming you are using the correct crank bolt I'd think there is a bad thread internally in the drive side of the crank.

[Lamaddict]

Thats what it looks like but I don't want to pull the crank out it and mess out with the shop on getting another one, it's a 62mm crank etc. If I knew what the size was i'd get a tap into it?

[Grumpy225]

8x1 tap

Pretty common and not too expensive. If you seal off the main bearing I'd think you could carefully fix the threads on the crank

[johnny LIS150]

why don't you get one of these thread pitch guages and do the job properly.

They are only £2 quid ffs at least you'll order the right pitch tap then
http://www.ebay.co.uk/itm/20-Blade-55-W ... 565fdb41b7

[e type]

Is the crank hardened at all as most look like they have a ground finish ..if so I wouldn't tap it ..

[johnny LIS150]

surely best to order a new bolt then you'd be sure that you had the right thread pitch, length and bolt hardness.

[tavspeed]

if you used a m8 coarse tap,which will have a 1.25mm pitch,it will try and cut a new thread,which is why it feels stiff, using a m8 fine with a 1.0mm pitch will follow the original thread and reinstate any dodgy parts of the thread,use plenty of cutting oil and go carefully,if you snap the tap the crank will be scrap.

[Lamaddict]

Thanks all, getting there. Got a new tap and die set for about 12 quid. For good measure I ran an 8X1 die over the bolt but it messed it up, so I got a new one.

[tavspeed]

be careful with cheap taps as they could be brittle and snapfor instance ,a m8 presto tap would probaly be 5 or 6 quid on its own