Hi there

the middle set of threads for the rear mudguard bolts on my 2010 evo are shot (the ones that go into the frame in the 'seat' area), due to them being rubbish from day 1. I am working on them currently being a 5mm thread at present.(I think the 2011 evo has 6mm threads?) I want to tap them out and fit fresh bolts in, but have never tapped before. Am i right to presume i need to drill the hole out to say 6mm so it is therefore unthreaded, then cut fresh threads with a tap to suit a 6mm opening, say a 7mm tap, then fit 7mm bolts.

I happen to have a new 6mm tap to hand which needs a 5mm hole, but once the threads are drilled out maybe a larger tap is needed?

Or should i just use a 5mm tap in the poor threads as they exist and hope this cleans them up suficiently?

Any advice from anyone who has done this ( there must be a few out there) or someone who knows a little more about it than me would be appreciated.

Cheers

Drill the existing threads out with a 5.0mm Drill. Do not move the drill up and down as you will make the hole too big for M6 !!!

Now tap the hole M6 making sure the tap is square to the hole. Do a couple of turns clockwise and then reverse the tap the clear the material it has cut, repeat this a few times during the tapping of the hole. If you have any grease handy put some

on the tap cutting threads, it will help cut the new thread cleanly !! Clean the tap before you start the next hole and grease it again.

Cutting compound is best but grease will do it .....

Note, Its very easy to tap aluminium !!!

depending on how screwed the threads are you should be able to re tap them with not even having to drill them out. Im a machinist and i work with aluminum all the time as well as various other metals. Its very easy to fix threads without having to drill. If you try to drill them you have to be very careful and remain square with the original hole. Drill press of mill is the easiest way of staying strait. I would attempt to retap them first before you drill them and only do so if you have to. Also make sure when you tap them that you are taping into the original threads. you can very easily cross thread with a tap.

Tapping drill for M6 is 5.3 so you should have no problems, other thought and more lasting solution would be to helicoil them trouble with that is you need the tap and helicoil and tool to wind it in.

if they are knackered, and won't clean out by re-tapping m5 then drill 5.0 and tap m6, 5.3 is too big, to work out the tapping drill size for metric threads minus the pitch of the thread from the size i.e(m6 - 1 pitch = 5), they have upgraded them to m6 on the 2011 evo

If the threads are shot, i agree with chewy, helicoils the way to go,you can get helicoil kits on ebay for about a tenner or there abouts.

cheers,

tom,