C15 side cover fitting

[Spaceman]

I would buy a Helicoil set and repair the thread which is easy to do - having done all this work, the last thing you want is to get an oil leak because you haven't been able to tighten up one of the screws fully!

[DAVE BRADY]

Hi,

Repairing the thread is definitely the best option but some times even with the correct length screw there can be some unused thread at the bottom of the hole.  If you have to correct tap, gently run it down to the bottom of the hole.  This will clean the threads really well.  You can then determine the depth available and fit a slightly longer than standard screw. Again being careful not to over tighten.

Dave.

[Barnsey]

Thank you both.  Having measured a bolt they look to be 1/4" BSF  ? 

Is this a good option?   https://www.ebay.co.uk/itm/281957227770?epid=28023463283&hash=item41a5f5dcfa:g:b2UAAOSwLVZVwG65 

As per suggestion I will also buy a 1/4" tap so I can try cleaning up the original thread first before committing to helicoil.

  Regards,

     Ian

[Spaceman]

They are actually 1/4" BSC but have the same tpi as 1/4" BSF and, in an Aluminium casing, the difference is a little academic.

If you have any doubts about the threads, it's best to proof test each one with the inner cover off to see whether it will take the required torque (whatever that is). If a thread fails the test then Helicoiling is the best repair.

[Barnsey]

OK, I've ordered Taps, and a helicoil kit in BSC.   I had bought stainless steel bolts sold as being for a BSA bike, but suspect they were BSF. I wonder if they would grip as well as BSF.?

[Spaceman]

The only difference between 1/4" BSC and BSF is the thread angle is 60 deg for the former and 55 deg for the latter. In practice, that normally makes very little difference and in most circumstances they can be treated as interchangeable.

In terms of using Helicoils, it's best to practice on something scrap first because, if something goes wrong, the Helicoils can be difficult to extract and re-do. Using the drill provided to drill out the old thread can be challenging because, if you use a hand drill, it has a tendency race into the hole and be difficult to control. Using a pillar drill is probably safer.

The most important part, apart from the drilling, is to make sure that the new thread for the Helicoil is very carefully tapped and to the correct depth. You then have to be very careful how you screw in the Helicoil spring making sure it screws in smoothly without much force being used!

[Barnsey]

Slightly worrying when you talk of using a pillar drill,as the engine is in the bike.  I wasn't planning to completely strip it down in order to do this job. 

  I had considered using a hand drill, but I might end up using my makita rechargeable as it will run good and slow.

My normal technique is to use several drills of enlarging sizes to avoid the hole ending up being oversize.

  Thinking on it I am wondering about using a drill 0.5mm undersize and then finishing with a hand reamer.

  Whatever way I go I will certainly practise on the old cover which is now scrap.     

[Spaceman]

I didn't mean an old fashioned hand drill but an electric one. The problem you have to be careful with is that the thread in the existing hole will tend to draw the Helicoil provided drill in very quickly which can be hard to control. Using smaller drills first to gently remove the thread will certainly help but the final one must be the one in the Helicoil kit which is of the correct size for the Helicoil tap provided.

[Barnsey]

Thanks! I expect I'll be doing dry runs next weekend, I'll let you know how it goes.

  Ian

[Barnsey]

OK it has been a couple of weeks but I have made some progress.  Tapping out the holes a little deeper and then cutting the bolts to the right measured length did the trick and saved me from having to drill and helicoil.  I'll save my shiny new helicoil kit for next time.

Having done up the side cover I am now worrying over whether I should have shimmed the gearbox having changed the layshaft bush.   What do you all think? Is this vital or am I OK to take a chance on it?

  Regards,

     Ian