Oil drain plug size for helicoil

[andy120t]

My Cb650 oil sump threads are stripped (for the oil drain bolt). Part numbers are the same for the CB550. I bought a helicoil 12.5 x 1.25 kit but it seems far too big for the new bolt I bought from DS. So, question is - what size kit should I have bought to fit this bolt? Thanks!

https://www.davidsilverspares.co.uk/CB650B-1981/part_189216/

[ka-ja]

Hi,
    I couldn't find a part description, but its a good guess that the diameter will be correct, but the thread pitch on the plug will be different than the standard 12mm pitch, so a standard 12mm helicoil will not do the business, will dig deeper
    It appears it may be 12mm by 1.5mmpitch-will continue search!
   
    Standard pitch= 1.75mm    fine=1.5mm    extra fine=1.25mm

[andy120t]

..hard to describe, but when i introduce the sump bolt to the helicoil insert, the bolt slides through without touching the helicoil edge/threads. So feels as if the helicoil is far wider  than the bolt - so i wonder, if i insert the helicoil, will it compress/narrow to a smalller diameter than it has before used...?

[hairygit]

Yes, it will, the insertion tool (if you haven't got one, it wont work!) winds the spring into the re sized thread and the insert makes up the difference between the new thread and the bolt I get the impression you have't used a helicoil before. If that's the case, get someone who knows what they are doing to show you, or get an engineering firm to do it, bot expensive.

[Bryanj]

Hold the insert tap up against the new plug , if the tap is about 1.5 mm bigger its correct and make sure that the bolt threads fit into the tap to check pitch

[Trigger]

Are you sure that it has a standard sump bolt ? Many I have seen have already been tampered with. I have many members mail me asking for the correct size as they want to order a magnetic sump bolt. When they have got there new sump bolt, they find it doesn't fit.

[andy120t]

I bought a replacement from DS to see if that fitted / if I could avoid having the threads remade. The new bolt is exctly the same as the one already in there so looks standard.


Just watched a youtube video and the process is: -
- drill the hole out
- tap it to a larger size
- wind in the insert:....in the kit I have (M12x1.25) - it's this insert that is bigger than the sump bolt. I assumed that the sump bolt would be a snug fit into this before it was inserted - as the insert becomes the  new thread. So if my bolt is smaller than this insert, is that OK or does that sound wrong?

...think I may have bought the wrong pitch though - wemoto has M12x1.5 for these sump bolts,  so I'm not sure how I bought the wrong one, but I won't be using this one..... sounds like a trip to the local bike shop might be the cheapest way annd hey might let me watch the process too.  (unless anyone is in the Hertford area and know how to do this?!).

[matthewmosse]

Personally I would be just as keen to swap the sump, if it is the same as cb550 they are easy to come by ( I have a few somewhere). I think helicoils do kinda get tighter when installed as everything moves a bit as locked, the coil is diamond shaped in cross section I think, but I find it hard to believe the bolt should hardly touch the insert when tried losse / un installed. A cheap set of thread gauges on the plug should identify the thread size of that. Or compare to other easier to identify threads on that or other bikes.

[andy120t]

..I wimped out and had a local firm out a thread inser in. Pretty cheap and would have been cheaper than buying the wrong helicoil set anyway.... Pick it up on Saturday so hopefully I'll be back up and running oil-tight at the weekend!