Gearbox backplate thread size

[peteyg]

Hi all,

Can anyone tell me the thread size of the 2 bottom bolts that hold the backplate and silencer mount on the back of the 'box? Trying to fix a leak and some monkey has screwed up the threads on the bolts as well as the holes. Need to tap and possibly helicoil. Maybe the legendary @dsvitesse1 will know off the top of his head?

Thanks in advance,

Pete

[Sparky]

Pete, I'm probably not going to be overly helpful here, but I recall they're slightly larger than all the others?  An M6 will rattle around in there so it's possible they're not damaged...

[910Esprit]

Aluminum back cover is 7mm with an exception for the bolt securing the speedo drive.   Nuts are 10mm securing silencer mounting to gearbox mounting

[dsvitesse1]

8 hours ago, 910Esprit said:

Aluminum back cover is 7mm with an exception for the bolt securing the speedo drive.   Nuts are 10mm securing silencer mounting to gearbox mounting

Hi, correct all M7 except the speedo securing bolt that is M9. For these 2 mentioned you can make it M8. No problem. M7 helicoil is very, very hard to find.

 

cheers,

 

Harry

[semi42]

https://www.cromwell.co.uk/shop/materials-and-maintenance/thread-repair/wire-insert-thread-repair-kit-m7-0x1-00mm/p/KEN6211280K

 

[peteyg]

Thank you all. I'll see if I can tap out with M7, if not go to M8 and helicoil. Do you know if the pitch is 1.00 or 1.25?

Pete

[dsvitesse1]

Pitch 1.00 mm

 

cheers,

 

 

Harry

 

[peteyg]

Thank you Harry!

[gvy]

Pete,

I am not sure, but may be Harry says, if M7 thread is screwed, you can try , without using a helicoil, drill 6.8mm and tap to M8 and use M8 bolts?

furthermore :  standard  Metric coarse thread size :  M7 is pitch 1mm, but M8 is pitch 1.25mm

of course you could start using fine thread sizes. then M8x1

 

Geert

[peteyg]

Good call @gvy that would save having to get the helicoil. I'll try this first. I think the main problem has been people's attempts to seal the back plate and nasty gunk has accumulated in the bolt hole. Below is what I dug out of each hole, a mixture of silicone and various other sealants: