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SOHC.co.uk Forums => CB750 => Topic started by: captaink on April 06, 2017, 11:43:17 AM

Title: Oil Filter thread size
Post by: captaink on April 06, 2017, 11:43:17 AM

Hi , does anyone know the thread size for the oil filter bolt that screws into the lower casing.
I need to clean the thread, so want to order a tap to suit

Regards Keith
CB750 1977

Title: Re: Oil Filter thread size
Post by: captaink on April 06, 2017, 12:28:48 PM

Thanks, but I think that's too small, have been told M20 x1.5 which sounds correct but thought id ask others

Title: Re: Oil Filter thread size
Post by: philward on April 06, 2017, 01:14:56 PM

Just measured a spare - its m20 x 1.5

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Title: Re: Oil Filter thread size
Post by: Trigger on April 06, 2017, 06:44:34 PM

Why not just buy a new bolt ?

Title: Re: Oil Filter thread size
Post by: hairygit on April 06, 2017, 07:03:37 PM

Quote from: Trigger on April 06, 2017, 06:44:34 PM

Why not just buy a new bolt ?

My thoughts exactly, with such an engine life critical part, if the thread is damaged, heat and vibration will only make it worse, and the engine would not last long if it started leaking while riding it, if you survive the inevitable accident caused by oil spewing on the road directly in line with the rear wheel. Seen it happen on a 400/4 many years ago.

Title: Re: Oil Filter thread size
Post by: hairygit on April 06, 2017, 07:07:02 PM

That said, I take it that the thread in the crankcase is dodgy if you're looking for a tap, do it properly with a Wurth insert, damaged threads in alloy will not hold for long!

Title: Re: Oil Filter thread size
Post by: philward on April 06, 2017, 07:22:18 PM

I agree Hairy - and doing an insert on a thread that size with hand tools may not be that accurate - probably need a machine shop to carry out that job?

Title: Re: Oil Filter thread size
Post by: hairygit on April 06, 2017, 08:03:54 PM

Quote from: philward on April 06, 2017, 07:22:18 PM

I agree Hairy - and doing an insert on a thread that size with hand tools may not be that accurate - probably need a machine shop to carry out that job?

  To be 100% safe about it, yes, a good engineering firm will be needed.

Title: Re: Oil Filter thread size
Post by: Tomb on April 06, 2017, 08:34:48 PM

If it helps find a tap, electrical conduit size is M20 x 1.5

Title: Re: Oil Filter thread size
Post by: captaink on April 17, 2017, 05:53:54 PM

Thanks for the replies.
Got an M20 x 1.25 to clear the thread.
The thread wasn't damaged but the process of aqua cleaning it, it needed clearing and as I did all the 6mm threads in the casing it was worth doing this one as well.
Because most of the threads had bolts put in some 40 years ago they should be ok but the oil filter has most likely been apart a few times , so could suffer from wear.
If it was worn I would most likely have fitted a spin on oil filter adaptor as supplied by Cycle X. which would eliminate the need to remove the adaptor fitting from the casing.
I may even fit one anyway, but not sure !