Frame HoleThread Type

pwaltham · Post by **pwaltham** » Mon Mar 21, 2005 2:21 pm

I have a 1960 model 31 with duplex frame.
The previous owner in his wisdom used a thinner nut and bolt to hold the engine 'head steady' bracket to the front of the frame.[:0]
I assume it originally used a bolt screwed into the threaded hole in the frame.
Does anyone know the correct thread pattern for this as the existing thread is somewhat chewed up by having this previous smaller bolt stuck through it and possibly not tightened up too well?
I want to run a tap thorugh to reistate the original thread, or at least get a correct bolt to screw in without tightening up after a few turns.
Thanks
Peter [:)]

Eric · Post by **Eric** » Mon Mar 21, 2005 6:16 pm

It should be cycle thread this is a special thread that was in general use throughout the cycle and motorcycle industry when our machines were made. Without checking I think the one you are looking at is 5/16" dia. It will have a thread pitch of 26 tpi as do almost all cycle threads. This was useful for manufacturers as it meant they could use the same die blocks for almost everything when using a Coventry die head some of you will know what I mean.

Charles · Post by **Charles** » Mon Mar 21, 2005 6:31 pm

My three duplex frames (1960 and 1961) all have 5/16 by 26 tpi for the head steadies, even the single that has the fixing under the tank is tapped that way on the lug used on a twin.

regards
Charles

lawrence · Post by **lawrence** » Mon Mar 21, 2005 11:08 pm

Yep, and mine. The 5/16" cycle tap has to be the most useful tap when rebulding an Ajay!

Lawrence [}:)]

Biscuit · Post by **Biscuit** » Tue Mar 22, 2005 9:06 am

Eric, I would disagree with you regarding using one set of chasers for 'almost every thing' in a single TPI range. For every diameter of thread the helix angle would differ. Certainly, manufacturers of die chasers for the Coventry and similar die heads specify different part numbers for varying thread diameters in the BSB range, which is also 26TPI.

pwaltham · Post by **pwaltham** » Tue Mar 22, 2005 12:16 pm

Gentlemen, thanks for the info, you are all saying the same, great.
I just need to find someone selling the tap mentioned (got lots of other sizes and tread types but not that one.........I'll put it on my Christmas list from the boss.......... list....who am I kidding!
Anyway, thanks again
Peter

lawrence · Post by **lawrence** » Tue Mar 22, 2005 10:23 pm

Hi Peter
I can heartily recommend Tracy Tools 01803 833134 www.TracyTools.com

They are very reasonable, 5/16 cycle tap is £2.00! They are also very friendly and exhibit at many shows, Stafford is the next one coming up and they carry a huge range of stock. tell them what you want it fo and they will advise you of the best type.

Lawrence [}:)]

pwaltham · Post by **pwaltham** » Wed Mar 23, 2005 1:11 pm

£2 !!!!!!!!!!!!
Everywhere else I've looked are more like £5 to £6, and they are like hen's teeth on ebay
Thanks for the info Lawrence and its nice to know you stopped your head leaking (bike that is)
Peter[:D]