Low Head Allen Bolts

Post Reply
Mick Taylor
moderator
Posts: 168
Joined: Mon Aug 11, 2008 8:59 pm
Location: Ivychurch, Kent

Low Head Allen Bolts

Post by Mick Taylor » Sat Feb 24, 2018 6:21 pm

Tinkering with my Classic today, I removed the upper and lower steering yoke clamp bolts.

They are a bit of an oddity; the cap head of the bolt has a reduced height......(low head) about half the height of a typical Allen head, and underneath this reduced height head in each case is an aluminium spacer, I didn't measure it, but maybe 2.5mm thick.

Added to that......my eyes might be playing tricks on me, they're not brilliant at close up....but the seat where the spacer sits doesn't look square but slightly tapered..but I could be wrong.

The parts book just shows Allen bolts, no mention of special features or spacers......they appear to be original in so far as they were manufactured as low head bolts......and the upper pair take a smaller Allen key than the lower pair despite having the same thread which suggests a reduced torque.

Anyone know what the purpose of these spacers might be?

Mick.

User avatar
Richard Negus
moderator
Posts: 914
Joined: Mon Jun 18, 2007 5:11 pm
Location: Wilds of Lincolnshire

Re: Low Head Allen Bolts

Post by Richard Negus » Sat Feb 24, 2018 7:19 pm

The wonders of Italian logic! I never worked that one out either, and always replaced them with standard stainless bolts as a matter of course.
Just checked the Classic here; lower bolts are low head 10mm, 8mm recess, marked 10.9 grade, with aluminium washer.
The uppers are full head 10mm, 7 mm (seven!) recess, marked 8.8 grade, no washer.
The only other application of a 7mm recess I ever met was also Italian - the head bolts of a Lambretta sc##ter.
Slower slower, no faster faster - the joys of old fogey mode to hooligan mode at the flick of a switch

Mick Taylor
moderator
Posts: 168
Joined: Mon Aug 11, 2008 8:59 pm
Location: Ivychurch, Kent

Re: Low Head Allen Bolts

Post by Mick Taylor » Sat Feb 24, 2018 11:48 pm

Thank you for that Richard.........as it happens I was planning on replacing them with stainless and getting all the originals bright zinc plated as soon as I have enough to justify a trip to the platers.

I assumed (which is always fatal) that the smaller hex in the upper bolts might relate to reduced torque....or not exclaim

In short ........ no known reason for it ......it's weird, but that is good enough for me, many thanks.

Mick.

johnbirchjar
moderator
Posts: 1117
Joined: Sat Mar 07, 2009 11:20 pm

Re: Low Head Allen Bolts

Post by johnbirchjar » Sun Feb 25, 2018 12:02 am

All four bolts on my Classic are exactly the same,and I have owned the bike from new Very Happy,J.B.

Mick Taylor
moderator
Posts: 168
Joined: Mon Aug 11, 2008 8:59 pm
Location: Ivychurch, Kent

Re: Low Head Allen Bolts

Post by Mick Taylor » Sun Feb 25, 2018 9:40 am

You would imagine there must be a reason, surely they wouldn't go to the trouble of using specific (odd) bolts with alloy spacers without a good reason, .........would they?

That was what stopped me from just replacing them, in case I'd missed the bleedin' obvious......I think I'll turn the heads down on some stainless bolts and use those with the original alloy spacers......

Mick.

johnbirchjar
moderator
Posts: 1117
Joined: Sat Mar 07, 2009 11:20 pm

Re: Low Head Allen Bolts

Post by johnbirchjar » Mon Feb 26, 2018 12:55 am

Do IP2's have odd bolts and spacers?'cos I have always been under the impression that Classics were(more or less) naked IP2's wink,J.B.

Mick Taylor
moderator
Posts: 168
Joined: Mon Aug 11, 2008 8:59 pm
Location: Ivychurch, Kent

Re: Low Head Allen Bolts

Post by Mick Taylor » Mon Feb 26, 2018 7:00 pm

There are a few odd threads in the mix too......the vast majority of threaded parts on the Classic appear to be metric ......... but there are a number of parts where a UNF thread is shown. The rear torque arm, for instance, has a UNF threaded bolt at the front end and a metric one at the other end exclaim

Mick.

Post Reply