18S Rockerbox Fitment

LoneStar · Post by **LoneStar** » Tue Jul 10, 2007 7:48 am

Folks,

A couple of questions about the rockerbox fastening on my 1954 18S:

- The spares list shows 9 bolts, all 5/16" BSF, and each fitted with a flat washer. Does oil tend to seep out past the bolt heads, and if so would it help to use some gasket sealant on the washers?

- Despite all the bolts being 5/16", and the threads in the head being 5/16", two of the holes in my rockerbox are easily large enough for 3/8" bolts (see http://www.vincent-hrd.co.uk/images/rockerbox.jpg). Any ideas on why this should be so? Should a sleeve be fitted over the bolts? (Can't find one in the spares list.) Or possibly it doesn't matter, as the other bolts will locate the cover and there won't be sideways force to contend with in any case?

Cheers,

Dave

bag-o-nails · Post by **bag-o-nails** » Tue Jul 10, 2007 9:07 am

Hi dave
i don't know about your bike but on my 250csr
two of the bolt's are for mounting the top engine to frame bracket
CHEER'S
Phill

Biscuit · Post by **Biscuit** » Tue Jul 10, 2007 10:50 am

Someone has drilled these out for whatever reason. You have two courses of action here, either make up a sleeve or fit an extra thick washer under the head of the bolt, at least 3/32".

The two centre bolts should indeed have threaded extentions to take the head stay. When assembling don't forget to put these two bolt and the one nearest the rear, in before fitting the rockerbox, you won't get them in afterwards.

As long as the hole does not overlap the gasket, then oil cannot creep up the bolt.

Don Madden · Post by **Don Madden** » Tue Jul 10, 2007 5:53 pm

Hi, Dave. The head material is quite soft & it is not unusual to have stripped out threads for the rocker bolts, especially the two central ones with the extensions which fasten the top mount.

Easily repaired by a helicoil & since this size is often a problem, it is worthwhile to get a kit.

The threads in the head are British Standard Fine & kits are available in the US from British Tool & Fastner, (www.britishfastners.com). They have a broad range of tools & hardware in the various British Standard forms.

The gasket normally seals the bolt holes but if you have oversize bolts, they may not seal.

Cheers, Don.

Chazzyb · Post by **Chazzyb** » Wed Jul 11, 2007 11:49 pm

On my 18S, the heads on the bolts for the extreme forward and rear rocker box fixings have 0BA heads! Well, 0BA box and open ended spanners fit *exactly*. Threaded bit is the same as all the others.Edited by - Chazzyb on 11 Jul 2007 10:49:54 PM

Don Madden · Post by **Don Madden** » Thu Jul 12, 2007 3:50 am

That's right Charles, the bolts do have smaller but longer heads to improve access. They are all 5/16in. BSF at the lower end but 5/16in. BSC on the short extensions.
Cheers, Don.

Biscuit · Post by **Biscuit** » Thu Jul 12, 2007 11:04 am

Yes, but they should not be 0BA heads, they are 3/16" Whit. There is 20thou across flats difference, so who ever made them cocked up their dimensions.

56G80S · Post by **56G80S** » Thu Jul 12, 2007 1:45 pm

Just in case it gets lost in the volume of response, do heed Biscuit's advice:

When assembling don't forget to put these two bolt and the one nearest the rear, in before fitting the rockerbox, you won't get them in afterwards.

I found this out the hard way when I first took the rocker box off in my Dad's front garden 250 miles from home (long story). It's a very frustrating experience to start again.

When fitting the small head steady bracket, I usually cut a piece of old inner tube and put it round the frame top tube inside the circular strap.

Johnny BEdited by - 56G80S on 12 Jul 2007 12:46:07 PM

Biscuit · Post by **Biscuit** » Thu Jul 12, 2007 3:24 pm

Isolastic engine mounting John?

56G80S · Post by **56G80S** » Fri Jul 13, 2007 1:38 pm

The sophistication of my assembly techniques knows no bounds!

It's amazing the uses one can find for a screwdiver with the end broken off, but a really strong, impact resistant handle, particularly when refitting the engine and lining up the engine plates and mountings; ha ha.

Johnny B