16MS (500cc)

Information relating to the Matchless G3 or AJS Model 16 350cc Heavyweight
Locked
Andy E
Member
Posts: 32
Joined: Wed Aug 10, 2016 4:26 pm
Location: Wiltshire, UK

16MS (500cc)

Post by Andy E »

Hello all

I wonder if anyone can help? My 1956 16ms was converted to 500cc about 30 years ago.

I am reassembling the top end of the engine after carrying out a top end overhaul. I noticed when dismantling the engine that there was not much in the way of a seal at the top of the push rod tubes, although there had been no leaks form the tubes.

The problem that I have is that there simply is nowhere near enough space to fit the correct pushrod tube top seal. The seal measures 12.8mm in length. If I fit the two steel washers to the tubes, but not the seal and not the lower gland, and then fit the cylinder head the vertical play in the tubes in only just over 3mm. As the lower gland measures 5.2mm in section, there just is not the space to compress this gland and the 12.8mm top seal.

Taking advice from this forum, I bought Viton O rings to use in place of the top pushrod tube seals. If I fit one of these O rings into the cylinder head and fit the lower gland, this does seem to fit ok with reasonable compression of the seals. Do you think that a single O ring will suffice? If not, can anyone recommend what I should do?

The engine number is 56 16MS29496. The cylinder barrel seems to be pre 1956 as it has the two lubricating holes drilled through the base and the cylinder head seems to be pre 1955 as the exhaust valve guide did not have the circlip. The pushrod tubes are part number 010952, 7+9/16" in length.

Thanks for any advice.
User avatar
Rob Harknett
Member
Posts: 11236
Joined: Mon Jan 01, 1990 12:00 am
Location: ESSEX UK

Re: 16MS (500cc)

Post by Rob Harknett »

Have you got the correct tubes? would 6 5/16" tube be what you need?
Andy E
Member
Posts: 32
Joined: Wed Aug 10, 2016 4:26 pm
Location: Wiltshire, UK

Re: 16MS (500cc)

Post by Andy E »

Hi Rob

My first thought was that maybe the tubes are wrong. I can see only two lengths of tube shown in the parts catalogues. The tubes that should have been fitted to my 1956 engine seem to be part number 022288, length 6+5/16". These tubes would be too short to be used on my engine.

The tubes that I have do seem to be correct for the earlier cylinder head and barrel that I have. It seems that the part number 010952 length 7+9/16" tubes were used from 1949 until 1955.

What I find confusing is that there is also only the one pushrod tube top seal shown for all models from 1949 to 1955.

Regards
User avatar
Rob Harknett
Member
Posts: 11236
Joined: Mon Jan 01, 1990 12:00 am
Location: ESSEX UK

Re: 16MS (500cc)

Post by Rob Harknett »

There is a rubber tube that goes on the top of the tube and a rubber ring at the bottom. There is also a metal disc at the top. Sometimes the top rubbers are tight, so you may need a little oil on them to get them fully in place. Otherwise the tubes may appear to be too long to fit in the head. Make sure you do not have extra washers in the head, these are difficult to see.
User avatar
clive
Member
Posts: 5657
Joined: Mon Jan 01, 1990 12:00 am
Location: LONDON UK

Re: 16MS (500cc)

Post by clive »

My guess is you have a pre 56 ally cylinder head but pushrod tubes from the earlier iron cylinder head. There are three lengths of pusrod tube. The short one for 56 on, but you have the earlier cylinder head. The longer type 7 9/16 for the earlier alloy head and the longest at 7 15/16 for the iron head. Now thats only a 3/8 inch difference but the additional sort of gap you need to fit the topseal. Finally only one of the washers was fitted above the seal except when a base decompression gasket is fitted, most unlikely on your conversion (there is also the angled one below).
I suggest you measure your tubes again and see if they are in fact 7 15/16 if so you need to get the slightly shorter ones or mix and match with some o rings.
clive
if it ain't broke don't fix
Andy E
Member
Posts: 32
Joined: Wed Aug 10, 2016 4:26 pm
Location: Wiltshire, UK

Re: 16MS (500cc)

Post by Andy E »

Now I feel really silly!

Yes, the pushrod tubes that I have are indeed 7+15/16" in length. I saw that there were only 2 lengths of tube for the engines with ally heads, 7+9/16" and 6+5/16". With the tubes fitted to the engine, I roughly measured them in situ and saw that they were clearly not the shorter tube and as they seemed to be 7+", I jumped to the wrong conclusion. I think this is called "Confirmation Bias".

I think that I'll buy two new tubes from the club spares scheme. I can only get one O ring onto the longer tubes and I'm not convinced that this will provide enough of a seal.

Thanks Rob and Clive for your help, much appreciated.

Best regards
Locked