I need to replace the primary chain on my Brum and do not know what it is or where I can get one from.
Can anyone tell me what size the chain is, the number of links and a source?
From Technicalities I have seen that a Replica engine needs a ‘4305’ with 70 links, but this is from a 1930 catalogue reproduced in Yowl in 1978 so I guess the reference number is not much use today!!!
I have looked on the spares scheme but can only see a final drive chain and the Technicaliites has a different reference number for it so I assume it is not the same size.
I once wrote i my Logbook: primary chain, ½”x .380 (428) 70 rollers.
It is not that difficult to get the new chain on with a long peace of hooked wire
Thanks for the feedback.
I believe I am now sorting out the codes via checks on the internet and think you may actually have an error in your numbers.
Going to the Technicalities reference of 4305 I believe that the first digit is pitch in eighths i.e. it means 4 eighths = half inch which matches your numbers. I then think the next three numbers are the inside width of the side plates (i.e. width) in thousanths of an inch i.e. 0.305″ whereas you have this as 0.380″. From a web site of chain types and sizes, I cannot find a 1/2″ with 0.380″ and the widest they give is 0.305″ (though for drive chain the Technicalities give 5380 which would be 5/8″ by 0.380″ width and this is an available size).
As confirmation (I think), the web site lists the various codes for chain size and your 428 is given for the 1/2″ by 0.305″ width (which is also noted as 1/2″ x 5/16″ but don’t ask me where the 5/16″ comes from).
I also note that you and the Technicalities give 70 links.
Hene I think the chain references 4305 & 428 both mean 1/2″ by 0.305″ width and 70 links are needed.
If anyone can confirm or correct this I would appreciate it.
Hello Colin,I think you will find the 1/2″ pitch x.305″ roller is the size used for mag. chains, the primary chain will be 1/2″ pitch x .335″ roller. (69 links plus connector) If the old chain is in place use it to pull the new one over the flywheel sprocket. Jeff Reed.
Thanks – this has confirmed what I thought
I went to a web site http://www.sproketsunlimited.com to get chain size info and they use three dimensions to define the chain – pitch, width and roller diameter.
I was quoting the width as 0.305″ but did not give the roller diameter. For a 1/2″ pitch and 0.305″ width the roller size is 0.335″ i.e. as you say. Hence I believe we are talking about the same size i.e. 1/2″ pitch by 0.305″ with 0.335″ rollers.
Also, we are talking about the same length – a length of chain with 69 links which needs a split connector to make a total of 70 links in the loop. This corresponds to 70 rollers in the chain length (the web site uses this definition for length).
Having had to fit the primary chain before, I will certainly use the old one to pull it through as I found it really problematic to get a length of wire to work. I also expect to have to remove the oil tank to get enough space which is another awkward job on a Brum
For future reference, the original Reynold chain was No. 110046 and as you have found out, was 69 links (which means one link was cranked) plus the spring link. If you ask Sprockets Unlimited for an equivalent chain, they will offer you a choice of three – correct sizes but of different quality. You get what you pay for!
For reference, the Reynold final chain reference No. was 110056. Length dependant on drive sprocket size.