Page 28 of the owners manual (1961) mentions a sealing screw for the primary chain adjuster. This is to allow a rod to be pushed up inside the adjuster to assess the chain tension. I cannot find a screw in my box of bits to fit. It is small - a 3BA screw just catches the thread but wont tighten. Anyone any ideas? I have hunted through various parts manuals but cannot find a part number or any info.
Hi Adrian,
I have looked at a couple of parts books and cannot see the screw you have mentioned. The chain tension is checked on the top run rather than over the tensioner. Do you have a photo of the screw and where it goes?
Dave.
I have a 1963 A65 and looking at the workshop maual page B28 which deals with primary chain tension there is no mention of the sealing screw you can only adjust the chain correctly on the early models with primary case removed , you remove the cap nut which exposes the adjuster the you adjust the chain until you have no more than 1/8" movement on the top run. The A50 was the same.
The 1961 owners handbook describes this sealing screw.
I'll endeavour to put a copy of the relevant page on the site..
The hollow adjuster is threaded inside. The caps on the chain case do not allow for manual feeling of the chain on the early bikes. The later bikes had the domed nut to fit over the adjuster which performs the same function but they are difficult to obtain.
Hi,
The adjuster screws in from inside the primary case and then has a lock nut, the dome nut or both depending on the year but the function is same. I am interested to see how pushing up through the slipper would work with such a small amount of slack allowed in the chain. On the bottom run chain comes under the front sprocket, over the adjuster slipper and then under the clutch. It would be at its tightest here and adjusting to give the 1/8" slack at this point would result in too much on the top run where it is supposed to be checked.
Dave.
I agree Dave. I'm only quoting the handbook.
As said, I will try and post up a copy of the page tomorrow when I get chance to.
Hi Adrian,
I have found what you have been referring to. Yes, page 28 of the Owner's Handbook. I found it in the scanned documents of the Members' Area.
So pushing up against the underneath of the slipper will detect if there is some slack. How does a bit of movement of a rod pushed up under the slipper translate to movement of 1/8" on the top run.
It would be interesting to set the chain tension to the 1/8" on the top run and then see how much movement there is of the slipper. I do not think I have an early adjuster otherwise I would try it as I have the primary cover off one of my bikes. Are you able to check this as it might be useful to others with the very early set up?
Sorry I cannot help with your initial query re the thread of the screw.
Dave.
I had just put my engine back together when I found this page in the handbook.
I did have a slight oil weep from the adjuster hole so when I saw this I thought I could seal the hole off.
If I had known before I put the adjuster in, I would have taken it to my nuts and bolt supplier to see if they could help.
If 3BA is nearly there then it might be 8-32 UNC which is fairly close, a little coarser. Diameter almost identical but tpi of 32 where as 3BA is almost 35
It's quite hard to measure a female thread so small!
Hi,
The story continues. I have just dug out a Instruction Manual from October 1963. It is page 27 in this one that deals with primary chain tension. It mentions the hollow adjuster but no sealing screw so the cap nut must be meant to do that job. The other thing that can be gleaned from this is that the 1/8" of slack needed will be able to be measured using this method. So something learnt by me at least.
Dave.
I think the screw must have changed to a capped nut early on as the tiny screw could be lost easily.
Try getting one of those capped nuts! I can get the adjuster lock nut but no one seems to have the capped nut!
Hi,
If you use a lock nut to secure the adjuster use a dome nut to seal the end until you can get the right one. Use some thread locker to secure it or try to get a ny-lok dome nut.
Dave.
The dome nut needs to be quite long as there is a good 1/4 to 3/8 inch of flat adjuster before you get to the thread.
Hi,
There are different adjusters, 1 with the tell hole one without, looks like you have the 1 with. There is no thread inside its sealed by the cap nut. Might be on the early years as the cap wasn't utilised or could be a modification.
I seal the cap with a dowty seal between the cap and casing.
Best wishes...
Mine definitely has an internal thread as stated in the 1961 owners handbook.
Hi,
I guess your adjuster is part number 68-0246, fitted without a cap. I don't doubt its threaded and a screw is mentioned in the owners handbook, however the parts book doesn't illustrate a screw. Also the parts book shows a spring 68-0238 which fits between the top of the adjuster and adjuster spring peg. It is illustrated but not listed in the text of the parts book. If that spring is used it keeps the peg extended so when a rod is pushed into the hole the slackness cannot be gauged as the spring takes up the slack.
The later adjuster part number 68-0278 isn't threaded and is sealed with a cap, it hasn't got a spring to extend the peg.
Perhaps the handbook and or parts book were printed before the final machined parts were assembled.
Curious...
Hi,
Probably worth trying a 5/32" CEI.
Best wishes...
Quote from: Bess on 17 Feb, 2021, 08:36
Hi,
Probably worth trying a 5/32" CEI.
Best wishes...
I think 5/32 cei is slightly smaller than a 3 ba screw which doesn't quite catch the threads.
I've gone through my box of mixed screws and bolts and they are either too big or too small!
Hi,
The only thing in the ball park is as Calum suggested 8-32 UNC.
Or 8-36 UNF.
Or 0.1583" dia, 40 tpi bscy
Or 0.175" dia, 32 tpi CEI
If not, you have a choice of 5, 3/16" diameter between 24, 26 or 32 tpi British threads.
Regards...