BSA Owners' Club Forum

The BSA Workshop => Twins => Topic started by: bikerbob on 05 July, 2017, 11:27:15

Title: Small end problem
Post by: bikerbob on 05 July, 2017, 11:27:15
I have a1956 swinging arm A7 for a few weeks now I have had noise coming from the engine at certain revs about 25 mph in second gear 35 in third gear and 45 in fourth gear. So decided to take head and barrels off, on first inspection could find nothing wrong but when I removed the pistons one of the small end bushes has turned in the con rod blocking off most of the lubrication hole. This has resulted in the internal diameter of the bush being 5-6 thou bigger than the gudgeon pin. I have ordered a new bush but suspect that it will not be a tight enough fit in the con rod the original worn bush still had to be removed using a home made extracter but it came out too easily. How do I make it a bit tighter would bearing loctite be the answer or I could do what we used to do years ago when I worked in enginering and we had this problem we would tin the outside of the bearing then press it in this was the solution before loctite. Or does anyone have another remedy. Thanks.
Title: Re: Small end problem
Post by: JulianS on 05 July, 2017, 18:36:32
Providing the rod has not been damaged - by heat or by scoring etc within the eye - you could consider loctite. Worth researching their website there are many grades available, some extremely strong and durable,  for different applications.
Title: Re: Small end problem
Post by: bikerbob on 05 July, 2017, 20:19:26
Thanks for that Julian have looked at their website did not realise there were so many different products will wait till new bush comes then will see if  some type of loctite is required. The con rod does not look to be damaged the hole is still round and not scored don't know why the bush has turned no heat damage.
Title: Re: Small end problem
Post by: Bess on 05 July, 2017, 22:04:58
Hi bikerbob,
                 I would fit an oversize bush to have peace of mind especially when racing those modern bikes ;), SRM can supply:

Best wishes.........
Title: Re: Small end problem
Post by: bikerbob on 06 July, 2017, 15:39:39
Thanks for that info I have checked the con rod and it is still round and no bad scoring just a few minor scratches no sign of any heat problems, have ordered a new standard bush did not realise you could get oversize ones and will see if it is a tight enough fit if not I have a small lathe and will turn a bush to suit, I am by no means an expert on lathe turning but will have a go and if it does not work out I will order an oversize bush. Looking at the bush that turned it would appear that sometime in the past a previous owner has fitted a bush that was maybe a little to small and has tried to compensate by putting a series of pop marks all over  the bush to make it a tighter fit, I have had the bike for about 3 years now so it did work for a while. I have been down to a local metal stockist and bought a small piece of phosphor bronze the correct grade, If anyone out there needs to buy any type of metal be it sheet or round bar or sectional bar then I can recommend going to a company called the Metal Supermarket they have branches around the country, they will cut to order and are very helpful and not expensive, acouple of years ago I made my own motorcycle lift  and they cut all the parts to the sizes I required and did not charge for the cutting I just paid for the cost of the material.
Title: Re: Small end problem
Post by: DEAN SOUTHALL on 06 July, 2017, 18:05:38
I have had this problem in 2 A10s. The first one I ignored until it cost me an exploded engine. I had to sell the bike to pay off the cost of repairs. Many years on and I am more cautious and whipped the barrels off as soon as I heard the small end rattle.
I wonder if it is down to people not reaming the bush when they press a new one in, leading to it tightening up on the gudgeon pin?
Title: Re: Small end problem
Post by: Mike Farmer on 07 July, 2017, 09:29:26

That was a good deal getting your metal cut at no extra cost.  I checked some out very recently and was quoted 1.00 per cut.

Didn't buy.

Title: Re: Small end problem
Post by: Bess on 07 July, 2017, 09:53:28
    I must admit in the past I would sometimes pop mark loose fitting components or knurl the outside if I could (knurling with loctite was more successful). I never really found the technique a permanent solution and often revisited.

I recommend the oversize bush every time if its possible...

Best wishes...
Title: Re: Small end problem
Post by: paulm on 08 July, 2017, 23:17:28
people fit the bush then ream with a adjustable reamer MISTAKE ONE the they check it with the end of the gudgeon pin problem is the part of the pin never wears and then when they push the pin in there is play MISTAKE 2 , ALWAYS fit a new pin with new small ends and use a fixed reamer that way you know you have the size spot on