C15/B40 primary chain tensioner

[Greenfield]

The primary chain tensioner on the B40 is simple and effective. However, the chain slides over the steel surface of the tensioner gradually wearing grooves and releasing particles of steel into the primary case which in turn increases the wear of chain and sprockets. The primary chain, sprockets and tensioner can be regarded as renewable service items. As far as I can remember, the surface of the A50/A65 tensioner is a hard rubber material and nylon is used on other brands. Has anyone tried a modification to reduce the steel on steel wear that has proved effective?

[rhyatt]

Once the initial wear has  taken place, many decades ago , it will be the rollers of the chain gliding over the tensioner thereby very little if any further wear.

[Greenfield]

Yes, mine has reached that point. The depth of the tramlines is around 1mm which is equivalent to the height of the chain edges above the roller surfaces.
The tensioners that I've seen advertised look far less robust compared with mine; how will they cope with three tramlines 1mm deep cut into the surface.
Secondly, the tramlines on mine are 1mm deep, the centre one is around 4.5mm wide and the outer ones are 2.5mm wide each. They are near enough 40mm long. Assuming that the 'corners' of the grooves have a 1mm radius, a rough calculation means that 245 cubic mm of steel have been worn away and dispersed around the primary case into the clutch bearing, chain, etc - not ideal. When you've just spent time and money refurbishing your pride and joy, this is less than desirable.
Thirdly, why did BSA decide to line the tensioner on the A50 etc?
Drags make their A50 tensioners inhouse, so I've asked them what they use as a liner.

[DAVE BRADY]

Hi,

Why not try attaching a magnet on the underside of the tensioner to attract the metallic sludge?  Easily removed and cleaned and as the amount reduces it will indicate the point at which no more or very little wear is taking place.

Dave.

[Greenfield]

Good thinking Dave. I always fit one to the engine drain plug/sump cover but didn't think of adapting the idea to the primary case. The brain's clearly not firing on all cylinders!
I'll still investigate the 'rubber' liner for curiosity.

[cdsdorset]

If you put a magnet on the underside it will attract slivers of steel to build up in the slots. You would be better off having a magnet on the drain plug.

[Greenfield]

I would definitely glue the magnet to the alloy case rather than steel. You might get away with it on the back of the inspection plug, then it could be checked without removing the cover, but the best place would be the bottom of the case where it will be covered in oil and be more effective.
The little magnets in the children's magnetic sticks are very useful being only a few mms in diameter. They're not very powerful but sufficient to collect the fine metal particles in these situations.

[Keith R]

I have a similar issue with my Mod B40.   I was thinking of filling the groves with weld and grinding back. Does anyone know if this could cause problems going forward?

I really like the magnet suggestion.

Regards

[rhyatt]

The welding would upset the heat treatment of the slipper plate

[SJCLARKE]

Do not over-adjust your chain and it should be fine BSA designed it that way and it has been good for years the oil should lubricate enough to cope

[Greenfield]

I wouldn't fill the grooves with weld as there're bound to be irregularities in the metal which would result in excessive chain wear. You'd also then be back to square one with the slipper bedding in and having to deal with the metal debris.
My thoughts were to line the slipper with the rubber material as on the A50 tensioner, which would be kinder on the chain, but Drags say they buy them complete from a supplier. I can't find what the rubber is so I'll refit my existing tensioner which is bedded in and should last for many miles to come.