B25 Primary chain is tight

[AltcarBob]

I am in the middle of fitting a new drive chain and sprockets plus new clutch plates and clutch springs. I am reassembling the primary drive and I have noticed the primary chain is very tight. The primary drive was stripped last summer before I got COVID which stopped all bike time and I vaguely remember the chain was tight then. I thought it was just a tight spot but turning the back wheel it never goes slack.

Everything has been reassembled using the BSA parts book to check I have everything in place, chain lines up and I have removed and replaced the clutch basket and engine sprocket several times changing the orientation of the splines to try and find a slacker position. The chain comes off okay and goes back on okay there's just no slack.

The chain was replaced by the previous owner and it doesn't have a brand name I wonder if it's worth fitting a new good quality chain. Engine sprocket and clutch basket teeth have some wear but aren't hooked or worn on one side.

[Spaceman]

I would double checking what sprockets and chain are fitted. It should be 23T / 52 T and 70 chain pitches.

[idie]

If it is a foreign made chain the rollers maybe metric and not impe. rial, these will sit higher on the sprockets

[AltcarBob]

I would double checking what sprockets and chain are fitted. It should be 23T / 52 T and 70 chain pitches.

Checked and everything seems to add up

[AWJDThumper]

Have you checked the chain pitch with a digital vernier?

[AltcarBob]

Have you checked the chain pitch with a digital vernier?

Not sure what the pitch should be I don't know anything about the sizes

[rhyatt]

I'm not conversant with the B25 , but the C15 has an adjustable slipper to tension the primary chain,

[AltcarBob]

I'm not conversant with the B25 , but the C15 has an adjustable slipper to tension the primary chain,

Yes there is a adjustable slipper tensioner but the iproblem is the chain is taught even before the tensioner is touching the chain.

I have ordered another chain in the hope that the current chain is not to spec.

[Rog1]

There are industrial spec. chains which might be the same nominal size as, but differ from, motorcycle spec. chains; I think maybe the rollers are different dimensions. But industrial chains have the advantage of being cheaper, or possibly "free".

[Spaceman]

 

Have you checked the chain pitch with a digital vernier?

Not sure what the pitch should be I don't know anything about the sizes

The correct chain pitch is 0.375" / 9.525 mm and the roller diameter should be 0.25" / 6.35 mm. Assuming it's the correct pitch (3/8"), I would have thought a tight chain could only be produced by the wrong roller diameter which would be worth checking.

[AltcarBob]

Right I think I have cracked the problem the engine sprocket is not lining up properly with the clutch sprocket. The engine sprocket is too far out. Did a lot of googling and it seems there's a distance piece between crankshaft seal and sprocket see item 88 on the Draganfly parts charr.

https://draganfly.co.uk/product-category/triumph/triumph-sparesparts-for-1968-71-250-singles-models/crankcase-250/

I have a .327 thick piece part number 40-325 and I think I need a 40-326 (Triumph number 70-8141) which is.310 thick.

However this part seems to be unobtainable anyone know of a source or has one in the spares box I can buy.

[AltcarBob]

Further update I have found the distance piece on eBay

[AltcarBob]

Everything back in place and the chain is still tighter than I would like it but as far as I can tell everything is lined up the crankshaft bearings are good and I just need to get the rest of the bike bolted together.

[rhyatt]

From memory, the c15 primary is about 3/8" I think.
As long as its aligned sprockets and some slack allowing for tight spots , should be fine.
I use affiliates in my primary chaincase to assist the clutch

[AltcarBob]

I use affiliates in my primary chaincase to assist the clutch

What are affiliates never come across that before