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.
I would double checking what sprockets and chain are fitted. It should be 23T / 52 T and 70 chain pitches.
If it is a foreign made chain the rollers maybe metric and not impe. rial, these will sit higher on the sprockets
Quote from: Spaceman on 21 May, 2023, 12:49
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
Have you checked the chain pitch with a digital vernier?
Quote from: AWJDThumper on 22 May, 2023, 08:14
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
I'm not conversant with the B25 , but the C15 has an adjustable slipper to tension the primary chain,
Quote from: rhyatt on 22 May, 2023, 17:32
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.
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".
Quote from: AltcarBob on 22 May, 2023, 11:13
Quote from: AWJDThumper on 22 May, 2023, 08:14
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.
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.
Further update I have found the distance piece on eBay
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.
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
Quote from: rhyatt on 27 May, 2023, 11:23
I use affiliates in my primary chaincase to assist the clutch
What are affiliates never come across that before
Sorry ATF
Spell check love it.