Effect of shortened boom on gear changes?

[Time Waster]

I got my recumbent out at the weekend to ride it to a police bike marking event in the village.. It's not been ridden for a year and the small chainring kept jumping and the large chainring meant the year cassette didn't run cleanly in certain cogs

I didn't know why them I got home and realised my legs were more bent than when I last rode it. So could a boom that was shortened by inches cause the gear change issues at the top and bottom of the gear range?

BTW with the hill I needed to ride up I needed the granny gears I didn't have working. So I had to push it up the hill. That's hard work indeed. Plus going downhill I had no bite to the middle ring gears that worked. So I freewheeled down. Still, that was too fast for comfort for me. I had it on brakes from halfway down!

 

[a.twiddler]

Has the boom mysteriously adjusted itself then, since you last rode it? Surely you haven't grown? It might just be an issue of perception if you've been riding other bikes in the meantime. Maybe that's the way you'd been riding it before you put it away. If you didn't adjust it, is there someone else who might?

I don't know what chain lube you've been using, but it's possible that the lube has dried out during the last year, making the chain a bit stiff, and is causing issues getting round the jockey wheels and therefore engaging with the sprockets. Simple solutions first, a good spray of the chain with something like GT85 while you turn the cranks backwards, wipe off the excess with a cloth, do it several times until it improves. You might have to ride it a bit, trying it through the gears round the block. I mention this because while getting to grips with the Grasshopper last year I didn't ride the Spirit for some months and the chain became jumpy when I got round to riding it. This has chain tubes, which can get gunked up too. I did the above, and just rode it, and it was fine afterwards.

Similarly, could the cables have become sticky? Though I would look at lubing the chain first before delving into those.

 

[Time Waster]

It is quite possibly I did shorten it at one point. It depends on when I last used it. For example I have to shorten it when I take it on my tow bar bike rack. I also have shortened it when I have to stored it for some time in the past. Any adjustment would have been done by me.

I realised it's short because my legs were too bent even so full stretch. Whilst I never really had it in the exact length I truly needed, it's a secondhand one and I suspect ideally I'd need a longer boom. It used to be long enough to allow my extended leg to be only slightly bent when the pedal is furthest away from me. A little too bent but nowhere near as bent as it was Saturday. My leg was closer to 90 degrees bend than full, straight leg stretch with pedal extended.

The chain was moving well in the middle ring. I don't think it's needing lube or use of GT85. No stiff links from what I could tell. I've had stiff links and you feel those. The chain was running smoothly enough in the middle chainring. That's why I asked about the boom length being wrong as being the potential cause. Most of the issues was with the small chainring. The big chainring issue might be something other than the boom length it could be two issues not one.

The reason I think it's the boom is because in think if the chain is too long then wouldn't it show more on the smaller chainring when there's less teeth to take up the slack?

I know when I lengthened the boom without adding links when I first test rode it there were issues at the top end. Until I got a new chain put on at the right length.

 

[a.twiddler]

If the chain is too slack due to this you risk the rear derailleur arm folding back too far and jamming or being carried round by the cassette at worst. It certainly won't help the gear change if it's slightly slack. Once you've got the boom right and the chain properly adjusted it might help to use a laundry marker pen on the sliding part of the boom so there'll be no guesswork next time.

 

[Time Waster]

There's no guesswork you get on it put your pedal at the furthest point and straighten your leg until the boom is in the right position. Then you straighten it up at that point so the chainring aligned and then tighten. It's no harder than that.

 

[a.twiddler]

You have answered your own question ! The solution lies in your own hands. If the adjustment is right, the problem should solve itself.

 

[grldtnr]

Is the boom 'straight' i.e. the bottom bracket square to the main frame? It shouldn't matter too much , but if it isn't square then there will be some twist in the chain, but seeing as recumbents have to be flexible in the drive train in regards to length of chain , that isn't likely the cause,
Like Twidds said I suspect the chain will require a clean & lube, I it certainly won't do any harm.