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D14 jumping out of 4th gear
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bikeandsteam
North Yorkshire
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May 2, 2017 - 9:48 am
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Following a rebuild to replace a broken gearchange lever selector spring, the previously well performing gearbox has started to throw itself out of 4th gear at about 40ish mph, usually if I am applying anything more than a little power. I stripped the engine down again and the teeth on the pinion for 4th looked fine (I am mindful of comments on other discussion threads ref wear on the pinion teeth) - as did all of the pinions. All the movement seemed OK and the pinion had the correct amount of lateral movement along the mainshaft. The cam plate was checked for correct alignment before reassembly. Road testing after the second rebuild showed the problem had not gone away! If I hold up the gearchange lever with my foot, it does not jump out of gear and will take all the power I can give it. So, another engine/gearbox dismantling session is on the cards. Has anybody got any suggestions as to what to check next please?  Has anybody had a similar problem - if so, how did you fix it? Any insights will be gratefully received. Thanks.

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Mags 1
Northamptonshire.
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May 2, 2017 - 12:58 pm
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Was the ball bearing in good condition, how about the selector fork rollers too? Bent selector fork?

What sort of wear in case bushes and bearings too.

You need to check all moving parts really as you go when you have a problem like this.

Four now on the road and at least several in bits.

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bikeandsteam
North Yorkshire
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May 2, 2017 - 2:46 pm
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Thanks. Good points - and the start of a list of things to check. I'm sure the bearings/bushes are all OK, but will examine bb and selector fork. I wondered if the spring (which is a new replacement) is strong enough?

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BASIL
Hamstreet,Ashford.
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May 2, 2017 - 4:26 pm
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Don't think it would be the spring most likely worn dogs on 4th sliding gear, I have had that problem before. Regards Basil.

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johnsullivan
east sussex
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May 2, 2017 - 4:38 pm
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3 speeds are good enough for most of us ....As Basil says it will be the dogs ...oh well...

67 D10. and a D7    2007 Honda Hornet FA. Suzuki 89  DR 250S, Sinnis SC 125. 78 Honda 90  75 Montesa Cota 247

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bikeandsteam
North Yorkshire
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August 7, 2017 - 5:47 pm
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So...... there is a happy ending to the 4th gear problem. Sourced original parts for both the fixed and sliding pinions from Vale-Onslow in Birmingham (really nice and helpful gang) that was fitted by my engineering mentor down south who took pity on me as I had zero time being up to my armpits in the midst of trying to get a 5" steam loco rebuilt and its boiler tested & certified (success!). He also made a top hat to shim out the selector spring just in case, so it made sure it was giving a really positive force. Comparing old dogs to new (got to be a joke there somewhere) the ones on the old sliding pinion did seem a little worn (rounded), but not massively so. Interestingly there was 4 thou play at right angles to the shaft, which may have also been a contributing factor to the lack of engagement at speed. However, everything is running as it should now with 4th staying put, even when loaded whilst going up stiff gradient, and my comfortable 50 mph cruising speed is happily achieved without jumping out of gear. On the way through this saga I bought a pattern (modern) manufacture sliding pinion part number 90-1693 from Kidderminster Motorcycles (also a helpful gang). This is unused as I luckily found an original part, but it looks fine and if anybody wants to buy it half price, let me know.

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cocorico
Central France
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August 8, 2017 - 8:03 am
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Congratulations on both counts - I've been involved in boiler preparation back in the day! I remember Vale Onslow from the 60s - bought my first helmet and goggles from them (Cromwell and Stadium, of course). Steam engines and old bikes - they both have a distinctive aroma...

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BASIL
Hamstreet,Ashford.
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October 26, 2018 - 11:08 am
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Hi, I know it was a far time ago but have you still got that 22 tooth sliding gear which I believe was part no. 90-1693 I have just rebuilt a B175 engine and find that it had been assembled with a 21 tooth gear, if you still have it and want to sell it I would be very interested. Regards Basil.   

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