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B175 Gearbox Noisy.
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Bee175
Felixstowe, Suffolk
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November 25, 2018 - 1:51 pm
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Hi all.

Seeking advice regarding a noisy and stiff gearbox. 1st, 2nd and 3rd are all stiff to select and quite noisy. It's not a whine, but more of a worn bearing sound. The bearings are brand new and I don't think I damaged them putting them in. I guess it's not impossible for a bearing to be faulty from new?

4th gear drops in and out more easily and is as quiet as a mouse, no undue noise at all.

The engine has just undergone a rebuild due to a seized crank. The gearbox was slightly stiff before the crank seized but was very usable. The clutch was disengaged before the crank seized, so there was no great pressure on the gearbox and no rear wheel lock up.

The gears themselves all look to be fine. The 2 sliding gears are on the correct shafts. With the gearbox assembled in the right side casing, everything seems to turn smoothly, although gear selecting is not that easy.

The detent spring appears to be much stronger than in another gearbox I rebuilt which makes it hard (almost impossible) to turn the selector plate manually from one gear to the next. It's either that or the recesses in the plate have become worn (deeper) over the years making it harder to turn as the ball bearing would sit deeper into them. I do have another selector plate but to be honest the recesses look pretty much identical.

Would appreciate any ideas as I'm currently stumped on this one.

Cheers,

Gary.

BSA Bantam B175 1971 and BSA C15 1966

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not henpecked
Near J 11 of M42
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November 25, 2018 - 5:58 pm
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Hi Garry

Stupid question and teaching your grandmother to suck eggs - is there oil in the gearbox?

1st, 2nd, & 3rd gears use the layshaft to transmit the power, however, 4th gear is a straight through drive on the main shaft only so hence it being quiet.

My only thoughts are, did you change the bronze layshaft bushes, because of their design are they possibly nipping up the lay shaft.

Don

B175, being updated & now much closer to completion. Honda XBR 500, and ....... Suzuki Burgman 200 scoot! Nicknamed "The hair dryer" - by me I hasted to add; & great storage under the seat when you get to your destination.

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stubaker58
Sunny Felixstowe
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November 25, 2018 - 5:59 pm
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Hi Gary,

were the two little hollow rollers that fit on the selector there when you dismantled the engine? I think that their absence would make the gear change stiff.

Regards

D7/14 hybrid (4 speed with D7 crank etc.) on the road, D10 Bushman awaiting rebuilding.

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b175er
saltfleetby
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November 25, 2018 - 6:11 pm
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That's a good question Stubaker; but it probably wouldn't account for the noise. Mind you, both of my B175s are noisy in the three lower gears !

two B175s and a CB360

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Bee175
Felixstowe, Suffolk
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November 25, 2018 - 6:13 pm
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Hi Don. 

Not a daft question regarding oil. People have done it before and it will be done again! However, this time that's not the case.

Good point rear 4th gear. A friend had suggested that it might be a direct drive in 4th. So that would indeed point to a problem with the layshaft, layshaft bush or bearing. All bearings were changed but the bush was not. I have to hold my hands up and admit I didn't even check it for wear.

Hi Stubaker.

Both the rollers were in place on strip down and are in place now. They are also relatively new. Nice to see someone else from Felixstowe.

BSA Bantam B175 1971 and BSA C15 1966

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Bee175
Felixstowe, Suffolk
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November 25, 2018 - 6:19 pm
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Hi b175er.

I wonder why yours are noisy in the lower gears? I presume gear changing isn't too difficult on yours? The gear changing on this one isn't so good. I also have a B175 that's quiet and slick in all gears. 

Gary.

BSA Bantam B175 1971 and BSA C15 1966

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b175er
saltfleetby
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November 25, 2018 - 6:49 pm
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I'm not complaining as they've both had quite a bit of use since I've had them and been o.k. One of them has that thing where you often have to press down lightly on the gear lever before you can change up from third to fourth and the other one doesn't; but they both clatter a bit in first, second and third. It's most noticeable in third, of course, as first and second are only used for a few moments. I've left well alone and done rides of up to a hundred and seventy four miles, though, and so far so good.

two B175s and a CB360

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Bee175
Felixstowe, Suffolk
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November 25, 2018 - 6:53 pm
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Good to hear they are both serving you wellthumbs-up

BSA Bantam B175 1971 and BSA C15 1966

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AdrianS
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November 28, 2018 - 9:33 am
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4th gear is a direct drive and if there is any play in the 2 bushes on the output gear to the mainshaft that will give a bit of clearance to relieve anything that is tight.

I think you need to strip the engine again if you are not happy. Leave the crank out and refit the gearbox components leaving various bits out to find what makes it tighten up. Are the new bearings squarely fitted? Are they the correct size - are they nipping up the gearbox shaft play? The changing mechanism appears to be working and shouldn't add anything to the tightness of the gearbox or contributing to noise. Was it working OK before the engine rebuild?

Lots of questions but you only need 1 small problem to cause an issue!

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Bee175
Felixstowe, Suffolk
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November 28, 2018 - 10:36 am
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Hi Adrian and thanks for your reply.

When I said this:

"which makes it hard (almost impossible) to turn the selector plate manually from one gear to the next."

I should have also said that the gearbox was empty at that point. Just the selector mechanism was in place and bolted in. On the other B175 I've rebuilt, I can put a thumb and finger on each side of the plate and rotate it fairly easily from one indent to the next. Not so on this one. I even greased the edge of the plate to try and help. Even with the gear lever on it takes a bit of a push to move it, and it doesn't always reach the next indent. Fitting the rest of the gearbox in doesn't make it any harder to move. So even if there's a problem within the gears and shafts, I think there may be a problem with the selector too.

The gears were a little stiff even before the rebuild, but it was usable and not noisy at all. Sometimes changing down into the lower gears was tricky. Around 500 miles were covered like that before the crank seized.

I didn't check the float on the gear shafts, so that's something I'll do soon. 

I'd thought about the possibility of the bearings not being square, but the left casing does drop on without too much wiggling, indicating that they're not far out. The cases were heated to facilitate fitting the bearings making it a lot easier to tap them in. The bearings came from Rex, so I would say they are the correct ones given his experience.

You said "I think you need to strip the engine again if you are not happy."

I think "extremely unhappy" would be the correct phrase in this case. The noise in the lower gears is bad enough that only disaster lies ahead 😀

Thanks again for your comments, all taken on board.

Gary.

BSA Bantam B175 1971 and BSA C15 1966

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