Topic: Countershaft Bearing Seating and Gear Selector Drum Installation

[The Lone Builder]

So, having solved one problem, I have another query. Well 2 actually.

• Is the right hand countershaft bearing, shown in the pic, seated correctly? It looks as if it is sitting very proud. It is seated against the case. The bearing is SKF 6304.
• Does the gear selector drum have to be oriented in a particular way (I know it only fits in one way length wise) when installing it? I.e. does the neutral switch dimple have to be at the bottom, or somewhere else? Or do the selector grooves have to be set at a certain position? I've looked at a few other posts on this, but none quite answers the question exactly.

Cheers, Sean

[Bodi]

Well, there's no pic.
As long as the selector forks are in the right order and orientation, you can only see the correct groove looking down the pin hole... so it will only assemble one way. Position doesn't matter, get the forks in the gear slots and put the pins in.Then cycle through the gears - you will need to turn the shafts to get the dogs to engage - without the detent assembly you have to guess a bit on when the drum is in the right spot for each gear but they should all engage. If it shifts OK to all gears then leave it in neutral just so both shafts turn freely for case reassembly.

[The Lone Builder]

Oops, sorry about the pic. Here it is.

I have the shafts in now. Your comment re the position of the drum is spot on. I put in the neutral switch and the drum shifted to the left, relative to where I had it. Now, although a little notchiness remains, I can cycle through the gears just turning the end of the drum; previously they were sticking at nearly every change.

Joy!    I guess that means the bearing is OK too. Even more joy 

Further assembly tomorrow

[PeWe]

I have had same thoughts about that bearing since it is not completely covered by the case. I saw however, that the bearing was seated as it can. I heated the case and let the bearing fall in.

[The Lone Builder]

Yes, it goes in very easily.

I put the bearing in the freezer as well as heating the case. As soon as the bit of oil I put on the on the bearing melted again, on contact with the hot case, it slipped right in, with barely a belt of the hammer.

Curious tho, why it overhangs so much.

[PeWe]

I used bearing NTN 6204 from Yamiya750. SKF must be 6204, right?

[The Lone Builder]

Sorry, my mistake. 

6204 indeed.

[The Lone Builder]

Another part of my frustrating day revolved around the countershaft bearing - the internal one.

Previously I queried whether to was seated properly as it didn't seem to be sitting fully into the casing. However others noted the same thing, so I went on with teh job.

Well after cleaning everything up following my gear shifting issues (another post), I struggled to get the bearing in at all.

Finally - with hot and cold - I got it in and tried to fit the countershaft. No way! I battled for quite a while until I finally realised the problem was the bearing. It was sitting even more proud than previously. Gentle persuasion failed to move it in any further.

So I thought maybe there was a small burr on the housing. A gentle wipe with some 400 grit revealed the two lines shown in the attached pic. These were not palpable, but were clearly visible. Everything was baby's bum smooth, so why wouldn't it go in.

I retrieved the old bearing and whaddya know? It slipped in with no bother; no oil, grease, heating, cooling or hammering!

The old bearing sits 3mm proud of the housing while the new one sits 6mm out. And looking behind the old one, it is nearly all the way in to the back - poorly shown in pic no 2.

I mic'd both bearings - new one an SKF and the old NTN - and while there was no measurable difference in OD, there was a difference. The new bearing just wouldn't fit into the gap left by the old.

Two reputable makes of bearing, with just enough difference in manufacturing tolerance to allow one to fit and the other not. Has anyone come across this situation before?

Sean

[disco]

I mic'd both bearings - new one an SKF and the old NTN - and while there was no measurable difference in OD, there was a difference.

If you used a micrometer to measure the two bearing OD's you should be able to determine a value for the difference? When I replaced that bearing it was a snug fit. Not loose, but by no means really tight. You can check from the backside, if the bearing has 'bottomed out'. You can also tell as you drive it in. When it 'bottoms out' the sound changes.

It may be possible to drive the new bearing in using the old bearing? Take care that bearing doesn't become 'cocked' in the bore. If that happens you'll never get it all the way in.

[The Lone Builder]

Just to finish the story.

I put the bearing in the freezer overnight and smoothed the housing with a bit of wet and dry.

Dipped it in oil and it slipped in with a little persuasion. It now sits nicely and "looks" right from both sides.

The gears now switch smoothly up and down.