Primary Gear Mishap

[shunt]

Had my first post 'Running In' ride of my 96 Dirt Squirt (Super Rat Barrel & Head, 24mm Carby, SH Exhaust and Ports & Transfer Ports cleaned up & matched) fantastic took me back to the 70s. Now for confession time, yes I have read about the potential damage clutch-less gear changes can bring about, and yes my over exuberance and a great wash of adrenalin over rode that fear of that potential damage. Now for the carnage of this 30 minutes of over exuberance and adrenalin:
Primary Gear (now missing 4 teeth [rear wheel had had new Rubber Dampers fitted in rebuild]) options: as the current Primary Gear is already a Spur/Straight Teeth Gear (from what I can see with the Parts Schematic it is normally helical), is the 98 Super Rat Cushioned Primary Gear/Clutch Pinion an option or alternatively is the 93B Primary/Clutch Pinion Gear the no brainer, or is there a more effective option (and yes I do plan to be more disciplined in relation to the use of the clutch when changing gears).
Dislodged Sprocket Shaft Bush: I have replaced all shims, bearings and bushes (casings were heated pre fitting of bushes) in the gearbox as part of the mechanical refurb process, is there any reason why this bearing would have dislodged as per photo, is this the result of my over exuberance, or an assembly error.
The above aside, Ed I now understand what you mean about the Squirt being such a fun bike to ride, especially in one wheel tight 2nd and 3rd gear trails!

Your input is appreciated guys.
Shunt.

[hodakamax]

Dirt Squirts were after my time but the countershaft bushing is the same. The bushing installs from inside the cases and bottoms out on a decreased diameter ridge that prevents the bushing from coming out as yours did. If the bore is too loose it can be machined to accept a needle bearing 931004. The machining if done correctly leaves a new ridge to prevent the bearing from coming out. If the bushing is reasonably tight in the bore it can be reinstalled and you can carefully decrease the case outside diameter with a few punch marks.

As for the gear failure, the cause may have been the bushing coming out. It's hard to tell what happened first for now. You might have to turn the bushing around with the taper in. that way the case diameter will not have to be reduced as much.

Thats my input, I hope this helps.

Max

[shunt]

The Needle Roller Bearing sounds like an option Max, I have a lathe so the machining out of the original bore for a Needle Roller to be fitted along with forming a 'keeper' Shoulder would be something that could be done on a Face Plate. From what I could see on my initial quick look last night, was that the bush had not come out far enough to have come in contact with the Primary Gear, my current line of thought at present is that they are two separate issues, but I am very open to input on both whether they be two separate issues or one of the same.

Shunt

[Bullfrog]

Shunt,

I am virtually positive that clutchless shifting had NOTHING to do with the tooth breakage on your primary gear. The damage is far, far more likely to be the result of the wandering parts in your engine (and the wandering parts were not persuaded to wander by clutchless shifting either). When done properly, clutchless shifting is a low stress way of handling shifting gears.

Note that the cushioned primary gears have cushions to reduce shock loads to the gears inside the transmission - they are not there for the protection of the primary gear teeth (though they do reduce shock loads there too).

Ed

[Zyx]

It's hard to tell detail in the photos but the tooth damage doesn't look like stress fracture. It looks like foreign object impact. Is there anything in the cases now that the cover is off that is laying loose that shouldn't be? You should be able to find the tooth fragments. Look for anything in addition to those fragments. Doesn't take much.

[dcooke007]

The second picture shows gouge marks on the outside edge of the primary gear. Could be caused by foreign object. Might be a good idea to split the cases and look for a broken part. You could install the stronger super rat primary and clutch gear but would have to adjust your final gearing.

Danny

[Zyx]

I saw those shadows and didn't know what to make of them. Is there anything mounted inside the case that uses a key? I know they can go astray easily and would be a time bomb if left rattling around in there.

[shunt]

Thanks for the input guys.
Visually the oil from the drain plug (Crankcases) looked to be clean, oil from the Clutch Cover contained what appeared to be gear fragments, plan is to run the oil through a strainer this coming weekend.
Danny re marks on the outside edge of the Primary Gear, went out to the shed tonight wiped the oil off the outside surface of the Gear and had a closer look, there does not appear to be any marks on the outside face.
Arizona Shorty & Ed looking (tonight) into the face of the damaged teeth, as per your consensuses this appears to be damage from a crush load rather than a stress load.
In summary looks like the Crankcases are going to need to be split .

Dislodged Sprocket Shaft Bush: is it a common occurrence for this Bush to displace as per picture, when I reassembled the Crankcases originally (with new Sprocket Shaft Bush), the Sprocket Shaft was tight to turn so I did use a Hand Reamer to cut more clearance in the Bush, what is the normal clearance between the Bush and the Shaft or how neat should the Shaft to Bush fit be?
Primary Gear & Pinion Gear options: is the 98 Super Rat Cushioned Primary Gear/Clutch Pinion an option (is it a straight retro fit) or alternatively is the 93B Primary/Clutch Pinion Gear the easiest option?

Shunt

[hodakamax]

Back to the bushing. Before you split the cases I would get the clutch off and carefully inspect the situation. I doubt any pieces have migrated to the inner crankcase or came from there. The bushing can probably be tapped back in place and secured with a number of small punch marks in the perimeter of the hole. Keep the indentations close to the bearing as possible so you will have enough material for a new shoulder should you decide to install a needle bearing. As for the clearance shaft to bearing, It should just turn freely with no resistance.

Maxie

[Zyx]

To answer your question, I would think it is not common for the countershaft bushing to walk out as it did. Apparently you don't have a retaining shoulder, or at least not anymore. Force has to be applied for the bushing to move it sideways. If it were lateral contact from the countershaft I would think it would not move as far as it did. If it is sticking out as far as it appears, the back side of that bushing has to be deeply pocketed in the side case. So I think it has to be interference between shaft and bushing. Take it apart and you will probably see galling on the bushing, and if it slid out that far, it very likely spun the bushing, so the case is going to have to be remediated before a new bushing will even stay in place. Staking the old one likely will not work. Your best option at this point would be upgrade to bearings but this requires a re machine of the bearing/bushing pocket and that depends on whether the pocket is severely damaged. If all else fails, a new case half will work.

[shunt]

The condition of the Sprocket Shaft Bush 'pocket' is going to be a bit of a wild card, at present I see two options if the pocket is scored (which is more than likely), is to machine it to clean up (& machine in a 'keeper' shoulder) on the Lathe and machine up a Bush to fit with a corresponding shoulder or alternatively I have a set of crankcases I got as part of a basket case motor that maybe an option (depending on condition).
I agree with you Max in relation to the low level of chance of something migrating from the Crankcase area of the gearbox, to the Clutch cover area and more than likely whatever has done the damage will have originated from the Clutch cover side of the gearbox, plan is to remove the clutch and thoroughly inspect pre dis-assembly of the gearbox.
Clearance (or lack of) between the Sprocket Shaft and the Bush seems to be the culprit for the Bush dislodging, the Sprocket Shaft was tight to turn during pre assembly, I did ream the Bush out but I am now wondering whether the clearance I gave it, was substantial enough taking into account the running temp and the corresponding expansion of the Sprocket Shaft .

[hodakamax]

AZ may be right. I doubt or at least I've not seen, the bushing spin and damage the case, but it could have. A careful inspection is in order. The hole in the case is about 21mm while the needle bearing is 25mm. You will have plenty of material should you choose to replace it with the needle bearing.

Max

[shunt]

If the Bush has spun, 4mm should clean up any damage and also leave enough meat to machine a 'keeper' shoulder in.

[hodakamax]

Shunt, on my 94A that I purchased I discovered that the countershaft had eaten completely through the bushing and into the case about 3mm. We saved the day by machining the case and installing the needle bearing. The hole was oval and we had quite a time figuring out where the center was. My clever machinist did an excellent job, but I did have to replace the countershaft. I suspect the cause in my case was lack of lubricant. Anyway, that's my story on this type of repair.

Maxie

[Zyx]

If you have the equipment and experience to make a bushing from scratch, you should have no problem repairing whatever you find. What I have never seen is a spec for the bushing to shaft clearance. For that matter, I don't think I have seen specs for the bushing to case clearance, but I would expect it to be a firm press fit requiring a bench press to install.

[shunt]

Thanks for the encouragement guys I completed an apprenticeship and worked as a Fitter & Turner (Mill Wright & Machinist) in my teens to late twenties and have always dabbled over the years along with the occasional turning project on my lathe. Re interference and clearance specs I am sure I can find this on the Web with a bit of surfing, will update you once I have had an opportunity over the weekend to run the gearbox oil thru a strainer and to also remove the Primary Gear and Clutch as the first level of the identification of the cause.