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Got a '67 TR6C that slips out of 3rd gear when not under load. Other gears seem fine. I started disassembling the gearbox tonight and was wondering what I should be looking for. What are most likely candidates for the cause? Worn cam plate? Worn dogs? If the latter, which gears do i need to be paying particular attention to? Thanks for any and all advice.


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Also, look at the edges of the holes that the dogs engage.


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Look on the mainshaft,at the 2 gears closest to you when you take off the inner gearbox cover.
Even using a gasket on that cover will reduce the engagement between these 2 gears.
Before you remove the cover,select 3rd gear.You might be able to feel how much more engagement is possible,if you slide the mainshaft in and out against the mainshaft 3rd gear (after you remove the kick-start pinion).

Check everything else after you remove the cover:like camplate, shift forks.

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Also camplate plunger spring and shift pawl springs.


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Originally Posted by Pete R
Look on the mainshaft,at the 2 gears closest to you when you take off the inner gearbox cover.
Even using a gasket on that cover will reduce the engagement between these 2 gears.
Before you remove the cover,select 3rd gear.You might be able to feel how much more engagement is possible,if you slide the mainshaft in and out against the mainshaft 3rd gear (after you remove the kick-start pinion).

Check everything else after you remove the cover:like camplate, shift forks.


Does this mean that I should not be using a gasket between inner cover and case? I have been using a gasket there but I can see how it would increase play between the gears. Can the mainshaft be shimmed to reduce this play? I generally shim Norton gearboxes using a dial indicator but have never seen any instructions in shimming Triumph gearboxes.


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Gearbox gaskets weren't standard equipment.
Before you fit a shim,check that the bearing is securely located by the circlip.
You could put a shim on the mainshaft,then fit the cover and bearing.Just make sure there is still some clearance when 3rd gear is engaged.

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Got gearbox apart but nothing obvious jumps out at me. I don't have that much experience with Triumph gearboxes so maybe someone here can spot the problem

Some wear on both selector forks. Can feel the wear ridges with a fingernail:

[Linked Image]

[Linked Image]

[Linked Image]

Camplate appears pretty good except one small divot out of it. This is where selector fork sits when 3rd gear is selected so could be candidate. However, amount of play introduced by this little indent is pretty minimal:

[Linked Image]

Dogs between gears show some wear but I am not sure if this wear is signficant:

[Linked Image]

[Linked Image]

[Linked Image]

So I am still not sure what might be causing my problem. Any thoughts? Thanks.

Tobin



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The wear doesn't look severe enough to cause much loss of engagement on 3rd gear.In any case,it can be counter-acted with a shim on the mainshaft.
A shim against the mainshaft bearing will affect primary chain alignment,so you'd probably need a shim on the engine sprocket as well.

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Originally Posted by Pete R
The wear doesn't look severe enough to cause much loss of engagement on 3rd gear.In any case,it can be counter-acted with a shim on the mainshaft.
A shim against the mainshaft bearing will affect primary chain alignment,so you'd probably need a shim on the engine sprocket as well.


Thanks Pete. I will try to find a shim.


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Originally Posted by Pete R
The wear doesn't look severe enough to cause much loss of engagement on 3rd gear.In any case,it can be counter-acted with a shim on the mainshaft.
A shim against the mainshaft bearing will affect primary chain alignment,so you'd probably need a shim on the engine sprocket as well.


What size shim? What is the limit I can go and still have the box work correctly? Thanks.


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Put it in 3rd gear and bolt the cover on with no gasket.See how much you can move the mainshaft in and out.Allow for the gasket thickness,and leave some clearance when the gasket is fitted.
If it had exactly no clearance without the gasket,it's probably OK.

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Did a short road test tonight and gearbox appears to work just great! 3rd gear seems to stay engaged, even upon deceleration. I installed a homemade 0.065" shim behind the mainshaft low gear next to the bearing shifting the mainshaft towards the primary. I think I must have hit it just about right because I had a fair bit of endplay prior to shimming and now only a barely detectable amount of endplay with the shim installed. I also did not use a gasket on the inner cover but used Blue Hylomar instead. I haven't yet shimmed the engine sprocket to keep the primary in line but will do that when I completely disassemble for cosmetic restoration.

Thanks to everyone for all the great advice!

Tobin

Last edited by Tobin Peever; 09/30/11 3:07 am.

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Originally Posted by Tobin Peever
I installed a homemade 0.065" shim..... I haven't yet shimmed the engine sprocket to keep the primary in line but will do that when I completely disassemble for cosmetic restoration.


On a triplex-chain primary, this alignment could be disastrous....are the duplex chains that forgiving? Just curious....

Steve


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Originally Posted by JubeePrince
Originally Posted by Tobin Peever
I installed a homemade 0.065" shim..... I haven't yet shimmed the engine sprocket to keep the primary in line but will do that when I completely disassemble for cosmetic restoration.


On a triplex-chain primary, this alignment could be disastrous....are the duplex chains that forgiving? Just curious....

Steve


Good question!! Don't really know. My chain is pretty worn out and needs replacement so that presumably would give it a fair bit of flexibility side to side as well as in length. Do you really think 0.065" would make much of a difference even on a triplex chain? I could see that it might cause more rapid wear but would this be enough to derail it? Seems to me that the alignment procedures we use on the primaries of these old bikes aren't very precise and I am guessing the majority of old Brit bikes are running primaries that are out of line by at least this much. I don't even know if my primary chain was perfectly lined up before I put in the shim. I remember aligning my Commando primary with a ruler which didn't seem to be a very exact science to me! How does one even measure it precisely?


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Quote
Do you really think 0.065" would make much of a difference even on a triplex chain? I could see that it might cause more rapid wear but would this be enough to derail it?.


At the center to center distances of a Triumph engine, Triplex will not tolerate more than .010" miss alignment. At .065" it would be trying climb a tooth and looking to escape the primary case with each revolution.

The Duplex will tolerate a bit more miss alignment, but .065" is "pushing the envelope." That's 1/16 of an inch smirk

Given a precision straight edge, alignment under .010" is routine.

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Originally Posted by John Healy
Quote
Do you really think 0.065" would make much of a difference even on a triplex chain? I could see that it might cause more rapid wear but would this be enough to derail it?.


At the center to center distances of a Triumph engine, Triplex will not tolerate more than .010" miss alignment. At .065" it would be trying climb a tooth and looking to escape the primary case with each revolution.

The Duplex will tolerate a bit more miss alignment, but .065" is "pushing the envelope." That's 1/16 of an inch smirk

Given a precision straight edge, alignment under .010" is routine.


Thanks John. I will give it a go. So is the drill to place a straightedge along the face of the drive sprocket and eyeball the alignment with the clutch basket? I think I remember doing that on my Commando. Is there a more precise way to do it with a dial indicator or similar?


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Originally Posted by Tobin Peever
How does one even measure it precisely?


Tobin,

Get yourself a good (known) straightedge to span the distance between the two sprockets. Remove the chain and bolt up the clutch and engine sprocket. Lay the edge along the outer run of the teeth on the clutch basket and measure the gap/distance between the straight edge and the outer run of the teeth on the engine sprocket.....

Shims are made for the crankshaft behind the engine sprocket, so measure from the clutch to the engine sprocket.

Steve

Last edited by JubeePrince; 09/30/11 4:54 pm. Reason: shims are made...

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