750 SF re-installing gear change mechanism

[TeddyG]

Greetings,
I'm re-installing the gear shift mechanism of my SF750 and have questions about the alignment of the marks on the selector drum and the internal gear, and unsure if what I'm seeing is correct w/ the motor in neutral- please see the "Current setup" pic. When I removed the housing (shown in the "Previous" pic), I didn't note what gear it was in, and looking at Pirhana's notes, he stated to put it in neutral before removing everything- so my mistake.

As I shift thru the gears, the selector drum and spring loaded "hammer" don't seem to be engaging all the time, and I've noticed that the lock nut on the eccentric screw adjuster is loose, so what what's the result of rotating the adjuster up or down?

Thank you

 

[Ernesto]

Set the gear (with pliers or a screwdriver), so that the mark is in horizonztal position (neutral pos.)
And insert the drum, so that the marks match (horizontal, too)
Use the eccentric screw to adjust, so that the pin on the drum is in the middle of both "hooks".
Of course tighten the locknut then.

 

[Vince]

The excentric is best done on 4th gear as that shows the C best being equal gap top and bottom. Any binding as you tighten the case can result in the loss of selecting 1st or 5th gear. There are dozens of posts here about finagaling gear selection. Do some searching. It's hit and miss, I once spent 6 months chasing this before all the tricks got posted.

 

[TeddyG]

Thanks guys- I've looked at a few previous posts and see that this can be a bit fiddly- I didn't want to take it apart but had to since I'm installing new pistons and had the valves serviced, so I had to tilt the motor and remove the chain. Also wanted to be sure all was well inside there since the bike PO was a hack and noticed that the eccentric lock nut was loose. I've had the bike since last Nov and haven't ridden it much, but felt the gear lever and selection was a bit sloppy, and possibly from that loose adjuster nut.

Right now, with the engine in neutral, the mark on the internal gear is at about 5 o'clock (see my "Current" pic posted above), and forcing that gear with pliers or screwdriver to be horizontal sounds a bit drastic- any other suggestions?. And the marks on the selector drum is also at about 5 o'clock.

Thanks again

 

[Tippie]

You need to have the gear coming out of the gearbox at 3 o clock for the motor to be in neutral. At the position in your picture your motor must be in a false neutral. It is fine to carefully turn this gear with grippers as you rotate the gear shafts a bit back and forth to allow the large selector dogs to engage and disengage. You are only working against the locater spring mechanism, and it should move smoothly. Then fit the outer cover and the matching gear with the mark aligned with the inner gear, facing straight back at 9 o clock. Remember to ensure a bit of backlash between these gears when the outer cover is tightened.

 

[TeddyG]

Thank you very much Tippie for your clear and concise info- I also looked at the Green Book which was somewhat helpful.
I rotated the inner gear so it's at 3 o'clock, and inserted the drum housing with the marks at 9 o'clock, so both are aligned to each other.
But now it's only staying in neutral and won't go into first, but it will go into second, so I'm guessing the eccentric needs some adjustment.
I've read some more previous posts and this seems to be an issue w these bikes

 

[Tippie]

Take Vince´s advice and do it in a higher gear. As you click up and down as you rock the gearbox shafts you can look carefully and find the middle position. Make sure the cam part of the adjuster is facing forward to allow the most movement, if it is towards the rear the movement is less.

 

[piranha-bro2]

Teddy, unless you can easily rotate the mainshaft fwd and back a decent amount it's very difficult to get it into all gears (eg you prob with 1st) because internally, the engagement dogs on the gears are butting up against each other and not slotting into place. It's much easier with the engine and chain in place so you can rock the rear wheel back and forth while selecting gears (I put the gear lever onto the splined shaft without the cover on).

Also make sure the large spring can't get fouled between the adjuster cam and fork (this can even happen when the cover is on).

The trick with fitting the main selector cover is just tightening by hand and then introduce the drum with the gear. Once it's in place tap the large cover fwd or back until you can feel backlash between the gears (ie the internal one with the alignment mark and the half size one on the drum) - tap to reduce the gap - the drum should slide in freely but have minimal play (so you'll get full up-down movement transferring to the internal drum). Check again after fully tightening the internal cover.

 

[TeddyG]

Thanks again Tippie and Pirhana, and I will heed your advice and attempt this again later today weather permitting in my unheated garage.

I had a feeling that the chain and rear wheel need to be on- both are removed since the motor has been tilted to remove the cylinder and head for rebore/new pistons/valve work.