XJ750 Seca - pops out of first gear

Hi everyone,

New to the forum.

I acquired an XJ750 barn find. Got it running and have done a cafe-style build on it.

One problem, it wont stay in first gear.

Engine idling, clutch in, select first (seems normal clunk), then start to let the clutch out and the gear pops out immediately into neutral.

The rest of the gears are fine and shift great under all conditions.

I have read a lot about the 2nd gear dogs rounding off but not finding much information about first gear.

Any suggestions?

Thanks in advance.

 

Check the selector claw mechanism behind the gear shift cover for wear first.

 

Thank you. I will have a good look. I'm fairly certain it's the gear dogs. I'm just looking for anything to stop me from splitting the cases

 

If you do split them change the alternator/starter clutch chain guide and check the starter clutch. When the guide breaks up plastic parts affect gear selection.

https://www.xjcd.org/emergency_guidectomy

 

That is very likely the problem he has now. First gear dogs aren't likely to be rounded off, unless someone who didn't know how to downshift was riding the machine for several years. In that case it would still be more likely that the second gear dogs were worn as well.

 

Thank you gents. I will be looking at this asap.

 

Just an update. Opened up the side cover and could not find anything out of the ordinary.

Shifted through the gears fine. No black pieces of the chain guide that I could find, but I agree with the previous posters that there may be something stuck deeper down.

Ordered a second hand transmission from Germany and a new starter clutch and primary chain guide from the US.

Time to pull the motor out!

Any tips for this or a guide anywhere. I have a manual: just after pointers from people that have done it before.

Thanks!

 

Here is a good thread on it.
https://www.xjbikes.com/forums/threads/xj750-engine-removal-and-split-pictures.38545/

 

First gear dogs are very shiny and rounded, unfortunately.

Primary chain - incredibly slack. Has been wearing on the oil nozzle. I am assuming it has stretched?

Will be replacing both. Also, I will give the cylinders a quick hone with a new set of rings.

Is anything else worth doing while I am in there?

Valve stem seals and lap valves? Timing chain guides look good.

 

Check the starter clutch hub for signs of cracking, if ok change the plungers and springs. Change the primary chain guide, heat the guide bolts before removal to prevent them shearing off. My chain was the same. The guide eventually breaks up.

 

Oh right, so the primary chain is probably slack due to the guide being worn down? Would you recommend replacing the chain? They are quite expensive....

Thanks for the great advice. Very much appreciated.

 

I have not seen the guide worn down, they break up, but if your guide is in one piece I would definately replace the chain especially due to the fact the oil spray nozzle has been damaged by the chain. The chain is worn. The nozzle is usually damaged in these engines because the guide has broken up.

 

Brilliant. Thank you very much. Good to hear that I'm on the right track!

 

I had a similar problem with my 81 xj750RH seca. It'll shift into 1st and back into neutral but when I try to go into second the gears clatter
and will not engage. side cover removed, no broken spring or debris, no debris in the oil, looking into the hole over the shifter hub, nothing in there either.
I hope this can be fixed without splitting the case. I have another engine in my shed 5G2-109778 is this also a 750 seca engine ? Maybe I can swap.