XJ650 Seca Seized Engine Help

It is much easier (imho) to have the pistons on the connecting rods before lowering the cylinders onto the pistons. Getting the pison clips in correctly is quite difficult, and I can't see myself being able to do that with the cylinders blocking part of the access to them. You'll need to make a set of wooden wedges to help rest the cylinders on as you slip the rings in.

 

Thanks guys. I found an online FSM but would still be good to have an offline copy.

@rocs82650 - I have an original (still in its package) Yamaha head gasket. Hopefully that will suffice.

@k-moe - Good advice. I read the other way of doing it in this forum somewhere but I see your point with the clips, however what do you mean by "slip the rings in"? Do you mean the clips? Do the wedges simply stop the pistons from moving as you muck around with them?

 

@rocs82650 - I have an original (still in its package) Yamaha head gasket. Hopefully that will suffice.
Good deal.

@k-moe - Good advice. I read the other way of doing it in this forum somewhere but I see your point with the clips, however what do you mean by "slip the rings in"? Do you mean the clips? Do the wedges simply stop the pistons from moving as you muck around with them?[/QUOTE]
The bottom of the jugs are tapered to receive the piston and rings.

Gary H.

 

That ^^he ^^ said.

By slip the rings in, I mean the slipping the piston rings into the cylinders. The base of the cyliners ar chamfered to assist with installing the cylinders with the pistons on the connecing rods (which is the usual manner). The wedges are used for the cylinders to rest on as you lower them onto the pistons so that you don't accidentally break a ring or ding a piston. What's even beter is to have a helper lower the cylinders as you put the pistons into place in the bores. In both cases you'lll want to have one pair of pistons further up on their sroke than the other pair so you only have to deal with two sets of pistons at any time.

 

Well it's done. Wasn't as hard as I thought and yes, the chamfered edges of the cylinders made it real easy. Double checked TDC with my bicycle wheel truing stand even!

 

Yesterday was a disappointing day. On the one hand the rebuilt XJ started on the second go and apart from the obvious need for some carb tuning, it ran ok with little to no smoke (other than the usual new build burn off). No oil leaks anywhere which I was pleased about.

After giving it a bit of time to warm up, I noticed some blue smoke from the exhaust and rough running. Cylinder 3 wasn't firing (cold exhaust pipe) so I checked its ignition lead and I think I got it going because the exhaust got hot from then on. However after some stop/starts I noticed the blue smoke creeps in after a few mins of running. It's not there initially and we also saw smoke coming from the join in the bottom of the exhaust, almost like there's oil on the inside.

So I did a compression test and cylinder 3 is well down on the others. Not sure about the accuracy of the compression gauge but I get 120 on 1,2,4 and 90 on 3.

So I'm a little upset at the moment and seek your guidance. I've spent a lot of time rebuilding and I'm tempted to leave it here for a bit. Please help me focus so that when I can get the time to return to the bike (in the middle of moving house!!) I can be methodical. Sorry to ramble but I'm at that point we all get to with a project.

In summary:
- Head has new seals and lapped valves - could a seal have popped off?
- Valve gaps are within spec or damned close - I will revisit this when I have it running though.
- Cylinders honed and rings in spec and orientation - maybe I missed something here?
- New gaskets and an OEM head gasket - would a failed head gasket leak elsewhere as well?
- Carbs have been to church. Twice actually! But she is running rich - spark plugs came out dry but dark.

Thanks yet again guys. Love this forum.

 

You have to break the new rings in. They aren't going to seal very well for a few hundered miles.
Vary your engine speed; no constant-speed runs of more than a few minutes until the rings bed in.
It's possible that the oil control ring on #3 isn't doing it's job correctly (collapsed, stuck, installed upside down). But give it a while before you decide to take it apart to check.

In the mean time tend to that ignition wire/cap issue. If you can wiggle it to make it work, the road can wiggle it to make it not work.

Also go back and retorque the head nuts after another heat cycle or two. Undo the nuts, clean and oil the threads, then bring back up to torque per the service manual procedure.

 

While it's POSSIBLE that a seal popped off, it's unlikely.

Valve clearance - in-spec is in-spec; damned close isn't.

BUT- that won't be the cause.

I'm gonna side with k-Moe on this until we know more...... rings issue of some sort, or just not bedded in yet

 

Thanks gents. Gave it another go yesterday and it seems better. I'm not able to run it down the road for a test ride as it looks like the clutch isn't engaging (disengaging??). Will have to look at that.

I found a couple of simple things - the choke cable had slipped and I had a degree of choke the whole time. I also backed the mixture screws off half a turn but will re-visit this now I know about the choke. I didn't detect the blue smoke from the exhaust this run but there is still something burning off the bottom of the exhaust. Again, I'll keep an eye on this. Oil level was a concern so I dumped the (relatively fresh) oil and topped up to spec.

So now on to the next fix : clutch!

Random question : I have two exhaust sets, a 4-1 and a 4-2 (Jama). The 4-2 is really nice looking and I want to use it but even with new crush washers, it's loose in the exhaust outlets so I'm wondering if I'm missing another collar or spacer? Photo attached. What is really strange is that the 4-1 doesn't fit with crush washers. It has sloped/curved ends welded to the headers and fits perfectly when I tighten down the alloy collars.

 

Update : First ride!!!! Took her down the street and the damned bike it rideable. It's been a long time to get to this point so I'm pretty happy.

Clutch was fine - when I opened it up it all looked new in there but the push bearing was missing! Put one in and adjusted everything and it works better now.

During the week I completely stripped, tested and replaced parts on all the coils and leads. Found numerous small issues and tested again after resolving them.

The only problem with the run up the street was a misfire until 3000rpm (after that it flew!) and trouble getting the revs to come back down to idle. I had it idling ok at rest but out on the street it seemed to hit about 2-3k rpm and then stay up there. Any suggestions on where to look next?

 

Have the carbs been synched yet?

 

Good point - no. Waiting for my sync tool to arrive. See this thread : http://xjbikes.com/forums/threads/digital-manometer.111789/

Anything I should play with until then? What are the symptoms of unbalanced carbs?

 

No. If you have not checked your valve shim clearances, now is the time to do so!

The symptoms you are describing.

 

Some aftermarket pipes use a pair of collars that fit around the pipe to hold the head pipe in place. The aftermarket headers you have seen to have a very small lip, unlike oem ones.

 

Tried to get the bike to run long enough to get the synch tool connected and working. These carbs were bench synched and the bike runs reasonably well when cold but once warm I can't rev it past idle. It just stumbles and stalls when I turn the throttle. That feels like a lean burn to me but I'm no expert with 4 carbs. I also can't seem to get the idle screw to make much difference to to the idle speed - winding it in and out makes little difference.

Any tips on what to do next? Maybe I've stuffed up the mixture screws and should go back to basics.

 

I think this may be a good theory..!

 

Thanks Chacal. I'll reset and try again. 1980 4K1 engine Hitachi carbs, course thread mixture screws from what I recall, so that's 1.5 turns yeah? I'll pull one out and double check.

 

Yes, you're correct

 

They were at 1.0 turns so I have reset them to 1.5. Now I recall turning them in half a turn when I thought the plugs were coming out a little too rich. Should have run the bike a bit longer I guess.

Will fire her up in the next few days and see if that helps, then on to the digital manometer for a synch.

 

Exact same behaviour. Not sure where to go next with this.

Is there a "reset" position for the idle speed screw? Not that it's making any difference to idle at the moment but it would be nice to know that I've set everything to "default".