XJ650 Seca Seized Engine Help

Wow pricy parts ! So what kind of $$ does a nice 650,750 seca sell for?

 

Ouch! I'm guessing there's no after-market choices.

...Chacal's pricing is far better. That's about $220 AU plus shipping. Much more reasonable!

 

Long time no post - I had to take my carbies to church and fix a few issues with them. In short, I bought another "donor" bike and got a better set of carbies so took them to church also! I think I'm over the whole rebuild thing.

Speaking of rebuilds, I got the bike started. Electrics are all good and the fuel system is obviously great now. As predicted though, there was a regular yet light stream of oil smoke from the exhaust so I guess the rings are shot. Next step is to try the engine from the donor bike and see how I get on. It's in pieces though, so another project.

Is it viable to replace just the top end on these engines? i.e. head and cylinder components of the engine.

 

Or it could be valve stem guides are worn or dried out.... have you done a compression test or leak-down test?

I'd confirm those before testing an engine apart. It would at least give you an idea of which direction you're heading.

If you end up pulling the cyls, then you can check them, the pistons/rings, do the head while it's off, etc.... whole top-end job!

 

I agree , do the compression test , and how bad is the smoking really , when the engine is warmed to operating temps and on the road ?
If it were only using a litre of oil every 2000 miles or so , it's not urgent imho

 

A litre down on an engine that only holds 2.5? Seems pretty bad to me, especially if it's air cooled!

 

I say ride it a 100 miles and re do the compression test and check the oil smoke. If it's not better that all you did was get to ride it a bit before you do the top end rebuild.

 

I meant burning that amount !!!
Not running it continually that way
If you didn't understand that , then What else Can I Say????

 

The Suzuki 650 that competed with this model used that much oil when nee

 

Thanks for the opinions guys. Smoke wasn't crazy bad but there was a significant oil leak down the front of the engine while running, so I think I'll replace the stem seals and do all the top end gaskets before doing a proper compression test. My guess is that the head gasket is leaking like a sieve.

 

I did understand that. That's why I was concerned. In 2000 miles, you've lost 40% of your oil. If you don't understand that something is amiss in the engine, what else can I say????

 

Look at the valve cover gasket first. The vast majority of leaky head gaskets turn out to be valve cover gaskets.
It could be a head gasket problem, but why not take care of the easy things first?

 

I'm sure the oil is checkef frequently, it's not like a brand new car.
If it was a 35 year old car one was driving , oil would be checked at least with each tank of gas

 

Yes, will do, but I could see it flowing out below the jugs. Literally flowing. Back when I was getting this thing to turn over, I removed the head and the jugs came away from the lower end. I'll put a gasket kit in to be sure.

So after reading a few threads for rebuilds and your comments, I'm going to look over the two heads I have here and choose the best. Then I'll lap the valves, replace the stem seals, check and set the valve clearances. While that's off, I'm considering pulling out the jugs and checking the cylinder tolerances. Maybe just do a visual of the rings. Am I way off here or is it worth doing? I have another engine (in pieces) that I can cannibalise if I need to as I go, and it has a better running history than this one.

 

if you take it that far apart it would be foolish not to measure the rings. You place them in their corresponding cylinder without the pistons and measure the gap between the ends of the ring. Measure near top of the stroke and bottom, easy. Also measure the piston relative to each cylinder as you're planning, that will tell you if a next size up piston and bore is needed or just a quick cylinder hone and new rings or existing rings go back in. I've lapped valves using my electric drill - there are youtube videos demonstrating this, it's fun.

 

+1. As you know...the rings affect compression.

Gary H.

 

Excellent advice Simmy. I have that second engine so I could do a side by side comparison of all the parts.

 

Specs from the manual will do you better. Comparing one used engine to another used engine won't tell you much.

 

Yes, that's what I meant K-Moe. My eyes aren't good enough to compare visually, nor would that be of much use. I have the Haines manual and all the measuring gear.

 

"Man who wears two watches never knows what time it really is."

 

But with a stereopticon could see the time in 3D.....

 

So, by way of update... Pulling the jugs revealed piston rings stuck fast in their grooves. Not all of them but most and they aren't budging even after days of soaking, so I turned to my spare engine parts. What I discovered was a set of .5mm over-bored cylinders and matching pistons which appeared to be in good condition. Sent them off to the machining shop and they came back honed and with a clean bill of health! Bonus.

I've also stripped the head and everything there looks like it's in great nick too. Before stripping the engine I checked the valve gaps and all were within spec. Will need to re-do that after I lap the valves though I assume? Can't wait for the gasket kit to arrive and start the rebuild.

I almost bought another donor bike the other day but it had a YICS engine and a few other issues. It's funny how many things I've already fixed on mine that I'd forgotten about and would need to do all over again if I had another XJ to do up. Fixed electric harness issues, new fuse box, rebuilt a diode in the headlight, fixed the indicators, new horn and starter buttons, took the carbies to church...

 

Yes!

 

Yes, as Chacal said......

After the valves have been lapped, they will sit ever so slightly deeper in the head. That means the other end of the valve stem will be closer to the cam. That means your clearances will be less. So.....you will have to recheck and adjust the clearances as needed.

Dave

 

If you kept track of the shims start with one size smaller in each one so you can actually get a feeler gauge in there.
Shame your so far away I have a couple of spare XJ 650 engines.

 

Oh come on, it's just the other side of the world in the most isolated capital city in the world!

Thanks for the responses guys. I have all the shims set out in order and I'm tracking it carefully. The donor engine has different ones so I'll check them against the chart and see what I can come up with.

 

Update : Everything has been cleaned up and I'm ready to re-assemble the engine. Rings have been orientated on the pistons and I've inserted them into the cylinders ready for conrod attachment. Surfaces are clean and ready for new gaskets, oh and I stripped, hotwashed and reassembled the head with new seals and freshly lapped valves. I did this same job about 30 years ago on my Datsun 180B SSS so it felt pretty familiar!

For the head re-assembly, I'd really like a step by step to make sure I don't miss anything. I have the Haines manual but is it worth getting the factory one? If so, does anyone kindly have a link? My bike is a 1980 XJ650 4K1 model.

 

When I was putting my engine back together I had both the Haynes and FSM open and would refer to them both. They complement each other pretty well, and if I wasn't quite getting something it was helpful to see it worded a little differently sometimes. That was my first time doing any engine work though, besides a lawnmower engine in high school. It sounds like this isn't your first rodeo, so it might not be necessary for you. One cool thing about the FSM, at least the one for the 750, is a sweet picture it has of the engine in the back of the book, I kind of want to get it framed, ha ha.

 

@Rebem: I know you're on the other side of the planet but I hope you don't have to learn what I did on two rebuilds, THE HARD WAY, and bought oe gaskets and seals from Len or a reputable dealer instead of the less expensive kit(s). You've put a lot time into this project. Re-building a engine then having the/a head gasket blow is not a good feeling. Just saying.

Gary H.

 

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".