XJ650 Seca Seized Engine Help

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.