1977 XS Top End Project Mikes XS 650 replacement

[motorshag]

So, I decided to go ahead and replace the whole top-end. I don't really know anyone that I trust enough to bore or hone the heads, so I bought the whole replacement kit from Mikes. We took the engine out 3/28/2012 and had fun doing it. Now I am on to figuring out how to get the head off. I need to figure out if the valves are good, and just need to be lapped back in. I really don't know much about anything, so I figured I would start a thread and just update it as I go. I have a book, and have been reading on the forum, I just thought I would pick your brains on a few questions.

The compression was at 120 on the left side. The compression was at 78 on the right side. I then did a second test, in which I put a spoonful of oil in the sparkplug hole, and compression was at about 120 on the left side, and went up to 110 on the right side. Any thoughts on that, regarding head work, or valves?

I've posted some pic's of where I am today. I just plan on bringing the bike back to original best I can. I have been riding it all year, and It is so much fun!

 

[retiredgentleman]

It does not matter what the compression is now that the engine is apart.

Once an engine is opened up for repairs, you read the Yamaha Service Manual, available on line at places such as www.biker.net . You compare your engine parts against the specs that are in the Service Manual. If in spec, then all is good, if out of spec. then machining or replacement is required.

Things like valves, you inspect to see if they are badly pitted, which may mean they need to be replaced. On my bike, my valves looked fine so I just lapped them. You need to use a dial indicator to decide if the valve guides are worn out or not.

Once an engine is apart, you always replace valve seals, gaskets, o-rings, oil seals etc. Also very wise to replace the front cam chain guide and the cam chain itself.

 

[angus67]

why are you rebiulding it? did it run good?

 

[racerdave]

Adding oil made the rings seal better for a higher compression reading. Adding oil won't raise the compression reading if you have head/valve problems.

 

[scabber]

Make shure you have the rings gaped to specs hoos raceing does head work. Check conecting rods for end play and small end wear they should have a copper coating around the inside.

 

[motorshag]

It was running a little slow up hills, and I may have jumped the gun on buying the XS Replacment Kit, but I own it now. I wasn't sure if low compression on the right side would mean a total valve replacement, or if they would need to be just be lapped back in. I havent' oppened the engine yet, but plan to in the next few days.

So Racerdave, you think because the compression went up when oil was added, means that the valves/head should be fine, it's more rings, pistons?

Sorry if these are dumb questions...

Thanks guys!

 

[5twins]

The valves probably need some attention as well. Test them for leaks and you'll probably find some. A hand lapping usually cures them. You will want to replace the valve guide seals, they're 30 years old. Guides are usually OK. Once the spring is off, check that the valve is a slip fit in the guide with no side to side "wiggle".

 

[retiredgentleman]

It was running a little slow up hills, and I may have jumped the gun on buying the XS Replacment Kit, but I own it now. I wasn't sure if low compression on the right side would mean a total valve replacement, or if they would need to be just be lapped back in. I havent' oppened the engine yet, but plan to in the next few days.

So Racerdave, you think because the compression went up when oil was added, means that the valves/head should be fine, it's more rings, pistons?

Sorry if these are dumb questions...

Thanks guys!

Yes, you probably did not need a new replacement kit. Your original engine likely just needs the standard top end re-build. You certainly want to read as many engine repair books as you can in order to bring your knowledge up to a reasonable level.

There's really nothing to be gained by speculating about what may be worn out inside an engine. Once you decide to do the work to open up the engine, open it up, and the engine itself will tell you what needs to be machined or replaced. Of course you need to have the ability to be able to inspect the engine parts. I can't overly stress the importance of reading the Yamaha Service Manual for your year..............that is your guide as to what needs to be done to your engine.

 

[PHeller]

My right side cylinder had low compression, 65 psi or so. Added ATF, got it up to 150. I was bummed. Surely this meant my rings were shot.

Then I waited a few days, ran it, rechecked the compression, adjusted the overly tight valves this time MAKING SURE TO HOLD THROTTLE OPEN and suddenly I had 150psi again.

These old engines are funny like that.

 

[motorshag]

So. I spent most of the weekend taking my time, getting it down to the cylinders, and getting the head off. I have someone that is going to take the head, and check it out for me me and do any necessary work needed. I trust him way more than me to to that right. I have included some pictures, if you see anything weird let me know. It's been fun so far.

 

[5twins]

In your last pic, note the sheet metal oil baffle stuck in the head at the bottom center. That's just a slip friction fit in there. You may want to pull it out and bag it before giving the head to your buddy so it doesn't fall out on it's own and get lost.

 

[motorshag]

Thanks 5twins. Will do.

 

[5twins]

Check the 2 locating dowels as well. Sometimes they're loose and can fall out.

 

[motorshag]

I checked those last night, they looked/felt tight. However, I did find a new problem; I have a broken Tab on the right arm in the Advance Unit. I looked on Mikes for a new one, and couldn't fine the unit, or just the arm. Anyone have any ideas on how that happened? Are if I need to buy a whole unit, where would I find one?

 

[Tim of DO THE TON]

Right now they don't seem to be available new from MikesXS (they used to sell the whole kit). eBay or a friendly member here might have what you need. You just need the one weight, not the whole thing.

 

[motorshag]

Right now they don't seem to be available new from MikesXS (they used to sell the whole kit). eBay or a friendly member here might have what you need. You just need the one weight, not the whole thing.

Yes Tim, just the one weight. I can't even find mention of it on a parts maual.

 

[Tim of DO THE TON]

Won't have its own part number - it's an assembly. Someone will have a spare weight they can mail you I'm sure.

 

[motorshag]

I had a couple of friends over helping me with the disassembly. We neglected to note where this wire came from. The bike is almost all back together, but I have an extra wire. I have looked in all my books and through all the part manuals for my year, 1977, XS 650 D. But I cannot locate where this wire goes. I know it's got to be for power. But I just don't know where it attaches. Any help would be great. Or a pic of where it goes would be even better.

Thx!

 

[Tim of DO THE TON]

Do you have a negative lead attached to your battery yet?

 

[motorshag]

I don't have the battery installed back yet. The leads were never removed. Could this be a lead that is the main ground? I feel stuip that this is the MIA piece.