Valve Lapping Results

OakBehringer

OakBehringer

XS650 Guru
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First time lapping valves. This is what they look like when finished. It appears that I have some rings/grooves on the valve seats. What did I do wrong?

I put valves/springs in, filled the combustion chambers with gas, and they didn't leak, implying decent seal, so I'm probably going to go with it.

Just want to get to on the road, this bike is my daily rider/beater, not doing a major sexy build.

- Adam
 

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That happens sometimes. Did you use both coarse and fine compound? Finishing with the fine can reduce that ring effect. Also, after lapping you should measure the width of the newly lapped sections. I think original is 1.6mm but they don't want them over 2mm wide. If they come out too wide then the approach angles in the seat need to be cut to narrow the seat back down.
 
I did use both compounds. I think I might have overdone it with the coarse, turning it too far as well. I gave one valve a few more applications of the fine grit, but it didn't do much to relieve the rings.

I didn't measure the seats. They did look a bit wide to me, but like I said, I just want to get back on the road and I'm pretty broke right now (tax time, self employed, when you're getting your returns I'm sending 5-figure checks to the IRS). I'd rather pour what little money I have into my sexy 160 cafe project.

Even if the seats are a bit wide, I expect/hope to get a season out of them? I'm going to do some sort of major project with my 650 next winter, I'll revisit the engine with a performance mindset at that time.
 
Where you spinning the valve in a complete circle when you were doing the lapping? Did you rotate the valve a quarter turn between the tap, tap, tap? 5twin has a really good write up on valve lapping somewhere around here. I'll see if I can find it. What is the width of you sealing surface? If i recall correctly it should be about 1.3mm- 1.6 according to my factory service manual. Are you doing rings while younhave the top end off? I'm looking forward to seeing how things turn out. I know you have been putting a lot of effort into this build after reading the threads. Hope it turns out the way you wanted!
 
Just to clarify. I think it was a old race nut that told me to rotate the valves a bit over half a turn back and forth until you hear/feel the compound change consistencies. Once that happens lift the valve and tap it a couple times drawing in new compound and rotate it a quarter turn then repeat the process until there are no pits. Then go over it with the fine compound.
 
Patches said:
Just to clarify. I think it was a old race nut that told me to rotate the valves a bit over half a turn back and forth until you hear/feel the compound change consistencies. Once that happens lift the valve and tap it a couple times drawing in new compound and rotate it a quarter turn then repeat the process until there are no pits. Then go over it with the fine compound.
Click to expand...

Yup, that's pretty much exactly what I did, but I think that I was doing too large of rotations when I was doing the spinning/firestarting motions?

I'm not doing rings/jugs. I had no reason to think that they needed it. I removed the piston circlips without removing them from the jugs. All I really have left to do is figure out how to clean the crowns of the pistons without getting a ton of crap in the ring grooves :)
 
Why not just remove the pistons from the bores? It's a fallacy that you lose ring seal doing so. You don't need a ring compressor or anything special to put them back in. The bottom of the bores are beveled so just squeeze the rings in with your fingers and wiggle the piston back in, one ring at a time.
 
5twins said:
Why not just remove the pistons from the bores? It's a fallacy that you lose ring seal doing so. You don't need a ring compressor or anything special to put them back in. The bottom of the bores are beveled so just squeeze the rings in with your fingers and wiggle the piston back in, one ring at a time.
Click to expand...

I'm not worried about getting them back in. I don't claim to be an engine building expert, but I've been through a few top and bottom ends over the years, and getting rings into the jugs isn't beyond my skillset :)

In regards to the rings seating... I have heard both sides of the coin, and tend to agree with you: it is a fallacy that ring seats are lost when you remove them from the jugs. It's certainly been proven that rings will rotate when an engine is running. However, I wouldn't be surprised to learn that those tests were done on newer bores. It's certainly common for bores to wear to an oval shape, and it would logically follow that the rings could wear to match the ovals. If this happens, the rings may sit in the same spot, no longer rotating. I thought it might not be best to risk it.

Anyway, that's just my own thoughts and logic applied to my scenario. I'd be eager to hear everyone's responses and opinions on the matter. It sure would be easier to just slip them out. I could even mark the pistons and rings with a sharpie to get them back in their barrels in almost the same spot.
 
Is it a fallacy that bores wear oval? If they do, then why is the ring still circular?
 
xjwmx said:
Is it a fallacy that bores wear oval? If they do, then why is the ring still circular?
Click to expand...

Not a fallacy. That is definitely true. Whether or not it influences ring-seating is what remains unclear to me. In any event, the ovalness of the bore or ring wouldn't be visible to the human eye, so how are you confirming that the ring is "circular"?
 
^I'm not confirming that. But if it doesn't matter how the rings go back, that means they're circular.
 
Scraping the piston tops and allowing it to fall down into the rings, would be the wrong thing to do. Do it right; take the pistons out of the cylinders. Just as 5twins said, its very easy to re-install the pistons from the bottom. The chamfer makes it simple............I used a popsicle stick to ease the rings in.
 
You already have it torn down this far so I would recommend not cutting corners now. Pop the pistons out so you can properly clean them and the bores. Measure the bores or at the very least measure the ring end gap at top, middle, and bottom of bore.

Rings are one of those things that I never reuse. When you consider the total cost and time involved in a rebuild, ring are relatively cheap. Throw a ball hone through it, clean it thoroughly, then put it all back together knowing it will be right.
 
In the past I have just hit the cylinder walls with a glaze breaker or ball hone then finish with a 45 degree final cross hatch and put some new rings on the pistons. Now I have never done this with a XS650 so somebody please feel free to correct me if I'm wrong.
 
Yes, I very seldom find ring end gaps in spec, I think it only happened once. Something my dealer told me is that ring end gap isn't the only factor. You have to consider the tension that the rings will exert onto the cylinder wall. Old rings can lose some of that tension.
 
mrriggs said:
You already have it torn down this far so I would recommend not cutting corners now. Pop the pistons out so you can properly clean them and the bores. Measure the bores or at the very least measure the ring end gap at top, middle, and bottom of bore.

Rings are one of those things that I never reuse. When you consider the total cost and time involved in a rebuild, ring are relatively cheap. Throw a ball hone through it, clean it thoroughly, then put it all back together knowing it will be right.
Click to expand...

Sure, I guess, but I have good compression, don't burn any oil... I'd have to buy a hone and new rings, why? There's always more you can do to "be safe," but it's definitely not necessary.
 
xjwmx said:
One of the people giving you rebuild advice in this thread has stated that his rebuilds burn a quart of oil in 1000 miles.
Click to expand...


Well that only leaves 5twins, retiredgentleman, mrriggs, Patches, xjwmx. I would guess you wouldn't be talking about your own advice so it would have to be the one of the other 4.

So you are to scared to come clean and confront the person you are referring to and pleased to discredit the others by your first action.
 

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