Smiles' Top End Rebuild Thread

[smiles79]

Hey Jim,

I've come across your thread before and I plan to follow it when I put the motor back together, thanks!

What gives away that this motor has been apart before?

 

[Jim]

What gives away that this motor has been apart before?

The green (Athena I think) cylinder base gasket. At least that's what I noticed. Maybe Gary saw sumpin' else?

 

[gggGary]

Jim as usual zeroed in on it.

 

[grizld1]

Wonderful job, Jim! Pompous? Nah! Why write it all again when you can post a link?

I do a couple of things differently, though. First off, heating copper cherry red and letting it air cool will soften it; but copper isn't like steel, which hardens when quenched; quenching copper will soften it further. I avoid Athena gasket kits like the plague; the head gasket is around .017" thicker than OE. Vesrah gaskets are made in Japan to OE specs.

There's more than one way to skin this cat, but the XS650 motor is prone to oil and compression leaks between the combustion chamber and the crankcase via the cam chain tunnel, and a bit of sealant is good insurance. I shoot both sides of the head gasket with Permatex Copper Spray-A-Gasket. It's nonhardening so there's no rush to assemble, and it releases easily.

 

[Jim]

First off, heating copper cherry red and letting it air cool will soften it; but copper isn't like steel, which hardens when quenched; quenching copper will soften it further.

Right you are Dick. That's how I taught it in school for 15 yrs. Thinking that's how I described it, I went back and looked at my article..... sumbich..... only thing I can figure is I was thinking steel while I was typing. Guess I better go back and fix that. Add "unpaid tech proof writer" to your long list of abilities.

 

[smiles79]

Thanks for all your input everyone! I have no idea what I'm doing for the most part so it's great to have guys around that she experienced.

 

[grizld1]

Oh, I've done much worse than that, Jim! Know how Yamaha factory service manuals used to have typos in their metric-to-English torque spec conversions? One of those screwups was listing 42.5 footpounds for the 8 mm. damper rod bolt in the forks. Now I'd never try to crank down that hard on an 8 mm. fastener, and I'd done plenty of fork assembly on plenty of bikes, so you'd think I'd just write 14 footpounds off the top of my head, wouldn't you? Oh, no. Writing an article on fork service for the Yamaha 650 Society News, I cracked the manual and repeated Mama Yama's 42.5. Realized what I'd done after the article had gone to press and ran a correction in the next issue. My face got just a very little bit less red when somebody pointed out that Clymer had repeated the error too.

 

[59Tebo]

Don't be so hard on yourself...nobodies prefect...

 

[grizld1]

Well, Tebo, at least I didn't get any calls informing me that my instructions had resulted in a trip to the machine shop and a new damper rod, and would soon result in a country ass whuppin at a location of my choice! Seriously, though, misinformation can have bad consequences for folks, so I try to be careful.

 

[smiles79]

This is moving faster than I thought it would! Today I welcomed the pistons and valves to our world. Everything seems ok to my untrained eye.

A couple questions: when I bring parts to the machinist, should I have cleaned them already or is that a task generally done by the machinist?

What's the best way to clean carbon off heads, pistons, and valves?

In the second to last picture it looks like someone tried to smooth out the intake or exhaust (I can't remember which) runners. Is this ok in this state or should it be looked at?

The part circled in the last picture, is that the valve guide? Does this need to be removed before being taken to the machinist?

The part at the end of what I assume is the valve guide (looks like black rubber with a steel wore around it), is that the valve stem seal that needs to be replaced?

Thanks for all the help answering all my questions!

 

[Jim]

when I bring parts to the machinist, should I have cleaned them already or is that a task generally done by the machinist?

Ask 'em. You might get a break on the cost if you clean. If they say it doesn't matter..... same price, let them clean the parts.... but call and ask.

What's the best way to clean carbon off heads, pistons, and valves?

Multiple coats of paint stripper and a wood scraper. Scotchbrite pads.... anything that cuts carbon and not aluminum. A brass wire wheel works good, just be careful.

In the second to last picture it looks like someone tried to smooth out the intake or exhaust (I can't remember which) runners. Is this ok in this state or should it be looked at?

Looks to be cleanup of casting flash. Should be just fine.

The part circled in the last picture, is that the valve guide? Does this need to be removed before being taken to the machinist?

Yes, that's the guide. No, if it needs replacing, your machine shop will do it.

The part at the end of what I assume is the valve guide (looks like black rubber with a steel wore around it), is that the valve stem seal that needs to be replaced?

Yes, don't forget to give them the new ones when you take the head in.

 

[smiles79]

Thanks for the input Jim! While you're here...

My intake valves required a small amount of persuasion to come out, is this expected? Anything I should do so they install easier?

What do you recommend for valve lapping compound?

 

[Jim]

Once they're cleaned up, stickiness should go away. If you're taking them to a machine shop, they should lap the valves in.

 

[smiles79]

I was planning on lapping them myself. Think a rookie could get the hang of it without causing damage?

 

[Jim]

Sure you could... it's not that hard. But it's something the machine shop will do on a valve job. So now I'm curious... why are you taking the head to the machine shop if you want to try and do the valves yourself?

 

[smiles79]

Still figuring stuff out, but yeah I guess they don't need the head of I'm doing the valves myself. Is replacing valve stem seals easy enough? If I can do that myself then I may do all the head work myself.

Edit: spelling

 

[Jim]

Depends on the condition of the valve stems, valve faces, valve seats and the flatness of the head mating surface. To judge all that, we're gonna need some good closeups of everything after it's all cleaned up.
You have access to mic's and ball gauges?

 

[smiles79]

No, I don't have much for precision measuring tools. I think I'm a little lost as to what is required or what should be done with a rebuild other than the obvious (bore/hone, new rings, new cam chain and guide, etc.).

 

[Jim]

How many miles on the engine?

 

[smiles79]

The tach says 11000 (4000 probably was mine, bought the bike in 2014) though I wonder how accurate that is since the motor has been opened up and the cam chain guide is in need of replacement.