Cleaning piston, valves and combustion chambers

peterg

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How aggressive can I get with cleaning pistons, valves and combustion chambers? Carbon was 2 - 3 millimetres thick! I used paint stripper, Gunk and the end of a hacksaw blade to remove most of it. What should I use to finish up?
 

Signal

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A tip I picked up from this site is to soak them in water. I have tried it and it works. I left them soaking a couple of days
 

willis

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The valves are hardened. Chuck up a wire wheel in the drill press. You won’t hurt them.
 

5twins

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Yes, the valves are hardened steel so a strong wire wheel is fine. I use the knotted brush type in a 4 1/2" grinder, very aggressive and cleans them up fast. For the combustion chambers and pistons, after the paint stripper, I use plain old chrome polish on them. Any little remaining spots of carbon I'll carefully scrape off or use the little wire wheels in a Dremel. The paint stripper has usually softened the carbon up so it scrapes off pretty easily.
 

peterg

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Thanks for the replies. I’ll try the water soaking method on the valves followed by my dremel with a wire brush (I don’t have a drill press). Any concerns about the stems getting marred?

5twins. I was concerned about wrecking the chambers with a wire brush but I’ll go ahead with it now. Thanks.

How about the piston tops? I’ve lightly used a scotch bright pad on them but they are still stained.
 
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5twins

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Try chrome polish with an old toothbrush. here's one I cleaned up that way (after paint stripper) .....

4PUZcl8.jpg


0Bt3Ap5.jpg


9squd4e.jpg


This is about as good as you'll get it.
 

cra-z1

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I throw my pistons in the ultrasonic cleaner, then what's left a little scrubbing pad. The valves I blast with SS media since they will be resurfaced.
 

peterg

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Try chrome polish with an old toothbrush. here's one I cleaned up that way (after paint stripper) .....

4PUZcl8.jpg


0Bt3Ap5.jpg


9squd4e.jpg


This is about as good as you'll get it.
I’ll give it a go. Thanks.
I throw my pistons in the ultrasonic cleaner, then what's left a little scrubbing pad. The valves I blast with SS media since they will be resurfaced.
I wish I had access to that equipment!
 

Jan_P

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Thinking out loud here aren't the piston skirts a bit scratched
Indicating some miles driven
+
Carbon was 2 - 3 millimetres thick!

Not saying what is right or wrong here other factors can be important
but if it is a high mileage bike with the intention to keep and make better
Other options could be considered

There are inspection routines in service manuals on line
 

5twins

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Yes, I was going to mention the piston wear. I measure and check them against the bore to make sure they're still OK to use before going through all the trouble of cleaning them up.
 

5twins

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Well, with that many miles, I'm going to guess that the piston wear combined with the bore wear is going to be out of spec and call for an over-size bore and pistons.
 

Jan_P

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Well, with that many miles, I'm going to guess that the piston wear combined with the bore wear is going to be out of spec and call for an over-size bore and pistons.

Yes Sir probably right .. but if the financial aspect is important
A bore is expensive here $ 300 range
I feel that compression is not so important for the bikes performance Ignition and carburetor adjustment plays a bigger role
It Can rattle a little and feel soft on the kick ..Bur run fairly well The measurements will tell.
 

Jan_P

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The bike has about 50,000 K (32,000 miles). I’ll look into measuring and checking some more. First time top end rebuild for me.

Quick Easy and Entertaining turn the cylinder head upside down level ... with spark plugs in pour gasoline up to the edge
Start the stopwatch see if the gas stays there preferably outdoors and be careful with fire
 

cra-z1

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Out of all the engines I have done none of them had bores that would qualify for just a hone. Yes the bike would probably run with just a hone and new rings but the bores were all out of round, that's even with engines with less than 20,000 and some had around 12,000. The material they used back then was just not that good. So I end up with new pistons and rings with bore and hone. I do this because I do not want any surprises after the build. It gets a bit expensive but its nice when you start the bike up for the first time without any problems.
 

Jan_P

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I’m in for the long haul so I’m going to get a rebore and oversized pistons. No point in doing a top end rebuild unless I do it right.

Thinking out loud again
It is a in my view interesting and rewarding hobby to work with these machines As with other Mechanical equipment.
But in the rebuilding decisions there is also the economical aspect. It cost money
Even though the XS 650 is the perhaps best in that sense .It does not have to cost a lot of money
At least not in the past .Given that there are lot of parts. Available .At times at low prices

How is the status of the lower end con rod small end and crank ?
What year model ?
 

Team Junk

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Roughly a 9 per displacement increase. Anyone have an idea of the CR of these pistons. In theory the displacement increase would result in 9.3 CR.
You could spend a lot of money on pipe,carb , foam filters etc to get about the same gain. There ain't no substitute for cubic inches.
I think they use the stock liners bored to 87mm. Good chunk of the 750 kit advantage without dealing with sleeves etc.
https://www.cruzinimage.net/2017/08/29/74-81-yamaha-xs650-706cc-bigbore-pistons-kit-78mm-447type/
 
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