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RFVC Rebuild advice/opinion wanted.

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Hey all, new member here. I don't actually own a XR but I do have a 1987 CBX250 that's powered by a xr250(or possibly xl) engine. I'm in the middle of a rebuild and there is almost no info online regarding my bike so I figured this is my best chance of getting some help.

I've got a Clymer '78-'00 xr/xl250/350 repair manual and more than a little experience working on cars and engines. That being said, this is my first bike. It's a 1987 CBX250, a small(115Kg) street/commuter bike with just shy of 30,000kms(19,000miles).

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So what's wrong/why rebuild? I parked the bike a little before the end of riding season last year because one day after sitting cold for a few days it suddenly had a lot of trouble starting(the bike is equipped with an electric start). After 15 minutes of trying to get it going it started but was spewing smoke(black and blue). As the bike warmed the smoking decreased but didn't go away completely. At this point I could ride it but there was definitely less power than normal. Checking the oil showed it to be low and I had also noticed increased oil consumption leading up to this. I figured I had fried the rings.

Fast forward to now and I've got the engine out and disassembled on the work bench. This is what I've seen so far, I still need to disassemble the head and cover.

This is the cover:

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It looks great to me except for some slight scouring at one of the cam bearings(circled in picture).

Here's the head:

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Again, looking pretty good but does anyone know what that white/creamy stuff stuck to the valve springs is?

This is the first bit of concern I've seen:

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I know it's hard to tell from a picture but does that look useable or not?

How about this:

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Can someone identify these two mystery bolts? They weren't mentioned in the manual and I can't discern any purpose for them.

Then the head came off to reveal this:

IMG_1369web800.jpg

Lots of carbon build up on the piston. There's also some strange corrosion in the top two cylinder/crankcase bolts. I guess the gasket must have failed at some point to allow moisture to penetrate in there.

Finally, as with any engine tear down, something unexpected came out:

IMG_1371web800.jpg

That's a European earwig and a bunch of dirt/debris. It was all crammed in a crevice in the head who's purpose I am still unsure of. It's on the intake side of the head between the the cylinder and the cam chain hole. At first I was thinking an oil line but it's sealed against the head gasket. So I don't know what the hole is for, how the earwig/dirt got in there or what, if any, effect it had on the engine.

I don't have any pics yet(I'll post them once I do) of the valves but they were completely black and covered in carbon. The exhaust ports look like someone dumped a toner cartridge in them(but the intake is clean). I'm thinking a valve seal went on the exhaust side.

So what does everyone think? Is this a good candidate for a rebuild? Any glaringly obvious problem from the images? I've hoping all that needs to be done is new valve seals. I've looked at the rings but contrary to my original thoughts, they look fine. That being said, is it worth my while to upgrade to a 77mm piston while I've got it apart? I need to spec it first but I think the rings and cylinder are fine as they are.

Well, thanks for any help gang.

-Andrew

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It looks great to me except for some slight scouring at one of the cam bearings(circled in picture).
Not a problem.
Can someone identify these two mystery bolts? They weren't mentioned in the manual and I can't discern any purpose for them.
The bolts are shown in the XR250R Service Manual. They serve to seal the cylinder head cover to the head in the area around the cam tower. Unlike the dense parts of the solid head, the cam tower opening being void of metal, will cause distortion of nearby metal unless clamped by the 4 bolts (2 here and 2 on the tensioner). They only need 7 lb-ft torque, but that's enough to stiffen the area and seal the gaskets.
Lots of carbon build up on the piston.
Not so, that is almost NO carbon buildup. Many riders find their pistons totally carbon covered. Looks great to me.
It was all crammed in a crevice in the head who's purpose I am still unsure of. It's on the intake side of the head between the the cylinder and the cam chain hole.
There are cast-in channels leading from the bottom of the spark plug pocket along the nearby fins and to open air. This allows fluid (water, other) to exit the spark plug pocket and drain away. A good practice when removing the spark plug is to remove the plug lead, then blast some air from the sides of the head where the drains are. This pushes debris out of the spark plug pocket and allows you to remove the spark plug and not have debris fall into the combustion chamber.

Your channels look like they got plugged by animal and vegetable matter. Blast the channels clean with air.

I'm thinking a valve seal went on the exhaust side.

I agree. One or both. But do replace all 4!
I've looked at the rings but contrary to my original thoughts, they look fine.
Looking at rings to check them is ok, but you need to put them in the bore, about 10-20 mm from the top, and check the end gap. If they're out of spec, they need replacing, no matter how good they look.
is it worth my while to upgrade to a 77mm piston while I've got it apart?
I wouldn't hesitate to put a larger piston, new rings, new pin, maybe new valves, cut the seats or at least re-lap the current valves. Check the cam chain and plastic cam chain guides/tensioner.

As you reinstall the cam and bearings, check the bearing feel and cam runout and cam lobe wear; replace as necessary. And check the valve guides for slop.

Nice post, pictures and all.

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Excellent advice from ramz. The engine in your CBX 250 is the same basic engine as the 84-85 XR250 and 84-87 XL 250, 75mm bore, 56.5 mm stroke. The largest Wiseco piston for that engine is 76mm, don't know about other brands. Check the cylinder bore dimensions, piston diameter, ring end gaps per the service manual to determine whether or not a bore and new piston/rings are needed. Kibblewhite valves and springs are superior (R&D springs are good too) to OEM if you need valve replacements. It is most likely that the cam chain will need replacing, check it out. Really neat bike, :) I'd like to see one in the flesh.

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Back from the dead...

Thanks for the advice guys.

Ok, so after a bit of a break due to school, exams and a terribly timed computer crash I'm back at it.

I've got some parts ordered through the local dealership, specifically; 4 valve stem seals, 4 exhaust manifold studs and a new OEM cam chain. I've noticed everyone suggesting replacement of the chain, but is using a new OEM piece ok? Are the OEM chains failure prone? I was considering a K&L chain but the OEM was $41 canadian vs. $80 american +shipping.

I'm starting to wonder about my valves, the build up on them is pretty thick and hard. I'd prefer to not have to buy new valves but will if there's no other choice. What's the best/preferred method for cleaning carbon build from them?

Oh yeah, whats the preferred gasket set? Dealer quoted me $110 cad. for just a top end OEM kit. I'd actually prefer a full kit so I could pull the side covers for painting.

So on the to do list for this week:

Find a damn bore gauge and finish spec'ing the cylinder, piston and rings.

Clean the valves if possible, if not find somewhere to order some KibbleWhites in Canada. Will I be fine with my stock springs or will I need the matching kit if I get new valves?

Finish stripping the frame and get it sanded, primed and painted. How concerned should I be that it looks like the swing-arm grease nipple hasn't be used in years?

Ok, that's it for now. My apologies for the lack of pictures, the aforementioned computer crash has prevented me from getting them off the camera and uploaded yet. Hopefully I can change that today or tomorrow.

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I'm starting to wonder about my valves, the build up on them is pretty thick and hard. I'd prefer to not have to buy new valves but will if there's no other choice. What's the best/preferred method for cleaning carbon build from them?

Oh yeah, whats the preferred gasket set?

Will I be fine with my stock springs or will I need the matching kit if I get new valves?

.

Use a rotary wire brush on an air motor or high speed electric drill to remove the carbon from the valves. If the valves don't have any obvious wear and the seats are in spec, they can be reused, but Kibblewhite valves are excellent insurance against future problems. If you reuse the old valves, be sure to give the seats a light hand lap before installing. I have had best results using the OEM gaskets. The stock valve springs will sack out from heat at some point. Measure the spring lengths according to the manual. If the length is OK, the springs will be satisfactory. I prefer to install the Kibblewhite or R&D springs if the engine has much more than 500 or so hours on it, just my being safe rather than sorry.

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