87 xr600 top end

Hello again! I've pulled the head off my xr600 and discovered that it will need bored over. Just a couple of questions. My main area of reasoning to bore it out is that there is a spot that is rough in the cylinder. It feels like sandblasted aluminum feels to the touch. I'm just wondering what would cause that so that I can make sure it won't be a reoccurring issue. Also, I'm wondering what the "MK2" on the top of the piston means? There is no other markings aside from the "IN" for intake. I'm guessing its standard bore. Everything else looks sparkling clean on the engine. Really there isn't even any slack in the piston. I've grown up working on motorcycle engine rebuilds.. So I shouldn't need any long drawn out topics on a rebuild of the engine (I hope). Lol. Anyways, thanks in advance for any input!

I should probably also add that the spot is at the front of the cylinder about half a stroke down. I know that it could be where water may have sat in the cylinder and rusted the wall then after running the rust would have worn off but I have a feeling it may be something else.

I rebuilt an xr200 that had a bent intake valve. It sat a month orwhatever before teardown. Coastal moist air. Condensation got in and made a rust spot that you could feel with your fingernail. I honed it and it didnt completely remove the mark. Reused piston with new rings and no smoking. Bike definitely has more compression. I dunno. We were on a budget. (15 year olds bike) But if it were mine, id have longevity in mind and would bore it or buy a new sleeve. Good luck

Where is the spot,,,intake or exhaust side of the the cylinder???

 

B

Oh and I do plan on boring it. I want to make it highly reliable and I know that this would hinder that. I can feel it without my nail. It might be better to describe it as a very fine grit sandpaper feel. Anyways, yeah it's exhaust side about half way down the piston stroke. Which, I'd guess would put it around 1/3 of the way down the cylinder if the jug was removed

Btw with no markings other the ones mentioned in my first message it would likely be std bore right? If so it should have plenty of thickness left on the sleeve for a bore rather than a new sleeve

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Looks like it was on the intake side. Whats this signify Brian

Hope this helps dope band

I wish my pics would post. From what I can see its similar however you can see more various flaws in other areas of my cylinder. My iphone app never wants to let me post photos.

That's just what my XL had. on the exhaust side about halfway down,1/4" or so wide band of roughness, but I had 2 patches on each side of the exhaust side 1inch tall by 1.5" . Cleaned up with the hone, but near the limit. Runs great, no smoke, won't last like a bore but I'm sticking the money into a replacement motor with all the goodies.

I have seen those same marks on a few cylinders for sale on Ebay also.

Edited by jjktmrider

This is an engine I bought off of eBay. It had marks all around the cylinder. The main one I mentioned is just the one that stands out the most. Hopefully I can get some pics up soon.

Click on "reply to this topic" at the top of the page.  Once there click on "attach files" at the bottom then upload your pictures and add them to your post.

"The upload failed. Please contact a member of staff to rectify the problem" is all it says anytime I try.

When i do it from my phone. I have to go to "full version" of the site. Than reply button. Than in the reply box it says, more reply options. It switches up and theres a choose file and attach file button. Choose a file from your phone's gallery and load it then attach it.

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If youre on a budget you can hone, polish the piston skirt, new rings and you should be good. That 200s mark looked worse than yours even after a hone! If you bore, you gotta get a whole new piston and matching rings. You could buy a new sleeve too. Depends on how long you wanna NOT go back into your motor for. New sleeve and new rings might be as much as a bore job and new piston. But youd have peace of mind

The damage is deep enough that honing isn't gonna take all the flaws out. I'd rather have it as fresh as I can get it. I'm pretty sure it's at std bore right now. Is it really worth considering a new sleeve if it is in fact on standard bore? I'm not trying to go cheap on this. I'm gonna split the crank and check for anything that might need repairs before it becomes serious enough to notice later on down the rd. I may send in the engine for powder coating even. I'm just trying to have it ready for next summer at this point.

Oh, I hadn't mentioned it in this post but I did in another. Before disassembling the engine I had suspected some mud getting past my crap air filter. My last ride on it was in some serious mud. Anyways, I found dirt grit jamming the piston rings closed. It makes me wonder if all this damage could have come from a little mud

Id get a new sleeve the. Xrs only has em. Ive put one in with an oven, heat cylinder old sleeve comes out. Freeze new one and press in with a vise with two blocks of wood under the cylinder and one flat on top.

I dont think you should powdercoat your aluminum motor..the heating process will anneal the aluminum.

And in my opinion, paint it either. Your motor will run hotter. Theres been a study on it i think on advrider. But its done all the time. I just got it real clean.

I've thought about just sandblasting the main crank halves. My dad did his old xs650 like that. It looks pretty nice. Shouldn't 1st bore be good with the same sleeve? I will get a new sleeve if I need to though. I'd considered boring it over to a 619cc but I've read that it doesn't have too much effect.

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