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XR600R Break in - Valve Lash Increasing???

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TLDR: Valve lash is increasing considerably during break in, does this mean it's eating my cam/rockers or should I adjust and continue?


Hey guys. I need some advice on my 96 XR600R break in that is maybe not going so well. I guess I'll start with a quick history of the bike...

I swapped it over to a Kansas titled XR650L frame and registered just in time to leave for a week long trip to Colorado with some buddies.  We went down by Telluride/Ouray and rode a bunch of jeep trails.  It was blast and the XR ran great.  However it burned oil like CRAZY! I probably put 6 quarts of oil in it over that week, and my buddies said they could see it smoking like my 2 stroke.  I almost made it home too, about an hour away she gave up, would not run and made clunking sounds when I tried to kick it over - was not locked up though.  A buddy came and saved me.  

Upon tearing down the motor, I found that the top end all appeared to be fine.  I was surprised to find that what I thought was a stock motor had a 100mm JE 10.5:1 piston... Evidently it had been detonating on the highway while I had my music plugged in and could not hear it.  Damn.

I sent the crank off to Ken O'Connor racing and ordered a Wossner 100mm 9.3:1 piston.  I am planning to take this bike to baja and need it to run on whatever kind of gas I can get, so I figured I'd go for the lower compression piston.  After rebuilding it I put it, I mounted it in the frame and got ready to break it in.

Here's the details on my bike setup and break in:

  • Maxima 15W-50 Break-In Oil - High Zinc.  Website says it is safe for wet clutches and motorcycle transmissions...
  • Jetting: 155 main, 68 pilot, 2.5 turns out on fuel screw.
  • Stock CDI; UNI air filter; Stock header with inlet welds ground & FMF powercore muffler
  • Put 1 liter oil in frame, 1 liter oil in through one of the valve inspection covers.  Waited several minutes for the oil to all drain to the bottom end.
  • Cycled kick starter over until I saw oil coming out of the external line at the head.  Bolted it up.
  • Motor had sat for ~3 weeks between assembly and start up. Didn't add oil until day of start up.

Upon starting it up initially, it was making a loud tapping sound. What the hell? It ran maybe 15 seconds like this; I shut it down and found the valves were set loose.  Could have SWORE I set the valve lash properly with the motor on the bench.  Oh well; reset lash and tried again.  Sounded much better after this, I ran it for maybe 5 minutes varying throttle from idle up to 1/4 throttle or so.  

I let the bike cool down for a couple hours and then did a similar exercise.  Rode it up and down the street a few times, seemed to be either running lean or missing? Didn't really seem right.  Didn't want to start after this and the lever kicked back real hard on my leg several times.  Brought it back in the shop; found that the valves were pretty loose again.  Intake went from .10mm to like .18 or something like that (.003" to .007").  

Lash should not increase during break in, right? Does this mean I am eating through my cam or rockers? Cam, rockers, valves, springs, etc. are all the same parts as before rebuild.  I did lap valves.  Is this a normal thing that I should not be concerned about?  I have done full rebuilds and top ends on other bikes and never experienced this.  I am planning to remove the valve cover and investigate later tonight.  

I will post updates later if nobody advises me otherwise before I tear it down in a couple hours.

Thank you for reading and for advice.  Any knowledge/time is greatly appreciated.  Sorry for the long post.

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No, lash should not increase.

I'd first verify you're locked down well after adjustment.  It can be difficult.  I have to use a crow's foot open end on the torque wrench to get into the adjuster jamb nut.

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Hmm. I'm pretty confident that I have the adjuster nuts locked down very solid. They are still very tight when I go to check them later.  Next time I'll see if I can find a paint marker and put a line across the adjuster, nut and cover so I can be sure they aren't moving.

I took the valve cover off.  Everything seemed to be okay.  I checked cam timing and reinstalled the cover.  I set valve clearances, intake at 0.004" and exhaust at 0.005".  The bike fired up pretty easily.  I let it idle for a few minutes and then rode it up the block. I rode it for maybe a minute or two... Parked it and shut it off.  Went to fire it up a few minutes later, and then it was kicking back against my foot hard. 

Took the tank off and checked valves again.  Left intake was 0.006", right intake and left exhaust seemed okay, but right exhaust seemed way tight. I couldn't get any feeler in it. I turned the bike over to the next TDC (always checking valves after intake stroke, before exhaust stroke at T mark) and it was still tight, turned it through again to next TDC and then it seemed just fine, .005". I think the reverse auto decompressor might be giving me hell? Do those ever cause problems?


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Also, I forgot to mention - It seems like it is missing or lean or something around half throttle... Is it possible I need to change my jetting or move the needle since I lowered compression from 10.5 to 9.3? Bore is the same.

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Lowering the compression will make it a little leaner. If it's your mid throttle , raise the needle a notch.

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Sorry I disappeared for a minute. Life got a little crazy, but I finally got some time to start working on the bike again yesterday and today.

I put a hot cam in the bike. I mostly just wanted to get rid of the auto decompression/ reverse decompression mechanisms. The bike starts much more easily and consistently now. I'm not sure how this makes sense, but it definitely started much easier and better after installing the hot cam. Maybe something to do with the hot cam calling for larger valve clearances? Also I was using straight feeler gauges before and this time I bent them for the exhaust so I could get a more accurate reading.

The bike still misses really bad as soon as you get on the throttle. I've been trying not to idle it at all with the new cam yet. I've tried a bunch of stuff:

-First I raised the needle one notch. Didn't seem much different. Raised it another notch (highest needle position). Still not much different.

-Swapped my 155 main for a 162. It says AB162 on it, it's a different brand I guess. I hear that sizes vary by brand sometimes? Didn't help the misfire.

-Swapped spark plug. Same

-Swapped coil off of my junk 83 XL600R parts bike. No difference

-Tested stator (Ricky stator 200W dual output). It only showed about 100 ohms on my meter and gave about 40-50V AC when kicked over. I don't trust the meter a whole lot. 

-Stator on XL parts bike test at ~200 ohms and 70VAC. Swapped XL stator into XR. Did not make any perceptible difference.

-I tested the pulse gen resistance. I thought it was in spec but I will double check later.

-Tried stock CDI and a spare hotshot CDI I have. Doesn't make a difference.

I can try swapping the pulse gen from the XL later. I will clean the carb really well when I get a chance as well... It was working great before, I drained the gas all out of it when I tore the bike down before the rebuild and if I remember right I gave the jets a quick once over with carb clean and compressed air before I reinstalled it.

The cam chain is new. I lapped valves during the rebuild, and I got them all to hold water with the exception of one exhaust valve that had just the slightest leak.

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I found out why it was missing so bad. I fixed this a few days ago and thought some might find it interesting.

There was far too much clearance between the rotor on the crank and the pulse generator. It's supposed to be somewhere around 20 thousandths, and my 0.030 feeler was sliding in pretty easily. I pulled it off and it looks like it's shaved down... I think when the bottom end went out the crank had some run out and the lobe shaved some metal off of it. I pulled the pulse gen from my parts bike and it measured out at 0.020", and the bike runs worlds better now.



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