Hey guys, I've been riding now for about two years and have decided I want to get more familiar with the machines we ride. I picked up an 05 250r for a project bike and it is just that. Lots of questionable wrenching, gasket maker, snapped bolts, you name it. Today I went through and checked timing, valve clearance, and addressed a snapped off bolt for the timing chain tensioner. Timing is slightly off, valve clearance is questionable, and I successfully removed the bolt without causing further damage (woohoo). My thought right now is to do shims, get the timing correct then compression test the cylinder. Any thoughts on what would be the next best thing to do?
Intake side tolerance: 0.09-0.15, includes the +/- 3mm
0.10 fit both of the intake side (snug/loosie goosie)
0.15 only fit the right side (snug)
exhaust side tolerance: 0.25-0.31, includes +/- 3mm
0.25 did not fit either side (extremely tight)
Here's some photos of the bike and its current state. 
Meant to touch on the exhaust side valve clearance. It's already at the lesser end of the tolerance. I did go through and set the motor TDC before checking. Not sure how to address this, any info appreciated. Thank you all!
If you are just looking to get it up and going then I think you are on the right track. If you are wanting to keep it for a while I'd put a new piston, rings, cam chain, and cam chain tensioner in since it doesnt sound like this bike was well maintained. Use oem parts if you rebuild the top end. You can also inspect the crankshaft if you pull the top end apart.
Right now im trying to do it on a budget. If the compression test comes back good I'll be using the cylinder that's in it. If not then it'll get a new one. Previous maintenance seems pretty non existent. Im getting ready to order a stator cover, cracked with a bit a jb weld slapped in there.
You want to do a leak down test, not a compression test. Compression tests won't really tell you anything.
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Leak down to pin point the issue? The more im digging into this the more I think I will be following @96motorheads advice and doing a top end with it. I read through some forums about valve clearances and I think the valves are no good also. The smallest size of 0.25 was too big to clear the rocker on the exhaust side. Next closest size to fit was 0.20. Im thinking the valve is elongated and toast from what I've read on here. Looks pretty shitty in there too.
I would also add inspecting the clutch and changing suspension fluids to my list.
I looked into the clutch today, it will need replacing. Also will need to do the bump stop on the shock, it's falling apart. Lots of dirt and debris on threads and stuff. The clutch had lots of heat wear on the steel plates, friction plates were discolored and worn. Fork seals are leaking so those are going to get done too. Ive got harness and motor off the bike so here in the next couple of days I'll be going through to deep clean everything. By the time im done it'll practically be a new ride 🙂
If no shims will fit then the valves are toast. The valves dont stretch they wear at the valve seat interface. The cheapest option for the head would be to have the seats re-ground and valve guides replaced if needed by a machine shop and install new oem exhaust valves and new aftermarket steel intake valves along with all of the springs, seals, etc. These bikes came stock with titanium intake valves which wear faster than steel. Up to you if you want to do the titanium intake valves or the aftermarket steel valves. The steel valves weigh more than titanium so you will lose some performance if you go that route with the trade off that steel valves last much longer.
Would you consider lapping the valve seats with the old exhaust and intake valves to bypass taking to a machine shop? ill be doing the upgrade to steel valves for longevity/ reliability down the road.
No I would just have the seats reground or cut. Beware that you cant lap titanium valves because you will take the coating off. If your intake valves have no clearance then the coating is already gone and the valve is toast. What clearance are you measuring for each valve?
If I were to lap the valve seats I would do it with the old ti valves (sacrificial) and install new steel valves then do a leak down test. Getting ready to pull the head to have a look at that.
Intake side tolerance: 0.09-0.15, includes the +/- 3mm
0.10 feeler gauge fit both of the intake side (Left side snug/right side loosie goosie)
0.15 feeler gauge only fit the right side (snug)
exhaust side tolerance: 0.25-0.31, includes +/- 3mm
0.25 feeler gauge did not fit either side (extremely tight)
0.20 feeler gauge fit (snug) but well under minimum tolerance.
Those clearances dont seem bad. What size shims are currently in the head? I would shim the exhaust valves and call it good for now. The intake valves are typically what go out of spec first since they were titanium from the factory, so the fact that they are still within spec is a good sign. Someone might have already installed steel valves. I take back what I said previously, I wouldnt jump to rebuilding the head quite yet. If you have a valve spring compressor I think that it would be a good idea to pull the valves out, clean everything up and inspect them while you have the head off.
Ok so right now the shims that are from a hot cams kit.
Intake side: left side has 1.90, right side has 1.85.
Exhaust side: left 2.65, right side no number can visually see that it is smaller. Don’t have a micrometer yet. On my list of tools to get.
Id change the shim to get the exhaust valve in spec and I think you will be ok.
Awesome, thanks man. Here’s some pics of the head and piston.
I dont see anything out of the ordinary. I'd check to see if the valves are magnetic. If they are steel the magnet will have a strong attraction, if stainless steel they will likely be very slightly magnetic, if the intakes are titanium they wont be magnetic at all.
Pull the cylinder off and check the cross hatching and see what the piston skirt looks like.
Valves are titanium. Since I’m here just going to go ahead and do a new piston. Seems to me like there was some piston slap before removing it and that ring is flopping around more than it should seems like. What’s your thoughts?
Looks like the cases have been split! It’s got a hot rods crank in it! Crank has some play side to side, nothing up & down.
Pit Row
It is possible that all 4 valves are titanium but that would be very rare as it would be a very expensive setup. Usually only the intakes are titanium if anything. I think it is more likely that your valves are stainless or inconel.
It is hard to tell from pictures what condition the cylinder is in but if there isnt any scoring that you can feel with your finger nail and the nikasil coating isnt chipped then the cylinder is likely good and I would reuse it. I usually have my cylinders honed before installing a new piston, there are a lot of different opinions on this but I've been doing it for years and it has always worked for me.
I think you are making a good call by replacing that piston, it looks like it has a lot of hours on it.
If the small end of the connecting rod isnt scored where the wrist pin slides through and there is no vertical play the rod the crank should be ok to reuse.
Unsure about the connecting rod. Is this what you would consider a blemish?![]()
No I was talking about the inner bore of the connecting rod, the surface that touches the wrist pin. Just make sure the inner bore is smooth.
you got it. Calling it a night, I’ll follow up in a few days. Thanks again for your help dude, much appreciated!
Wiseco diamond flex hone.. is it any good? Looking to clean up the cylinder myself. The nikasil coating looks good to me, no obvious abrasions or gouges. Finger nail also doesn’t catch an edge.
recommendations are appreciated!
I wouldn’t hone it. From the pictures you submitted it looks like there’s visible cross hatch. Like Motörhead said there’s a lot of controversy on honing a nikasil plated cylinder.
Pre-2006 CRF250's had soft valve seats that would wear extremely quick and wear out the valves at the same time. If it needs it, You can send the head off to get new valve seats installed, but it may be the same price as a new head.
Here is a poor mans leak down test:
Cylinder Head Leakdown
You've made lots of progress here. Look at the bright side -- you already have the requisite black plastics that came with the bike!
Thanks for sending this over
Hey guys, I just finished rebuilding the carb today and I’m having some trouble with the performance of said carb. It’s a flat slide carb. It’s cutting out when I wack the throttle. I bench tested the carb prior to taking it apart to make sure the accelerator pump worked. It passed, I did a complete rebuild of the carb including the mid body gaskets and pump. The bike starts and idles fine, the throttle response is good overall minus when I twist back on it with the quickness!
The fuel mix needle is set to 2.25 turns out. My guess is a vacuum leak somewhere. Any help would be appreciated, thanks dudes!
It sounds like it might have a lean bog. If it had an air leak the bike would likely pop a lot on deceleration. You can put a smaller leak jet in the carb so that the accelerator pump squirts more fuel at the twist of the throttle. This sounds counter intuitive but a smaller leak jet forces more fuel into the intake by allowing less fuel to bypass back to the bowl.
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