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To Shim...or not to shim??

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It's a 2006 WR250F. Trail ridden and maintained regularly for 4 seasons. Never had any top end work or valve shimming.

Had some trouble getting consistant jetting settings. Checked valves for the first time.

Exhaust spec: 0.17-0.22 mm

Mine: 0.15 - 0.20, 0.15-0.20

Intake spec: 0.10-0.15 mm

Mine: 0.10-0.13, 0.08-0.10, 0.08-0.10

Any good reason to re-shim at this point? Two intakes are at about .009 mm and min spec is 0.10 mm. I'm leaning toward leaving everything bolted together and waiting to re-shim?

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Ok. Will shim. Thx for sharing the advice of experience. :smirk:

Just to be sure, I checked the intakes again. Got the same measurements.

I was anticipating having to do this and already bought a shim kit and the small Motion Pro feeler guages. :bonk:

DSCN0457.jpg

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So far, the steel framed WR250F has been easy to work on. Got this far by just removing the seat, tank, and shrouds to get access to the valve cover.

That's a YZ vent hose. No venting back to airbox. :bonk:

DSCN0453.jpg

Unhooked the two valve cover vent hoses and removed valve cover without even having to removed top engine mounts.

Had good access to make measurements. I found the largest feeler guage that would fit and then double checked that the next size up would not fit. Those are the numbers I recorded. Actual gap would be between those two limits.

DSCN0454.jpg

Here's the marks on the cam at what I believe to be TDC. There's a mark on the exhaust gear pointing forward that lines up with the top of the head. There's two marks, one on each side, that line up on the intake side.

DSCN0458.jpg

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I would recomend that you NOT reshim at this time. The valves are still close to the low limit. The problem is the shims are only available in increments that that will put your clearance over the reccomended specs once you reshim. Running the valve clearance over the spec, even by a very small ammount will hasten the life of your valves.

There IS a reason for this; the cam profile is ground with a closing ramp so the camshaft slows the valve to gently contact the seat on closing. If the valve clearance is too large, the valve hits the seat before the closing ramp has a chance to slow the valve down.

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This is one subject which will always attract a difference of opinion. I will always run my clearances as close as to the minimum clearance as I can get.

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Thx for the advice, though too late. I went ahead and re-shimmed the two out-of-spec intakes. Just re-torqued the camshaft caps. going to recheck clearances.

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Ok. What's up with this?

After installing the new shims, it measures as though there is less clearance?

Here's what I did:

Right side intake. Installed pad number was 179 (180 rounded). Measured clearance .09 mm. Intersection of of 180 and 0.09 on intake table is 175. That's what I installed. Am I doing it wrong?

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Ok. I know these might be stupid questions, but did you check the clearance with the engine stone cold? (before and after adjustment)

Had the bike been sitting for a few days or was it run a day or two before you checked the valves the first time?

Did you use any asembly lube on the cams when you put them together?

The correct torque value (in US units) is 7.2 lb/ft or 86 lb/in. Are you using a quality torque wrench?

Did you install the cam chain adjuster correctly? (i.e. was it fully retracted when you put it back in the cylinder?)

The shim selected is correct but did did you verify the shim dimention with a micrometer or caliper?

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Oh, and one more thing that will give you false low readings after you make a shim adjustment. If you put any oil or assembly lube on the tip of the valve stem before you set the shim or any on top of the shim before replacing the bucket you may have to roll the engine over a few dozen times before the clearance settles in.

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Thx. Checked most of those as ok. Just used engine oil on everything as I reassembled. I haven't verified the shim thickness with a micrometer.

I took the buckets off again and tried re-seating the shims into the valve retainer area better. I didn't realize it was such a tight fit with the diameter of the new shims.

Clearance checks out now. Intake clearance (cold 65F) now measures 0.10- 0.13. Spec is 0.10-0.15 mm, so I think I'm good to go. :bonk:

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Re-seated the shims inside the ends of the valve spring retainers and then put buckets on. Worked better.

DSCN0461.jpg

Intake spec 0.10 - 0.15

Final clearances after torquing and cam chain tight:

Left intake: Unchanged ~0.10

Center intake re-shimmed: 0.13-0.15

Right intake reshimmed: 0.10 - 0.13

Here's the final orientation of the cams. I tie wrappped the chain to the exhaust cam when working on it.

DSCN0465.jpg

I could get a torque wrench on the bolts. The 7.0 ft-lbs seems high for the size of the bolts?

Got it put back together. Put in new spark plug. Fired up the bike. It started right up. Guess I didn't screw things up. It's late. I'll test ride in the morning. :bonk:

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2grimjim, i see that u asked if the bike had run within a day or 2.... I just did a bottom end in my wr 450 and i hadn't checked them before ripping it apart but just before finalizing the job i checked them and they seemed kinda tight. .20 -.25 is spec and mine seemed about .175. Should i run the bike a while and break it in for a more accurate reading u think? its been apart about a month now. running them tight is worse than loose or vice versa? thanks man!

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