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Hey I need a little help here, I'm trying to help my friend adjust his valves. Both our first time. Exhaust valves are in spec, both intake were super tight couldn't even get the smallest feeler gauge in there so were assuming the clearance is .000.

it's a used bike so we don't know how many times it has been shimmed. One shim is a 1.65 the other is unreadable we're getting. A caliper shortly here. My guts telling me these are really small shims and the valves are just worn out, but we just were told by the previous owner both intake valves have been replaced. Can we still shim these valves? It's an 05 crf450 spec is .006 intake and .011 +-.001.

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You can re-shim it, but the question is, will it last without breaking a valve?

It is a possibility that the previous owner is correct about the valves being replaced, and maybe whoever cut the seats took enough material off to bring the shims down to a small size.

But without receipts, work orders, ect you don't really know and run the risk of total engine loss, if you drop a valve.

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are you sure you have it on the correct tdc position?, try turning the crank around slowly [ with the shims reinstalled] to the other tdc[360 degrees forward] and see if you have any clearence

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Yeah I told him to shim it to get through this weekend of riding and then replace whatever's necessary.

And we did try turning the crank and tryin to feel it at different positions, no luck.

Can anyone double check my math as this is my first adjustment?

SpecClearance - .16 mm

Recorded clearance - .000

Current shim - 1.65

So my new shim would be a 1.49 which in that case I'd use a 1.50?

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Well we got the caliper, measured the unknown shim and it was the same size. We did the math and replaced both shims, re asembled and the new measurements were .0015 left clearance .004 right clearance. Recorded that, took apart again, did the math, reshimmed, reassembled, and this time all valves came out in spec. What a good feeling! Got the bike back together and it seemed to run great, my buddy said its the best its been since he bought it. Was not that hard of a job at all, just spent the day running around getting tools.

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usually once the valves start moving and require reshiming, they're no good.

Each adjustment will only last a few hours.

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usually once the valves start moving and require reshiming, they're no good.

Each adjustment will only last a few hours.

Yup these valves are on their way out. We're gonna ride it this weekend, check clearances after, and replace them either way.

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If you have ever seen the inside of an engine that had a valve drop? Not good! I just recently had my 450R zero out on the intakes for the first time. I am not taking any chances. I don't want to potentially do a complete motor rebuild because I shimmed one to many times and dropped a valve and grenaded the motor. My 2 cents.

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If you have ever seen the inside of an engine that had a valve drop? Not good! I just recently had my 450R zero out on the intakes for the first time. I am not taking any chances. I don't want to potentially do a complete motor rebuild because I shimmed one to many times and dropped a valve and grenaded the motor. My 2 cents.

ImageUploadedByThumper Talk1381418032.274322.jpg

Meet my husq tc610 supermoto. This thing was a beast til my mechanic adjusted the valves wrong. Yeah this is why I told my friend he must get new valves after the weekends, we might even check em after the first ride. I've been there before, still haunted by it.

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The valve wont drop because of a worn face. The valve can get broken because of a weak spring, manufacturing defect, but not wear on the face. Ive pulled valves out that had the margin worn to a razors edge. They ran fine, just no more room to shim. Not that they dont need to be repaired, because they do. 

 

Dont be surprised if the bike runs fine, starts easy all up to one long ride. Then it wont start without a bump start. Depending on how bad the wear currently is, sometimes on the first shim you'll get about 15-20 hours, then the second shim only gets you about 5 hours...then usually you cant get a shim thin enough to get your lash. 

 

I havent seen a 165 come out of an OEM head yet, so its probably been shim once before. The thinnest stock shim I've seen was a 172. 

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The valve wont drop because of a worn face. The valve can get broken because of a weak spring, manufacturing defect, but not wear on the face. Ive pulled valves out that had the margin worn to a razors edge. They ran fine, just no more room to shim. Not that they dont need to be repaired, because they do. 

 

Dont be surprised if the bike runs fine, starts easy all up to one long ride. Then it wont start without a bump start. Depending on how bad the wear currently is, sometimes on the first shim you'll get about 15-20 hours, then the second shim only gets you about 5 hours...then usually you cant get a shim thin enough to get your lash. 

 

I havent seen a 165 come out of an OEM head yet, so its probably been shim once before. The thinnest stock shim I've seen was a 172. 

 

 

The valve wont drop because of a worn face. The valve can get broken because of a weak spring, manufacturing defect, but not wear on the face. Ive pulled valves out that had the margin worn to a razors edge. They ran fine, just no more room to shim. Not that they dont need to be repaired, because they do. 

 

Dont be surprised if the bike runs fine, starts easy all up to one long ride. Then it wont start without a bump start. Depending on how bad the wear currently is, sometimes on the first shim you'll get about 15-20 hours, then the second shim only gets you about 5 hours...then usually you cant get a shim thin enough to get your lash. 

 

I havent seen a 165 come out of an OEM head yet, so its probably been shim once before. The thinnest stock shim I've seen was a 172. 

 

Please correct me if I am wrong. I was of the understanding the valve face and valve seat when wearing don't wear concentrically.  If the two don't wear concentrically then the tensile load on the valve is not distributed evenly on the valve face and causing the valve shaft to bend on a micro level. Could stress of a micro bend on a valve shaft not cause it to fracture over time. An engine turning 10K rpm that had eccentric valve wear, would that valve not fail at some point in time?

 

Last thing I want to worry about is my motor seizing in the middle of a big double jump because I might have shimmed it one to many times. I live very close to a guy that his motor seized in the middle of a big double. He lost his leg. Lucky he didn't lose his life.

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Some of the heads have a concentricity issue, but the valves spin in the guides too. So the valve wouldn't be bending in the same position. If the guides are worn, really really worn, your example of side loading is valid, but even then, it usually doesn't result in a valve that snaps. Most of the time when you see a valve that's had the head snapped off, your looking at an exhaust valve that got tagged a couple times by the piston when it floated off the cam, or the OEM chain tensioner did what they're known to do, fail and then reset themselves but even then it usually goes to the retard, and not advanced where the piston would tag that ex valve again. 

 

Its been my experience that valves that break are often fairly new, not ones that have been annealed from use and are fairly flexible. I'm not saying it'd be safe for an MXr that's charging a 110 footer to go willy nilly about the maintenance of the top end of a thumper, but its not as precarious as some would suggest. 

 

For what its worth, IMHO, the OEM tensioner is more dangerous than the intake valves. I did a motor for a guy recently who's tensioner did what they do, allowed the chain to bunch up in the bottom end and lock the engine up. He was charging a 100+ footer at Perris and luckily it locked up and skidded to a stop just past the lip of the jump. It rolled backwards, unlocked the engine and he rode it back to the truck with the timing off one tooth. I told him to replace that 'fn thing, he said he thought it'd be fine. When he showed up at the house for me to fix it, he'd already bought the Tokyo Mods MCCT. A very, very nice piece. 

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