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czechalien

2006 yz450f

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2006 yz450f well taken care of, but now I have about 55 - 65 hrs on it after top end done by Mark Klein aka MxTuner.

Now I'm being told top end is needed along with valves which I just measured at intake: .004 .005 <.004 exhaust both .008 had that adjusted yesterday because I had some starting issues (fixed now).

I'm being told valves need to be replaces every 100 hrs and top end every 40 hrs.

Could you, please, advise me as to what I should do

Thank you very much.

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There's nothing wrong with those measurements, and if there are accurate, no adjustment was necessary. That was a waste of time and money. Specs are .004-.006" intakes, .008-.010" exhausts. The factory sets them at the minimum.

As far as the top end goes, it depends a little on how you're using the bike. If it's a full time serious racer, 60 hours is quite a bit, and it wouldn't hurt to freshen it, especially if the same cylinder and piston was used last time. A play bike is a different matter. In either case, having a leak down test done will tell you more.

It also depends on what maintenance philosophy you choose. Are you going to wait until the parts are worn to the limit, and it needs attention right then, or are you thinking more of refreshing the engine on a preemptive basis, doing the work before it's strictly necessary. The former plan carries the risk of having something actually break, causing major damage. The latter plan always discards a certain amount of useful life, and in that sense, is a waste to some extent.

Unfortunately, this isn't the definitive answer you probably wanted, but that's how it is. People have ridden YZ450's for more than 400 hours without doing any major service to them, while others have blown them up at less than 40 (not many, though).

On what basis does your mechanic tell you that you need to rebuild?

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you're helpful a lot. I did replace the cylinder 55 hrs a go because of vertical scratches, i guess the previous owner never replaced it.

Reading the manual last night, looks like I should take it a part and meassure the cylinder and piston first before buying it.

According to manual if I understand it, there are some parts such as gaskets, circle clips, cam chain etc. you should replace every time you open it, but as long as everything else is in the right measurement It's good to work for many more hrs.

While I'm doing it I probably will replace the springs, in hopes to keep the valves tight against the seat.

Mark

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I ride just about every week and would say I'm an intermediate rider.:ride:

Edited by czechalien

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you're helpful a lot. I did replace the cylinder 55 hrs a go because of vertical scratches, i guess the previous owner never replaced it.

Reading the manual last night, looks like I should take it a part and meassure the cylinder and piston first before buying it.

According to manual if I understand it, there are some parts such as gaskets, circle clips, cam chain etc. you should replace every time you open it, but as long as everything else is in the right measurement It's good to work for many more hrs.

While I'm doing it I probably will replace the springs, in hopes to keep the valves tight against the seat.

Mark

Mark your measurements are dead on...I assume this is after they were adjusted. Grey is correct nothing needed.

55-65 since the top end hrs is a spread/guess - are you using a hour meter or guessing? I know MXTuner - he won't tell you, you need something unless he has taken apart and shown the problem to you. Tell him I said so :ride:

Yes to be be 100% safe follow the 100/40hr rebuild rule. This will insure the bike is at it's peak performance. Do this especially if you race and want peak performance.

Realistically though you can go much farther on valves and top end if the bike is maintained correctly. But you may want to check the cam chain for wear and the cam chain adjuster - Mark Klein knows how these wear - he replaced mine.

GreyRacers quote:

As far as the top end goes, it depends a little on how you're using the bike. If it's a full time serious racer, 60 hours is quite a bit, and it wouldn't hurt to freshen it, especially if the same cylinder and piston was used last time. A play bike is a different matter. In either case, having a leak down test done will tell you more.

It also depends on what maintenance philosophy you choose. Are you going to wait until the parts are worn to the limit, and it needs attention right then, or are you thinking more of refreshing the engine on a preemptive basis, doing the work before it's strictly necessary. The former plan carries the risk of having something actually break, causing major damage. The latter plan always discards a certain amount of useful life, and in that sense, is a waste to some extent.

I agree 100%!

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Well, I can ride any day of the week so anytime there's a Sunny day and looks dry enough I'm gone riding.

I don't race so it's just for fun. I like MxTuner he does everything on my bikes.

Let me rephrase the valve issue. intake were .004, .005 and <.004 Exhaust were .008, .008 that's all before adjustments.

I don't know what he reshimed it to, I didn't ask, but seems like you all think it wasn't necessary, well too bad it's done.

I had it done, because I couldn't start the bike in the morning after I arrived at Durhamtown, so I replaced the spark plug and still nothing. But when I push started, it started right up even cold, now when in operating temperature the bike kick started just fine.

MxTuner suggested checking the valves so I did that night and I came up with the above mentioned measurements.

After having the valves adjusted, the bike starts no problem again.

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Well, I can ride any day of the week so anytime there's a Sunny day and looks dry enough I'm gone riding.

I don't race so it's just for fun. I like MxTuner he does everything on my bikes.

Let me rephrase the valve issue. intake were .004, .005 and <.004 Exhaust were .008, .008 that's all before adjustments.

I don't know what he reshimed it to, I didn't ask, but seems like you all think it wasn't necessary, well too bad it's done.

I had it done, because I couldn't start the bike in the morning after I arrived at Durhamtown, so I replaced the spark plug and still nothing. But when I push started, it started right up even cold, now when in operating temperature the bike kick started just fine.

MxTuner suggested checking the valves so I did that night and I came up with the above mentioned measurements.

After having the valves adjusted, the bike starts no problem again.

good deal - valves probably needed adjustment

lets go ride it is snowing.....:ride:

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Didn't notice the "less than" .004 on the one intake.

That raises an important question: How much less? Find out how much he hed to change the shim size in that valve. If it was .10mm (.004") or more, the valve is bad.

It will be prudent to recheck that valve again at 4 and 8 hours more time to see if it's holding at a stable clearance. If it continues to close up, that's another indication it needs replacement.

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