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Top End on my 426, what a waste of time!

33 posts in this topic

Okay, so maybe Gorrs arcticle got to me a little bit, so today I tore down the top end on my 2002 YZ426. I tore it down only to find the piston and rings still looked like new, the valves where still in spec too. The cylinder still has the cross hatch marks in it too. This bike does not have an hour meter on it, but I bought it new, rode the chit out of it, and changed oil every other ride, and I think it would've lasted 2 more years at least on this top end.

So I guess the only good thing that will happen now is a high compression piston and a 450 cam. How many of you recommend a high compression piston over the stocker? Is it a big difference in boost?

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That article got to me too....now my 450 is in a bunch of parts and pieces new piston rings, valve springs..cam , cam chain :cry:

FYI: My valves were in perfect condition with 150 hrs on them, seats were all in spec - decided to swap springs add a new modified 450 cam, cam chain - tentioner is fine - that really scared me the article ...bah humbug! :cry:

Well at least it is fresher now than before - suspension going to Enzo next week, as I bought used Enzo sub tanks and happy with my 03 until I see what churns out for 06.. :cry:

This motor/valves looked new - I will stick to Mobile 1 - red cap ,,,, 4R in my 426s and the valves always looked cooked. :cry:

amen Yamaha you build the most reliable 4 stroke! May not be the best , but it is the most reliable!!!!!!!!!!!! :cry:

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The article was the biggest waste of reading time I've had next to reading The Hobbit.

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You can get more hours out of one of these motors than was said in that article before rebuild time. Just depends on how hard you are on your bike. That article was really a bunch of bull.

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I don't know the article in question but this saying comes to mind, "if it ain't broke..... :cry:

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Would someone please post a link to the article in question?

I read it in Dirt Rider Magazine (Feburuary 2005). I don't know if it was online or not. I think we should send out a lynch mob for Gorr. :cry:

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Engine rebuilds and upgrades are the life Blood of Eric Gorr's business (and he does Great work!). I totally expect that kind of article out of someone who needs the business to survive. The funny thing here is that many folks are falling for it after many of us have reported for years that it was completely unnecessary. This is just another expensive lesson for those who figure "If it's in Dirt Rider, then it must be true."

Bonzai :cry:

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Would someone please post a link to the article in question?

it is in December part 1 and January part 2 DirtRider mag

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I bet Mr Gorr knows what he is talking about. Maybe he just sees and repairs more of the bikes that have been ridden harder the same amount of hours as you (we) run more gentle. And maybe he talks generally about bikes not taking into consideration the blue ones are in another league when it comes to reliability.

Those who have opened up the engine "invane", have you measured the piston/rings and cam chain stretch? The cylinder will always have the cross hatch marks, that is no guarantee of troublefree hours.

Remember if you blow it up, it is easily 2 grands to fix it. And it usually blows up without a warning. Do it cheap voluntarily, cause when it is obligatory it really can be expensive. With 150 hours I would not even consider leaving it undone. JMO.

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I've heard horror stories from guys at the shop about those that don't do their top end in a timely fashion. As SureBlue says, if something goes wrong (the timing chain snaps or even just jumps a tooth), the result is a $2500 problem. That has me concerned!

I raced my '03 450 about 25 weekends in 2003. Rode hard many others. Raced about 4 times in '04 and rode another dozen times. Is it time to pop the top and spend preventative $$ on it? I'd rather not if it is in good shape and will continue running fine. I probably won't ride/race as much in '05, either. Other priorities last year and this year. Which makes me even more reluctant to undertake a task that may or may not need to be done. And since this is my first cam-and-valves bike, the whole thing makes me nervous. Unless I take the REALLY expensive route and just roll it into the shop.

It starts easily and runs fine. Restarts when hot easily. Just a couple kicks whether first time that day or the 30th time. No problems at all, no indication of unhappiness. But I've heard that doesn't mean much.

To open it up or leave it alone - that is the question!! Feedback welcome!

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Its just what SureBlue said people look at there piston and rings and think they are fine. Well unless you start to measure them you really wont see anything wrong with them. And yes it is good to see no lines in the cylinder you want to see the hatch marks. Those pistons see wear big time look at the compression and rpm that piston is seeing. Its just like 2-smoke riders that dont think they need to change the piston all the time.It will always catch up to you in the end.

I've done my 450 3 times already and it has tons of power for what is done to the motor. Also the valves might be in spec with the cam but flip your head over and to most ppl they wont notice, but to a 4-stroke guru will see that, at least 1 or 2 valves will be leaking. TI vavles with Alum head they will pound themselves into the head. Theres nothing you can do about it.

just my 2 cents

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Also when you have the cam chain out you need to check every link on both sides closely! I found half of one link broken! It still freaks me out to think of what would've happend had I not found that.

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Also when you have the cam chain out you need to check every link on both sides closely! I found half of one link broken! It still freaks me out to think of what would've happend had I not found that.

If you want to be freaked out read your owners manual. I finally opened my book and started reading, it shows you need to check your valve clearance every third ride and replace the piston rings every fifth ride. Who does this?? Not me! Oh yeah I have a new cam chain to install while I'm doing the top end.

That beer can framed 250 is starting to look better. Hell of alot cheaper to overhaul, thats for sure. :cry:

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Buy a leak-down tester

A leak-down tester will tell you nothing about the real condition of the cam chain nor the piston. It only tells if your valves leak or the piston rings blow-by. We all have a leak-down tester; the foot that fires up the bike. Learn to read what the foot says when you try to start the bike invane.

The #1 mistake I see at tracks with thumpers is that they are revved right after starting the engine cold. That is the mother of all problems.

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Dang! You guys are scaring the gel out of me! Should I send it back? Just bought a YZ 426.

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Dang! You guys are scaring the gel out of me! Should I send it back? Just bought a YZ 426.

Oh no, biznet, you have bought the most reliable real racing thumper, don't worry about that. I would anyway have the condition checked/evaluated if you don't know how many hours it has been ridden and how it has been serviced.

Just with hours the risk of a big bang increases and therefore better to do something in good time. As somebody here said, these are more reliable than some of the cars out on the streets. :cry:

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