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Gravesdigger

2010 YZ450F Season rebuild. Which Piston?

28 posts in this topic

Looking for reliability. I've got a 2010 YZ450F that I rode this year in 10 USRA desert races.

I ride track usually once a week and usually trail ride another 2 hours one evening and again on Saturdays.  

I estimate I've put 140-160 hrs on it and I purchased it in January with 20 hrs.... it's time for a full top end.

I've ordered Pro X stainless Steel intake and exhaust valve kits with new valve springs, a Yamaha Timing Chain and Top End Gasket kit and valve seals.

 

Wondering which piston I should order for the best reliability?

The bike has plenty of power for me, so I figure I'd like to stay stock 12.5:1 compression.

 

Pro X? $119

Wiseco? $126

Stock Yamaha? $109 

Something else?

 

What are the differences between them?

The last piston I did was in my 99 Yz400f and the stock piston was junk sintered powdered aluminum. While the new Wiseco was a beautiful forged piece.

 

Is the stock piston in my '10 a nice forged piece or should I buy another Wiseco?

 

 

I've been having stalling problems off and on all season and hard hot starting. Even with my Rekluse EXP 3.0

Two races I wasted 15-20 minutes with it not wanting to hot start for me and was stuck watching on the side of the trail until the bike cooled down enough to start again.

 

I've reshimmed the valves 3 times on the intake and 1 time on the exhaust.

Intake valves are down to .145 shim and they are going out of spec in 20-30 hours which is unacceptable at this point.

I'm inspecting/ adjusting valve clearance every 2-3 weeks. 

I figure I'll do it all myself but have the local shop recut the valve seats and match them to the new valves for me.

 

Anything else I should do?

I can check the valve guides and crank for movement.

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I've been running je pistons for my last three rebuilds. always come out nice. cnc aluminum. whenever I get a new piston I take some fine sandpaper and take the sharp edges off the valve reliefs so I don't get a hot spot in the piston. A heavy abrasive pad will also work.

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Neither of the other two pistons is as good as the OEM Yamaha in the first place, never mind that they both cost more.

 

You can't plan on doing everything to the head on your own because the vale seats have to be refinished professionally by either cutting or grinding with high precision equipment. 

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Good info, thanks guys. Looks like I'll order the stock piston.

 

Just as a side question: what makes the stock piston better?

 

 

Neither of the other two pistons is as good as the OEM Yamaha in the first place, never mind that they both cost more.

 

You can't plan on doing everything to the head on your own because the valve seats have to be refinished professionally by either cutting or grinding with high precision equipment. 

 

 

 

I figure I'll do it all myself but have the local shop recut the valve seats and match them to the new valves for me.

 

 

 

I know, I don't plan on buying the $600 tool to recut my valve seats

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Since your doing all this work I would look into a chain tensioner as well. Stock piston is going to be your best bet for reliability, as far as hot starts you need to richen your map down low and it should help. Also if you have a tuner, you should be able to get the run time on your motor by going to monitor and units I believe. You can also clear it out when you do your motor so you know how much time you get out of it this second time around. Make sure you hone your cylinder if it's in spec and buy a B,C piston depending on cylinder tolerance. Use ticker oil to take up some of the play In the rod as well.

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Make sure you hone your cylinder if it's in spec and buy a B,C piston depending on cylinder tolerance. Use ticker oil to take up some of the play In the rod as well.

 

Yamaha makes no such pistons, only one standard size.  The wear limit tolerable in the bore is .002", so it's out of spec before the piston/cylinder clearance needs adjustment.

 

Using "thicker oil" does nothing at all to compensate for clearances that are looser than specified.  It will slow down oil flow to critical parts, however.  Do not use excessively viscous oil beyond that specified in your manual for the range of temperatures you ride in.  If your crank measures out to be too loose, replacing or rebuilding it is the only right way, not stuffing bananas in the crankcase.

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Anybody have any real info on why the stock piston is better?

 

Good info, thanks guys. Looks like I'll order the stock piston.

 

Just as a side question: what makes the stock piston better?

 

 

 

 

 

I know, I don't plan on buying the $600 tool to recut my valve seats

 

 

Plan on becoming educated in its correct use, too.

 

What does this mean? Seems pretty straightforward

My local shop is will be recutting the valve seats

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See my post in this discussion #53, It will answer some of your questions, Oh and for Desert racing Go American Pistons they should have the experience and feedback to have their pistons cam ground with the needed clearances to live in that environment, Some very nice pistons such as German Wossner may be fine for some twenty minute motos but a long hard run in the desert is another thing.

 

Yamaha Pistons are OK but the focus is Motos in the design dept after all when it comes to Japanese factories Honda is the only one to consistently pony up to run in the Desert so the others will not have that hard earned knowledge base to refer to unlike Honda who have learnt how to survive in the Desert and that does flow down into the production models.

 

Here is the linked post.http://www.thumpertalk.com/topic/434311-2-stroke-oil-in-4-stroke-fuel-yey-or-neh/page-3

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Hard earned knowledge or not, the stock piston in my '06 went over 300 hours in 5 seasons of desert racing.  :excuseme:

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I figure I'll do it all myself but have the local shop recut the valve seats and match them to the new valves for me.

 

Anything else I should do?

I can check the valve guides and crank for movement.

 

Your being a little short sided with him arnt ya Gray?  Did you read his post entirely?

 

 

You can't plan on doing everything to the head on your own because the vale seats have to be refinished professionally by either cutting or grinding with high precision equipment. 

 

 

Hard earned knowledge or not, the stock piston in my '06 went over 300 hours in 5 seasons of desert racing.  :excuseme:

 

Those are great numbers... what kind of continuous RPM did you run over those 300 hours?  How much of that time do you think you spent  within 15% of the peak HP RPM?

 

I think you know my point... Longevity is directly related to RPM, along with... as we know, many other factors.

 

I just assumed with your knowledge and love of Yamaha 's you would be more forth coming with the op.

 

I'm not sure who makes the OE piston, but I would be willing to bet it's not Yamaha.  Many of the pieces of these bikes are sub-contracted and designed in such a manner to serve the purpose as inexpensive as possible.  This is the reason why it is a great choice to go outside OE... If there are any issues with the OE component (even if it is with the original manufacture of the piston) the after market replacement may have the fix.  The after market suppliers produce much smaller runs and can make adjustments to each run if they see fit or find a problem that R&D didn't expose.  This is also one of the main reasons aftermarket in this area is usually more expensive... cost per piece comes down the more pieces you make.

 

Just for the record, I'm not a fan of the heavy stainless valves. 

 

In my experience the bottom end wears as fast or faster than the piston and cylinder.

 

Sounds to me like you don't like to be inside your engine very often so If I were you I would give some thought to valve guides, connecting rod, big end bearing, and main bearings along with everything else you mentioned.  I don't think these parts will make it another 140 to 160 hours.

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Those are great numbers... what kind of continuous RPM did you run over those 300 hours?  How much of that time do you think you spent  within 15% of the peak HP RPM?

 

I think you know my point... Longevity is directly related to RPM, along with... as we know, many other factors.

 

I just assumed with your knowledge and love of Yamaha 's you would be more forth coming with the op.

 

I'm not sure who makes the OE piston, but I would be willing to bet it's not Yamaha. ...

 

Just for the record, I'm not a fan of the heavy stainless valves. 

 

 

I probably spend quite a bit of time within 15% of the peak power RPM during a race, honestly.  But not more than about 15% of the time at full power, most likely.  That's just how desert racing works.  You are, of course quite correct in that horsepower /hours, followed by time at speed are significant factors in figuring engine longevity.

 

The operative statement was that the OP is interested primarily in reliability.  In answering that, and in particular given the two alternative pistons explicitly mentioned, I do not see that any aftermarket solution offers a piston that will produce more of it that the OEM.   While the best that CP has to offer may be different, neither of the two candidates offered by the OP is as durable or completely compatible with the OEM bore as the stock.  You may disagree on any basis that you choose to. 

 

The OEM pistons are made by ART in Japan, a company that supplies OEM pistons for most of Japan's motorcycles, and has for a good many years.  They are made using current pressure forging technologies that allow using low expansion alloys and tight operating clearances.

 

But, we do agree on the stainless valves.  I don't see the reason for them, as they simply don't offer a significant longevity advantage over the OEM Ti valves, and what might appear to be a savings on the valves themselves is often made up for in the expensive engendered by having to upgrade the springs and retainers to address the extra weight.

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My 450 spends most of its time in Supermoto trim.  I usually replace stock pistons at 100 hrs for piece of mind and they are always in spec.  I have gone as long as 170ish hours with no issue and that is the majority of the time in the peak power range.

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We finally had poor enough weather for long enough to warrant me tearing down the bike for rebuild

 

Exhaust ports

20150106_210852_zpsniibg5wm.jpg

 

Intake ports

20150106_210935_zpsj40crohz.jpg

 

As you can see the shop did not install the new valve guides I provided for them, nor did they even clean the exhaust port...so I'll be visiting them tomorrow. They did reassemble and reshim the head correctly however (I double checked their work).

 

New stock Yamaha piston and cam chain.

20150106_220419_zpswtu6h2th.jpg

 

 

New valves.

 

20150106_210959_zpslrlwnina.jpg

Edited by Gravesdigger

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As you can see the stock valves were toast.

I can't imagine what would cause so much carbon deposits on the stems and the valves themselves.

Bad tune maybe?

I'm very strict about maintenance.  

 

DSC_9180_zpsa2413b08.jpg

 

Intake

DSC_9183_zps71754875.jpg

 

Exhaust

DSC_9184_zps06a315b5.jpg

 

I'll get them to check the valve seats too when I take it back to have them reinstall the valve seals. I'm sure they just forgot to swap the seals.

 

I'm not sold on Ti valves. Yes they are light and yes they are fancy, but the stock valves in my YZ400 looked better than these and didn't require as frequent adjustments.

Edited by Gravesdigger

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As you can see the shop did not install the new valve seals I provided for them, nor did they even clean the exhaust port...so I'll be visiting them tomorrow. They did reassemble and reshim the head correctly however (I double checked their work).

 

New stock Yamaha piston and cam chain.

 

No we can't see.  You didn't post a picture of the stem seal area.

 

 

As you can see the stock valves were toast.

I can't imagine what would cause so much carbon deposits on the stems and the valves themselves.

Bad tune maybe?

I'm very strict about maintenance.  

 

I'll get them to check the valve seats too when I take it back to have them reinstall the valve seals. I'm sure they just forgot to swap the seals.

 

I'm not sold on Ti valves. Yes they are light and yes they are fancy, but the stock valves in my YZ400 looked better than these and didn't require as frequent adjustments.

 

Do you think the valves are "Toast" because they have some foreign material on them?

 

Being strict about maintenance is a matter of opinion here.  I'm guessing here but I think the maintenance you are thinking of doesn't have much to do with deposits on the valves.  Having deposits on the valves will not directly effect longevity and in my opinion is not a major concern at this point. What I see is fairly normal in this type of example.

 

The tune will effect the amount of deposit on the valves but just because there are deposits on the valves doesn't mean the tune is bad.  There are many factors that contribute to deposits on the valves, including the simple ones like the type of fuel used and how much oil is getting into the combustion chamber.

 

Remember the oil can get in there in many ways: are you adding any or anything to the fuel/air stream? (in the fuel tank or on the air filter) Cylinder or rings not sealing as desired?  Valve stem, guides, and or seals.  Those are just the main culprits.

 

There are many race engines that don't even use stem seals.  Not because they weren't designed to use them but because the builder chooses not to use them.  Sometimes a little extra oil in there is not a bad thing.

 

I'm not going to state the differences between TI and Stainless now and the pro's and con's, doesn't seem to be the venue and obviously your mind is made up, you already spent the money.

 

I few things I would be more concerned with If I were you: Not only did they not clean the ports, the edges of the seats I can see don't appear to be clean either.  (Even though that is not the area that gets cut it is usually cleaned thoroughly) That tells me that most likely they did not cut the seats.  If the seats are not cut your new valves will need continuous adjustment just like what you replaced.  I think you need to step back, slow down, put some more thought into your rebuild, and ask more questions.  Just my opinion.

Edited by kx450f63

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Do you think the valves are "Toast" because they have some foreign material on them?

 

Being strict about maintenance is a matter of opinion here.  I'm guessing here but I think the maintenance you are thinking of doesn't have much to do with deposits on the valves.  Having deposits on the valves will not directly effect longevity and in my opinion is not a major concern at this point. What I see is fairly normal in this type of example.

 

 

I agree.  The carbon deposits are entirely normal, have nothing to do with how fastidious your maintenance routine might be, and have nothing to do with whether the valves are serviceable as is.  They are simply a function of how long and how hard it's been ridden, and of the fuel used. 

 

Where the problem with the exhaust valves is is at the arrow point in the picture below.  You see the detectable ridge there at the edge of the contact zone on the face?  That valve is worn out.  Ti valves are not naturally hard enough, and depend on an extremely thin coating of an exceptionally hard compound based on titanium nitride (technically a ceramic) to prevent them from wearing too rapidly.  Once the wear becomes visible, the coating is gone, and it's time to replace them.

 

But many, if not most, aftermarket stainless valves are treated the same way now instead of by hardening, so in the end, they don't last any longer, and they aren't any stronger.

 

Additionally, let me point out that a shop doing a valve job would not ordinarily clean the exhaust port except just under the seat so as to keep the seat cutter/grinders out of the carbon.  Maybe knock off some of the big pieces, but certainly not go in with a stone and clean it down to the metal. 

DSC_9184_zps06a315b5.jpg

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I was waiting on his response and I was too lazy to blow the pic up to see the seating surface, but now that you did and I have, notice the circled area.  Does it appear to be running out?  Basically the distance between the seating surface face and the head appears to be getting smaller.  Like it is wearing off center. (Another reason to suspect the guides are worn) The face appears to be concave, which is typical wear and the seat is a mirror image of this.  This is the reason why just replacing valves is not the best method for longevity.

 

 

Actually  the more I look at it, (the circled area) it may be an optical illusion. 

To the op, open up a true repair manual and read the section on valve seat repair.  It's a good read on the basics of valve inspection.

NewPicture_zps8498f102.png

Edited by kx450f63

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