2009 Engine Maintenance

I have noticed the compression on my 2009 YZ450 is very weak. It doesnt take much force to kick it over. It has over 80hrs but it still starts easily.

 

Does this mean piston needs to be replaced, but the valves may be good? Please excuse my ignorance as I am trying to learn proper 4 stroke engine maintenance .

 

If my hypothesis is true, I was planing on doing a top end, which looks fairly straight forward per this tutorial but was wondering if I also need to replace valves and the timing chain as well.

 

I will inspect the crank once I have it all apart to see if that needs replaced.

 

Is there anything else I should consider replacing?

Weak compared to what? The engine has auto decompression that reduces the compression stroke from 120 degrees of crank rotation to about 20-25.

If you are suspicious, check the cam timing. As the chain wears, the timing becomes slightly retarded. Not a full tooth, but it delays the reseating of the exhaust valve by the AD mechanism when this happens, and that reduces cranking compression.

The definitive test of cylinder sealing is a leak down test. Have one done by a shop and you'll know if it leaks too much, and from where.

The compression felt weak while kicking but I was comparing that to my new '13 RM450. Maybe I was wrong to compare Blue to Yellow. 

 

I will check the cam timing

 

Looks like leakdown gauges cost about $70-$150. I will call the shop to see how much they would charge. If I bought the gauge is it straight forward to learn or will I be wasting my time?

You need an air compressor to go with it.  The process is simple, but there's a percentage of injury risk.  The crank has to be held near TDC because the air pressure will drive the piston down to bottom dead center, where one set of valves or the other will be open, dumping the pressure.   Holding the crank with a wrench against 100 pounds of pressure can be dangerous if the wrench slips and smacks you in the hand or elsewhere and sends the wrench across the shop.

OTC makes a pretty decent leak down tester for the price $60. It's worth the investment.

A shop will charge you 1 hours labor to perform the test considering you have to remove the gas tank. One hour at the cheapest shop is $60, all the way up to $100 at a dealership.

The piston could need replacing at 80 hours. I've been doing mine @ 80 hours and are ready to be replaced.

Valves should be fine but should be removed & inspected as well as the seats. But a leak Down test will tell you how much leakage. Also you can out the head on its side and fill the intake or exhaust port with solvent. You should see no leakage per the manual.

Always replace the timing chain they are $20 and stretch quickly. I even sell them when I do valve clearance checks.

Crank should be fine but inspect side to side clearance when you do the piston.

With this maintenance the bike will last you a long time.

I have noticed the compression on my 2009 YZ450 is very weak. It doesnt take much force to kick it over. It has over 80hrs but it still starts easily.

Does this mean piston needs to be replaced, but the valves may be good? Please excuse my ignorance as I am trying to learn proper 4 stroke engine maintenance .

If my hypothesis is true, I was planing on doing a top end, which looks fairly straight forward per

but was wondering if I also need to replace valves and the timing chain as well.

I will inspect the crank once I have it all apart to see if that needs replaced.

Is there anything else I should consider replacing?

Save your money and ride it for a couple hundred more hours. Use a high quality synthetic oil, keep the air cleaner fresh and your good to go. I just put a new piston in an 09 with well over 300 hours. The top compression ring was out of spec but that's it. Valves were all in spec and timing chain had virtually no stretch.

Save your money and ride it for a couple hundred more hours. Use a high quality synthetic oil, keep the air cleaner fresh and your good to go. I just put a new piston in an 09 with well over 300 hours. The top compression ring was out of spec but that's it. Valves were all in spec and timing chain had virtually no stretch.

I ran Motul, changed it every 5-6 hrs and kept a clean filter and got 100 hrs (hr meter from new) before my piston and rings were done. Everything else was fine. Wonder why such a huge difference? I don't bounce off the limiter either.

The difference is usually the total number of "horsepower hours" on the engine.  Like watt/hours, that's a measurement of how much energy has been produced over a period of time an engine that is required to produce 40 horsepower for 100 hours will wear faster than an identical piece that's only required to deliver an average of 30 for a hundred hours. 

 

I got considerably more than 300 out of my original piston and rings, but in desert racing, there are long periods of time where you're just rocking and bouncing along at a semi-steady speed, and other than the duration of the races, there's a much lower percentage of the time spent at full throttle than in MX.  It's also true that I ran the piston just a little farther than I should have, as the ring lands were beginning to come into contact with the bore walls.  No damage as a result, because it apparently just did start that at the time.

 

Get that leak down done, and/or open it up and have a look.

Thanks for the comments guys,

 

Here is what I am thinking, if i buy the Leak Down gauge at $64 + Air compressor at 100ish, thats $164 to tell me I will probably need a new piston.  So should I just go ahead and change the piston without doing the test or will it tell me other valuable information?

Thanks for the comments guys,

Here is what I am thinking, if i buy the Leak Down gauge at $64 + Air compressor at 100ish, thats $164 to tell me I will probably need a new piston. So should I just go ahead and change the piston without doing the test or will it tell me other valuable information?

If you open it up at least you'll KNOW. If you don't it might be one of those things that would sit in the back of your mind and nag at you. It would me. Just a little peace of mind.

The best part of the leak down test is it will tell you if the valves and valve seats are leaking and which side- intake or exhaust. At 80 hours they shouldn't need replacing as long as your clearances are still in spec and not needing shimmed more then once max.

One other test is upon removing the cylinder head full the intake and exhaust ports with a solvent and let it sit. Watch for it to leak past the valves and seats. There shouldn't be any at all.

Personally if replace the piston, mine are worn at 80 hours and I don't feel it's worth running any longer to save a few bucks. That and if it blows it could be 5x what that $200 piston costed. That and you stated the kicking compression seemed lower then what it was. Me I do rings on 2 strokes but not on these bikes, time is money and if I'm tearing off the head and cylinder I'm putting a piston in. Just my .02. Hope it's helpful

The best part of the leak down test is it will tell you if the valves and valve seats are leaking and which side- intake or exhaust. At 80 hours they shouldn't need replacing as long as your clearances are still in spec and not needing shimmed more then once max.

One other test is upon removing the cylinder head full the intake and exhaust ports with a solvent and let it sit. Watch for it to leak past the valves and seats. There shouldn't be any at all.

Personally if replace the piston, mine are worn at 80 hours and I don't feel it's worth running any longer to save a few bucks. That and if it blows it could be 5x what that $200 piston costed. That and you stated the kicking compression seemed lower then what it was. Me I do rings on 2 strokes but not on these bikes, time is money and if I'm tearing off the head and cylinder I'm putting a piston in. Just my .02. Hope it's helpful

What type of solvent do you use for that test?

 

What Piston brand would you recommend? Back in the 2 Stroke days I used to run Wiseco but I dont know who is making the best for 4 strokes.

 

Also I am in the Southern California area, more specifically north San Diego. Do you guys know a reputable shop to work with?

One other test is upon removing the cylinder head full the intake and exhaust ports with a solvent and let it sit. Watch for it to leak past the valves and seats. There shouldn't be any at all.

 

I can almost guaranty there'll be some seepage at least with a used head.  If the area around the valve gets wet, that's one thing.  If it leaks more than about 5-6 drips a minute, that's another.

 

Use any sort of petroleum solvent: mineral spirits, paint thinner, etc.

Per the manual there should be no leakage.

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I never had a used head leak solvent that didn't show some leakage on a leak down test and leakage on a vacuum test. This is over 40 years building race engines professionally.

I've been using JE pistons exclusively for all our motors even pro mod 800 plus cubic inch motors with great results for decades. They make a nice high compression piston for the yz450 at a great price. Wiseco also makes a decent piston as well and are good quality.

x 2 on the Wiseco forged pistons.. I have been running wiseco 13:1 pistons in my 09 450R, runs great, and they last a long time.!

 

JL

 

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Per the manual there should be no leakage.

I never had a used head leak solvent that didn't show some leakage on a leak down test and leakage on a vacuum test. This is over 40 years building race engines professionally.

 

 

There shouldn't be, but the reality is that there will be.  As far as showing up on a leak down test, maybe it would and maybe it won't, but a head that leaks just enough to wet the margins of the valve can actually go to a total seal under the additional pressure of the air in the cylinder during the test.  Speaking as a professional with over 40 years in the trade. 

 

Either way, that amount of leakage wouldn't represent more than a fraction of what's lost in a "perfectly" sealed engine past the ring gaps.  That's why no one ever legitimately gets better than 98% sealed on such tests.  Then you have tool variations, as there is no standard for the construction of the testers.  The test is only valid when used to compare an engine's current condition with a previously recorded test, or a known good example of the same engine type, which is why I recommend a shop do the job; they'll have a reference where most hobbyists or DIY guys won't.  Otherwise, it's only useful in locating leakage points and gross leaks.

There shouldn't be, but the reality is that there will be. As far as showing up on a leak down test, maybe it would and maybe it won't, but a head that leaks just enough to wet the margins of the valve can actually go to a total seal under the additional pressure of the air in the cylinder during the test. Speaking as a professional with over 40 years in the trade.

So the manual is wrong? Every cylinder head I have seen weap solvent has showed a leak during vacuum and pressure testing the valves and seats. That's unacceptable for racing. We tear down our Yz450's at 3 percent leakage with our Total Seal Gapless Rings. That 3 percent can be the difference btw a podium and a last chance qualifier.

This is from experience working over 40 years for the number 1 race engine shop in the US. Not 40 years in a garage or dealership doing a engine a week.

Good discussion fellas,

 

If the valves are seeping, what would I have to do to fix that?

 

and if they are good, I assume I put in the new piston and rings and I am good?

 

Gray, I am not opposed to a shop doing the test, however I am relatively new to north county San Diego and not sure who would be good to go too. Is a local Yamaha dealer capable of this or would this need to go to a race engine shop.

 

Also part of me wants to learn how to do the work: 1. because I like to do all of my own work and 2. I am tired of not knowing how to work on a 4 stroke!! They arent going away and I am not going to stop riding. Its a damn shame that bikes have literally become disposable, most friends sell it and get a new one before tackling a job like this.

been told by a local bike fella the wiseco pistons are forged and are a much harder and longer wearing piston as you say , problem is he says because they are harder they tend to wear the bore/cylinder more,

where as the stock pistons being softer piston wears ,hence bore/cylinder lasts much longer

x 2 on the Wiseco forged pistons.. I have been running wiseco 13:1 pistons in my 09 450R, runs great, and they last a long time.!

 

JL

I'd rather see you purchase the tester yourself and test it. That way you can let us know and we can help. Also you will know where your at now and after the rebuild. It's a great tool that you will use on all 4 stroke bikes, definitely worth the investment.

The leak down test will show you the leakage and you can pinpoint it the intake or exhaust by listening for air leaking in the muffler and at the air filter.

Once they are torn down you can then do the solvent test. You should have no seepage per the service manual.

As far as the forged wiseco pistons. All aftermarket pistons for the yz450 are forged. Wiseco je vertex wossner etc. also with the aftermarket you can go for a high compression piston for more mid range torque.

I prefer a forged piston myself.

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