Is this normal

[JOEX]

There seems to be alot of carbon, most which I rubbed off. Underneath the carbon the piston surface looks pitted. It a stock 2001 400ex with not a ton of hours on it. I know it was running rich mostly from removing exhaust discs to reduce the sound level.

The pitting is what i'm mostly concerned about. I've always used 92 octane fuel and don't recall it ever pinging while riding.

[Rich250RRacer]

That appears to be the normal finish of a stock Honda piston. I believe that's the way they are cast.

[JOEX]

I was thinking that because the pitting is so uniform. Thanks.

[cals400ex]

looks normal too me. mine had a fair share of carbon build up on it too.

[wilkin250r]

Are you doing your own rebuild?

A word of advise, don't skimp on the rebuild and the time it takes to do it right. If you get the cylinder on and the deck height isn't right, take the time to pull it apart and correct the issue. Check the squish. Go through all the steps. It's time-consuming for sure, but well worth the rewards. I've seen stock-bore 400s with nothing more than high-comp pistons (but still running pump gas) and an XR400 cam outrun 440s, just because they were built properly.

[BLEEDRED]

A word of advise, don't skimp on the rebuild and the time it takes to do it right. If you get the cylinder on and the deck height isn't right, take the time to pull it apart and correct the issue. Check the squish. Go through all the steps. It's time-consuming for sure, but well worth the rewards. I've seen stock-bore 400s with nothing more than high-comp pistons (but still running pump gas) and an XR400 cam outrun 440s, just because they were built properly.

Couldn't agree more. It's a painful process and a bit of a numbers game, but take the time to do it right...I know I have my quad dialed in...had to have .010" decked off the cylinder...gasket thickness is very important too. Good luck.

BTW, that is exactly what my stock piston looked like.

[pegfoot]

Thats what mine looked like when I took it out, except there was alot more carbon.

[JOEX]

Thanks for the advice:)

How do you check the deck height and squish, I haven't got that far yet:ermm: I'm not building a speed machine, just somthing with a little more grunt and keeping reliability which i'm sure the deck height and squish will play a factor;)

[BLEEDRED]

Deck height will play a huge role along with gasket thickness when it comes to final set up of your machine. In order to get your desired compression ratio you will HAVE to know your deck height and gasket thickness. Squish is always good to check and if done correctly will lead to a cooler head and a cleaner burn.

This might help to get you started:

The Squish Band or "Quench" is defined as that area between
the flat of the piston and the flat of the cylinder head at
top dead center (TDC). On the compression stroke, as the
piston approaches TDC, the compressed mixture of fuel and air
is "squished" to the remaining space of the combustion
chamber where the spark plug and valves reside.
The "squeezing" of the mixture creates turbulence and is
expected to promote a better and more complete combustion.

Deck Height: The distance between the flat "quench" surface
of the piston and the top of the bare cylinder (no head
gasket). Typically an engine is set to zero deck height with
the head gasket (compressed value) defining the "squish band"
value. If the value is negative this indicates the
piston's "quench" surface extends above the top of the bare
cylinder.

You will have to use a set of callipers to measure your deck height. Most people use modeling clay or solder to measure the squish. You set your engine up and then put a chunk of solder or clay on the edge of the piston and then turn the engine over by hand, then measure the solder or clay with a set of callipers. Ask more questions as needed, you are on the right track. Good luck.

[chad502ex]

informative thread here

[BLEEDRED]

There are actaully tons of threads exactly like this out there. The search option is very useful. But I never mind helping. Anyone with a wrench can set up and engine, but getting it right is an art.

[wilkin250r]

Bleedred nailed it on the head, except that I don't think it will be possible to use calipers to measure the deck height. The best method is a dial indicator and magnetic base, but a set of feeler gauges can work well.

Joe, even though you're not building an all-out drag racer, you're still looking for an increase in power. Think of it like blueprinting an engine, proper setup is one of the few modifications that add both power AND reliability.

As Bleedred has said, deck height is the distance from the edge of the piston to the top of the cylinder wall at TDC.

Get a GOOD set of feeler guages and stack them against the edge of the piston at TDC, and feel for a lip. You might not be able to feel .001", but you'll easily feel 0.003", and that's close enough. You might want to rotate slightly before and after TDC to make sure you truly have an accurate measurement, and you're not accidentally measuring 10 degrees before TDC.

[wilkin250r]

Feeler gauge method. Remember, we're only concerned about the lip. This should be done initially using an old base gasket, we don't want to ruin the new one.

It doesn't take a rocket scientist to figure out that base gasket thickness will affect the deck height.


http://www.macdizzy.com/images/feeler.gif

[wilkin250r]

The squish band, or quench band, is the distance between the piston and HEAD at TDC, measured at the edge of the piston. The squish will get larger as you get closer to the center of the piston, this is called the squish angle. We don't really care about the squish angle, our primary concern is the squish measurement at the edge of the piston.

Again, it doesn't take a rocket scientist to figure out that the squish height is going to be the deck height plus the gasket thickness.

[wilkin250r]

Now, here is where it starts to get tricky on the 400EX. For some unfathomable reason, Honda built a huge deck height into the 400EX, like 0.040". Combined with a gasket thickness of about 0.030", this gives a total squish around 0.070". This is huge, and it is the whole reason aftermarket pistons often fail to reach advertised compression ratios.

To correct this, most people get rid of the base gasket altogether, and use a high-temp sealant in it's place (usually Honda HT). This shaves about 0.020" off the deck height. Combined with a thinner head gasket (usually XR400 Gasket), this brings the squish very close to 0.040", which is right about where you want to be.

[Doibugu2]

I did the rebuild myself and didn't adjust for any of this. I knew it going in, but didn't take the time to figure this out.:eek:

And I think I'm not running as strong as I should be.

If I ran the cometic gaskets and a Ross piston 10.8.1, does anybody know if I'm even close?

I'm sure someone has done a rebuild with the same piston and gaskets.

[wilkin250r]

So, on the original topic, Joe, my advice to you is to take your time and measure these things. You may find yourself putting on and pulling off the cylinder a few times to measure and correct everything. It's time-consuming, certainly, but the rewards are definitely worth it.

A proper squish will help prevent detonation, allowing higher compression on pump gas. I assume you're not looking to run race gas.

The compression ratio of the piston is dependent upon the proper setup. If you have a squish of .070", it's a pretty sure bet that your 11:1 compression is actually 9.5:1.

This is the true key to high performance. An 11:1 compression will give you much better low-end torque and performance, and greater acceleration. Plus, the proper squish will give you resistance to detonation. Power AND reliability.

As the old saying goes, the devil is in the details. :devil:

[wilkin250r]

Originally posted by Doibugu2
And I think I'm not running as strong as I should be.

I think you're right. If you're using the stock-thickness gaskets, it's a pretty sure bet that your compression is below 10:1, probably around 9.5:1.

You would be surprised at the difference in low-end power between 9:1 and 11:1. I just recently rebuilt my 250X with an 11:1, and I was shocked. The top end feels about the same, especially since I'm still running the stock cam, but the low-end punch has dramatically increased. Acceleration has improved, and I had to changed the gearing because it revs quickly. It's much easier to bring the front end up.

[rneal]

Originally posted by wilkin250r
I think you're right. If you're using the stock-thickness gaskets, it's a pretty sure bet that your compression is below 10:1, probably around 9.5:1.

You would be surprised at the difference in low-end power between 9:1 and 11:1. I just recently rebuilt my 250X with an 11:1, and I was shocked. The top end feels about the same, especially since I'm still running the stock cam, but the low-end punch has dramatically increased. Acceleration has improved, and I had to changed the gearing because it revs quickly. It's much easier to bring the front end up.

Wilkin250r, do you have to run an adjustable cam sprocket to compensate for a thinner base gasket? I'd assume running a thinner gasket would advance your timing?

[wilkin250r]

I think that's the wrong direction, I believe it will retard your timing, not advance. Thicker gaskets would advance.

The answer is yes and no. Yes, it will retard your timing, and you can get an adjustable cam sprocket to correct the issue. However, you don't HAVE to, because 0.040" change is only about 2 degrees of camshaft rotation, or 4 degrees of crank rotation, which isn't a huge issue.

In theory, retarded camshaft timing will shift the power higher into the RPM range, which may actually work in your favor. The increased compression will give you more low-end power, and the retarded cam timing will give you more top-end power.

However, I doubt you would see a significant difference in a small change in camshaft timing.

[duke416ex]

Ok, tell me what you think of my setup and what you think I should do. I did a rebuild 2 winters ago as follows: cometic 400ex gaskets, 10.5:1 wiseco 416 piston, full p&p.

This is what I was maybe thinking of changing to, I have a stage 1 hot cam and 450 chain to install, maybe getting xr400 gasket, no base gasket, and new rings. I am also getting a 450 carb and 8 plate clutch and new basket. Do you think that the gacket change would be worth it or should I just leave it alone and install the cam?

[wilkin250r]

If you're changing the cam chain you're going to have to tear it down, so you'll need new gaskets regardless. If you're changing the gaskets, then I would surely advise taking the time and doing it right, and setting the proper deck height and squish.

Before you tear it down, measure the squish. Take a piece of solder and insert it into your spark plug hole, and bend it so that it will reach the edge of the piston. Now rotate your engine BY HAND through TDC. The piston will compress the soft solder to the squish band height. Pull it out and measure it with a micrometer or calipers, being careful not to use too much pressure.

You might not find solder thick enough at Radio Shack, they typically carry up to .040" If you have a squish of .070", you'll need somewhere around .100". You should be able to find it at a hardware store in the plumbing section, it is used to seal copper pipes.

[BLEEDRED]

Good God Wilkin250R you are the MAN. Sounds like you have forgotten more about engines than I will ever know. Fantastic pictures and advice. Thanks for taking the time to help these guys out.

Wilkin is speaking the gosible right now, listen to him.

It is also helpful to go to www.rosspistons.com and check out the compression ratio calcutator. You will see how a tiny bit of difference in deck height and or gasket thickness will change your compressoin. And remember the bottom line is that nobody is going to be able to do this for you over this forum...you have to physically take the measurements yourself and crunch the numbers if you want to do it right. None of this:


Ok, tell me what you think of my setup and what you think I should do. I did a rebuild 2 winters ago as follows: cometic 400ex gaskets, 10.5:1 wiseco 416 piston, full p&p.

We're here to help, but you gotta do the math my man...

[FoxRacing81]

I just bought a Ross 11:1 426 piston witha cometic full engine gasket kit. If I put the gaskets on it came with, does that mean it'll lower my compression? I'm trying to understand this but it's kinda hard for me to comprehend when I don't know much about motors....Would runnign the high-temp sealer instead of base gasket and cometic head gasket work?

[RiderTRX400ex]

i doubt you can run that sealant as a head gasket if thats what you were thinking... and from reading this thread... yes your right... the gaskets will lower your compression

[JOEX]

WOW!:eek:

Thanks for all the info and the pics are an enormous help:cool: I've read many of the past threads about the squish and deck height and had a general idea of what they were but this thread made things much clearer;)

I don't want this to get off track but does the timing advance key have an effect on any of this?

Thanks again, Joe

[wilkin250r]

Uh, erm, timing is a gray area for me. I only know the basics, and I have no idea what the timing map looks like for a stock 400EX, so I have no idea the full consequences of changing it.

Theoretically, it will increase the likelyhood of detonation, and also increase cylinder heat. If you're running a true 10.8:1, it might be the proverbial straw to break the camel's back, and push you into a need for race gas instead of pump gas, or at least a mix.

The timing key is supposed to increase low-end and throttle response, giving you a crisp throttle off the line. Personally, I believe if your motor is set up correctly, the compression will give you all that and you won't need the timing key.

[JOEX]

Originally posted by wilkin250r
Uh, erm, timing is a gray area for me. I only know the basics. Theoretically, it will increase the likelyhood of detonation, and also increase cylinder heat. If you're running a true 10.8:1, it might be the proverbial straw to break the camel's back, and push you into a need for race gas instead of pump gas.

The timing key is supposed to increase low-end and throttle response. Personally, I believe if your motor is set up correctly, the compression will give you all that and you won't need the timing key.
OMG! THere's something you're not sure about!?!:eek2: :devil: :blah:

I've had the key in for awhile and was wondering if I should take it out. Others have said they run the key on built motors with no problems but how dialed in their motors are could be debatable. I'm just wondering if it makes a difference if you're running the key with true numbers or published numbers:ermm:

[wilkin250r]

Don't tell anyone, I'll lose all respect... :eek:

I suspect you're correct, many people running the timing key on built motors aren't dialed in correctly. Or, they might be already running race gas, so detonation or added heat are already compensated for.

I do know that a few experts have seen motorcycle and dirtbike engines with TOO much timing built in stock, and retarding the timing slightly and leaning out the mixture a tad produces a 5% or so increase in power. This was many years ago, I don't know if it's still prevalent in modern engines...

[JOEX]

Originally posted by wilkin250r
Don't tell anyone, I'll lose all respect... :eek:
OK, it'll be just between you and me;)

[BLEEDRED]

Would runnign the high-temp sealer instead of base gasket and cometic head gasket work?

That is the set up I run plus having .010" decked off the cylinder. Haven't had a problem yet...fingers crossed. I know plenty of other people run without base gaskets too, Cals400ex being one of them I believe.

[duke416ex]

I talked to the local shop that sponsors me about the xr gasket. His comment was that they blow a little easier than the 400ex gaskets. He said that the heads were designed a little differnet, he said the difference was that the xr400 was built a little heavier arounf the bolt hole and stuff. What so ya'll think about this?

[BLEEDRED]

I have never heard that...I would go as far as to say that I don't believe it. If there is any doubt in your mind then go with a 3 piece flex steel gasket from Cometic.

Cometic Gaskets (440)354-0777

[400exredrider]

i have the flex steels, sofar so good

[duke416ex]

I am running a 3 plate cometic gasket right now, and I wouldn't say that I wouldn't believe it, I have seen Honda do stranger things.

[BLEEDRED]

The reason that I say I don't believe it is because I hear of people running XR400 gaskets on 400EX's all day long and this is the first complaint I have ever heard. AND it was just what some guy said, not a first hand experience. Just my $.02. Good luck.

[wilkin250r]

I don't really know either way. People don't use the XR400 for added strength, they use it because it is thinner to increase compression and get the proper squish.

I have never had a head gasket blow. Perhaps that is because I take my time when assembling, I make sure the head and cylinder are flat, and I torque my head in 5lb increments. Perhaps I'm just lucky. Whatever the reason, because I've never had a head gasket blow, I can't really tell you what is "stronger". Whether it is cometic, or the stock gaskets, I've never had a problem with either one.

[BLEEDRED]

Let's be logical here. Does the fact that oil starts leaking from around a steel head gasket ever have anything to do with the gasket itself? Isn't is more common to be the mating surfaces and/or studs pulling or possibly broken or improperly torqued bolts?

I blew oil out the head gasket area of my 440. At the time I thought it was the studs pulling but after further investigation I found that it was three small bolts that hold the head cover down and bolt through the head and into the jug. They help hold everything tight around the cam tunnel and they were stripped. I corrected the problem and now currently dealing with another problem...see thread if interested:

http://www.exriders.com/vbb/showthread.php?s=&threadid=161205

[duke416ex]

I have never blown a head gasket either and hope not to. I just did the rebuild for a little extra pep. I guess for the trouble it will be to swap the gaskets over I will probably just not do it seeing as how I am making good power now and I do not burn oil or have a blown gasket.

Bleedred, not for arguement, but he was speaking from experience. I have known him for years and I know that he has been working on 400's in his shop since they came out. Also, on your oil leak, are you sure that the oil isn't leaking from the oil channel in the cylinder to where the stud is and coming up there or that the cylinder does not have a crack in it anywhere?