Screw it! I Just went for it.

[BuzzAlmighty]

While I was putting my 400EX motor back together, I had a question about cam timing. The book I was using didn't have the answer so I caled the Honda shop. I asked the head mechanic what would happen if you installed the cam 180 degrees out (upside down) with the piston at top dead center.
His answer didn't seem quite right. I asked the kawasaki head mechanic and got the same answer. Well I decided to just try it, turn the cam 180 out and try to start it. I got my answer, do you know what happened?

[GPracer2500]

Should I explain the answer or let the pole run it's course??

[BuzzAlmighty]

I want to see what the poll does, you can PM me with your theory on the matter.

I'm not a motor guru, but here's my guess...

The cam 180 degrees out, and the piston at TDC kinda offset each other, and the motor ran fine.

[BuzzAlmighty]

I will eventually tell you guys what the Honda guy said would happen and then I will tell ya what actually happened when I tried it. I'm just gonna give the poll some time to get some more votes.

Originally posted by BuzzAlmighty
I will eventually tell you guys what the Honda guy said would happen and then I will tell ya what actually happened when I tried it. I'm just gonna give the poll some time to get some more votes.

I'm also thinking you were pretty sure you already knew what was gonna happen...and that helped me cast my vote.

:D

[BuzzAlmighty]

I wasn't positive, what I thought was from pure speculation.
The answer I got from Honda sounded like they were making it sound a lot more complicated than it actually is, just to get me to bring it to them.
I was willing to have my head redone if something went wrong, so I just went for it and tried. I got my answer, and soon you'll have it too.

[rooster300ex]

I bet it ran like crap or something like that.

[BuzzAlmighty]

Be sure to vote, even if you are not sure, just guess. I need as many votes as possible.

[projectram]

Something about this just dont sound right so i guessed piston hit the valve but i still dont know much about these motors.

[stalefish_132]

if the cam is 180 deg. out the valves will hit the piston.normally when the piston is travleing down the valves would be opening where as if its 180 out the valevs will be opening when the piston it travling up, it won't run.

Originally posted by stalefish_132
if the cam is 180 deg. out the valves will hit the piston.normally when the piston is travleing down the valves would be opening where as if its 180 out the valevs will be opening when the piston it travling up, it won't run.

But its the cam that actuates the valves, right? I'm asking.

So, if the cam is 180 degrees out AND the piston is 180 degrees out ( @ TDC ) , then the valves and the piston would be back in synch, right? It should run.

That was my thinking.

This all assumes the cam and the piston are both exactly 180 degrees out - if slightly off, the engine would run slightly crappy.

[GPracer2500]

garandman is on the right track...

It is impossible for a cam to be exactly 180 degrees out of time. This is because the cam spins at exactly half the speed of the crankshaft. The crank spins around twice for every one revolution of the cam.

What you've got to remember is that there are TWO top dead centers (TDC). One is on the compression stroke and one is on the exhuast stroke. It takes 720 (360 x 2) degrees of crank rotation to complete all 4 strokes. The only thing that distinguishes one TDC from the other is the position of the valves (which, obviously, is controlled by the cam). Look at it this way, with no cam installed in the engine, which stroke is the exhaust stroke and which is compression? Answer--> it's undetermined until the cam is installed. Install the cams with the lobes facing up and you've just set that TDC as the exhaust stroke. Install with the lobes facing down and you've just set that same TDC as the compression stroke. It's all the same as far as the engine is concerned because the plug fires on every up-stroke (even the exhaust stroke).

Lets say the piston is at TDC on the compression stroke. That means the cam lobes are facing down (on a rocker arm equipped head like the 400EX) and the valves are all closed. Now we spin the crank around 360 degrees to the set the piston to the other TDC, the exhaust TDC. The cam only spun around 180 degrees and now the lobes are facing up. We could remove the cam and reinstall it 180 degrees from where we started. What's happened? All we've done is flip-flopped the compression stroke with the exhuast stroke. The engine doesn't care or even know that anything has changed. We're right back to where we started--TDC on the compression stroke and everything is still perfectly in time even though we've flipped the cam 180deg.

Make sense?

BTW, at the time of this post the poll is at 7, 3, 9, 4 top to bottom.

Usually you gotta pay cash money for the ejumakashun GPracer just gave us.

Great topic.

[GPracer2500]

:p

This concept would be a lot easier to illustrate with an engine in front of all of us. It's tough to use words to describe the motions of the crank and cam while keeping it clear and simple but not leaving anything out....

Originally posted by GPracer2500
:p

This concept would be a lot easier to illustrate with an engine in front of all of us. It's tough to use words to describe the motions of the crank and cam while keeping it clear and simple but not leaving anything out....

Just slow down your avatar, and throw a crank and cam in there.



:cool:

[Quaddog3]

My Guess is if you were 180 degrees out, you ended up with 5 reverse gears:D

[exrider008]

Originally posted by Quaddog3
My Guess is if you were 180 degrees out, you ended up with 5 reverse gears:D :huh :huh

[Quaddog3]

Originally posted by exrider008
:huh :huh

Just taking the mick........ I would imagine it ran like crap.

[projectram]

GPracer,

That was by far one of the best posts i have ever read. I know that will come in handy once i do my rebuild this winter.

[exrider008]

i agree. we need to have a member of the year cuz GPracer2500 would deff get my vote.

[RiderTRX400ex]

it will run.

[RiderTRX400ex]

and yea gpracer is the f00ken man!!!

he my idol

[buster024]

i agree. we need to have a member of the year cuz GPracer2500 would deff get my vote.


:D :D :D

He does have some pretty sick stuff. How do you sleep at nights with all that in their!!

[procircuit406ex]

Originally posted by GPracer2500
:p

This concept would be a lot easier to illustrate with an engine in front of all of us. It's tough to use words to describe the motions of the crank and cam while keeping it clear and simple but not leaving anything out....

here this ought to work,its my screensaver,it takes like 5 minutes but it builds the whole thing it really neat :cool:

http://feerc.ornl.gov/video/index.shtml

[GPracer2500]

Originally posted by procircuit406ex
here this ought to work,its my screensaver,it takes like 5 minutes but it builds the whole thing it really neat :cool:

http://feerc.ornl.gov/video/index.shtml

That's a GREAT animation....maybe the best of its type I've seen. Thanks for the link!

Answer?

[procircuit406ex]

Originally posted by GPracer2500
That's a GREAT animation....maybe the best of its type I've seen. Thanks for the link!

no problem:)

[procircuit406ex]

Originally posted by garandman
Answer?

I think it ran fine,it may be just me though:ermm:

[ohsobad_chevy]

That was an awesome link to the engine. I agree 110% about GPracer!! Lots of knowledge on the subject!!!! Much appriciated GP!!! :)

[BuzzAlmighty]

Well, I must say, I wasn't expecting so many responses so quickly. Thanks to all of you for your poll votes.

The answer is: The motor ran fine. In fact, its still running today and this was around a year ago. I purposely installed the cam exactly 180 degrees out from what the installation manual told me to. To prove to my non-believing friends that nothing would happen.

One interesting thing is, I never saw anyone post the ONE thing you must have in order for this "cam flip" to work. The spark plug must fire at every TDC. The 400EX has a crank sensing type ignition system. Every time the crank does 360 degrees, the spark plug fires once. Therefore, the plug fires just after the exhaust stroke when it doesn't need to because there is nothing there to burn.

Furthermore, I consulted the head mechanics at my local Honda and Yamaha dealerships. They both said that piston and valve contact would result. When I told them that I thought they were wrong, they said the classic "I went to school and learned all this, what would you know".

What I know is that I have common sense, and anyone who thinks for 1 minute about what goes on in an EX motor would know I was right. It upset me that my intelligence was put down cause I didn't have some stupid degree, that degree obviously can't prove anything.

Thats my knowledge from experience.

Originally posted by BuzzAlmighty
The spark plug must fire at every TDC. The 400EX has a crank sensing type ignition system. Every time the crank does 360 degrees, the spark plug fires once. Therefore, the plug fires just after the exhaust stroke when it doesn't need to because there is nothing there to burn.



I wonder is this matters, or not.

I can't think of a reason why it would be bad.

Good job on acquiring info, and using your head. Bah on the silly mechanics.

Just cuz they are paid to do it as a profession doesn't actually mean they are "professionals."

[BuzzAlmighty]

I guess the whole reason I decided to go to such extremes to prove my point was that I wanted to know, for sure and without doubt, what would happen. In my mind it would work but I wouldn't know for sure unless I witnessed it myself.

The moral of this story would have to be that, don't make decisions and spend money based soley on the advice of a so called "professional". I'm sure most of them know thier stuff, but how do you know they are telling you from experience or from a slightly educated guess. Do your own research, find out for yourself. You know that these "pros" won't ever give the answer "I don't know".

[GPracer2500]

For whatever reason, it seems that dealership mechanics are some of the worst around. I'm glad you trusted you instincts and made the right choice. :)


Originally posted by BuzzAlmighty
...One interesting thing is, I never saw anyone post the ONE thing you must have in order for this "cam flip" to work...
Umm, I did. I wrote, "...It's all the same as far as the engine is concerned because the plug fires on every up-stroke (even the exhaust stroke)..."

The EX (and the vast majority of 4 stroke quad/bike engines) have what's called a "lost spark" ignition and fires the plug on every stroke. Many older motorcycles from the 60's and 70's had their points mounted on the end of the cam. Very few engines with CDI ignitions time the spark off the cam(s). The early 80's XR200 is the only example I can think of that has a pulse generator on the cam. In those cases the valve timing will still be correct if you flip the cam 180deg but the spark will occur on the wrong stroke. Lost spark systems have no downside that I'm aware of.

While we're on the subject, I should note that the spark NEVER occurs right at TDC. It occurs at some point before TDC. This is what ignition advance is all about. On the 400EX, the initial ignition advance is 8 degress BeforeTDC. This small amount of advance is needed for starting and good low RPM throttle response. But after 4,200 RPM the ignition advance switches to 27 degrees BTDC for a more complete mixture burn at higher RPM. It takes time for the mixture burn to take place. You've got to start the burn at a certain point so that it finishes (and peak cylinder pressures are produced) at the point in the stroke that is most advantages for producing power (usually about 15 degrees AfterTDC).

You know all those other marks on the flywheel you see when looking for the "T" mark to set the piston at TDC? The "F" (Fire) mark indicates when the spark fires at the initial advance. Those other two "hash" marks that are farther away on the flywheel indicate the ignition timing at full advance.

[BuzzAlmighty]

Sorry GP, I must have just missed that part.

As far as all those marks, I didn't know that. Thanks for the info.

[GPracer2500]

Originally posted by BuzzAlmighty
Sorry GP, I must have just missed that part.

As far as all those marks, I didn't know that. Thanks for the info.

No worries. :) It's a good point to highlight and I just barely mentioned it.

[400eXr1d3rZ]

If you flip the cam 180 degrees in a single cylinder it wont matter. But if you did it in a car v6 v8 whatever your gonna need a new motor :p

[krt400ex]

Originally posted by BuzzAlmighty


Furthermore, I consulted the head mechanics at my local Honda and Yamaha dealerships. They both said that piston and valve contact would result. When I told them that I thought they were wrong, they said the classic "I went to school and learned all this, what would you know".

What I know is that I have common sense, and anyone who thinks for 1 minute about what goes on in an EX motor would know I was right. It upset me that my intelligence was put down cause I didn't have some stupid degree, that degree obviously can't prove anything.

Thats my knowledge from experience.

experience is better than any kind of schooling. this kind of stuff get me so p!$$ed off. one person thinks that they r better than the other because they were schooled. bull $%#!.

[400eXr1d3rZ]

Yeah, I find people who learn by themselves and not by a school do things alot better.

[Caseys 300ex]

Yeah, all a atv mechanic wants is your money. If the owner of the atv just figures everything out himself they will know more so in the future they will know what the problem is from past experience . So it helps u out if you just try your own methods.

[jtjpilot]

good info and all but I think this guy needs to get laid

[krt400ex]

Originally posted by jtjpilot
good info and all but I think this guy needs to get laid

:huh that was random :huh

[ohsobad_chevy]

Originally posted by jtjpilot
good info and all but I think this guy needs to get laid

Your mom still game for Friday night...I'm ready to tear it up!! I'll smack it once for everyone on the forums!! :p :p

[AR15 guy]

Originally posted by 400eXr1d3rZ
If you flip the cam 180 degrees in a single cylinder it wont matter. But if you did it in a car v6 v8 whatever your gonna need a new motor :p

Not true. You can install a camshaft 2 different ways on a small block chevy.

You can install with the mark at 12 oclock or 6 (180 degrees). Long as your crank is positioned at 12 it doesn't matter.

Originally posted by AR15 guy
]

Hey....don't I know you from another website?

[ohsobad_chevy]

M1 garand and AR15...what a cute couple :p :p

Originally posted by ohsobad_chevy
M1 garand and AR15...what a cute couple :p :p

Yes quite a couple, just like Chevy's and repair shops.... :devil:

[BuzzAlmighty]

A V-8 would run fine with the cam 180 out, if the distributor was modified to spark every cylinder at TDC. Without this modification you just crank on it all day without a fire. But you wouldn't have piston to valve contact.

Don't believe me? I guess you could try it and see. But how much do you trust my opinion? Probably not much.

Does anyone have a website that shows a real close look at cam and valve a piston operation? Something you can pause would be awesome.

[ohsobad_chevy]

Originally posted by garandman
Yes quite a couple, just like Chevy's and repair shops.... :devil:

That did it...where do you wanna meet!! :macho :macho

:p J/K

Originally posted by ohsobad_chevy
That did it...where do you wanna meet!! :macho :macho

:p J/K


LOL....I figgered that would get a response.

:D :D

I find it funny people are still answering "it hit a valve" even after the answer has been revealed.

I guess they just don't beleive it.



:devil:

[krt400ex]

Originally posted by garandman
I find it funny people are still answering "it hit a valve" even after the answer has been revealed.

I guess they just don't beleive it.



:devil:



ya.....lol

[Rafikie]

Originally posted by BuzzAlmighty
Well, I must say, I wasn't expecting so many responses so quickly. Thanks to all of you for your poll votes.

The answer is: The motor ran fine. In fact, its still running today and this was around a year ago. I purposely installed the cam exactly 180 degrees out from what the installation manual told me to. To prove to my non-believing friends that nothing would happen.

One interesting thing is, I never saw anyone post the ONE thing you must have in order for this "cam flip" to work. The spark plug must fire at every TDC. The 400EX has a crank sensing type ignition system. Every time the crank does 360 degrees, the spark plug fires once. Therefore, the plug fires just after the exhaust stroke when it doesn't need to because there is nothing there to burn.

Furthermore, I consulted the head mechanics at my local Honda and Yamaha dealerships. They both said that piston and valve contact would result. When I told them that I thought they were wrong, they said the classic "I went to school and learned all this, what would you know".

What I know is that I have common sense, and anyone who thinks for 1 minute about what goes on in an EX motor would know I was right. It upset me that my intelligence was put down cause I didn't have some stupid degree, that degree obviously can't prove anything.

Thats my knowledge from experience.


You got to love how some people treat others. I called Honda one day to inform them that the parts break down of the starter clutch assembly for the 400ex was not acurate. It wasn't anything major just that 2 of the spacer/bushings were mixed up and the woman on the gave me the classic "I'll be sure to let our tech know" bs just to humor before letting me go. I showed my local dealer and they confirmed it. oh well what can you do

[BuzzAlmighty]

I have lost all faith in Honda around here, if that guy was allowed head mechanic, can you imagine the nut cases that work with him. They aren't touching anything of mine.