having some wierd bike issues

while we wait, What about the Ninja 250?

We are all waiting for Matt to work all the bugs out of his 86 vf 500f. But as long as you (jporter12) have a Ninja 250 why don't you tell us about how it rides compared to your Interceptor?

I'd like to know if it (the Ninja) came with a wider wheel and tire or if you were able to put a low wide tire on the stock wheel. My son's Ninja was a late 80's model and it was equipped with spindley narrow Pirelli's the one time I saw it.

Which of the two bikes do you prefer to drive and why? What do you like about the one that is not your favorite that makes you hold onto it? Finally, my 84 Magna V30 does low 6000 revs at 70 to 75 Mph (stock sprockets and chain), how fast is the Ninja spinning as a smaller twin at highway speeds? For that matter, how fast does your Intercepter spin at highway speeds?

 

The Ninja 250 rides a bit stiffer than the 500, but can't corner quite as well, which is contrary to what I've heard from Ninja 250 sites. I think it has to do with the weight and the center of gravity.

As for tires, the Ninja 250, 89-07 came stock with a 130/80-16 on the rear, and a 100/80-16 on the front. That is the exact same tire as the front of my VF500, and slightly wider than the rear on my VF500, which has a larger rim size. I have Bridgestone Battlax BT45's on both. I'm really liking the BT45's.

I prefer to ride the Interceptor. The seat (was modified before I got it) is softer, cornering is a bit better, and the power (duh!) is much more fun. The 250 does "feel" smaller, too. The fuel mileage sucks though, comparatively. I get close to 70 on the 250, and around 35 on the 500. THAT issue needs some work!

I have several reasons for keeping the Ninja. For one, the wife rides it (a few miles here and there.) Also, I'm still not all that confident in the 500. It rattles quite a bit, and it's getting worse and worse. It really sounds like cam chain noise (I work on cars for a living, so I know engine noises) but I haven't verified that yet. Until I get that sorted out, I don't feel all that comfortable riding it longer distances.

My interceptor does nearly identical revs as your magna V30, and the ninja turns 7000 at about 57 MPH. The Ninja DOES turn 14,000 RPM's though, and doesn't really start making power until 7000-8000 RPM's.

 

Chain noise? We don't haeve no Stinkin Chain Noise.

I hear you on the chain noise. I've gone through it or will go through it. I have 2 Magna V30's. They both have under 30K miles. My son did the valve adj (his first) on the '85. It has pronounced valve train clatter. I did the adjust on the 84, quiet as a mouse. I don't like to drive the '85 as a result of the difference in noise level. Still, I get noise out of the '84 too. When I was answering "magnavmx5" about being afraid to spin the motor to 12K, I went out and did it to check my redline 1st gear terminal speed. I over reved it (past 13.5K on the instrument dial) and I was ready to wet my pants over the noise. I thought it was the sign that I had screwed the cam chains and she was gonna croak there on the street (the quiet running '84). No, she was just protesting that I was driving too hard. She is fine with that little bit of being over revved. The Vf valve train and chains are just noisy. You have to grow used to the noise and trust it not to change.

I have one other tale about valve train noise. My son was hot to buy a Vf500f . I wanted him to get a Magna type cruiser type bike. But he persisted and he got this guy who had gradually come down from $2300 at the beginning of summer to $1500 at the end of summer on his 1984 Interceptor 500. We went out to see it and we took a compression gauge and pulled the radiator down to get at the front plugs to test compression. It was 140 psi all around. My son drove it for about 5 or 10 minutes but all the practice he had riding was done in the safety course he had taken to get his licence. I heard some noise but the compression was OK. He was angry because I seemed to nix any bike that he came close to buying. I had reservations about the bike but not for mechanical reasons. But what could I say, it had Ok compression and it ran. He paid the guy the $1500 and rode it home. It ran hot.

I live apart from my son and I was not around to see him ride the bike. After 1 month it was parked. I came over several months after purchase determined to find out what was wrong. The previous owner or his mechanic had taken a thick rod or large punch and beaten down the top chain guide on the rear cylinders to the point that it looked like a low wide "M" sitting on a bench top instead of the tall thin "C" that its supposed to look like when sitting on end. The hard plastic material on the underside of the guide was cracked through where the punch had been placed centermost on the guide. When the bike was running for the few seconds he had it on and running close enough for me to hear chain noise I noticed nothing out of the ordinary. But when I checked the cam timing as best as I could ( not an easy thing on a Vf motor) I couldn't make the valve timeing operate normal. The bike ran with the cam timing out far enough so that the guide could be deformed the height of the guide. I believe this was the reason the bike ran hot. I believe it had lost tention in the automatic valve train adjuster or it had stretched the chain beyond acceptable limits and the owner was doing what he needed to do to palm it off on an unsuspecting buyer.

Valve train noise is par for the course, get used to it. Otherwise the Vf is a great "light middle weight" cycle.

 

the carbs are on and my tank will be done next week so we shall see how much better it will run YouTube - my vf500 part 2 video of it before the carbs where rebuilt

 

So Matt...when they re-jetted your carbs they didn't clean or rebuild 'em?

 

no sir they didnt just installed the jet kit

 

From what I can tell from checking my bike, and calculations from compression ratio, 140 PSI is a little bit low. Mine has somewhere around 170-175 PSI (at least it did on the front, the rears were out of time when I checked compression, and I didn't retest when I got it back in time.)

From what I've learned, you basically multiply the compression ratio by about 15, then add 15 (I think it is actually 14.5, or something like that) to get the approximate PSI for a compression test to come out to. So, for 11:1, it would be somewhere around 180. That makes the 170-175 I was getting a good reading. Keep in mind that few engines will be perfect, it's more critical for the numbers to be within 10% from the highest to the lowest, and somewhere in the ballpark of what is expected from the calculation above.

 

Actually, it's the compression ratio times atmospheric pressure minus atmospheric pressure (14.7psi). So, for 11:1 it's 11*14.7-14.7 = 147psi. Your comment about not being 100% is spot on, that's why 140psi is fine.

This is because compression gauges are reletive and not absolute. Holding it in your hand it reads zero.... except atmospheric pressure is 14.7psi. That means it's reletive to the atmosphere. A 2:1 compression ration would yeild 14.7psi, 3:1 would be 29.4psi, and so on.

 

I must've been asleep when I posted that! I knew it was 14.7, and was pretty sure it was equal to atmospheric pressure, but really couldn't remember for sure!

I'm not sure i agree about subtracting 14.7 from it though. If that IS right, why did I get 175 PSI on my front 2 cylinders? Maybe I remember it wrong and need to check it again, but I'm VERY sure it was in the 170 range...

When the gauge is static (atmospheric pressure) it reads 0, which is ACTUALLY atmospheric pressure, which is right around 14.7 PSI. That is why you're saying to subtract. I need to think about this a little further, I can't get my head around it, and anymore explaining isn't going to help!

 

Actually "Atmospheric pressure" is local. If you are taking your reading on an average day at the beach the local atmospheric pressure is @ 14.7 psi. If you were suddenly transported to the top of Mt. Whitney the local atmospheric pressure there would be considerably lower (say around 11-13 psi). I believe you have to add local pressure. Also there are day to day pressure events that cause local Atmospheric pressure to change. If you read the factory manual you will find the factory is asking for a result around 180-190 psi. But I can't repeat chapter and verse on the why's and wherefore's of compression test at this moment.

 

I did not know what to expect!

I guess I tripped both you guys up with the 140 psi statement. I did not know that the Vf 500 was running 11 to 1. My experience was with cars that usually ran rotgut low octane. 140 psi is perfectly acceptable for a low compression car engine at 7-8 to 1. I made an assumption that the Interseptor would not be that much different than a car. I was wrong. But I had no manual to referance and my son was hot to buy.

Anyway, my V45 factory manual (I got it as part of the deal from a Saber I purchased about a month ago) states that compression should nominally be 184 psi with a variance of +/- 28 psi. The V45 has 10.5 :1 compression. So I would assume the Vf500 has to be at least equivilent if not higher. I think I read much the same compression values in my VFR 700f factory manual.

Since you have caused my memory to get a zap of electrical pulses I seem to recal that there is a factor that has to do with cylinder swept volume or piston head surface Area (probably the former) that is factored into the compression equation. It was too complicated to keep in mind and I have lost the"recipe" for the calculation. I'm sure you can find it posted on Wikipedia or google search for some engineering professor who has it tatooed on his forehead. Sorry I led you astray!

 

Don't make me get the thermo textbook off the shelf!

You almost got it right but "engineering philosophy 200" tripped you both up. :frown:

Pressure @ TDC = (local barometric pressure) X Compression Ration raised to the power of the specific heat ratio of the fluid. In this case the fluid is air which has an adiabatic specific heat ration of 1.4. "Adiabatic" is a term used by engineers as way of admitting that you can only approximate the actual pressure by making certain assumptions and holding certain variables constant when they make the calculation. So carefully plugging into the “Pressure Calculation” using the "adiabatic"case, an engine with an 11 :1 CR at sea level would produce

P (tdc) = 14.7 X 11^1.4 =
= 14.7 X 28.7 = 422 psi

KNOCK KNOCK KNOCK:
Your answer if you please:

Your Vf 500 should produce 422 psi? I know that seems high but , well that’s in the “Adiabatic Case”. Whats that? Well if all variables are suspended and all assumptions agreed upon, your Vf 500 would produce 422 psi. What are the assumptions? Some of the assumptions might be that the valves open and close instantaneously, that air has no mass or momentum, that the cylinders are perfectly sealed at all times, that the fluid is “air” and not a mixture, that no superfluous heat is lost or gained during the process, that the compression and exhaust strokes happen instantaneously, and on and on.:crazy:

But what about the read world? You drive an ‘Otto’ engine and not a ‘Diesel’ (the two Germans who perfected the internal combustion engine).

You never mentioned anything about “real world”? We only deal in abstraction here. You’ll want to go to the basement where the experimentalist’s hang out. See you later but not if we see you first. :heh:

KNOCK KNOCK KNOCK

Yes, yes, we are the experimentalist. Yes, we can make an experiment for you.
Well, if you buy us some new lab coats and give us personalized parking spaces we could do an experiment, and of course you would have to furnish us with a complete lab and a few engines to be sacrificed on the alter to science. And well yes we will tell you what the real world Pressure at top dead center is with an error of say plus or minus 2 atmospheres Yes, we will tell you what the real world pressure should be.

KNOCK KNOCK KNOCK
Your answer if you please:

Somewhere south of 230 psi
Somewhere north of 160 psi

The reason you never saw or bothered to memorize the Pressure Calculation is because there is none. The adiabatic calculation makes so many assumptions it’s useless. The combustion process is so full of variables that you can’t make a viable pressure equation that works. That’s why motorhead magazines don’t have articles on calculating your compression pressure. You have to build it and then run it and make the measurement experimentally until you are satisfied that statistically you have determined a viable average compression pressure for the motor in question and then publish it. The more times you make the test :rofl: and the more motors you test the better the final answer.

And that’s just what the Little Red Hen did. :thumbsup:

Read the manual. That's why Honda put the compression pressure in there!

DKC

 

i was just having carb troubles :crazy: jamie why is it my thread turn into huge discussions ....what ever the reason i like it! :thumbsup: feed me more :biggrin:

 

Nothing like a scientific dispute among actual engineers !

Facts and formulae fly faster than fleas and fur in a dogfight.

Extra points for using "adiabatic."

 

DKC, you've applied something in the wrong place I fear. What you are referring to is the equation AFTER the gas mixture is ignited and the temperature ramps up. Specific heat ratio is just that, an indicator of what happens when the gasses are heated. During a compression test you aren't burning anything, so this equation does not apply.

The equation that you really wanted to use is:

PV = nRT

P = pressure
V = volume
n = number of moles of the substance
R = gas constant
T = temperature

Since we are talking about running a compression test, the amount of the substance is the same from BTD to TDC (ok, not exactly, but that's part of the inefficiency of the engine). Again, since the mixture is not ignited the temperature stays the same. R is a constant also. Taking the condition from BTD to TDC you get:

P1*V1 = P2*V2

or

P2 = P1*(V1/V2)

The ratio (V1/V2) is by definition the compression ratio. That means the final pressure is:

P2 = 14.7psi *(11) = 161.7psi

Since this is an absolute pressure, you have to subtract atmospheric pressure to get the gauge pressure (what your measuring instrument gives you):

P2_gauge = 161.7 - 14.7 = 147psi

Which is exactly what I stated before.

 

Don't forget the opening of the exhaust valve! Both have overlap which hurts efficiency. It boosts overall performance but at the expense of other things.

 

All the math that your using is useless, unless you know all the specifics of a given build of engine.

THE INTAKE VALVE CLOSING POINT WILL DETERMINE THE PRESSURE YOU GET.

I can take the exact same 11:1 compression engine with two different cams and get totally different compression pressures. A small duration cam with it's earlier closing point will create more cylinder pressure than a larger duration cam with it's later intake closing point. Your pressure doesn't start to build until the intake valve is closed. You would have to compare the different cams with the same LCA (lobe center angle) to see. Changing lca's changes the intake volume of air that will be compressed

The earlier intake closing the piston is down in the hole farther. So there is more of the cylinder volume being compressed. Later intake closing, the farther up the cylinder the piston is and less cylinder volume is being compressed. This is call DCR, Dynamic Compression Ratio, and is what the engine actually sees when it's running. Not the static compression ratio. Which is the TOTAL cylinder volume compressed in to the chamber voulme. ie 11cc cylinder, 1cc chamber = 11:1 static compression.

Maybe for a known given engine your equation might work. Even changing the intake closing point 1 degree on said engine will give different results. So just because you have a 11:1 compression you may have 140 psi or 200 psi compression readings depending on the cam and where it is install in reference to your crank.

 

Wow, this has gotten crazy!

I stand by my original post regarding compression pressures. Unfortunately, it only really applies to pretty much stock street CAR engines, that don't have a large amount of overlap. Those with a lot of overlap will be less efficient at lower speeds, such as crank speed for a compression test, so it's correct that compression will be lower, but I really don't think it will be that much lower.

With all that said, the important part of a compression test is the variance between cylinders. I always look for mo more than a 10% variance between cylinders.

 

Actually that's not true except for "those with a lot of overlap will be less efficient at lower speeds". I don't mean to get on your case but mis information about how motors really work is bad for the novices trying to learn. Over lap has nothing to do with compression per say. The motor doesn't know if it's a car engine or a motorcycle engine. The higher the reving engine, usually the more duration the cam has with more overlap for cylinder scavenging and possible ram effect at the higher rpms.

Your correct in that the standard is a 10% spread in compression readings is fine for street motors. Now how did you check compression? Throttle blades should be at WOT for proper comp test and the motor should be at least half or more of normal running temperature. If throttle was closed and a cold motor your readings are then considered bogus. Still if one cylinder is way out then it can be considered something is wrong with that hole.

 

Right, overlap has little to do with compression per se. Overlap DOES affect pumping efficiencies, correct? Since the internal combustion engine is an ait pump, it would be something to consider, correct?

The only reason I specified CAR enigine is because a stock-ish car or truck engine isn't going to have an agressive enough cam to affect compression much.

It sounds like we can all agree that all the cylinders should be close in PSI compression they make when running a static compression test. One other thing to consider is whether compression changes significantly when some oil is added to the cylinder. If compression is outside of expectations, a leakdown test will also provide some good information.