timing question

[plummer1111]

my timing is not advancing when i rev up the motor with a timing light on it. it wont hardly take off it is very doggy. what could be wrong?

[plummer1111]

what makes the timing advance

[wilkin250r]

Well, I've never mapped out the timing, so I don't know how much help I can be. I wouldn't have responded, except that I see you're not getting any answers or reponses to your questions, and that has to be frustrating.

The ignition system on these quads is fairly simple. You get spark energy from dedicated coils on the stator, called exciter coils (separate from the lighting coils), and the trigger is on the outside of the flywheel that passes a small sensor. The exciter coils and trigger are fed to the CDI. The CDI then sends energy to the ignition coil, which boosts the voltage up. The coil then goes to the spark plug.

The trigger doesn't move, and the ignition coil obviously can't advance anything, so the ONLY thing capable of advancing the timing is the CDI box.

However, the question should be asked; Are you SURE the problem is related to ignition timing?

[plummer1111]

im not real sure what the problem is now. i do know that this thing is really making me mad. ive tried 2 different carbs and i still have the same problem it is very sluggish and feels like im trying to take off in third gear.thanks for the response wilkin:)

[wilkin250r]

Well, let's start with the basics.

Are you experienced with riding 2-strokes? They don't have nearly the bottom-end grunt that 4-strokes have.

Have you done a compression test? Leak-down test? Checked your reeds? What factors have you checked before looking at the ignition?

Are you sure you have the proper jetting?

Is your pipe in good condition, no holes or air leaks?

[plummer1111]

i have a brand new pipe and silencer new reeds. ive done a leak down. it starts fine idles fine. revs up fine but as soon as i start to try and move it almost stalls out and it just wont go. i cant even pull a wheelie :) . i tried the stock carb with the same results as the 38 mm air stryker. ive tried 42 pilot and a 55 pilot with a little better results but still the same thing. on the main ive been everywhere from 150 to 185 clip up and down. and yes i try only one thing at a time. when i took the head off there was a gap at tdc of about 3/8 of an inch is that normal

[wilkin250r]

3/8? As in, over a quarter inch? That is definitely not normal, it should be very near the top, like less than 0.040 inches (about the thickness of 15 sheets of paper.

Did you try a compression test?

Do you have a spacer plate at the bottom of the cylinder?

I highly suggest you do a search (on these forums, and/or a web search) for "squish band". Better yet, start here (http://www.aircooled-rd.com/default.asp?txtPage=squish1.htm). The article is originally written about RD350 streetbikes (basis for the Yamaha Banshee engine), but the subject of squish bands apply to ALL two-strokes.

Right off the bat, I imagine your problem is related to compression, and right now I imagine your compression is really low. Increasing that to the proper level (at least 165psi) should give you back your bottom-end power.

[plummer1111]

i do have a spacer plate in the bottom. i took it off and reassembeled the motor and couldnt hardly kick it over.

[wilkin250r]

Have you done a compression test? If possible, I would highly recommend a good brand-name compression tester, but in reality ANY compression tester will give you some sort of guideline. If needed, you could pick up a real cheap tester someplace like Harbor Frieght.

How thick is your spacer plate? If you take it out, will it bring the piston very close to the top of the cylinder at TDC? Will it put your piston OVER the top of the cylinder at TDC?

[Dave83]

Wilkin has you going in the right direction,i just wanted to know if you have a long rod or short rod motor.I see that you list the bike as an 86,with that ,the original motor would be a short rod with no need for a spacer plate.

[wilkin250r]

Just to reiterate yet again.

Compression test.

Compression test.

Compression test.

[plummer1111]

i will do a compression test. how can i tell wich year the bottom end is

[trx310]

I think you guys are thinking too hard. It may be compression, and it may not be. It starts fine and runs fine but it is sluggish when he tries to take off. See how much play there is in your clutch, it may not be fully engaging and it may also be glazed over. Happened to me one time, i was pissed to find that it was just the clutch.

[plummer1111]

did a compression test and only have 90 psi!!!!!!!!!!!!
this is the number on the motor tb06e1011957.
can anyone tell me what year it is

[Dave83]

With or without the spacerplate?You held the throttle open and kicked the kicker until the tester stopped moving?I cant believe it will even start at 90psi.You can get the year of the cases with those #s you have,but if someone has changed the crank,it could still go either way.There are #s on the crank that will tell if it ts a long or short rod.

[plummer1111]

i did compression test with spacer plate in. what purpose does that plate serve.

[wilkin250r]

How much do you know about 250r engines and history?

1986 was the first year for 250r 4-wheelers. The previous year they had a 3-wheeler version, liquid cooled. Prior to that, all 250r 3-wheelers were air-cooled.

In 1987, they made some changes, the largest and most prominent was to make the connecting rod longer on the crankshaft, and a piston change to match it. The connecting rod was 5mm longer, but they also changed the pin-to-dome height on the piston 5mm shorter, so the actual piston dome was still at the same height as the 86 at TDC.

The longer rod changed power deliver a little bit, but also greatly increased reliability and piston life.

Again, since the rod is longer, but the piston is effectively shorter (not the piston skirt, but the height from the pin to dome), the total height at TDC is exactly the same as the 86 crank and piston. This means you can put the 87 crank and 87 piston into ANY year engine.

However, a very common modification is to use the longer rod (87) AND the taller piston (86). This would obviously increase the total height of the piston dome at TDC, so you would need a spacer plate to move the cylinder upwards to compensate for it. This has the effect of adding more crankcase volume, which gives a smoother power delivery.

If you do a search on here, you might be able to find diagrams.

[wilkin250r]

Did you read the article about squish? Do you think you have a fairly good grasp of the concept?

If I were you, I would remove the spacer plate, and measure the deck height and squish tolerance. You want the squish clearance to be about 0.040" (about 1mm).

After that, check your compression. If it's over 180, you might consider race gas, or at least a 50/50 mix. If it's over 190, you should REALLY consider race gas. If it's over 200, there is no consideration, you absolutely need race gas.

[Dave83]

To follow up on wilkin's reply,If you have an 87-89 crank and an 86 style piston you must use a spacer plate.All years cranks will fit any year cases so the #'s on the cases dont mean much if you dont know what all has been done to the motor over the years.Take the cylinder off and look on the rod.HA2 is the long rod and HA4 or KA4 is the short rod.Then determine what year piston you have by the #,s on top of it.If you come up with the long rod and 86 piston,use the plate.Short rod and 86 piston,no plate,long rod with 87-89 piston ,no plate.Short rod with 87-89 piston,throw the piston away and get the right one.You mentioned 3/8 clearance at TDC,Im leaning towards the one of the setups that doesnt require a plate,but someone put one on thinking it was going to help cause they had seen it on another motor.Let us know what you find on the rod/piston #s.

[plummer1111]

first of all i would like to thank you guys for all the help and insight. i took off the cylinder and the rod id is KA4. on the piston there is 8004 72.2 mm 2612f

[Dave83]

Ok,you have a short rod motor that is probaly out of an atc250r.There is no rod/piston combo using a short rod where you would need the spacer.72.2 or 72.25 is the bore which is a bigbore.Im not sure how to read the other #s to get what year it is for,but I bet it is the short rod piston.Leave the spacer out,install new base gasket and do a comp test this way.Be sure to hold the throttle wide open and kick until the guage quits moving.

[plummer1111]

i put the jug back on without the spacer plate and the piston is traveling almost over the top of the jug

[wilkin250r]

Measure the squish while you're in there. You'll need a set of feeler guages and calipers, both of which should be available at any automotive store.

First, while the head is off, measure the deck height (the distance that the edge of the piston sits below the edge of the cylinder at TDC). Also, if possible, measure the thickness of the head gasket.

To measure the actual squish clearance, you will need a bit of solder (If you're not familiar with it, it is very soft wire used for melting to electrical assemby, or plumbing to seal copper pipes, pronounced "sodder". Available at most hardware stores in plumbing section, or Radio Shack ). It will need to be at least 0.050" (about the thickness of 19 pieces of paper) in diameter. Radio shack may not have large enough, typically the larger diameters are used for plumbing.

When you reassemble the head, bring the piston close to TDC, but not all the way. Take a length of solder and bend it to insert it through the spark plug hole to the edge of the piston and cylinder walls, and rotate the piston past TDC. The piston will crush the soft solder to the squish band height.

Measure the thickness with the calipers (be careful not to apply too much pressure when measuring). This number is not only useful to have, but if you have any trouble from here with kicking or compression, the squish band and deck height are the first numbers I am going to ask about, along with a compression test.

[wilkin250r]

Originally posted by plummer1111
i put the jug back on without the spacer plate and the piston is traveling almost over the top of the jug

Are you looking at the center of the dome, or are you looking at the edges?

[plummer1111]

the walls of the piston are flush with the top of the jug. i did a compression test like this and it only went to 120psi. i kicked it over by hand without plug in and it felt as something was hitting at tdc.

[wilkin250r]

Flush, or just very close to flush, but still slightly below?

If it is indeed flush, than your head gasket thickness will determine your squish clearance.

I highly suggest the solder measurement I described above.

Also, if something IS hitting, you'll need to find it, and I'm not sure I can help you with that step.

If you can get machinists clay (or perhaps modeling clay at your local craft store, NOT play-doh) you can clay your cylinder as outlined in claying your cylinder (http://www.c-speedracing.com/howto/claymotor/clay.php). You obviously don't need to worry about piston-valve clearance, but it will still give you an accurate measurement of your squish clearance.

[slamdak8782]

not to be rude but 120psi is low how long since you put a set of rings in this thing.

[slamdak8782]

ok here is what i would try new rings with the spacer and swap the cdi the deal with the spacer is to gain displacement. I dont remember the particulars but it is a cool mod you need the spacer if it is there be cause someone with know how did the mod. the rod is longer in some years this alowwed engine builders to use the longer rod with a different year engine piston to make a stroker engine this required the use of the spacer so dont remove it. Also as the engine progressed port timing was improved that is why some people use the newer style cr250r cylinders Check out this site called macdizzys search for it. That guy is a genius when it comes to 250rs and he has a whole buch of stuff concerning the spacer plate mod

[wilkin250r]

Slamdak, no offense, but please please PLEASE do not give advice unless you know exactly what you are talking about.

I have already determined that his problem is most likely not timing related, so there is no need for him to swap his CDI with another.

I am very familiar with the spacer plate and modifications involving a spacer plate. I can tell you that the spacerplate in his motor is either WAY too thick, or completely unecessary altogether.

Also, a longer rod and different piston does NOT make a stroker motor, that is something entirely different.

And I am already a member over at Macdizzy.

[slamdak8782]

Alright mister official thinker you kinda ticked me off so i went and looked up the info. 85 to 86 used a shorter rod. on that your correct. i just read the post and saw that something was hitting:mad: Thats not cool so i assumed that something had to be wrong. If he indeed has a short rod it should not hit at all however he also said he only has a 120 psi compression. So what is left? valves? cant be valves no then it has to be rings? yes so i do have an idea about this and im just trying to offer a solution. He could try putting a small amount of oil n before the compression test to check my theory, if compression raises then its rings. Secondly he is getting no ignition advance the only thing that changes that is the cdi. furthermore he could easily figure out the compression ratio. Ross pistons has a calculater.
Finally deck height + gasket width determine squish, quench or whatever else you wish to call it. Most pros agree .040 is a good quench. If deck height plus gaskets equals .040 then you will be fine regardless of your combo. short rod 86 piston whateverr blah blah blah so set your squish try the oil trick and see what happens after that if you will know if you have good compression (rings} or fualty ignition of some type

[slamdak8782]

Oh yeah not to be a jerk or anything. I have an associates in the GM ASEP training as well as bieng master certified by ASE also i have worked on bikes for about 5 yrs so......
Anyways just trying to help a little and you dont really know if his ignition is ruled out as of yet Plus 250rs are very common for needing new rings as normal maitenence

[wilkin250r]

Perhaps you should read the first three words of my post. I'm not trying to piss you off. All I'm trying to say is don't add confusing information. His deck height of 3/8 is about 10 times what it should be, there is no need for his spacer plate, or at least not one that thick.

To be honest, I'm not all too concerned about the 120psi reading just yet. Yes, it might be rings, that's very common. It might also be his tester. On these smaller displacement motors, ESPECIALLY 2-strokes (because you don't actually start to build compression until the exhaust port closes, so the actual displacement to build compression is even smaller than 250cc) the length of hose from the spark plug to the actual guage can have a drastic effect on compression reading. I imagine his reading of 120psi is actually higher, and certainly enough to do some initial troubleshooting.

Plummer sounds like he has the mechanical ability, but doesn't know the details and nuances of the 250r engine. As such, I want to address one problem at a time until he's running properly. Right now, that problem is deck height and squish, because it will determine the proper assembly of his motor. After that we can deal with rings, but there's no point in replacing rings right now if he is going to be constantly disassembling his engine.

After proper assembly, squish, and good compression (rings), we can address timing issues, but there is NO way he can address timing issues until his motor is set up properly.

[plummer1111]

ok this is what i did,i checked the squish with out spacer plate in and it was about .010. i milled the 5 mm spacer plate down to 2.5mm, reassembeled with plate in and did squish test again and got .050. did leakdown no problems. did compression test got 155 psi :) put the 38 mm air stryker on and she runs like a raped ape :D :D. still need to make sure that the jetting is right. didnt get to ride it much only half of a lap in the field because of rain.
dave83 and wilkin thanks for the help you dont know how much i appreciate it. and thanks slam for giving your input.

[slamdak8782]

thats awesome glad you figured it out but if it was me id take her down to at least .040 no less than .035. If you did that it would equal higher compression basically free power. You might need higher octane but if your happy heck with it. And wilkin250r not discounting your info either it was right on. One thing, your right my first post was half *** anyways, might need your help sometime for the cr500 im going to slap in my 250r frame.:devil:

[Dave83]

Glad you got it going.Wilkin deserves the credit,that was an excellent diagnosis with little info.Now it may be time for rings.Although your compression is ok,I think that with the squish being where its at,it could be a little more.IDK,hopefully Wilk or Slam will have more input.

[wilkin250r]

Well I'm glad you've got it figured out, and I'm glad we could help.

Honestly, the difference between .050" and .040" really isn't too big a problem. If you're dead serious about maximum power, I suppose you could go through the trouble for that extra .010" and 2hp, but if you were THAT serious, there are better ways to achieve power. Personally, if it was me, I'd probably leave it at .050" and go riding!

Still, I'm wondering what type of wierd setup you have that would require a 2.5mm spacer plate. :confused: What do you know about the history of this motor?

To anybody else reading this thread, do you think it's possible he might have a stroker crank in there?

Also, plummer, concerning your 155psi compression reading. 155 is a little low, but not terribly bad. However, it might not even be accurate, and your actual compression is higher. Did you replace the rings with new, and a fresh hone on the cylinder? What type (brand) of tester are you using, and how long is the hose leading to the guage?

[QuadRacer041]

great info wilkin and dave, its awsome to see all the testing and info given out here work for someone.
very informative info.great job

[plummer1111]

this is how i got the quad. i was told that the 310 was purchased on ebay. esr piston. im pretty sure that it dont have but maybe 2 hours on the piston and cylinder. the pipe wasnt even discolored when i got it. as for the gauge it is an actron (cheapy) with an 18in hose.

[jon370r]

If indeed it has a 2.5mm spacer and its a Nics 310 cylinder there are two possibilities I can think of for a set up.

1. It has a 5mm stroked crank with a short rod on it, which I've never herd of anyone doing but it could be done.

P.S. long or short rod has nothing to do with the stroke lenght, that is controled by the location of the lower rod pin from the centerline of the crank.

2. I've herd of some builders using alternate piston configurations such as Yamaha YZ pistons. I would assume that some kind of special spacer would be needed unless the piston pin to the top of the piston was the same as the 250R piston.

[Dave83]

Jon,I too have seen the Yamaha piston used.I think Sparks did it with his 265 kit and it was a long rod setup.Not sure on it tho.Plummer,is this a stock cylinder or like a pro-x or similar?This has my interest.Ive never heard of a short rod needing the plate

[wilkin250r]

Originally posted by plummer1111
as for the gauge it is an actron (cheapy) with an 18in hose.

I'm betting this is where your compression reading is coming from, 18 inches is a pretty long hose for a single-cylinder 2-stroke. It's all about relation to combustion chamber size. It's not a big deal on a V8 engine, but it becomes very significant on a small 2-stroke, both because of the displacement AND because of the engine design (2-stroke vs. 4-stroke).

The hose itself will contain a small volume of air that will affect your reading, even if it is only a few cubic centimeters (cc's). To make things easy, let's assume you have 3cc trapped in that 18 inches of hose.

A normal 350ci V8 is about 700cc for each cylinder, and the ENTIRE 700cc get's used for compression, so at around 8:1, the combustion chamber is about 85cc. Adding the3cc from the hose will take it to 88cc, about a 4% change. If you're reading 150psi, your actual is 4% higher at 156spi. Not too bad.

For a 310cc two-stroke, you don't actually start to build compression until the exhaust port closes, so the actual displacement to build compression is much smaller, probably less than 120cc, so the combustion chamber is typically less than 25cc. Adding 3cc gives you 28cc, about a 12% change. So a 155psi, adding 12% will give you 174psi, a very respectable compression reading. A smaller combustion chamber of 20cc or 19cc will have and even greater effect.

I don't know if these numbers are accurate, but you get the idea. I have a feeling your actual compression is much higher than 155psi.

[wilkin250r]

Have you called ESR and discussed this setup with them? They're pretty good with customer service and tech support, even if you didn't buy from them directly.

You said your motor runs good, and that's terrific. However, I have a feeling it could probably run even better. You might want to place a call and see what they have to say about it.

[plummer1111]

how long should the hose be on the compression tester

[wilkin250r]

As short as possible.

[novaracr70]

ok this compression guage thing is irritating me if you have a good gauge with a check valve in the end it dont matter what size hose you use three feet six twenty it just you will have to kick more times to get up to pressure .

[beerock]

Originally posted by novaracr70
ok this compression guage thing is irritating me if you have a good gauge with a check valve in the end it dont matter what size hose you use three feet six twenty it just you will have to kick more times to get up to pressure .

exactly

one thing il say right now is cutting down a spacer to fix your problem is bad. if your motor is low on compression and you decide to bump up compression your just compounding the problem and more then likely the cylinder bore is worn and the piston skirt is going to break soon and ruin your bottom end.

i have a stock jug with about 3/8 from the piston to top of sleeve and it was 5mm, 88 crank 86 piston and the compression on that motor was 210psi

i believe your compounding your issue.

your also not being very smart by taking off the spacer plate and kicking over the motor????????? you are hurting the rod bearings doing that tremendously

it sounds like it could have a stroker crank like jon said , i beleive they did use to do that with short rods

+1+2+3+4 short rod cranks.

[plummer1111]

ok guys this post is from last year. and the problem ended up being that someone had milled the top of the jug:confused:

[novaracr70]

when it all comes down to it you want your piston at the top of the cylinder zero deck . use what ever spacer makes that happen then have your head machineed to make the squish right and compression right . beerock i think you piston should not b in the hole that far it works becouse your head looks like it has about a 10cc dome in it . its just not the right way to build motors 1 zero deck motor 2 machine head for compression req and squish 3 port cylinder for timing .

[beerock]

if you raced against it and got smoked you wouldnt be saying that ;)