How do I test a reed cage?

[thefox]

OK, I am still working on my brother's YT125. After some assembly MY bro put some starter fluid in it and it fired up and ran for 2 seconds, then when he went to pull it again it didn’t get any compression. So I think it might be the reed cage. The reeds are new and the cage was replaced with a used one that looks good. I can't see any gap in between the reeds and cage but I took a flash light and put it into the manifold and could see some light coming from around the reeds. I also tried sucking in fro the intake (that looked weird) and it blocked most of the air but not all of it.

So does it sound like my cage is bad? How else would I test it? Any thing else it could be?

[Unclediezel]

If you have a manual---they give you a "GAP" spec----
If you think 4stroke for a second---the valves seal the cylinder during compression stroke---your reed is asked to do the same thing---any leakage at all, is lost compression. Comp pressures -----upwards of 100 psi---can in no way be duplicated by "Blowing " thru it----so if it leaks by your mouth--it will definitely leak under normal operating environments.If you need the specs, Holler back --I can scan the pages for ya.

[thefox]

Yeah if you can send the specs. I can't find them in my book. I can't see any gap with it just sitting on the workbench but when I put a light behind it I can see just a little getting around the reeds.

[TeamGeek6]

Enough starting fluid to run 2 seconds, with no 2 stroke oil, is a recipie to finish off an already worn set of rings. Reeds arent causing this problem.

in a 2 stroke, the cylinder cant get compression until the piston rises above the exhaust port, and since the intake port is almost at the same level, the reeds even being taken out wont make a large difference. Ive measured pressure at the reeds on my 250R, its nowhere near the compression pressure - it would blow out the crank seals if it was.

[thefox]

Enough starting fluid to run 2 seconds, with no 2 stroke oil, is a recipie to finish off an already worn set of rings. Reeds arent causing this problem.

in a 2 stroke, the cylinder cant get compression until the piston rises above the exhaust port, and since the intake port is almost at the same level, the reeds even being taken out wont make a large difference. Ive measured pressure at the reeds on my 250R, its nowhere near the compression pressure - it would blow out the crank seals if it was.

It has a new piston and rings, well 2 seconds run time on them at least. And when I say no compression I mean my gage reads about 3 psi, if I hold my hand over the plug whole I can fell air come out but then when I put my thumb covering the hole I don't feel much compression.

[Howdy]

It has a new piston and rings, well 2 seconds run time on them at least. And when I say no compression I mean my gage reads about 3 psi, if I hold my hand over the plug whole I can fell air come out but then when I put my thumb covering the hole I don't feel much compression.

Put your hand over the carb and see if it is blowing back at all ( with the spark plug in it ). If it's not blowing back then there is a good chance the reeds are good. If it is blowing back then pull and inspect them. Every 2 stroke I worked on does allow a little blow back, but not to much.
Howdy

[thefox]

Put your hand over the carb and see if it is blowing back at all ( with the spark plug in it ). If it's not blowing back then there is a good chance the reeds are good. If it is blowing back then pull and inspect them. Every 2 stroke I worked on does allow a little blow back, but not to much.
Howdy

OK, I just tried that but since the engine is out of the frame it wasn't very easy. It didn't feel like there was much air blowing out of the intake but there wasn't much getting sucked in either. I will try again tomorrow when I can have someone pull it over while I hold the engine and put my hand over the intake.

[hrc85250r]

dude, to check your reeds just look at them, if they look worn or like they are cracking get new ones, since this thing is air cooled make sure you have the top end together right with the gaskets on it correctly....sounds like you have a big time leaky head gasket....

[Howdy]

OK, I just tried that but since the engine is out of the frame it wasn't very easy. It didn't feel like there was much air blowing out of the intake but there wasn't much getting sucked in either. I will try again tomorrow when I can have someone pull it over while I hold the engine and put my hand over the intake.

If your not sucking much in, then you need to find out why. As hrc85250r mentioned it could be a bad head gasket. Other things it could be: Bad base gasket, broken ring ( I have broke my share of them ), and more.

The more you describe the symtoms, the more I am leaning away from it being bad reeds. You may try putting the piston at TDC and hold it there. Then blow a little air into the cylinder via the spark plug hole. Look and feel for any air leaks and you should find your problem.
With the piston at TDC and air blowing in:
If it comes out between the head and cylinder: Bad head gasket
If you get a major air flow out of the exhaust: Bad Rings or piston to cylinder clearance

I hope this helps.
Howdy

[slow200s]

well sounds to me like you have a weak piston, and that your wrist pin is bad, and that your head is warped but thats just me.

[Huffa]

As far as I know the reed has zip to do with compression and your motor should run with out ANY reeds in.

All the reeds do is control the flow of fuel at slower rpms

If you put a teaspoon of oil in SP hole and it perks right up that's telling you the rings are bad. If it doesn't you may have a combo of bad head gasket and rings or just rings.

Maybe the bore is shot also?

A blown head gasket can sound like a bird chirping too when the air is being forced out. Tweet-Tweet!

Like said too, it could be the base gasket.

[TimSr]

Put a few drops of oil in the lug hole. You need the rings wet to seal. Starting fluid dries everything up. If you still have no comprerssion, you need to take the top end back off. Something isnt right. Reeds affect compression in a very minor way. They will not cause you to drop to 3psi. Basically, they are a one way valve for air flow BEFORE it begins being compressed. If you tear down an early 70's two stoke you will notice they dont have any!

When you go back in, the problem should be visible. If nothing with piston and rings stares at you, inspect the head very closely for a crack. Cracks are not easy to see.

[Mosh]

your crank seals could be bad too.this will let air out the seals and dramatically affect your compression.

[Huffa]

your crank seals could be bad too.this will let air out the seals and dramatically affect your compression.

Yep, and to test them am I correct to say it needs a leak down test then?

[Unclediezel]

soapy water around the cylinder and pull the cord----look for the foam --just like you would on a bicycle tire-----
By the way---GUYS-----If the trike would run without reeds-----then what keeps the intake charge in the crancase and not puffed back out thru the carb??????
2-stroke guys---2 stroke--think!!!

[TeamGeek6]

No, reeds and crank seals cannot affect compression, the piston cannot compress until it rises above the intake port, and that blocks the reed cage and crank seals.

The piston rising cannot increase the intake pressure either, because while the intake port is uncovered, the piston crown is rising to compress, but the underside of the piston has the same area going up to decompress. It comes out to zero pressure change.

Ive run 2 strokes without reeds installed. Not well, but it ran,

Sounds like the rings are wasted because the cylinder was honed or bored and not chamfered. That will destroy the rings instantly.

Uncle - the airflow through the engine keeps the flow going without reeds. It doesnt work well at low speeds - itll barely idle.

I intentionally make my 250R reeds leak a little.

[Unclediezel]

http://science.howstuffworks.com/two-stroke2.htm

As piston rises on Compression stroke----Intake charge is drawn into crankcase(NOTE- Intake port is covered--so charge is directed to crankcase)
As piston drops on power stroke----Reed closes and charge is directed to intake port which has been uncovered. the PRESSURIZED intake charge is then used to expell exhaust gasses, and fill the chamber with a fresh charge---???????

put your hand over an intake boot, block the air coming in---check compression with the intake blocked----Hmmmmm--very close to ZERO.
Im guessing you can remove the intake valve from a four stroke as well??????

[thefox]

OK, after trying Howdy's compressed air idea I know what the problem is. The rotor came loose so when I would pull the engine without the plug the motor would spin but once I pluged the spark plug hole with something (gauge, plug, thumb, ect) then the rotor would slip on the crank and the engine wouldn't turn over even though it would have resistance like it was. With any luck that will be all it needs but I won't know until tonight when I put the engine back in. Thanks for the ideas

[Howdy]

OK, after trying Howdy's compressed air idea I know what the problem is. The rotor came loose so when I would pull the engine without the plug the motor would spin but once I pluged the spark plug hole with something (gauge, plug, thumb, ect) then the rotor would slip on the crank and the engine wouldn't turn over even though it would have resistance like it was. With any luck that will be all it needs but I won't know until tonight when I put the engine back in. Thanks for the ideas

There is a first for me!! I haven't ever found a flywheel spin on the crank while doing a air pressure test. Anyhow, nothing would tickle me more than have you find out it is only a bad keyway. That would be a pretty cheap and easy fix! If you dig into it and find the flywheel , keyway, stator or such is thrashed let me know. I will send the parts right out via Priority Mail so you can have it running by the weekend. We can settle up once it running ( and the parts would be CHEAP! ). ;)
Howdy

[thefox]

Thanks for the offer Howdy.

I put the engine back in the frame tonight and tried to get it running. I put a few drops of oil in the cylinder an did a compression check, it was 90psi so now I now why it doesn't want to run. I did get it to fire twice but that was by putting some oil and carb cleaner (no starter fluid left) in the plug hole. I think I might just get it bored and new piston, and crank seals. There is already more $$ in this trike then it is worth so why not spend more to have it run.

[KASEY]

the reeds have NOTHING TO DO with compression,,,, when the engine is running ,,, the reeds are open when the piston is going up on the compression stroke,,,,,, think about it,,, the only time the reeds are closed is when there is a positive pressure situation in the crankcase and the only time that occours is when the piston is on the way down....... so if you have low compression its the rings or leaking gasket above the piston,,, compression occours when the piston goes by all the open ports ,,,so from the top of the exhaust port to TDC is where compression comes from,,, you don't lose compression from leaking crank seals it just won't run right :naughty:

[Unclediezel]

Ok----But--what gets compressed, If nothing makes its way into the chamber?---
That was the point of being sarcastic about removing an Intake valve from a four stroke----

[Unclediezel]

[QUOTE=KASEY]the only time the reeds are closed is when there is a positive pressure situation in the crankcase and the only time that occours is when the piston is on the way down....... QUOTE]

The Piston going "UP" causes Negative pressure(Vacuum) to draw in the next charge---Down pressurizes it---and where does it go if the reed doesnt block it---???Back out the intake---Which wont compress anything --because the chamber will be empty.

[KASEY]

hmmmm we just said the same thing,,,,, cause thats what i said,,,, the reeds are only closed when the piston is on its way down,,,, you can still do a compression test without reeds,,,, your not turning the engine fast enough to get a positive pressure situation in the crankcase ,,,

[tecatecrazy]

I dont know much about these motors but if the piston doesnt have ring stops then you need to make sure that your ring gaps dont line up with one another

[hoser]

the reeds have NOTHING TO DO with compression,,,, when the engine is running ,,, the reeds are open when the piston is going up on the compression stroke,,,,,, think about it,,, the only time the reeds are closed is when there is a positive pressure situation in the crankcase and the only time that occours is when the piston is on the way down....... so if you have low compression its the rings or leaking gasket above the piston,,, compression occours when the piston goes by all the open ports ,,,so from the top of the exhaust port to TDC is where compression comes from,,, you don't lose compression from leaking crank seals it just won't run right :naughty:

On some engines when you get up on the pipe the returning pressure wave from the pipe will stuff the fresh air fuel mixture that spilled out into the pipe back into the cylinder before the piston covers the exhaust port (piston on its way up) and build more pressure in the crank case than when your off the pipe.

See the animation at the top of this page http://12.215.122.222/tech.htm

[KASEY]

yeah your right about thatt,,, but that is with the engine running,,, oh by the way 2strokes have ring pins,,,,