porting and polishing.

[ruthlessxbeastx]

deal that works for me!
a guy on craigslist is selling a leakdown test and compression gauge for 100 bucks and i looked online and the leakdown tester he is selling is like 250 new :]
so i think im going to give him a call!

[ruthlessxbeastx]

well is it possible to do a leakdown test with the motor in?

[nutz4sand]

Yes. Just plug the intake and exhasut and connect you guage and pump to the fual pump siganl port coming out of the crank. The piston should be at bottom dead center or at least down past the ports.

[ruthlessxbeastx]

so then the leakdown test shows if the bottom end is good also? or bad lol but i can add pressure into the crankcase where the fuel line goes into?

[nutz4sand]

The leak down test IS a test of the bottom end mostly. But it also tests EVERY seal.

Once the intake and exhaust are sealed you simply need to be able to get pressure into and out of the crankcase.

The fuel pump signal port coming out of the crank is a good palce to do it so you don't need some kind of spark plug adaptor BS.

[ruthlessxbeastx]

ok so then just hooking up a airtank or little hand pump [with a gauge on it] and some just 1/4 line will do if all the ports are plugged up? and exactly how many lbs of air am i putting in? would a atv tire gaue work? since it measures a small amount of lbs? just make a T and the line to the pump and one to the crankcase. would that work?

[nutz4sand]

Any two stroke has seals in the crankcase. If these go bad you usually lean out the motor and fry a piston and can ruin a good cylinder along with that.
To pressure test a two stroke should be done BEFORE you tear it apart for a rebuild. (If it fails then a top end rebuild alone will fail due to the bottom end is leaking. If the motor fails a crank pressure test and the pistons is bad the bottom end is usually what caused it.) AFTER you rebuild it to check the seals (and gaskets) you just worked with. And at regular intervals (along with piston compression checks) to monitor your engines internal life.

To do a pressure check you need to remove the pipe and carb and go to a hardware store and get some stuff from the plumbing department to seal both holes. Rubber caps and a hose clamp usually work good on most exhaust pipe snouts and PVC pipe caps can normally be found easy that will fit in the carb boot. You then either need to make or get a fitting that allows you to put an air hose to either one of the caps or into the spark plug hole.

Basically you need to have a way to feed air into or out of the motor.

If you cannot find a way to use the sparkplug hole with a fitting then drill a hole in the PVC pipe cap thats in the carb manifold (Take it out of the manifold first if its already in there! I hope I didn't need to tell you that but just in case! I have seen people drill things where crap from the drill falls into the works. Not good). (My honda Pilot has a fuel pump hose fitting on the side of the cylinder (some motors have these on the crankcase) for the pulse to make the fuel pump pump fuel. If you have that fitting you can use it (on a single cylinder. In a twin it can only be used for the cylinder its under just so you know)

Once you KNOW the pipe and carb holes are sealed tight (The spark plug too if you have you air fitting there. If the plugs in it should be fine.) make sure the piston is down in the bottom of the cylinder (You don't want it blocking the ports. The very bottom is good. Just clearing the cylinder ports will be fine.) Then you need a vacuum gauge/hand pump ($20 to 30 bucks at any auto store for the hand pump version.) Put about 6 inches of vacuum to the crankcase. If it drops to 4 inches of vacuum in under three minutes the bottom end seals are bad or at least weak. Some say less than an inch of vacuum a minute is fine but as you regularly test your motor if you see it loosing its negative pressure faster then you will know the seals are getting weaker and its a lot cheaper to fix it before it toasts everything. (This requires you to make sure the carb and pipe plugs you made are good so you are only checking motor gaskets/seals.)

Thats a negative pressure test. You can go up a little higher in vaccum pressure. The motor should be able to hold some for over five minutes or the seals are toast.

Many also do a positive pressure test. Same deal as above. Seal the motor and get a hose connected with the piston at the bottom of the cylinder. In the NEG test above the pump stays in the line and holds the vacuum. For the POS test you will want a little on/off valve in the line. Then once you put pressure to it you can close this valve to hold the pressure in. As long as you have a setup that holds the pressure in at the hose your fine.

HERES THE CATCH. If you put to much POS pressure to the crack case you can literally Blow the seals out! NEVER JUST PUT A AIRCOMPRESSOR HOSE TO THE SETUP YOU MADE TO PRESSURE TEST IT AND "THINK" YOU CAN HIT IT WITH A LITTLE AIR AND TEST IT THAT WAY. You make one little mistake and its gonna need to be taken apart and repaired. So do this instead. Get one of those small portable air tanks. Put about ten PSI in it with the compressor. Then bleed it down to 6 PSI or maybe 5. This way you cannot put more than that to the crankcase. Better safe than sorry. Put the 5 or 6 PSI to the crankcase and seal the valve. It should not leak more than a pound a minute. Less is better. More is questionable.

You can get a gauge at the auto parts store that reads both POS and NEG on the same gauge. (They are NOT high pressure they are more for car manifold tests) This gauge can do both tests for you. I have in the past used these (I still have mine and use it) AND used a HUGE syringe to provide both the vacuum and the positive pressure. It sometimes takes a few pumps to get the pressures I wished but it can be done.

If that did not make sense GOOGLE pressure testing a crankcase and you will get some more insight.

Or pay a mechanic. Bill

[ruthlessxbeastx]

no that makes perfect sense im just curious if i have to take the motor out of the frame and do it on a bench. or can this be done inside the frame?

[TheDoc]

Unless you have a way of securing your motor to a bench it is probably easier in the buggy.
That way if nothing is wrong all you have to do is put the exhaust and carb back on and go out and enjoy.

Nick.

[ruthlessxbeastx]

hahah alright that works for me and then if somethings wrong then pull the motor!
ya you guys are a lotta help thx!