Compression check

[powerabout]

oops, egg on face
lots of air under the piston of a 2s relative to a 4s to the valve/throttle blade
Guess there is a bit of schnuerle effect at cranking, maybe to get the engines past w/tee?

I'll have to do a test

[Chaz]

Power ol buddie , it's not as complicated as area of stored vs captured volume x number of cycles @ rpm performed during test .
But rather a more simplistic logical explanation . Since my "closed door" analogy was not good enough , lets in part use yours .

Next time you have "runny eggs on your fork" leave your mouth shut when you eat.

And when you "expel the previous days fuel" leave your pants buckled up .

Is it written in the manual :

It is if you have a brand new "Huggies" gauge . If you have a real old one then it really .. "Depends" ...

[racer]

IMO what ever way you do it write down the results and make sure to do it the same each time as consistency is the most important.

[ChrisCarsonMarine]

oops, egg on face
lots of air under the piston of a 2s relative to a 4s to the valve/throttle blade
Guess there is a bit of schnuerle effect at cranking, maybe to get the engines past w/tee?

I'll have to do a test

Don't feel too bad,very little difference on a 2 stroke,in my experience.I would attribute this to several things...primarily,a 2 stroke is way overcarbureted by design,usually a throat per cylinder.This is done to better tune the separate cylinders...the cfm requirement could be met by installing one of a v6 mercs carbs on an intake plenum that fed all cylinders,remember only two cylinders are drawing at any given time.Secondly,the last time I saw a full throttle plate(butterfly)that was normally closed all the way was on a racing motor on a hydro...shutting the throttle in a flip kept fron hydraulicing the motor.Todays motors all have holes in the butterflys to allow idle with the plates closed,except yamahas,which idle with the plates slightly opened via a idle speed set screw.It seems this amount of air is adequate for an acceptable compression test.
My opinion here,there are folks that will vehemently oppose my opinion...so...go test for your self,and report back,Chris

[FMP]

I still think the best way to make a decent cup of coffee is boil water and use a French press plunger or hand pour boiling through a filter

[bullet123]

Since gauges vary and compression tests are just a quick diagnosis for even wear on an engine, test each cylinder exactly the same . Do a leak down for true health measurement. JMO

[RSWORDS]

Since gauges vary and compression tests are just a quick diagnosis for even wear on an engine, test each cylinder exactly the same . Do a leak down for true health measurement. JMO

Honestly probably the best advice so far.

[ChrisCarsonMarine]

Honestly probably the best advice so far.

Agreed,My comment was aimed at the wot or not age old question,Chris

[RSWORDS]

Agreed,My comment was aimed at the wot or not age old question,Chris

I agree that on a 2 stroke it doesn't make much if any difference. But to be TECHNICAL. It's the way mother merc wants is done.

I look at it like this. If I always do it. I wont ever get bit on that one in 1000 chance it hurts it. Kinda like grounding the plug wires when cranking. How often is something really gonna go wrong? Not very, but that one time..... and that one time for me was when I had first started, had spilled a bit of gas in the cowl from a filter change. Spun her over and BOOM. Thank god I had a fire extinguisher right there and nothing got hurt but my pride.

[phillnjack]

dont do a warm compression test, do it cold to get honest readings..
having throttle open or shut wont make a blind bit of difference on a 2 stroke.. your not firing so not expelling exhaust at high speed.
the top of the piston will get enough air.. I would make sure no fuel in motor too when doing this as again your cheating yourself if there is oil in the bores.
you only need a couple of seconds on each hole.. like said above dont keep the starter going your just going to kill the starter for nothing.

[flabum1017]

The least resistance there is to the air, the more that will go into the cylinder...................... simple

[powerabout]

The least resistance there is to the air, the more that will go into the cylinder...................... simple

the 2s difference is the exhaust port is fully open at BDC so if it needs air that might do the job?

[flabum1017]

the 2s difference is the exhaust port is fully open at BDC so if it needs air that might do the job?

With the door closed, there is a large area behind the piston that will have negative pressure and require filling as well. Every two stroke manual I have ever read says throttles wide open for compression test. I prefer not to argue with the engineers who design these engines.

But to be fair, there will be little difference between doors closed and open, but enough to make a difference. I bet 90% of the people out there do a compression test wrong anyways and use cheapo gauges that will throw them in every different direction.

I am constantly at odds with service managers who tell me 10 - 15 strokes to get the same compression as the other cylinders take three strokes to get is ok.... so, open or closed door is really a minor argument in these cases.

But bottom line is good quality gauge, equal treatment for each cylinder, warm cylinder and open doors. As said before, leak down test is the absolute best way to determine the condition of a cylinder.

[H2OPERF]

I have Always reached over and pushed the carbs open..need or not cant hurt,,, Dave

[tlwjkw]

if it bothers ya 'bout which is tha right way jus do it "both" ways and pick one...….