Compression testing question?

[houseofcash]

Hi everyone,

Another newbie question from your favorite member houseofcash.. Lol just a simple question. I picked up the compression tester today. The instructions say to take out ALL spark plugs when testing, however I swear I seen my friend only take 1 spark plug out ( the one he was testing) which one is correct?

On a positive note! I ordered myself some sea goggles off eBay!! I'm super excited. Last year I lost my favorite sunglasses while on the water. Here is Canada these sell for 70 bucks. eBay seller was 33 bucks! From Florida

Thank for all your help guys,
Houseofcash

 

[seadoo/skidoo]

The correct way is to test when all plugs are removed.

Nathan

 

[Dr Honda]

In a seadoo engine... I've noticed that it really doesn't mater. I generally will pull both. Also... do not put any extra oil in the jugs, that will hide problems... and hold the throttle open.

 

[seadoo/skidoo]

yup like Dr Honda said hold the throttle wide open. also I usually test each cylinder 2-3 times and average out the readings. make sure both cylinders are within 10% of each other :cheers:

Nathan

 

[houseofcash]

okay perfect! thanks for all your help guys. just curious, what is a normal compression? i was reading it can be anywhere from 120psi to 160psi, but what is important is that there generally equal. no more then 10% apart? is this correct?

Thanks again

 

[Dr Honda]

Normal good readings on an 800 and smaller seadoo will be 150 psi. The 951 engine will be about 135 psi.

 

[seadoo/skidoo]

120psi is rebuild time, 130 the engine is almost done and will go quickly, 150 is good. and yes no more than 10% apart

Nathan

 

[seadoo/skidoo]

lol Dr Honda you beat me to it. anyways yes like Dr Honda said 951 the compression wont be as high as the smaller motors. My last post i was referring to the smaller motors :cheers:

Nathan

 

[Seadoobuddy]

In a seadoo engine... I've noticed that it really doesn't mater. I generally will pull both. Also... do not put any extra oil in the jugs, that will hide problems... and hold the throttle open.

I've seen comments for both ways to test....should it be a cold or warm engine?????

 

[HighTrim]

Can anyone shed light on why to hold the throttle at WOT? Irrelevant on a 2 stroke outboard, so cannot figure out the difference for a seadoo....what am I missing here?

 

[LouDoo]

Cold, or at least cool.

Holding the throttle open ensures that the engine is getting a full stroke of air.


Lou

 

[Seadoobuddy]

OK, I looked in 3 manuals Mercruiser (for my boat), Yamaha and Seadoo......all 3 say to warm up the engine first.

My friendly mechanic said to check with warm engine, but I've seen comments for cold....that's why I asked.

A warm engine would expand parts so it would give "RUNNING" compression readings..... so ing still.

 

[Highmaster2]

So, based on Dr Honda's info, a 951 with readings of 130 & 120 is not too terribly bad?

 

[spx800]

being off 10 psi between cylinders is generally, not the best. A 5 psi difference between cylinders is acceptable.