COMPRESSION check with muffs?

[greg carr]

Should I Use Water Muffs When Doing A Compression Check Will It Make A Difference I Have A 115 Johnson V4 My Reading Came Out 115 85 On One Side And125 125 Onthe Other Do You All Think Tise Is A Simple Fix Or A Big Deal DO YOU THINK A DECARB WILL TAKE CARE OF IT OR DO YOU ALL THINK ITS MORE SEROUIS OH BUY THE WAY TRIED IT OUT BEFORE I BOUGHT IT IT RAN OUT FINE LOTS OF POWER THOUGHT IT WAS FINE BUT NOW IM A LITTLE WORRIED SHOULD I BE?

 

[coolguy147]

Re: COMPRESSION check with muffs?

decarb

how does it run?

 

[greg carr]

Re: COMPRESSION check with muffs?

Runs Out Really Good

 

[iwombat]

Re: COMPRESSION check with muffs?

With that big a gap in compression numbers there's something up with the 85psi cylinder. Time to pop the head and take a look.

 

[greg carr]

Re: COMPRESSION check with muffs?

Do U Think Its A Gasket Or Something More Serious How Do U Know If The Gasket Is Bad?

 

[jbjennings]

Re: COMPRESSION check with muffs?

If it runs nice, I'd recheck the compression (I figure you did that anyway, right?).
Any white greasy stuff on the spark plugs in the bad cylinder bank? Does it idle low and smooth? If so, I'd suspect bad compression measurements.
There's not a lot you can find out without looking at the pistons and cylinders. A peak in the bypass covers on the low comp. side-- if it has 'em-- would be an easy look-see.
If still bad results and it were me, I'd pull the head on the bad side and take a look at the head gasket to see if there's any evidence it was blown, and if so, fix it. If not, you at least get a good look at the cylinders and pistons on the bad cylinder bank. Try not to break any head bolts!
Just some thoughts---I know little about those big outboards!
JBJ

 

[Mas]

Re: COMPRESSION check with muffs?

Should I Use Water Muffs When Doing A Compression Check Will It Make A Difference

Running on muffs will not correct the low cylinder...nor is there any need to be running water through the cooling system while doing a compression test. You're not running the motor. Remove all plugs and make sure the "kill switch/lanyard" is activated to prevent frying your ignition. You do not want your ignition firing!

MAS

 

[tashasdaddy]

Re: COMPRESSION check with muffs?

you can try the decarb, it won't hurt, but i think you have a blown head gasket.

 

[emdsapmgr]

Re: COMPRESSION check with muffs?

125-130 are normal compression readings for crossflow 85 hp engines. The 85 lb cylinder is definitely low and is a concern. I'd have a look at that cylinder to see if both rings are still intact (no pitting on the head or piston crown) and to insure that the sides of the aluminum piston are not scuffing (transfering) onto the cast iron cylinder walls. Both rings need to be free of carbon and able to move easily in the piston ring grooves. Carbon around the rings will lower compression numbers and can cause premature ring failure. If you are lucky it's just a head gasket.

 

[Gary H NC]

Re: COMPRESSION check with muffs?

Did you do the test with all of the spark plugs out,throttle fully opened and fresh charged battery?
Put a teaspoon of oil in that cylinder and see if the reading comes up...