Did compression check bad news... :(

[randomact]

Well per the advice of the top notch people on the forums here I was able to go from knowing nothing about boats to replacing water pump, impeller, starter, sparkplugs etc... I was having a problem when I put the boat in nuetral when I have the water muffs on it will start on the first crank, when the boat is in the water I have to push the button in for neutral then move it forward to give more gas and then the engine turns over.

I check compression and got these readings.
Cyl 1= 40 PSI
CYL 2= 120
CYL 3=115

could this be part of my problem why it wont start when the lower unit is submerged in water until I pop in neutral crank and gas it..

Also what are the long term effects of using motor with a cylinder with low compression? i went out and tested the boat today and she ran great not a hiccup.

How hard is it to repair a low compresion cyl? Thanks alot

 

[steelespike]

Re: Did compression check bad news...

There is a chance a good decarb might help.Though one odd cylinder does not bode well.Running well is a good sign.Perhaps you messed up on the compression check.

 

[roscoe]

Re: Did compression check bad news...

Could just be a blown head gasket.

Have to pull the head to find out the extent of the damage.

 

[randomact]

Re: Did compression check bad news...

How do I go about replacing the head gasket? Do I need to empty out my gas tank, fuel filter etc? Or do I simpley pull the head off (where the spark plugs go) and replace the ring around it?

Are there any tests I can do to see if I do have a blown head gasket? Thanks

 

[Kajun37]

Re: Did compression check bad news...

How do I go about replacing the head gasket? Do I need to empty out my gas tank, fuel filter etc? Or do I simpley pull the head off (where the spark plugs go) and replace the ring around it?

Are there any tests I can do to see if I do have a blown head gasket? Thanks

pull off the head and take a look at the head gasket and cyl's..its the only way....you dont have to drain fuel or anything......be careful taking the bolts out....sometimes they snap off if the bolt is rusted in there...take ya time ....take pics of the bad cyl and gasket and post them up.

 

[baxtr]

Re: Did compression check bad news...

when re tightening the head bolts, remember the torque is in INCH lbs not foot lbs, they will snap right off.

 

[Frank Acampora]

Re: Did compression check bad news...

Long term consequences of running an engine with low compression on one cylinder?
If low compression is due to a bad head gasket, continued long term running will result in combustion gases leaking through the seal and eroding the block and head leading to the need to mill the head and/or deck the block. --worst case scenario? Need to remove too much material and head and/or block needs to be replaced.

If low compression is due to a partially melted piston: continued running will spread aluminum particles throughout the affected cylinder and crancase and clog the cylinder drain screens. Aluminum particles may even work back into the crankshaft bearings. Eventually, the rings will break and badly score the cylinder and dent up the head plus catch in the ports.

In either case, you can see that it is best to determine and correct the problem rather than blithly run the engine 'till it quits.

If low compression is due to worn rings, then the main problem will be lack of performance.