rebuilt engine shows low compression.

[inohv8]

3 cyl, new rings, one new piston, compression check = 75 psi in all cyl. how often do the heads warp? and since it the same in all cyl. is there a common link?

 

[Terry H]

Re: rebuilt engine shows low compression.

Is the motor broke-in yet? That can make a huge diference...just a thought

 

[Dhadley]

Re: rebuilt engine shows low compression.

Which 3 cylinder is it?<br /><br />Since you only replaced 1 piston we're assuming 2 cylinders were not bored. Since the compression is even we're almost assuming the other cylinder got a new piston but was not bored.<br /><br />What did the machine shop use for a finished bore size?

 

[inohv8]

Re: rebuilt engine shows low compression.

one cyl. was rebored oversized .020 and the other two cyl. were honed.. it was done by Litner and bush.. they specialize in marine machining..<br />new rings all round.

 

[inohv8]

Re: rebuilt engine shows low compression.

sorry forgot to add comment.. had engine running for about 1 hour after re-build on slow cruze with intermittent jump to plane..

 

[G DANE]

Re: rebuilt engine shows low compression.

Did you ever try your gage on something else ??

 

[Dhadley]

Re: rebuilt engine shows low compression.

I'd let it break in a bit more before trying to put a load on it. Recheck it after 5 hours to see if it comes up. Also try another gauge.<br /><br />Which 3 cylinder is it?

 

[mrc]

Re: rebuilt engine shows low compression.

Try re-torqueing head bolts (With a torque wrench <br /><br />Usually this is called for after the first few runs following a rebuild.

 

[inohv8]

Re: rebuilt engine shows low compression.

guage is a professinal model..,from an auto supply house had it for 4 years, never wrong before but you never know.. the engine is a 65 horse, 1973 , just so you know, I had to get the one cyl. rebored because it was scored, the previous owner used it for fishing and very rarely ran it full out to blow the carbon.. This showed because when I pulled it apart, the exhaust ports and plenium were caked pretty heavily...Litner and bush said they some carbon probably fell in and did the damage..

 

[voodoo]

Re: rebuilt engine shows low compression.

My 3 cyl had 90 in all three, 2 hours after a rebuild (not by me so I pulled the head to check the work)<br />10 tanks later and it's at 105 psi and runs like a top, with amazing grunt for a 1990 65hp. <br />Pushes a 16 foot doral tri-hull bow rider, seats 6 and gets on plane with 6.<br />Most of my other 2 strokes are in the 140-170 psi range so it freaked me out to see 90 psi.<br /><br />Wait till it's broken in for 10 hrs then judge by the power not the compession.