First Compression Test On Rebuilt Powerhead

[boatmon345]

Rebuilding 1997 Yamaha 150HP 2 stroke Saltwater Series II S150TXRV powerhead.<br />( Click here to view updated blog with new pictures )<br /><br />I got the heads installed this evening and ran a compression test (without the intake and carbs on, but I did add some extra lube in through the spark plug holes).<br /><br />Results:<br />Port Top 120 Stbd Top 117<br />Port Middle 119 Stbd Middle 115<br />Port Bottom 118 Stbd Bottom 110 <br /><br />(oversize piston in cylinder: Stbd Bottom)<br /><br />I measured Port first.<br /><br />I ran the test a second time and some of the readings were up to 5 pounds lower.<br /><br />I am unable to find compression specs in my book.<br /><br />Two questions:<br />1. Are these compression results proper for my engine? Where can I find specs for my eng...<br /><br />2. Stbd Bottom has the lowest compression. Could this be because the head was burred (or deburred, not sure of the correct terminology) and therefore there is more space for the gases to compress resulting in lower pressure?

 

[WillyBWright]

Re: First Compression Test On Rebuilt Powerhead

Compression tests on a fresh rebuild are a total waste of time. Break it in and see what you got then.

 

[boatmon345]

Re: First Compression Test On Rebuilt Powerhead

Oh<br /><br />I didn't want to get to far with the assembly before getting compression readings but they are useless I guess. These initial numbers really don't mean a thing? At least do they confirm a good seal at this point?<br /><br />Can anyone tell me where I can get the compression specs for my motor?

 

[Ray Neudecker]

Re: First Compression Test On Rebuilt Powerhead

There are none to get. You are in the ballpark now. Break it in before the numbers mean anything.