when can I do a compression Check

[liamtovey]

I am currently reassembling a Yamaha 1998 90hp 3 cylinder 2 stroke outboard that I've been rebuilding. I've very new to all of this, and have a fairly basic question.<br /><br />At what point can I do a compression check. I've assembled the crankcase, bolted the head onto the block, and put on the exhaust cover. Am I able to attached the starter motor to the engine block, hook it up to a batter, and check the compression before putting everything else back on. The carbs/ flywheel/ head water jacket etc are not back on the engine.<br /><br />Additionally, once I get all the other bits and pieces back on, can I run the powerhead before I put it back on the lower leg, bracket etc. The boat is located away from my workshop. I would like to be able to check that everything works before putting the powerhead back on the rest of the engine. My engine has a cooling attachment that plugs into the hose and feeds directly into the power head. I anticipate using this to keep the head cool. <br /><br />Kind Regards<br /><br />Liam

 

[WillyBWright]

Re: when can I do a compression Check

Here's what you need for a compression check on a 2-stroke. Obviously a completed block assembly (including crankcase, crankshaft, rods, and pistons), a flywheel, and the starter. You don't need the carbs attached, nor do you need the reed blocks installed. You also don't need an ignition system installed, or even cooling water.<br /><br />But you may be doing it for nothing. Compression readings on a fresh rebuild are basically meaningless. It'll tell you if you're getting compression, but until the powerhead is broken-in you won't have consistant readings.

 

[rodbolt]

Re: when can I do a compression Check

I usually just put it together correctly once, bolt it down and go play. about the only in water check that I do is timing at WOT.<br /> use the manual and do it once but do it right and there is no need to mess with it.<br /> good luck and keep posting