Compression Question

[RetroActv]

Checked my compression today, 92 yamaha 50 hp. got between 117 and 120 on all three cylinders. Is this normal? I've seen some posts where 140 is expected, but anyone know the specs on this yamaha motor?<br /><br />Thanks!

 

[rickdb1boat]

Re: Compression Question

Anywhere around 125, as long as Each Cylinder is within 10% of each. Yours sounds a Tad low, but that could be the way you check it or the gauge itself. Sound OK to me!

 

[Dank]

Re: Compression Question

Should the compression drop on successive tests? I tested my yamaha 90 cold, after sitting for a week. Top cylinder 115, then 110, then 105, then 100. Bottom 2 cylinders right at 100. The only thing I could figure was that oil was being pushed from the rings / cylinder, causing the drop on successive tries. I assume that the compression readings will come up when the engine is hot. Anyone know how much more to expect?

 

[rickdb1boat]

Re: Compression Question

Check it Hot! Your readings should be much better! As for the drop, Not sure what's going on there. Usually it's about the same.

 

[Hooty]

Re: Compression Question

I'm with you Dank. I think the more times you spin the engine, the less oil you have to seal the rings, therefore, the last cylinders you check will have lower readings. I've got a 10hr. compression test coming up on a coupla more running hours on my re-built engine, and I'm gonna start with nr. 6 and go backwards.<br /><br />c/6<br /><br />Hooty