Proper Compression for HP500
 

I have twin 500's. The Starboard engine is new and a compression test showed all cylinders between 175-185. The Port engine was re-gasketed about 30 hours ago but has about 300 hours on it. It showed compression between 160-170 on 7 out of 8, the 8th came in at 152. The boat has been sitting for a month or so on its lift in NJ. Could the one slightly lame cylinder be doe to that IE. winterize and worry next season or should I be concerned?

There are no signs of blow by at all. The spark plugs were just as they should be.

thanks
Dan

I would put a little oil in the cylinder and recheck compression. I,myself,would rather figure it out now than wait till spring. Our season is short enough as it is. When it was regasketed did you do a full top end job?

Interesting, I just did my Hp500efi and had 145psi all the way around w/ 170hrs. That is a lot less than 175-185. Eddie, what cha think bout that.

Chris

Well, there are a few things that can affect the comp. reading. The biggest one is battery condition. If the battery is hot, then you will get a higher reading than if the battery is only just a little low. Same goes for the battery cables and starter condition.
Any liquid (gas, moisture, oil, WD 40, fogging oil, etc) in the cylinders will give a higher reading.
Lastly, there is a difference is gauges. I have seen 2 different gauges read 20 psi different on the same cylinder.
I look for no more than a 10 psi differential between the highest and lowest. If there is greater than 10 psi, I will do a leak down to find the source. It may be nothing more than a little piece of rust or carbon stuck between the valve and the seat. If it seems to be leaking from one of the valves, then I will remove the valve cover and wack the top of the valve with a rubber mallet while the air is hooked up. If there is some crap in there, it will blow out when the air escapes when the valve opens.
Hope this helps.
Eddie

do a leak down test on the cylinder in question.it will tell the tale.

First and foremost, thank you for the feedback.
I have always seen readings on an engine with some hours of between 160 and 170. The Starboard engine is returning readings of 180 and 185 because it is a Mercury Re-manufactured engine. I had blown a head gasket towards the end of last season and Typhoon marine re-gasketed everything on teh "Old Engine" but we did not take the time to send the heads out. I regret that looking back.

thanks again
Dan