is compression too low?

[sergioy]

I am looking into purchasing a '85 rude 150 hp. The man selling it went ahead and started it up for me and let it run. It started right up and idled well. He told me that the compression was 80 to 85 on each cylinder. Does anyone know if this compression is too low or will it be alright? He is selling this motor for $1550. Do you guys think this is a fair price for this motor.<br /><br />Thanks...

 

[sparkroost]

Re: is compression too low?

That number is low.. was it running in a tank? It will run completly different in water due to backpressure on the exhaust. Another thing to consider is HOW the test was run. Cranking speed as well as if the butterflys are fully open will give best results.

 

[Walker]

Re: is compression too low?

I think the price is a little high regardless of the compression. That motor is 18 years old. Probably got a bunch of hours on it too.

 

[sergioy]

Re: is compression too low?

Does anyone know what the compression should be?

 

[Dhadley]

Re: is compression too low?

It depends on what heads and gaskets are on it. Try a can of Engine Tune and recheck. <br /><br />Good luck!

 

[papasage]

Re: is compression too low?

i checked my 55 hp 1979 it had 125 lb. if it was cold it may be higher when hot . that price i think is high. i wouldnt give it.papasage<br />i checked mine on muffs it had run till the water was warm.

 

[thehermit]

Re: is compression too low?

Everything I have seen (or heard) says you want greater then 100 on the cylinders with less than a 10 percent diff between. The diff being more troublesome than a low psi.

 

[Dhadley]

Re: is compression too low?

Yes the difference is what to look for. Some motors have staggered compression so some cylinders are slightly lower than others. The numbers have a lot to do with port timing, configuration and area. It also has a lot to do with swirl patterns and squish bands.<br /><br />Since the motor is all even I would tend to think its basically OK. It may have thick gaskets. 1985 was durring the "panic" time about the fuel. It may have the commercial heads. It may be the rings are starting to stick and a good dose of Tuner will raise the numbers 5 or 10 lbs. Not all gauges read the same either.<br /><br />Good luck!

 

[sergioy]

Re: is compression too low?

Thanks for the input guys. I would be lost with out a message board like this.