Compression Advice

[jordan.widz]

My dad is looking at buying a 1990 mercury 15hp to use on a tinny. it has 103 psi on each cylinder. He is not sure if that is good or bad. Can anyone tell me what good compression for this motor/age should be please.

Thanks Prawn Star

[Geoff]

My dad is looking at buying a 1990 mercury 15hp to use on a tinny. it has 103 psi on each cylinder. He is not sure if that is good or bad. Can anyone tell me what good compression for this motor/age should be please.

Thanks Prawn Star

103 psi is not good. New motors are normally around 130 - 135psi. However , the main thing is that they are even.

If the motor runs OK & the price is right then worthwhile considering

Geoff

[a boat]

Hi, different compression gauges will read different and as Geoff said with any brand of engine the critical thing is they are even and 100 odd PSI is OK for that little engine. Great little engines these ones and I do not care what other 15HP you want to compare them too the US built 15HP Merc with the gearshift in the handle, the very cool tilt system and the way they run, there has not been a better 9.9/15HP ever made. If the price is right buy it if the engine runs well, pumps water and no water in the gear oil.

Cheers,

Huey.

[jordan.widz]

Hi, different compression gauges will read different and as Geoff said with any brand of engine the critical thing is they are even and 100 odd PSI is OK for that little engine. Great little engines these ones and I do not care what other 15HP you want to compare them too the US built 15HP Merc with the gearshift in the handle, the very cool tilt system and the way they run, there has not been a better 9.9/15HP ever made. If the price is right buy it if the engine runs well, pumps water and no water in the gear oil.

Cheers,

Huey.

Thanks heaps for your imformative reply. I think I can pick it up for between $500 - 600, do you think it's worth it. The seller reckons its had little use, starts first time and pumps plenty of water.

Thanks, Prawn Star

[wrxhoon1]

Thanks heaps for your imformative reply. I think I can pick it up for between $500 - 600, do you think it's worth it. The seller reckons its had little use, starts first time and pumps plenty of water.

Thanks, Prawn Star

As Huey said, it depends on the comp gauge and the way the comp test was done. Was the engine cold or hot? was it WOT or not ? The correct way to check it would be hot engine and wot, you could also perform a leakdown test, that would give you a better indication than a comp test.

If both cylinders are the same she will be OK . On an old engine like this I would be concerned with corrosion , check to make sure she is clean, pumps water and runs smoth.

[ray henry]

hi prawn star all the other posts are great advice .consider this when you buy a car you take it for a test drive more important with an outboard or a boat you should do the same take it for a good run make sure it does everything it should do [try before you buy] good luck the bull .