Need help with 1985 Mercruiser 3.7L 170 HP Compression Issue

Hi All-

Just bought this 1985 Sea Ray Seville 21' Cuddy with 170 HP Mercruiser I/O. Owner had not run the boat in over 5 years, so I started with the basics. I put in new plugs, wires, rotor, engine would still not fire. During this time, I also put Mystery Oil in all 4 spark plug holes and let it sit. I put in new starter and slave solenoid. Engine now turns over, but no spark. We also drained old fuel and refilled with fresh. Also changed oil and coolant. Took boat to local marina to have compression check, and these were the results:
1: 175
2: 175
3: 75
4: 100

He is trying to tell me that it needs a rebuild to the tune of $4000, which is ridiculous. I don't believe this is necessary. Any suggestions on what to do next that would not cost so much? Thanks!

Re: Need help with 1985 Mercruiser 3.7L 170 HP Compression Issue

I would recommend you buy a compression gauge and verify the compression yourself. If those numbers are right the head needs to come off to see what the problem is, or you could do a Cylinder Leak Test to try and pinpoint the problem. Reguardless of the results of the cylinder leak test the head will have to be removed.

Re: Need help with 1985 Mercruiser 3.7L 170 HP Compression Issue

Ayuh,....... If those #s are Right,......

That motor Needs a Rebuild...........

If you do All the Work, Yourself,...... You otto be able to get that price down to about 1/2 that #......