What should the compression pressures be on 7.4L Mercruiser Bravo3 1996 Carb model?
What what is thr manufacturers recommendation for variance between cylinders?
Currently between 100 to 135. About to have headsdone.
Make (of engine): MercruiserModel (of engine): 7.4LYear: 1996Horsepower: 330
Motor model number OK004078
Hi. The spec. is 150 psi & 15 % between the highest & lowest reading, so you have some issues & I would have the heads done but also you may want to have the rings & pistons looked at. If you have not pulled the heads yet you may want to do a leak down test on the cylinders, this may help check the condition of the motor, valves, rings etc... I hope this helps. Please click accept. If I can further help please contact me. Good luck & Thanks.
Hi thanks for reply.
Can you please explain about leakdown test so that I know what I am asking when I talk to the mechanics.
Hi David. A leak down test is where you remove all the spark plug & install a leak down gauge kit (special gauge kit) which pressurizes the cylinder (with the piston at top dead center on the compression stroke), & you can see the % of leak down on each cylinder doing them one at a time & also see where the leak is, (thru the valves or rings etc...), you normally don't want more than 5% leak down max. I hope this helps, please click accept. Good Luck & Thanks. If I can be of further help please contact me.
28 YRS, JOHNSON & OMC COBRA MASTER TECH, MERCURY/MERCRUISER CERT,VOLVO & YAMAHA TECH. USAF TRAINED