2002 Mercruiser 3.0 Bayliner Capri 1750 speed/rpm

[langer4859]

Hey all, as the title states I have a 2002 bayliner Capri 1750 with a 3.0 mercruiser running a 14.25 x 19 prop. I’m hitting just over 4200 RPM WOT with a speed of around 32 or 33 mph. Does this sound right? Seems like I should be able to hit 4800RPM from the little digging online that I’ve done.

 

[Scott Danforth]

Weigh your boat
Check your throttle is getting full travel
Check your compression
Read your spark plugs
Inspect your exhaust shutter

 

[southkogs]

3.0 in a 1750 should go faster at WOT. Your RPMs should be up closer to 4800 and your top speed should be closer to 40.

I cruise in my 1950 at about 3200, making about 30MPH. Same prop as you.

 

[QBhoy]

Something isn’t right for sure.

 

[langer4859]

Weigh your boat
Check your throttle is getting full travel
Check your compression
Read your spark plugs
Inspect your exhaust shutter

I’ll have to figure out where to weigh the boat.

Front cylinder is only reading 75, other three are very close reading about 125.

Throttle has full travel

Spark plugs are gaped correct.

Didn't get to the exhaust shutter yet as it looks like I have a compression issue anyway so I’ll have to take a look at it when I figure out this compression issue.

 

[Scott Danforth]

Front cylinder is only reading 75, other three are very close reading about 125.

if those numbers are correct, you need a rebuild

new compression numbers are 150 psi. 130 psi and the motor is getting tired and will be down on power, 100 psi and it probably wont start

 

[Reserector_]

Could be stuck rings, a valve that isn't closing all the way, or a burnt valve. a little Kroil or Marvel Mystery oil squirted into the cylinder and allowed to soak may free rings that are stuck with carbon.
Swap a quart of oil for a quart of Rislone in the crankcase and run it for 20 or 30 minutes to free things up as well.

Your rocker arms may have been cranked down too far during a botched adjustment causing a valve not to close all the way. Could also be that a valve face or seat is eroded away and bypassing pressure.

If you remove the manifold, you can get one of those inexpensive endoscope cameras in there to see the valves. Inspect the open valves, and then crank it to open the others, and repeat. For the cost of a gasket, and a $20 eBay camera you can inspect your valve faces without removing the head.
Shine a bright light in each port on that #1 cylinder with the valves closed while looking in the spark plug hole. If light leaks, so will compression.

 

[langer4859]

if those numbers are correct, you need a rebuild

new compression numbers are 150 psi. 130 psi and the motor is getting tired and will be down on power, 100 psi and it probably wont start

Any recommendations on where to get a long block for a reasonable price versus having my engine rebuilt ?

 

[Scott Danforth]

Any recommendations on where to get a long block for a reasonable price versus having my engine rebuilt ?

since the motors have not changed much from 1991 on, look for a trashed boat with a good motor.

I would do a leak down test to determine if its rings or valves or what. could just need a head job

however Reserector also has a good point. you may want to try some of the decarboning solutions such as ring-free

 

[Reserector_]

These engines are very common. However, remanufactured and new replacements are scarce at the moment. I've been looking. When I do come across a vendor who has one, the price is close to $4k for a reman. A year ago you could buy a new one for not much more than that.

 

[Scott Danforth]

the cost of new and reman is higher than the higher volume V6's and V8's which started life as truck engines as this engine is a GM industrial engine and is only used in trash pumps, fork lifts and entry level boats.