Just finished a sea trial - need advise

[ks65609]

If I have to change the crankshaft bearings, does anybody have any idea on how much it would be?

I am not trying to dampen your day and add to the darkening senario, however, if in fact the issues get to this degree the scope is getting closer to a major engine overhaul (for example if the crankshaft bearings are worn, the crankshaft will likely be affected as well). Tearing an engine down to this point creates expensive labour costs. This type of wear may well have affected connecting rods, camshaft etc. I am not sure where the breakeven point may be but if the scenario merits it reman engines may be the solution. I am sincerely hoping it does not get to that point for you.
Ken

 

[ks65609]

I am not trying to dampen your day and add to the darkening senario, however, if in fact the issues get to this degree the scope is getting closer to a major engine overhaul (for example if the crankshaft bearings are worn, the crankshaft will likely be affected as well). Tearing an engine down to this point creates expensive labour costs. This type of wear may well have affected connecting rods, camshaft etc. I am not sure where the breakeven point may be but if the scenario merits it reman engines may be the solution. I am sincerely hoping it does not get to that point for you.





Ken

Just to clarify my remarks, I am not suggesting reman is a bad idea at all, just that it may be the least total cost solution.

Ken

 

[boatman37]

if the bearings are bad then you are likely looking at replacement engines or complete rebuilds. the crankshaft will likely need cut or at least polished, the rods should be re-sized, all parts hot tanked, at that point might as well hone the cylinders or bore if needed, new rings, pistons, etc. replacing bearings only is a band aid and will probably get you buy for awhile but if you are going through that much trouble might as well do it right.

main bearings rarely go bad unless there is a mechanical issue. the rod bearings usually go first and when they get bad enough will produce a knock.

it could be the oil, the oil pump, loose bearing clearances, or blocked return passages (not allowing oil to drain back quick enough, starving the engine of oil). i would definitely start with the oil change and would send the old oil in for analysis.

 

[BillK2632]

If I have to change the crankshaft bearings, does anybody have any idea on how much it would be?

I doubt that is the problem - not likely the exact same thing happened to both engines at the same time to cause low oil pressure. Still think it is related to the type / weight oil used. But, if it is, that would be a good time to walk away from the boat.

 

[Doc O Rock]

Oil change with oil analysis. Check how much is coming out of the engines. Are they low on oil? Low pressure could be low on oil. I saw a case where an after market dip stick showed full but the engine was 1 1/2 qts low.

 

[Ididntdoit]

+1 on oil samples......normal part of an engine survey - the fact that the oil is old will tell you the true condition of the engines via the metals found in the analysis.....if the oil was fresh, it could hide the true condition. if the samples check out (I use blackstone labs) I would proceed with the purchase....while your pulling samples, don't forget the trans and genny...

 

[kap2]

+1 on oil samples - they should be part of an engine survey. Here are the numbers from the engine manual and what it states about low oil pressure. Good luck and let us know how you make out.

 

[Jandcinok]

Maybe I missed it. Are the pressure readings coming from the gauges? Probably
just me but, I have a distrust of electrical gauges. I would feel better with pressures checked by a goid mechanical gauge.

 

[majoma]

Thank you for the specs. It looks like 20 PSI is still within specs and with a new oil should go higher.
Yes, the oil pressure was done with mechanical gauge.

 

[mnm99]

WOW.. There low. I just started up my 8.1's after sitting over the winter. Cold oil pressure at idle was at 50psi. Warmed up after 15 min i was at 47psi. I wonder why there is such a big swing in the 7.4...

Models	496 MAG HO	496 MAG
Propshaft Horsepower	4251	3751
Propshaft Kilowatts	3171	2801
Displacement	496 cid (8.1 l)
Maximum rpm @ WOT2	4600-5000 rpm	4400-4800 rpm
Idle rpm in NEUTRAL2	650 rpm
Oil Pressure @ 2000 rpm	60 psi (414 kPa)
Oil Pressure @ Idle	30 psi (207 kPa)
Thermostat	160o F (71o C)
Firing Order	1-8-7-2-6-5-4-3
Electrical System	12-Volt Negative (-) Ground
Alternator Rating – Hot Operating Amps	65 Amps
Alternator Rating – Cold Operating Amps	72 Amps
Recommended Battery Rating (Minimum)	650 cca/825 mca/150 Ah

Models	7.4L MPI	454 Mag MPI
Propshaft Horsepower (SAV1 Rating)	3101 (2752)	3851
Propshaft Kilowatts (SAV1 Rating)	2311 (2052)	2871
Displacement	454 cid (7.4 l)
Maximum rpm @ WOT3	4200-4600 rpm	4600-5000 rpm
Idle rpm in NEUTRAL3	600 rpm6
Oil Pressure @ 2000 rpm	30-70 psi (207-483 kPa)
Min. Oil Pressure @ Idle	4 psi (28 kPa)
Thermostat	160° F (71° C)
Timing @ Idle rpm4	8° BTDC
Firing Order	1-8-4-3-6-5-7-2
Electrical System	12-Volt Negative (-) Ground
Alternator Rating – Cold Operating Amps	65 Amps
Alternator Rating – Hot Operating Amps	72 Amps
Recommended Battery Rating	Minimum 650 cca/825mca/150 Ah

 

[majoma]

It looks like there is a big difference between the two engines.

 

[Ned]

Well did you buy it?