Boat engine ??? (1 Viewer)

[MTNRAT]

I know there are a few here who know alot about boats and boat powering, so I figured I would ask a few Qs. I have a 1981 18 footer (see pic). It has a Chev 305 volvo penta with a 280 Volvo leg. The designation is Volvo Penta AQ200D/280B. I completed dry and wet compresion tests and got these numbers:
CYL#, dry-psi, wet-psi
1 - 110 - 110
2 - 125 - 139
3 - 102 - 105
4 - 116 – 130
5 - 111 - 120
6 - 120 - 135
7 - 110 - 119
8 - 116 - 126

The factory specs are 142-156psi.

Some cylinders went from 0-50psi on the first compression, others from 0-75psi. Then they would go to near 100psi on the second compression, and get full readings after 5 compresssions.
Looks like the rings are going? What advice: rebuid the 305, get a 350 block and rebuild that, get a remanufactured 350 longblock and add parts, or get a complete 350 remanufactured engine?


Thanks,
Sean

 

[my64fj40]

Most times a little below factory specs isn't that bad..


What you need to look for is numbers that are all close to each other, maybe within 5 or 10 psi ..




I would be a little worried about ports 1 and 3

If it has been sitting for a while it could be a ring that is a little gumed up, try running some good powerful cleaner through it and try the specs again.

If 1 and 3 came up around the others I think you would be ok






Then when winter comes around you can have a project to do (swap)

 

[Capt. Jim]

Valves and/or valve seals may be the culprit, also.

 

[MTNRAT]

Valves and/or valve seals may be the culprit, also.

Thanks, will do leakdown tests on monday.
Sean

 

[MTNRAT]

The reason I am going through these tests is because I cannot pull any but the best slalom skiers up on a deep start and the top speed is now down to 45mph. This boat could easily deep water start anyone and many times pulled up 3 skiers. It used to be able to hit 58 mph. It seems to me the engine is just getting tired. It runs well enough but just has no grunt. Less every year. Suggestions? If it proves to be worn I am thinking putting in a remanufactured 350 longblock and using all the rest of the original parts which are compatible.
Thanks,
Sean

 

[cruiserdan]

Compression tests are usually performed with the engine at operating temperature and the throttle blocked wide-open. Was this the case in your test?

If not, your low readings may be the result.

D-

 

[Cruiserdrew]

The first thing I would do is look at it with a different guage. You compression may be OK. How much oil does it use? What kind of shape is the carb in?

I like the idea of a rebuilt motor, but unless this one is run wide open all summer, it seems unlikely the rings would go just like that. The leak down will be interesting, because if it's running lean, it may be burning up the valve seats-that could happen quickly.

Can you come down for Rubicon in August?

 

[MTNRAT]

Compression tests are usually performed with the engine at operating temperature and the throttle blocked wide-open. Was this the case in your test?

If not, your low readings may be the result.

D-

Yep done that way.
Thanks,
Sean

 

[MTNRAT]

The first thing I would do is look at it with a different guage. You compression may be OK. How much oil does it use? What kind of shape is the carb in?

I like the idea of a rebuilt motor, but unless this one is run wide open all summer, it seems unlikely the rings would go just like that. The leak down will be interesting, because if it's running lean, it may be burning up the valve seats-that could happen quickly.

Can you come down for Rubicon in August?

Cannot make it. Going to Powell River for a couple of weeks. BTW driveshaft on route.
Cheers,
Sean

 

[brownbear]

Any idea on how many hours are on the engine? Is it orginal?

If so I say replace it. 350 is the way to go. But you need marine heads right? I thought they were different. But I dunno. What kinda difference does the marine block have? Coated water passages? Do you do any saltwater?

You could try some seafoam in the oil/fuel and down the carb. I ran it thru a few different engines and was surprised how it improved things. Can be bought at Napa.

 

[MTNRAT]

Any idea on how many hours are on the engine? Is it orginal?

If so I say replace it. 350 is the way to go. But you need marine heads right? I thought they were different. But I dunno. What kinda difference does the marine block have? Coated water passages? Do you do any saltwater?

You could try some seafoam in the oil/fuel and down the carb. I ran it thru a few different engines and was surprised how it improved things. Can be bought at Napa.

Unknown hours, original engine. Yes do saltwater but it has a freshwater cooling system for the engine and raw water for the exhaust manifold and risers. Marine engines are quite different.
*Different Camshaft
*Pistons need to be heavy duty
*Piston rings need more gap than automotive
*Valves have to be SS
*intake manifold has bronze inserts in the water passages
*rod and main bearings are of a harder alloy than automotive
*oil pump is high volume
*crankshaft is steel not cast iron
*block and heads have nickel to make them corrosion resistant
*electrics are marine-spark protected
*balancer is differernt
*flywheel is different
*carburator has to be marinized or the fuel injected system be completely changed to a marine type
Cheers,
Sean

 

[brownbear]

Unknown hours, original engine. Yes do saltwater but it has a freshwater cooling system for the engine and raw water for the exhaust manifold and risers. Marine engines are quite different.
*Different Camshaft
*Pistons need to be heavy duty
*Piston rings need more gap than automotive
*Valves have to be SS
*intake manifold has bronze inserts in the water passages
*rod and main bearings are of a harder alloy than automotive
*oil pump is high volume
*crankshaft is steel not cast iron
*block and heads have nickel to make them corrosion resistant
*electrics are marine-spark protected
*balancer is differernt
*flywheel is different
*carburator has to be marinized or the fuel injected system be completely changed to a marine type
Cheers,
Sean

Good list. So you have a closed coolant system? They are rare. I have seen some 4 cyl closed systems, but not many v8's.. Not that I am a marine xpert.

But I grew up driving IO's Family had an 84 Doral with a 3.8 OMC IO.
Volvo's are nice. The old OMC's sucked. Lots of slipping knuckles.

 

[fsusteve]

Depending on the condition of the boat would make the decision on the amount of money I spent on the motor. Is it in good shape or a quality brand? If it's fair, I'd rebuild if that's the cheapest option. But as said before I'd double check everything first.

 

[honk]

Probably just needs a valve job. The progression of compression readings you described is pretty normal and is the reason that compression test instructions specify that the engine be cranked through several revolutions (usually six, seems like).

A different test gauge might well give you higher (or lower) readings, but I'd expect that the variations between cylinders would show up at any level. It's that variation that best indicates valves not sealing well. (BTW, changing the valve seals alone will not improve the valves themselves, they just help contain oil and keep most off it from entering the intake by being drawn down the intake valves to combust. So they help with smoke but not with engine power).

Beautiful old hull. I like those classic skiboats a lot, and can't stand the modern attempts to be every boat for everyman. They look horrible and do a lot of things not very well.

If it were mine I'd make sure, REAL sure, that the I/O drive is in good shape, make sure that the hull isn't blistering or delaminating on deck and has no cracks at or around the transom. Then I'd have the heads off to a marine machinist for competent valve job with all new valves, guides, springs with their seats. When done I'd expect good power so long as the right prop is on it.

Or, you can sell it to me for $500. or more.

 

[MTNRAT]

Thanks every one. The boat had all the stringers etc replaced 5-6 years ago and I have just redone the interior. The outdrive is in exellent shape. The old campions are know for their heavy well built hulls and this one has large trim tabs for rough water.
I did the compression test in a bit of a hurry yesterday so I got up early really let the engine warm up and did the tests with WOT and put alot more oil in for the wet test. Here are the new number. I think they are more ominous?
CYL#, dry-psi, wet-psi
1 112 130
3 105 118
5 110 130
7 119 138

2 126 150
4 126 137
6 125 140
8 120 135

The factory specs are 142-156psi

 

[MTNRAT]

Here is how she looks now.

 

[cruiserdan]

I did the compression test in a bit of a hurry yesterday so I got up early really let the engine warm up and did the tests with WOT and put alot more oil in for the wet test. Here are the new number. I think they are more ominous?
CYL#, dry-psi, wet-psi
1 112 130
3 105 118
5 110 130
7 119 138

2 126 150
4 126 137
6 125 140
8 120 135

The factory specs are 142-156psi

The cylinder pressures are a bit low but even, indicitive of a fairly sound, but a bit tired, motor in my opinion. I would overhaul that engine. Rings, bearings and a valve job should freshen it nicely. Do remember to add marine gaskets to your list as they too are different.

D-

 

[my64fj40]

Nice boat

 

[honk]

Yeah, a set of rings too.

Looks like a nice easy boat to work on - have the engine out and on a stand in less than an afternoon if you're equipped and work slow and carefully.

Nice. Good strong old boats. Clean looks - I love it! Sell it to me!!

Something more: Are the cylinder numberings that you use here taken down the sides - I mean are you countin 1 through 4 on one side and the rest on the other side? It's that 5 through 8 as you list them are more consistant than 1 through 4.

I'm getting at maybe a retorque of the heads will give some of your power back.

 

[MTNRAT]

The 1-3-5-7 are on the passenger side, and the 2-4-6-8 are on the drivers side.

bow
1 2
3 4
5 6
7 8
stern

Sean