COMPRESSION TEST.... Should i still buy it?

DjNiki4

Active Member
Sep 26, 2016
249
St Petersburg FL
Boat Info
2005 320 Sundancer
Engines
5.7 350s MAGs V Drives
UGH >...< Need some education guys. . .

2004 300 Sundancer

2 x 350 MAGs
Port hours 262 Starboard hours 265

So the Sea trial went okay but we did find few issues with this boat. . .

COMPRESSION:
The engine compression testing proved to be within the manufacturers specifications. Note: There is one cylinder on the starboard engine that is lower in compression and is of concern. It is recommended to the run the vessel, re do the compression testing. Monitor and remedy as necessary.

Port:
185 175
180 180
175 190
175 190

Starboard:
195 200
165 185
190 190
200 200

SEA TRIAL:
The sea trial proved the engines ran well at idle, the transmissions functioned properly and the trim tabs were operable. The manufacturers specifications on maximum RPM's at wide open throttle is 4600-5000. The Port engine reached 4200 while the starboard engine reached 4800 RPM's. The oil pressure appeared normal, the engine temperature appeared normal the charging systems appeared to be operable. The back down test was satisfactory.

The port engine did not achieve the manufacturers recommended WOT RPM's.

It does have few other tings to be repaired
  1. The starboard outdrives bellows are cracked and worn.
  2. The port outdrives cable bellows is not properly clamped.
  3. The air conditioning filter and unit is dirty.
  4. The fresh water pump cycles intermittently. Indication of a possible leak
  5. Port fuel gauge is inoperable.
The boat is very well priced, owner lowered it down by a lot after the sea trial, ill just say its way below $35,000 but over $30,000

I don't mind putting extra $5-$7k into it to get it running like it should... If you were me would you get this particular boat.
 

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Sure, if the rest of the boat is as clean as those engines. The low rpm motor should respond well to a tune and a fuel system cleaning, the compression is there.
 
Yes @scoflaw - rest of the boat is very clean. . front hatch has a small leak looks like it but nothing that will make me not buy the boat.
 

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I'd make sure the transom assemblies don't leak. That could get very expensive.
 
If that boat has been winterized and not run since last fall or longer, then an hour or two of runtime will most likely bring that cylinder up. What did the plug from that cylinder look like? When were the risers changed last (assuming this is salt water). Could be the very beginning of the riser failing. Still, based on the pictures the boat looks to be on pretty darn good condition, that one cylinder would not make me walk away -- yet. Something is keeping that motor from reaching RPMs, I would get to the bottom of it before I commit to the purchase. On the other hand, realize it is a 15yr old boat.
 
Not a bad deal on a very good looking boat are the engines raw water cooled? Has it spent her life in salt water? Risers and manifolds last invoices are a must if they can’t provide that I would treat it as if you are replacing them as part of the deal
 
If that boat has been winterized and not run since last fall or longer, then an hour or two of runtime will most likely bring that cylinder up. What did the plug from that cylinder look like? When were the risers changed last (assuming this is salt water). Could be the very beginning of the riser failing. Still, based on the pictures the boat looks to be on pretty darn good condition, that one cylinder would not make me walk away -- yet. Something is keeping that motor from reaching RPMs, I would get to the bottom of it before I commit to the purchase. On the other hand, realize it is a 15yr old boat.

@BillK2632 The Boat was winterized and it was put in the water just for the sea trial so yes last time it was ran was last season.
The plug i am not sure the tech who performed the compression test did not say anything about the plugs
This is a Salt Water boat and manifolds, risers and elbows were replaced in 2014. In 2017 then they did a reseal on those gaskets. engines temperature was normal under WOT as per survey.

the motor that has the 165 psi of is the actually reaching 4800 rpm under WOT
the other motor with all good reading is only reaching 4200 rpm under WOT so i am assuming a tune on this one should get it to 4800 rpms. l

i asked the owner if he will let me go with him on board and perform a leak down test on that cyl hopefully is under 20 %
 
Not a bad deal on a very good looking boat are the engines raw water cooled? Has it spent her life in salt water? Risers and manifolds last invoices are a must if they can’t provide that I would treat it as if you are replacing them as part of the deal


Yes salt water boat in NY Long Island . . .manifolds, risers and elbows were replaced in 2014. In 2017 we then they did a reseal on those gaskets. Also in 2017 on port outdrive we replaced gimbal bearing, u-joint assembly, bellows, seals.
 
I'm not seeing anything that would cause me to run away. It has MPI so the slow engine may just need the injectors cleaned.
 
I'm not seeing anything that would cause me to run away. It has MPI so the slow engine may just need the injectors cleaned.

a full tune up should take care of that issue.. however the engine with the low compression is the one who did better on the WOT test.
 
Not a bad deal on a very good looking boat are the engines raw water cooled? Has it spent her life in salt water? Risers and manifolds last invoices are a must if they can’t provide that I would treat it as if you are replacing them as part of the deal

I have not seen an answer to this critical question. If raw water cooled and original 15 year old engines I myself would not buy it. Fresh water cooled engine can run almost indefinitely if properly maintained.
 
I have not seen an answer to this critical question. If raw water cooled and original 15 year old engines I myself would not buy it. Fresh water cooled engine can run almost indefinitely if properly maintained.

You can tell by the engines it is raw water cooled. Fresh water cooled engines would have a tube in the front of them... why wouldn’t u buy a RWC ? My slip is in the river so it’s not as salty but I do boat in the the bay.
 
IMG_4230.JPG
I'm surprised that the engine with poor compression on the one cylinder reaches full spec while the good compression engine struggles. The RPM difference suggests a bad cylinder but the results are the opposite of what the numbers would suggest. I don't buy the idea that a boat fresh out of storage will not reach rated RPM. My boat was sea trialed right out of winter storage for a survey and ran at WOT numbers that were at spec and within 50 RPMs of each other. The buyer wondered about the significance of those numbers and the person doing the mechanical survey mentioned that a common cause of RPM differences is a weak cylinder. Of course there other causes of the differences as well.
 
View attachment 69856 I'm surprised that the engine with poor compression on the one cylinder reaches full spec while the good compression engine struggles. The RPM difference suggests a bad cylinder but the results are the opposite of what the numbers would suggest. I don't buy the idea that a boat fresh out of storage will not reach rated RPM. My boat was sea trialed right out of winter storage for a survey and ran at WOT numbers that were at spec and within 50 RPMs of each other. The buyer wondered about the significance of those numbers and the person doing the mechanical survey mentioned that a common cause of RPM differences is a weak cylinder. Of course there other causes of the differences as well.

My old 260 before tune up only did 4200 rpms after tune I was able to get 4700
 
Then these are probably due to be replaced if not now real soon. I would budget about $2500 for parts without labor for the two engines.

-Kevin
I’ve done risers before I can do it my self. But yes I am aware of it.
 
Agree with DjN, would not sweat this one bit, solid foundation with those numbers, simple fix although injectors can get pricey. I wouldn't panic on the 165 cylinder either. Motors that clean are probably just as clean on the inside as well.

I would be more concerned with leaking transom assemblies which are difficult to spot on a sea trial.
 
I still think for the price I’m getting it and the surveyor priced it at $42000 with 5-7k into it I should be safe for few years I’m not planning on keeping it for more than 2/3 seasons ‍♂️
 

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