Reman 383 Stroker - Low compression in rear Stbd cylinder

[jase34242]

Hi all, I have searched and have turned up some older info, just wondering for a little refresh on the data if there is any.

I bought a boat, in which the motor immediately imploded/died on the first weekend of ownership, even though it passed the survey and did great on the 1 hour trip to the home port.

Instead of going with the 350 that was in it, everyone advised me to go for the 383 Stroker, fresh water cooled.. which I did, even though it was more $$..

It was done at a professional marina and shop, using that term loosely, the total came to just under 20k.

This was 3 years ago.

From day one there has always been a gas smell at idle in the slip, I brought this to the attention of the now shut down shop (the state claimed eminent domain on the marina and the owners took the $$ and walked, I would have too) and they claimed it was just breaking in and it ran strong, which it did, I always did think it was slightly slower top end than the other models, but I figured I just weighed it down more with things, or it was built on a Friday, etc.. it has always run just fine around 27/30 and that's fast enough.

Fast forward to a little while ago.. after years of various mechanics working on it, one of them also didn't like the smell and brought to my attention that a spark plug didn't look great. Specifically that there was low compression on this cylinder (90 psi) vs the others that were all around 150-180.. ...

The boat still runs "okay" to this day, just very rich, but it's time to get this fixed.

Wondering if there is perhaps some new data on this specific problem as I do see older posts about it. The kicker is I paid for the extra warranty for 2 years, and even with me telling everyone who worked it about the gas fumes, no one thought it was a problem??

Oh well, it is what is now, anyone have any info on if this was a common problem? Thank you in advance!

 

[dubs283]

Low compression on a cylinder is bad

Best to remove the head(s) and inspect

What engine model is this?

 

[jase34242]

Low compression on a cylinder is bad

Best to remove the head(s) and inspect

What engine model is this?

From the invoice "383 MPI FWC BV-RM"
383 MAG MPI Stroker FWC Engine Only 350-hp (Plus-Series) for Bravo Sterndrive . Fresh Water Cooled (Close Cooling System).

Due to it’s size and power this is the ideal replacement engine for 350 MAG, 7.4L, and 7.4L MPI engines that power cruisers, small boats and large runabouts.
3-Year Factory Mercury/MerCruiser Warranty.

Specifications:

• Horsepower 350HP @ Crankshaft
• WOT Operating Range 4800-5200 RPM
• Engine Configuration GM Small Block V-8
• Displacement 383 CID / 6.3L
• Bore 4.030″ Stroke 3.750″
• Compression Ratio 9.0:1
• Idle Speed 600 RPM
• Gasoline 87 Octane
• Engine Oil MerCruiser 25W40 Syn Blend
• Cooling: Fresh Water Cooling

Marine Configuration:

• Engine Only.

Stroker Equipment:

• Fuel Injection with Cool Fuel System 4340
• Forged Steel Crankshaft.
• High Flow Flame Arrestor
• 1.6:1 Roller Rocker Arms
• Marine Roller.
• Camshaft Intake Lift 0.497″
• Exhaust Lift 0.497″.
• Gen+ Iron Heads Intake Valve Diameter 1.94″
• Exhaust Valve Diameter 1.50″.
• Hypereutectic Aluminum Pistons.
• High Flow Oil Pump.
• 160 F Thermostat.

First google result shows:

Mercury / Quicksilver Repower 383 Mpi Fwc Bv-Rm [8M0109404]

Free Shipping to New Jersey or Call for Quote383 Mpi Fwc Bv-Rm

boatersemporium.com

 

[dubs283]

I mean the original engine model. You stated you replaced the long block with a different size

Depending on model, specifically efi or carbureted there's a few different avenues of investigation

 

[jase34242]

I mean the original engine model. You stated you replaced the long block with a different size

Depending on model, specifically efi or carbureted there's a few different avenues of investigation

here is a picture of the original engine before pulling it out. This was during the sea trial. All of the additional storage and items down there were removed the first weekend I owned it. Nice idea and nice looking, but I'm not a fan of packing an engine room full of junk.

 

[jase34242]

While we're on the trip down memory lane, here is the picture of me trying to remove the oil 1 or 2 days into ownership.

 

[Scott06]

Would put compressed air into low cylinder and determine if low compression is out the valves, crankcase ,or into the cooling jacket.
if you have blowby the rings into crankcase the whole engine needs to come out. If its through the valves probably just the head.


would look in exhaust and see if yiu have water leaking into exhaust valve via manifold to riser joint.

 

[jase34242]

Ok, will do. Thank you for that.

Any thoughts on how this possibly could of occurred at the factory level? Or could this be a case of the marina not installing manifolds correctly etc?? As I said, it's been like this from day 1 as far as the unburned fuel smell.

 

[Scott06]

hard to say not seeing it apart. May have been a bad rebuild. I guess had they done a compression test after install you would know. Possible you have a bad injector and cylinder is running lean? What does plug look like in that cylinder.

looking at your photos you have dry exhaust which i have a hard time seeing leak. Possible the manifold has a crack internally, you can look inside when u get it apart.

 

[jase34242]

hard to say not seeing it apart. May have been a bad rebuild. I guess had they done a compression test after install you would know. Possible you have a bad injector and cylinder is running lean? What does plug look like in that cylinder.

looking at your photos you have dry exhaust which i have a hard time seeing leak. Possible the manifold has a crack internally, you can look inside when u get it apart.

Thank you for all your help here.. I'm trying to take this on as my own now because it seems like everyone is right, no one will take care of this as well as you do. However I will have someone else be doing the actual work.

The bummer is this motor has been out two additional times since being installed, could have taken care of this problem real fast!

I did reach out to a friend at Mercury this morning, I do not in the least expect them to pay for anything or even help with the cost, but just on the very slight chance they'll do something, anything, about it, I figured before I had anyone touch anything I'd give it a shot.

I would have assumed they would have done a compression test.

The very weird thing here is that if you replace the spark plug, she runs perfectly smooth for a very short while.. but at some point gets back to her old self within an hour or less and sometimes minutes or less.

I will have a picture of the spark plug in question next weekend when I get back to the boat and take it out. For now you have helped me figure out what path to proceed on. Thank you for that and I will update you as soon as I have something worth posting for your thoughts about!