Not Turning Over, Low Compression, Mercruiser 3.0

[alldodge]

I like those numbers much better. Would a machine shop recondition the block? Any advice on where to get a remanufactured long bloxk? I'm in NJ.

Recondition to me would be remanufacture/rebuild and most machine shops can take yours and do the whole job. Ask around locally and probably find a place, otherwise its send it off, or fine a rotted out hull with a good motor for even less

 

[ronaldreagan]

I'm hoping to resurrect this thread, if not I can start a new one if suggested.

In short, water got into my engine and now it has low compression, 30-30-30-100 psi

I had taken off the head to find the cylinder walls are fine, the tops of the pistons and head had surface rust.

I really want to determine the source of the decreased compression (ex. head gasket, rings, valves, bent rod....).

Could I have bent the rods trying to start it while not knowing there was water in the cylinders?

Maybe the water in the cylinders corroded the rings (it just looks like surface rust) and the walls mirror like?

I'm going to pull the engine and look for a used engine (wish me luck)......

 

[alldodge]

Its your thread so you can resurrect

The motor has been cranked over some so the rings could have cleared the rust from the walls. The rings could be damaged from the cranking, valves may be sticking from rust.

Could just rebuild what you have, but in any case good luck

 

[achris]

The check for a bent rod (or 3), turn the engine until each piston reaches the top of its travel. Measure the distance from the block deck to the piston crown. They should all be the same, and very close to zero. 2 pistons at a time will be at the top.

Chris...

 

[Scott Danforth]

Rust on pistons means you have had water in the cylinders.

 

[ronaldreagan]

Its your thread so you can resurrect

The motor has been cranked over some so the rings could have cleared the rust from the walls. The rings could be damaged from the cranking, valves may be sticking from rust.

Could just rebuild what you have, but in any case good luck

I would really like to rebuild, it seems like an easy engine to work on and would probably be fun. Any advice where to get the rebuild parts? Or walk through for the rebuild?

 

[alldodge]

Any advice where to get the rebuild parts? Or walk through for the rebuild?

Parts can be found at the local or on line auto parts house. To rebuild the motor needs to be torn down and see what needs to be done before parts are bought. The machine shop is where you will find out what it needs, unless you get the micrometers

There are several build threads here and other places. Only differences with a marine build are the gasket and core plug types

 

[ronaldreagan]

Parts can be found at the local or on line auto parts house. To rebuild the motor needs to be torn down and see what needs to be done before parts are bought. The machine shop is where you will find out what it needs, unless you get the micrometers

There are several build threads here and other places. Only differences with a marine build are the gasket and core plug types

Thank you! I plan to pull it this weekend and I've been reading the service manual. Would still like to determine the cause and all clues are pointing to bent rods but can not find the deck clearance specification. Anybody know this?

 

[Bondo]

Thank you! I plan to pull it this weekend and I've been reading the service manual. Would still like to determine the cause and all clues are pointing to bent rods but can not find the deck clearance specification. Anybody know this?

Ayuh,...... That's why ya need a competent machine shop,.....

 

[ronaldreagan]

I finally purchased an engine hoist and pulled the engine. Disasembled it down to removing the pistons expecting to find the cause of my low compression. No visual sign of failure anywhere..... it actually looked really good which is not good since I'm trying to find the cause of the low compression.

- the rods are not bent.
- no internal cracks in the block
- no marks on the cyclinder walls
- the rings are intact

What else should I look for?

One thing I notice but don't know if it's a concern is when I turn the fly wheel without the head on it requires some force but can be done with one hand...

I called a couple machine shops, they want $5,000 to rebuild it and are backed up for 6 months. Not a cost effective option. I'm near Philadelphia and the Jersey shore if anyone can recommend a machine shop.

Any advice or help is greatly appreciated.

 

[alldodge]

One thing I notice but don't know if it's a concern is when I turn the fly wheel without the head on it requires some force but can be done with one hand...

That would be normal with the pistons still in

the tops of the pistons and head had surface rust.

In resurrecting the thread rust was listed. The reason the cylinder walls didn't show rust was from several compression test and a bit of oil in the cylinders. The rings cleaned the rust off and were probably the main issue with low compression. In any case, its apart

 

[Scott Danforth]

What else should I look for?

.

prior to tear down, I would have done a leak down test. however since you found rusty plugs initially as well as the low compression, I would expect to see rust damaged bores

post a pic

however since the motor is currently tore down......

drop a bore gauge down the bores and look for taper and out-of round.
mike the piston and look for a collapsed piston
use die penetrate to check for cracks.

$5000 to rebuild what you can buy brand new for under $4k with a 1 year warranty or buy used for about $500 doesnt sound like a deal. should be able to rebuild it for between $1000 and $1500

typical costs

bake and blast block and heads - $150
align-hone, deck, bore and hone block - $165
recondition crank - $150
re-condition rods - $200
valve job - $150
new master kit - $500
misc - $150
rattle can paint - $15

 

[Scott Danforth]

so you started another thread on the same topic?

https://forums.iboats.com/forum/eng...my-engine-shot-low-compression-mercruiser-3-0

yes, your engine is shot.

 

[ronaldreagan]

prior to tear down, I would have done a leak down test. however since you found rusty plugs initially as well as the low compression, I would expect to see rust damaged bores

post a pic

however since the motor is currently tore down......

drop a bore gauge down the bores and look for taper and out-of round.
mike the piston and look for a collapsed piston
use die penetrate to check for cracks.

$5000 to rebuild what you can buy brand new for under $4k with a 1 year warranty or buy used for about $500 doesnt sound like a deal. should be able to rebuild it for between $1000 and $1500

typical costs

bake and blast block and heads - $150
align-hone, deck, bore and hone block - $165
recondition crank - $150
re-condition rods - $200
valve job - $150
new master kit - $500
misc - $150
rattle can paint - $15

Thanks, a lot of great information.

Would love to find a shop the Philadelphia / Jersey shore area to work at these prices....

Would you recommend I get a new block and go from there? It might eliminate the need for a machine shop assuming that the head is good. (engine only has 140 hours on it). If so, any recommendation on a web site to source the block and parts?

Another option is buying a long block. There are two companies that have it for around $2500, Xtreme Performance and Bishop Engine, all other companies seem to be $3,500 +. Does anyone have experience with either of these companies?

Links to long blocks:
https://spprecision.com/products/gm-...hoCP3UQAvD_BwE

https://www.ebay.com/i/163788036534?...RoCmYcQAvD_BwE

Sorry about the the two threads, I replied to wrong one this morning. It didn't work when I tried to delete my post.

 

[ronaldreagan]

That would be normal with the pistons still in



In resurrecting the thread rust was listed. The reason the cylinder walls didn't show rust was from several compression test and a bit of oil in the cylinders. The rings cleaned the rust off and were probably the main issue with low compression. In any case, its apart

Thanks for the response, it does seem like the probable cause was water in the cylinders. So you're saying rusting resulted in the loss of compression?

 

[alldodge]

Thanks for the response, it does seem like the probable cause was water in the cylinders. So you're saying rusting resulted in the loss of compression?

I'm saying the rust on the walls can damage the rings which would result in lower compression. How low is unknown and depends on how much rings may have been damaged

 

[ronaldreagan]

I'm starting to find a lot of automotive machine shops in my area.... I'm an idiot, did a search for "machine shop" when I should have search for "automotive machine shop"...... Shops around me are charging ~$275 to bake and hone the block and ~$300 to recondition the head.

This is good news...

 

[ronaldreagan]

I just got off the phone with a machine shop and really helpful talkative mechanic, he suggested that seized rings are cause of the low compression.

Should the rings move freely on the piston (removed from the engine)?

 

[Scott Danforth]

yes, however once you pulled the pistons out, you should re-bore and hone

the 140 hours is meaningless because you had water in the oil.

a well-maintained motor with 4000 hours will be in better shape than your rusty motor with only 140 hours.

 

[Rick Stephens]

I bought a boat with a zero hour fresh rebuilt V6 in it as a donor boat to install the running gear into my hull. The previous owner left the flash arrestor off the carburetor and a tarp over the motor. This dripped water into the carb and from there into the cylinders. I had to pull it down and rebore the cylinders again and replace brand new shiny pistons and rings with new oversize ones because of the pitting on the cylinder walls.