Does this sound right? Mercruiser 4.3 Low Compression

[nctrueconservative]

Hi all - Have a 2000 Crownline 180Br with a 4.3 MC. Engine had been "stumbling" a little bit for a while this summer and then last time we had it out, would not get over 3500 rpms, and was bogged down bad. Figured carb work was in order, so dropped it off at a shop I trust. Results came back that carb did need a rebuild, but one cylinder had low compression. 5 cylinders were at 150, 1 cylinder was at 120.

Mechanic said this meant either a burnt valve or piston trouble in that cylinder. He said we were looking at anywhere from $5,500 to $7,500 depending on if we did a tear down and rebuild or just a new crate motor. He recommended just cutting the boat loose at this point, as it would be going severely "Backwards" to do all that. Bummed to hear for sure, and don't think I want to go through with all that, but just wanted to check here to make sure that the work and prices that were mentioned are in the correct ballpark (I have no reason to doubt this shop, they are very reputable in our region of South Carolina, but just wanted another set of eyes to look it over).

Thanks!

 

[Scott06]

Hi all - Have a 2000 Crownline 180Br with a 4.3 MC. Engine had been "stumbling" a little bit for a while this summer and then last time we had it out, would not get over 3500 rpms, and was bogged down bad. Figured carb work was in order, so dropped it off at a shop I trust. Results came back that carb did need a rebuild, but one cylinder had low compression. 5 cylinders were at 150, 1 cylinder was at 120.

Mechanic said this meant either a burnt valve or piston trouble in that cylinder. He said we were looking at anywhere from $5,500 to $7,500 depending on if we did a tear down and rebuild or just a new crate motor. He recommended just cutting the boat loose at this point, as it would be going severely "Backwards" to do all that. Bummed to hear for sure, and don't think I want to go through with all that, but just wanted to check here to make sure that the work and prices that were mentioned are in the correct ballpark (I have no reason to doubt this shop, they are very reputable in our region of South Carolina, but just wanted another set of eyes to look it over).

Thanks!

If it was running lean would likely think it has a tuilped or brunt valve maybe a burnt piston. Is the oil pressure ok and does it have any death rattles? What is the rest of the condition of the boat ? Structurally sound

If it were mine I would look inside the spark plug hole with a borescope and see if piston is roached. If not pop of the head and take it to a machine shop.

A lot of folks want to just drop in a new engine, and in some ways this actually protects the owner in terms of you don't spend $2k now just to replace the engine because something else is wrong In a year or two... problem is this costs a lot of money.

That's not an unfair price for complete engine replacement, but I might try to find an independent shop or mechanic who may be willing to diagnose it a little further and pop the head off before giving the boat last rights. I would think this is only 2-3 hours labor to make a more informed decision.
Also I assume you have no skills or tools to do the work?

 

[Rick Stephens]

A shop with a mechanic wanting to be frugal for his customers would do a leak down test and in less than an hour tell you pretty precisely what was wrong without tearing things apart. Still end up having to pull the head if it's valves, but at least you don't start in on it and find the whole motor needs a build.

 

[Lou C]

Agreed the shop didn't do enough diagnostic work to really say what's needed. All that might be needed is a valve job! Not that hard to do on those engines and parts are cheap.

 

[achris]

A shop with a mechanic wanting to be frugal for his customers would do a leak down test and in less than an hour tell you pretty precisely what was wrong without tearing things apart.

Didn't even need to do a leakdown test, a simple wet compression test (add a squirt of oil) on that cylinder would have given a good indication of rings or valves...

 

[nctrueconservative]

If it was running lean would likely think it has a tuilped or brunt valve maybe a burnt piston. Is the oil pressure ok and does it have any death rattles? What is the rest of the condition of the boat ? Structurally sound

If it were mine I would look inside the spark plug hole with a borescope and see if piston is roached. If not pop of the head and take it to a machine shop.

A lot of folks want to just drop in a new engine, and in some ways this actually protects the owner in terms of you don't spend $2k now just to replace the engine because something else is wrong In a year or two... problem is this costs a lot of money.

That's not an unfair price for complete engine replacement, but I might try to find an independent shop or mechanic who may be willing to diagnose it a little further and pop the head off before giving the boat last rights. I would think this is only 2-3 hours labor to make a more informed decision.
Also I assume you have no skills or tools to do the work?

He said the carb was just dumping fuel and that sounds right based on how it was running before, the carb having to stay open, etc. Oil pressure was great, right where it should be even when it wasn’t running well the last time. Did seem to have some oil coming back up thru the carb when it was bogging down badly? When that happened the oil that was spit out was on the foamy side - oil on the dipstick always looked perfect. Rest of the boat is in good shape.

I am okay with tools but never done either a leak down test or a wet compression test - can these be done at home, or better taken to a shop? Might be worth diagnosing to know, even if I want to end up selling it. What should a valve job run if that’s what it is?

 

[Scott Danforth]

First, get a new mechanic

Do the work yourself

Work with your local machine shop

Head job between $100 and $400

Full remanufactured long block between $1500 and $1800

New GM long block $3400

 

[achris]

If you can do a 'normal' compression test, you can do a wet one...

Warm the engine. Pull all the plugs out. Set the throttle at wide open. Ground the main spark lead. Then record the compressions on each cylinder... If any are low, squirt a teaspoon of oil in through the spark plug hole and retest. Record the new pressure. If it went up (to about the same as the other cylinders) the problem is usually piston rings. If it started the same, most likely a valve or head gasket problem....

Simples.

Chris....

 

[tpenfield]

Mechanic is revenue focused, and probably not in your best interest. As the others have said, a cylinder leak test is warranted to further isolate the source of low compression. Most often it is a valve, but there are other possibilities.

The cost should not be anywhere near the figure you were quoted. Bring on the next mechanic/shop.

 

[nctrueconservative]

Mechanic is revenue focused, and probably not in your best interest. As the others have said, a cylinder leak test is warranted to further isolate the source of low compression. Most often it is a valve, but there are other possibilities.

The cost should not be anywhere near the figure you were quoted. Bring on the next mechanic/shop.

Understand. Weird because this guy has a spotless reputation, 5 stars on google with tons of reviews, and he's a real "Gearheads" mechanic. Has an amazing facility and keeps a spotless, vintage looking garage. Actually went to him because I was not pleased with the big dealer shop I was going to. If anyone knows a truly reputable mechanic in Upstate SC, let me know!

 

[Lou C]

Do a leak down test, if your bottom end is good, you might be able to just do this....
Here in Long Island NY parts prices were about $750 for the reman heads, new gasket set and ARP cyl head bolts.

 

[Rick Stephens]

Understand. Weird because this guy has a spotless reputation, 5 stars on google with tons of reviews, and he's a real "Gearheads" mechanic. Has an amazing facility and keeps a spotless, vintage looking garage. Actually went to him because I was not pleased with the big dealer shop I was going to. If anyone knows a truly reputable mechanic in Upstate SC, let me know!

He may be so busy that the fast and expensive solution is what comes to the top - no downside to him. While you may chose to take it elsewhere, there is plenty of spendy business to take your place. There are always ways to be more frugal, but it takes desire to make that one of your priorities. Counter to the make more money philosophy.

I have always done everything to my vehicles. If I don't know how to do it, the adventure is learning something new. He who learns the most new stuff before dying wins. Extra points for stuff outside your comfort zone.

If you want to jump in and fix your boat, or at least diagnose it and choose a best path for a fix, this is the place to be.

 

[Lou C]

Agreed there is better advice here than anywhere. When I took the old 4.3 apart 5 years ago it was the first real engine repair I ever did, (even though I maintained all our vehicles since the 70s) lots of small skills to learn along the way…cleaning parts properly, cleaning out bolt hole threads, removing gaskets without causing damage, measuring flatness, proper use of a torque wrench, etc. It’s all auto shop 101 but a lot to learn all at once.
Start with learning how to do diagnostic tests and report back….