To Rebuild or Replace, that is the question- Yanmar SB8 in 1979 Hunter 27

[RumRunner914]

Looking for some advice as to how to move forward with my Hunter 27 Yanmar SB8. In summer of '20, my motor kicked out on me at sea a couple of times. Felt like I was slowly down-throttling until it shut off and then took a while to turnover again, meanwhile putting out a black cloud of what seemed like oil into the water. That repeated a couple of times and then the motor stopped turning over completely and hasn't started since.

What's been tried and failed: replacing batteries, replacing injector, hand-lapping the valves, checked the fuel lines (no leaks or bad fuel). Finally, a compression test showed that there isn't enough compression for the motor to turn over. A mechanic who took a look said the next step in a repair would be to pull the motor and replace the piston rings and piston.

Trying to decide whether to invest in having a mechanic do this partial rebuild (out of my skill range/ don't have a place, tools, or time to do it myself) or bite the bullet and get a new motor all together. Other than this issue, the motor ran fine for three seasons and was apparently rebuilt by a previous owner around 2014 so no other issues I'm aware of other than what could have developed while the motor has been sitting. Other options are to sell with a motor that wont start though I'd be right back in the market to buy again so trying to choose the path that makes the most sense.

Any and all advice appreciated!

 

[kappykaplan]

Trying to decide whether to invest in having a mechanic do this partial rebuild (out of my skill range/ don't have a place, tools, or time to do it myself) or bite the bullet and get a new motor all together.

@jssailem just went through a rebuild of his engine. Here's the thread:

A story of the engine that could.... Then didn't…NOW DOES

I have been thinking about how to write this tale of woe. A couple of my friends here at SBO have commented about the drama I have been experiencing with the Perkins 4.107 engine in my 48 year old boat. While it came to me with evidence of abuse, with some normal maintenance and minimal fixings...

forums.sailboatowners.com

Welcome to the forum!

 

[twalker H260]

Won’t turn over or won’t start? They might be related but likely different symptoms and root causes.
Won’t turn over implies something is jammed or frozen. Can you swing the motor over a bit by hand in either direction using a breaker bar and socket on the end of the crank?if so - how far? If yes in reverse but not forward you may have a hydro lock. If no both directions a large number of mechanical failures come to mind. How was the compression test performed? I would assume this was done by cranking the engine with the starter?

to lap the valves - I assume the head was removed. How did the pistons and cylinders look? Any evidence of coolant loss? How did the gaskets look. Any head leak?

if it turns over but won’t start it could be again a number of mechanical failures including broken valves or springs, rings, timing chain, cam shaft, etc.

None of the repairs are likely to be inexpensive, but perhaps further exploration would help to make an informed decision?

 

[RumRunner914]

Won’t turn over or won’t start? They might be related but likely different symptoms and root causes.
Won’t turn over implies something is jammed or frozen. Can you swing the motor over a bit by hand in either direction using a breaker bar and socket on the end of the crank?if so - how far? If yes in reverse but not forward you may have a hydro lock. If no both directions a large number of mechanical failures come to mind. How was the compression test performed? I would assume this was done by cranking the engine with the starter?

to lap the valves - I assume the head was removed. How did the pistons and cylinders look? Any evidence of coolant loss? How did the gaskets look. Any head leak?

if it turns over but won’t start it could be again a number of mechanical failures including broken valves or springs, rings, timing chain, cam shaft, etc.

None of the repairs are likely to be inexpensive, but perhaps further exploration would help to make an informed decision?

The motor does turn over, it wont start. I'm not sure how the compression test was done, a mechanic did that and i wasn't there for it. He was the third mechanic to take a look. All the rest were stumped and he diagnosed it to be an issue with the piston rings being cracked, and therefore the causing not enough compression for the motor to start. No leaks or issues with the cylinders or head, looked fine to the extent of what I and the mechanic who took a look know.

Ultimately it seems like it's time to pull the motor and either have it partially rebuilt or bite the bullet on a new motor. Just not sure which rout to go. I bought the boat for $5k so it pains me a bit to spend more than that on a repair or replacement.

 

[jssailem]

Rum Runner.
I have had a similar story. I posted it here on SBO.

A story of the engine that could.... Then didn't…NOW DOES

I have been thinking about how to write this tale of woe. A couple of my friends here at SBO have commented about the drama I have been experiencing with the Perkins 4.107 engine in my 48 year old boat. While it came to me with evidence of abuse, with some normal maintenance and minimal fixings...

forums.sailboatowners.com

Evaluation of the boat and options led me to choose rebuild engine.
Factor influencing the decision:

• Motor block and head were in good shape and could be milled for rebuilding
• Boat design required VDrive transmission
• Cost of rebuild penciled out half the cost of a new Beta
• Engineering for the new engine/transmission add 30% to engine cost
• Boat had been refitted in 2018-2019 with sailing gear that would have little or no scrap value.
• Rebuilt engine and transmission was planned for 6 months completion, new beta was back ordered for 6 months and install was estimated to take an additional 3 months.

We each need to evaluate our situation and then choose the path that looks the best. Circumstances in the rebuild delayed the completion. I am not yet sailing but hopefully within the next few days I’ll complete the commissioning process and have a reborn boat.

 

[MikeHoncho]

When cranking is it pushing out any smoke? If so, blue or white?

 

[heritage]

The used motor in running condition is also an option.

Yanmar SB-8 Diesel Sailboat | intermarine

Model: YYANMAR SB-8 Marine Diesel Sailboat 8 HP complete engine/Transmission 2.5:1 This engine was take off a pleasure boat used/ low hrs only 1325 since new just removed off for re-powering project drop in running conditions engine package is good to go. Brand: Yanmar8 HP@3200 RPMSer#:N/AONLY...

www.intermarinepower.com

 

[RumRunner914]

Rum Runner.
I have had a similar story. I posted it here on SBO.

A story of the engine that could.... Then didn't…NOW DOES

I have been thinking about how to write this tale of woe. A couple of my friends here at SBO have commented about the drama I have been experiencing with the Perkins 4.107 engine in my 48 year old boat. While it came to me with evidence of abuse, with some normal maintenance and minimal fixings...

forums.sailboatowners.com

Evaluation of the boat and options led me to choose rebuild engine.
Factor influencing the decision:

• Motor block and head were in good shape and could be milled for rebuilding
• Boat design required VDrive transmission
• Cost of rebuild penciled out half the cost of a new Beta
• Engineering for the new engine/transmission add 30% to engine cost
• Boat had been refitted in 2018-2019 with sailing gear that would have little or no scrap value.
• Rebuilt engine and transmission was planned for 6 months completion, new beta was back ordered for 6 months and install was estimated to take an additional 3 months.

We each need to evaluate our situation and then choose the path that looks the best. Circumstances in the rebuild delayed the completion. I am not yet sailing but hopefully within the next few days I’ll complete the commissioning process and have a reborn boat.

Thanks jssailem, I appreciate your evaluation and recommendation- hope you're back on the water soon!

 

[RumRunner914]

The used motor in running condition is also an option.

Yanmar SB-8 Diesel Sailboat | intermarine

Model: YYANMAR SB-8 Marine Diesel Sailboat 8 HP complete engine/Transmission 2.5:1 This engine was take off a pleasure boat used/ low hrs only 1325 since new just removed off for re-powering project drop in running conditions engine package is good to go. Brand: Yanmar8 HP@3200 RPMSer#:N/AONLY...

www.intermarinepower.com

@heritage thanks for sharing. Looks great and costs less than I'd expect

 

[RumRunner914]

When cranking is it pushing out any smoke? If so, blue or white?

No smoke when cranking outside of an occasional small puff of black smoke out of the intake

 

[MikeHoncho]

No smoke would make me believe it is fuel starved. Can you feel blow by from the valve cover cap when cranking?

 

[kloudie1]

1000 mile. No data diagnosis .... Overheated scoured piston and rings and possibly cylinder walls.. Probably need to pull the head to evaluate.. could have also blown a head gasket.

 

[twalker H260]

Has timing been checked? Don’t know how many hours your motor has but could your gears be worn to the point that the timing is off on the camshaft and/or fuel injector? Looks like the motor uses gears with no chain or belt so unlikely - unless things are very worn or a component is sheared but it could result in low/no compression and/or fuel injection being at the wrong point in the engines cycle. I’m assuming that valves appeared to be moving properly/gapped properly when things were reinstalled after lapping?

 

[David in Sandusky]

We blew a head gasket on our SB8 when it was about 30 years old. It lasted another couple of years after replacing the gasket, then lost compression. It was hard to start, and wouldn't push our '77 h-27 past 4 knots.

Spent several months of the 2009 off season checking out the market, then found a 1 GM10 with only 50 hours on it from Torreson Marine. Total cost including installation by our marina was around $6,000. I am very pleased with the 1 GM10 which is still operating very well.

I like your idea of having it out and then evaluating a new piston and rings, since your last mechanic thought that might work.

When I think about cost, the big number is $3,000 to $3,500 per year for storage, slip, haul-out, and upgrades/maintenance. That's around $78,000 over 24 seasons. Well worth it in my opinion at about $120 per night on the boat. The boat cost $9,000 to buy, and I might get $5,000 tp $7,000 out of it when we retire from sailing, So the $6,000 for a like new engine is small potatoes in the big picture!

 

[MikeHoncho]

When I think about cost, the big number is $3,000 to $3,500 per year for storage, slip, haul-out, and upgrades/maintenance. That's around $78,000 over 24 seasons. Well worth it in my opinion at about $120 per night on the boat. The boat cost $9,000 to buy, and I might get $5,000 tp $7,000 out of it when we retire from sailing, So the $6,000 for a like new engine is small potatoes in the big picture!

Nobody here wants to hear your logical, financially responsible cost breakdown………we prefer not to know. Lol