Generac 15KW generator engine tear down

[pclausen]

As I'm preparing to install a new 20KW generator at my mothers, I picked up the failed 15KW unit and took it home to tear down the engine in the hopes that I can fix it.

As per the other thread (Which 20KW whole house generator would you choose and why), the Generac tech that came out said the engine passed compression test fine, but that cylinder #1 had a 28% leak down and #2 had 48% leak down. 28% the cut off Generac uses to replace engines under warranty. The tech said the air appears to be escaping from the oil dip stick hole (dip stick removed). So that would likely indicate an issue with the pistons and/or rings.

I started by removing the top and front covers. This whole genset looks very clean:

Close up showing the model number:

Here it is after removing the muffler, control board and "firewall":

Shrouds, intake manifolds and air box removed:

#1 valve cover removed. Top of valve train looks ok.

#1 piston:

#1 cylinder wall. You can still make out the honing marks:

#2 piston:

#2 cylinder wall. Again, you can readily make out the honing cross pattern:

#1 head on left, #2 on right:

Closeup of #1 exhaust valve. Any idea what that white buildup is?

#1 exhaust valve stem. Whatever that buildup is, it doesn't look good.

The head gaskets looked fine. I don't see any obvious signs that the piston rings are shot and causing leak by, yet the leak down test seemed to point in that direction. Could the exhaust valves be the only culprit here?

I'm wondering if I should continue with tearing down the bottom end, or fix the heads first and see if that fixes things?

From what I'm seeing so far, I would say the odds are good that I can get this engine running well again. What do you guys think?

 

[murphy1244]

Rebuild the heads. Looks like a run lean condition. Did it run rough? Seems to be a possible air leak.
Can you give me a close up on the spark plugs?

 

[KYErik]

Wow- so they let you keep the failed under warranty unit? That is quite a good deal. Worst case scenario is that you could buy a pto gearbox and turn it into a tractor PTO powered unit.

So, what was the issue? Did it simply fail to start when the power went off? Or did it just not have enough horsepower to produce the full 15KW?

The cylinders look nice. I agree that you may be OK with just removing and cleaning up that exhaust valve. Was it using any oil? If not, the black deposits would make me think that it was running a bit rich if it was a gasoline powered engine, but I am not that familiar with natural gas/propane engines.

What weight of oil did you have in it? Maybe you could get by with a thicker weight oil like 20w-50. Thicker oil would slow leakdown and reduce blowby, but would wear the bearings a bit more when starting in really cold weather (and would likely slow the cranking speed).

 

[tcartwri]

Do you mind if I post these photos on another site?

To me it looks like there's an additive in the lpg that the motor doesn't like. You should be able to rebuild those heads for pretty cheap. New guides and seals, valve job and you're golden.

 

[pclausen]

Looks like a run lean condition. Did it run rough?

It didn't really appear to be running rough. It was last serviced on 12/6/2011, at which time new plugs were put in.

Can you give me a close up on the spark plugs?

Here you go (#1 plug)

 

[pclausen]

Wow- so they let you keep the failed under warranty unit? That is quite a good deal.

I wish! This 15KW generator was installed in July of 2004, so it is way out of warranty. Instead of having the service company replace the engine to the tune of $2000 with only a 90 day warranty, we decided to instead get a brand new 20kw unit and try to fix this one ourselves.

So, what was the issue? Did it simply fail to start when the power went off? Or did it just not have enough horsepower to produce the full 15KW?

The main issue is that it would burn a quart of oil every 8 hours or so and then shut down. Even with keeping up and adding oil every 8 hours, after running for 3 days straight, it was no longer able to start a 4ton AC unit.

What weight of oil did you have in it?

5W-30 Mobil One synthetic. BUT, when I first refilled it, I used straight 30 weight. Once I read the manual I realized that 5W-30 synthetic should be used. So I drained what little oil was in it, and refilled with Mobil One.

I should also mention that the break-in procedure was not followed. It came factory filled with organic break-in oil. You are supposed to run it for 1 hour at 25% load, then 1 hour at 50%, then 1 hour at 75%, and finally 1 hour at 100% load. Instead, this generator was put into service with the break-in oil in it for the first 3 years of its life. From that point forward, the proper oil was used.

Despite that oversight, the generator had been performing with no issues until this recent Mid Atlantic storm which caused a 5 day power outage, where the generator shut down after 16 hours and then every 8 hours after that due to low oil pressure.

 

[pclausen]

Do you mind if I post these photos on another site?

Sure, no problem at all.

To me it looks like there's an additive in the lpg that the motor doesn't like. You should be able to rebuild those heads for pretty cheap. New guides and seals, valve job and you're golden.

I hope its not some additive in the lpg. If that was the case, I would think a lot of generators in my region would suffer from this issue.

I noticed that only the intake valves have seals:

I don't think the guides are replaceable, at least I don't see a part number for them in the Generac manual.

Here's a close up of the #1 valves after I removed them. It looks like oil deposits on the intake valve.

So would my best bet be to take the heads and associated parts to a small engine repair shop and have then redo them?

 

[murphy1244]

It didn't really appear to be running rough. It was last serviced on 12/6/2011, at which time new plugs were put in.


Here you go (#1 plug)

That plug does not look like a cylinder burning a quart of oil in 8 hours. That plug is too new.

 

[pclausen]

That plug does not look like a cylinder burning a quart of oil in 8 hours. That plug is too new.

I agree they do look quite new. I'll check w/ the Generac tech. He might have changed them when he did the compression/leak down test. That would mean these plugs only have about 10 minutes of run time on them.

 

[hr3]

I'd take the heads to a small engine guy and have him do a valve job on them.. Then put them back on.. Set the intake and exaust to .076mm Set at TDC cold..
Then I would do a oil and filter change useing 5w-30 syn... "we use mobile1" then run the unit for a few hours change it again.. then try a long run.. I'm betting you won't burn any oil..

 

[KYErik]

Was it blowing lots of blue smoke out of the exhaust under load while it was burning all of that oil? (blue smoke under load would indicate an oil control ring issue)

When you did change the oil did it look like it was full of shiny metal "dust"? Another culprit could be stuck oil control rings (the rings may be in spec but they are just all gummed up in the piston grooves and can't "float" and stay tight against the cylinders).

 

[kennyd]

I hope I never have to see the inside of mine!

 

[tcartwri]

I noticed that only the intake valves have seals:

I don't think the guides are replaceable, at least I don't see a part number for them in the Generac manual.

Here's a close up of the #1 valves after I removed them. It looks like oil deposits on the intake valve.

So would my best bet be to take the heads and associated parts to a small engine repair shop and have then redo them?

Seals on the intake only is fine. When they do the guides, the original is oversized slightly and then a new sleeve is pressed in and honed to size. The guides do 90% of the oil control. You would be far ahead of the game to go to a proper machine shop.

I still do not have an answer as to what is forming those deposits on the exhaust valve. I've never seen anything like that.

 

[tcartwri]

Ok, from a little bit of research it sounds like it was the oil you were using. 'Apparently' an LPG engine requires low ash content oils. The deposits on the valves are carbonic ash, that is distilled out of the crankase oil by the heat of the chamber. Never heard of this, but apparently it is a known issue with lpg fuel.

ConocoPhillips Lubricants Expands Natural Gas Engine Oil Offering

 

[pclausen]

I'd take the heads to a small engine guy and have him do a valve job on them.. Then put them back on.. Set the intake and exhaust to .076mm Set at TDC cold..

Appreciate the advice, that's what I'll do and make sure he does the guides as well.

 

[pclausen]

Was it blowing lots of blue smoke out of the exhaust under load while it was burning all of that oil? (blue smoke under load would indicate an oil control ring issue)

The exhaust had no color to it at all.

When you did change the oil did it look like it was full of shiny metal "dust"? Another culprit could be stuck oil control rings (the rings may be in spec but they are just all gummed up in the piston grooves and can't "float" and stay tight against the cylinders).

The oil did not look unusual at all. I poured an ounce or so of fresh engine oil into each cylinder about 6 hours ago. Its all still there.

 

[pclausen]

Ok, from a little bit of research it sounds like it was the oil you were using. 'Apparently' an LPG engine requires low ash content oils. The deposits on the valves are carbonic ash, that is distilled out of the crankase oil by the heat of the chamber. Never heard of this, but apparently it is a known issue with lpg fuel.

Thanks Tim! I read the link you sent me and it sure sounds like that is why it happened, especially being that temps were around 100 degrees and the generator was running at close to 100% load for days.

 

[murphy1244]

Pete, was this the unit with oil sending unit leak?

 

[pclausen]

Seals on the intake only is fine. When they do the guides, the original is oversized slightly and then a new sleeve is pressed in and honed to size. The guides do 90% of the oil control. You would be far ahead of the game to go to a proper machine shop.

Appreciate the advice. I'll ask around to see what is a good shop around here.

 

[pclausen]

Pete, was this the unit with oil sending unit leak?

No, that's my current 8KW unit. I got the new oil sending unit, but haven't installed it yet. The 8kw is a vertical shaft V twin with a belt drive. I'll probably swap it for the 15KW unit, and then tear it down to see what condition it is in. It will likely have similar deposits on the exhaust valves.