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Topic-icon IO-540 fouled plugs

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09 Jun 2021 14:42 #3035

Hi Al,
Very good.
Glad it's working again.

Steve

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08 Jun 2021 18:11 #3033

Hi Steve,
Thanks for all your help. I think you're right about replacing the high resistance plugs. We've gone ahead and actually replaced all 3 lower plugs with fine wire plugs. It seems to be running fine now.
We'll see how it does after a few flights. I'll make a point of taxiing lean as well.

Hopefully the problem will be resolved with this.

Thank you so much for your guidance here. It has been super helpful.

Al Lipper

Last edit: 08 Jun 2021 18:13 by Al Lipper.

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05 Jun 2021 13:52 #3025

Hi Al,
I strongly recommend that you replace all the spark plugs that have an internal resistance of more than 5000 ohms.
Then lean aggressively while taxiing and let me know if you're still experiencing plug fouling.
I want to know if those two actions solve your problem. Please do these actions before doing anything else.

Then if you are still experiencing problems with plug fouling on run up, we will take further steps.
From all you've posted, it seems to me that your engine is running well except for the plug fouling.
I am adding Lycoming SB 388C--which is related to testing for valve guide wear and the reduction of clearance in the valve guide to to carbonizing and coking.
Lycoming recommends that this be done every 400 hours, but the symptoms you describe don't sound like this is your problem
Steve

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04 Jun 2021 20:07 #3024

Hi Steve,
The plugs were tested for internal resistance and apparently had a bit of variation. Some were 1600 ohms and others slightly over 15,000 ohms. They were also tested on a plug tester and all tested good.

BTW, the engine only has about 300 hours on it since overhaul (including overhauled cylinders), so I want to fix it right.

I've summarized what we know below:

• Plugs get badly fouled at idle (not at higher power settings)
• If mixture is not leaned during a long taxi, both plugs in the cylinder will get fouled
• Leaning idle mixture helps a lot. In 2016 idle fuel flow was happy at 3.2 GPH but now I need to lean to 2.5 GPH to prevent fouling. I believe this suggests the issue is not mixture related.
• Overhauled cylinders were installed 300 hours ago.
• 3 cyls. all at the same time (within 100 hrs.) are having this issue. Others are fine.
• Problem cyls. are all on the same side of the engine (2,4,6)
• No blowby indicated in oil analysis. Oil is clean even after 25 hrs.
• No excess oil consumption (8 hrs. per qt. - same as 4 years ago, prior to the issue)
• Compression is good (73+ on all cylinders)
• No oil residue in exhaust pipes.
• Condition is gradually getting worse - not a sudden issue
• Engine logs from JPI 830 show no plug misfires in flight (just at idle on the ground).
• Spark plugs tested good (they are massive electrode type)

It seems unusual that this issue would appear on 3 cylinders at approx. the same time (within 100 hours of one another) beginning only 200 hours after overhauled cylinders were installed. And also that they are all on the same side of the engine.

Could there have been an error during installation of the cylinders on one side of the engine that would cause this? Perhaps mis-installed or incorrect oil control rings?

Could there be a crankcase ventilation issue on that side of the engine causing oil to be forced by the valve stems?

The engine only has about 300 hours on it, so I'd like to fix this right - it's not a matter of trying to get some more hours out of a high-time engine.

If the symptoms indicate an issue requiring cylinder removal, I'm fine with that. I want to fix the underlying cause (I just don't want to pull/replace the cylinders and then discover we still have issue.)

I'd be grateful for your feedback.

Thanks so much!

Al

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03 Jun 2021 23:07 #3022

Hi Al,
Did your mechanic do a spark plug internal resistance check?? When you talk to him, ask him if he did spark plug internal resistance checks. Other testing methods do not reveal high internal plug resistance.
I would not pull cylinders for this issue if I understand it correctly.
You have written that when you lean aggressively during taxi you get good mag checks.
Your power is good, your oil consumption is good, and you're not having any problems in flight.
Is your mechanic pushing your to pull the cylinders??

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03 Jun 2021 22:05 #3021

My mechanic just tested all of the plugs and he said they all worked perfectly.


In addition, I talked to a tech from Blackstone about my oil analysis and he said there was no indication at all of any blowby. Also, compression is good (73+ on all cylinders).

The JPI 830 engine monitor doesn't indicate issues during flight. It's just during taxi that they get fouled. I've often done mag checks after landing and they always test good.

I expect we need to pull the cylinders, but just want to make double-sure before we do that it couldn't be something else (like rich mixture or excessive crankcase pressure) that didn't require cylinder removal.

Would you say it's time to pull the cylinders, or is there anything else to check first?

Thanks!

Al

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