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Leak at Spark Plug Gasket, Lyc Special Tools ST-369, ST-370

Noah

Noah

Well Known Member
Doing a compression check, I heard air escaping and had trouble sealing the pneumatic fitting in the spark plug port. Careful inspection showed a scratch or dent in the cylinder head, just adjacent to the spark plug port, where the gasket goes - hissing and bubbling with snoop leak detector.

Lycoming SSP384 (https://www.lycoming.com/sites/default/files/attachments/SSP-384%202nd%20Edition.pdf)
specifies Special Service Tools, and tool ST-369 shows a shaft with threads that screws into the spark plug port. A counterbore (ST-370) fits over the pilot to maintain alignment when the tool is cutting what Lycoming refers to as the "Spark Plug Pad", or sealing countersurface for the spark plug gasket. Service Letter L234B ("Tool Rental Program", https://www.lycoming.com/sites/default/files/attachments/Tool%20Rental%20Program.pdf) says to contact a Lycoming distributor to arrange for tool rental.

Has anybody had success doing this? I spoke to several distributors but have not gotten any traction. Were rental prices reasonable? If so, what distributor did you go through?

Aircraft Spruce is listed as a Lycoming distributor but the person I spoke with never heard of Lycoming's tool rental program & hasn't gotten back to me.

Has anybody experienced a leak like this? Material removal / spark plug pad cleanup using the proper tools seems like the best option but if I can't ge these tools, is Liquid Metal a reasonable alternate? Red RTV? Its a small leak and its probably been leaking awhile so I don't think it would be a huge deal if the sealant failed. I really don't want to remove the cylinder and send it off for service.

Thoughts? Thanks very much.
 
Noah said:
Doing a compression check, I heard air escaping and had trouble sealing the pneumatic fitting in the spark plug port. Careful inspection showed a scratch or dent in the cylinder head, just adjacent to the spark plug port, where the gasket goes - hissing and bubbling with snoop leak detector.

Lycoming SSP384 (https://www.lycoming.com/sites/default/files/attachments/SSP-384%202nd%20Edition.pdf)
specifies Special Service Tools, and tool ST-369 shows a shaft with threads that screws into the spark plug port. A counterbore (ST-370) fits over the pilot to maintain alignment when the tool is cutting what Lycoming refers to as the "Spark Plug Pad", or sealing countersurface for the spark plug gasket. Service Letter L234B ("Tool Rental Program", https://www.lycoming.com/sites/default/files/attachments/Tool%20Rental%20Program.pdf) says to contact a Lycoming distributor to arrange for tool rental.

Has anybody had success doing this? I spoke to several distributors but have not gotten any traction. Were rental prices reasonable? If so, what distributor did you go through?

Aircraft Spruce is listed as a Lycoming distributor but the person I spoke with never heard of Lycoming's tool rental program & hasn't gotten back to me.

Has anybody experienced a leak like this? Material removal / spark plug pad cleanup using the proper tools seems like the best option but if I can't ge these tools, is Liquid Metal a reasonable alternate? Red RTV? Its a small leak and its probably been leaking awhile so I don't think it would be a huge deal if the sealant failed. I really don't want to remove the cylinder and send it off for service.

Thoughts? Thanks very much.
Click to expand...
FWIW, the last time I had a leak like that it turned out pretty bad. It held only 10/80. The scratch was barely visible. It turned out to be a crack. I removed the cylinder and took it to a local engine shop. I was told I was lucky because the crack went nearly halfway around the circumference of the cylinder.
 
Thats a bummer. Thanks for the concern. Thankfully in my case it's not a crack.. Compression is 77/80, even with the leak.
 
Noah said:
Doing a compression check, I heard air escaping and had trouble sealing the pneumatic fitting in the spark plug port. Careful inspection showed a scratch or dent in the cylinder head, just adjacent to the spark plug port, where the gasket goes - hissing and bubbling with snoop leak detector.

Lycoming SSP384 (https://www.lycoming.com/sites/default/files/attachments/SSP-384%202nd%20Edition.pdf)
specifies Special Service Tools, and tool ST-369 shows a shaft with threads that screws into the spark plug port. A counterbore (ST-370) fits over the pilot to maintain alignment when the tool is cutting what Lycoming refers to as the "Spark Plug Pad", or sealing countersurface for the spark plug gasket. Service Letter L234B ("Tool Rental Program", https://www.lycoming.com/sites/default/files/attachments/Tool%20Rental%20Program.pdf) says to contact a Lycoming distributor to arrange for tool rental.

Has anybody had success doing this? I spoke to several distributors but have not gotten any traction. Were rental prices reasonable? If so, what distributor did you go through?

Aircraft Spruce is listed as a Lycoming distributor but the person I spoke with never heard of Lycoming's tool rental program & hasn't gotten back to me.

Has anybody experienced a leak like this? Material removal / spark plug pad cleanup using the proper tools seems like the best option but if I can't ge these tools, is Liquid Metal a reasonable alternate? Red RTV? Its a small leak and its probably been leaking awhile so I don't think it would be a huge deal if the sealant failed. I really don't want to remove the cylinder and send it off for service.

Thoughts? Thanks very much.
Click to expand...
I had to call Lycoming direct and talk to the tool rental shop after trying to order a rental through ACS. I had a leaking intake pipe connector and needed to borrow a $13,000 swaging tool. ACS had no idea how to proceed-they initially placed an order to buy the tool. Several phone calls and a couple weeks later I had the tool. Rental cost is $100. Shipping both ways was about $250 (mostly insurance). Beware, ACS will initially charge tool replacement cost and refund when tool return confirmed. Bottom line; you have to educate ACS on the process.
 
That’s why they use a thick soft copper gasket, takes care of any small imperfections in the mating surface.
 
JonJay said:
Ya, but what way do you put the gasket? ;)
Click to expand...
The hard edge goes against the head, the slight radius edge is up against the plug. Sometimes hard to decipher if gasket is dirty. Also, if you reuse them, make sure you anneal them and quench in a cup of water. Use a torch to get the gasket cherry red, then quench. The softness comes back for reuse.
 
Jesse23 said:
The hard edge goes against the head, the slight radius edge is up against the plug. Sometimes hard to decipher if gasket is dirty. Also, if you reuse them, make sure you anneal them and quench in a cup of water. Use a torch to get the gasket cherry red, then quench. The softness comes back for reuse.
Click to expand...
This was a joke referencing the recent thread on orientation.

Spark plug gasket orientation?

A buddy asked me today if it mattered which way he oriented the spark plug gaskets. I was like, well yeah, the inner diameter has a sharp edge on one side and and a radius on the other. The radius goes next to the plug...right? Perhaps I'd better look that up. Now here we are hours later and...
www.vansairforce.net

Champion has a very good explanation for why annealing is not recommended. Also a topic that’s has been beat up here before.
 
JonJay said:
This was a joke referencing the recent thread on orientation.

Spark plug gasket orientation?

A buddy asked me today if it mattered which way he oriented the spark plug gaskets. I was like, well yeah, the inner diameter has a sharp edge on one side and and a radius on the other. The radius goes next to the plug...right? Perhaps I'd better look that up. Now here we are hours later and...
www.vansairforce.net

Champion has a very good explanation for why annealing is not recommended. Also a topic that’s has been beat up here before.
Click to expand...
So, don’t reuse a dozen times. 2 to 3x is fine for me. Agreed that heat/cool cycle numerous times will loose the OEM properties to some degree. I always lightly sand them flat on both sides and back on the shelf.
 
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