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95hp "K" Blowby around Spark Plug

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Ravenswood
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95hp "K" Blowby around Spark Plug

Post by Ravenswood » Sun May 05, 2019 2:18 pm

Just got the engine in my '41 Chris Craft Deluxe Utility rebuilt. After rebuild it was run on the block and then water tested by the company that rebuilt the engine.
When I went to run the engine the first time I noticed some staining in the new paint around the #6 spark plug. When I cranked over the engine, every time #6 came up on the compression stroke it puffed out air around the spark plug. I'm going to be calling the rebuilder on Monday but would like to have some advice as to what the problem might be prior to having a discussion with him.

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Captain Nemo
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Re: 95hp "K" Blowby around Spark Plug

Post by Captain Nemo » Sun May 05, 2019 6:22 pm

Did you pull check if the plug is loose? They don’t have to be torqued too much though. Pull the plug to see if the washer is intact.
Boats are to be made of wood, otherwise, God would have grown fiberglass trees.

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Bilge Rat
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Re: 95hp "K" Blowby around Spark Plug

Post by Bilge Rat » Mon May 06, 2019 7:47 am

Might be worth a try to change the plug. Even though its new, might have a manufacturing defect in the threads or even the porcelain insulator. Possible a Chinese product, there have been some documented counterfeit knock offs.
1966 Lyman Cruisette 25 foot "Serenity Now!"
1953 Chris Craft Sportsman 22 foot "Summerwind"

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drrot
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Re: 95hp "K" Blowby around Spark Plug

Post by drrot » Mon May 06, 2019 7:53 am

Bilge Rat wrote:
Mon May 06, 2019 7:47 am
Might be worth a try to change the plug. Even though its new, might have a manufacturing defect in the threads or even the porcelain insulator. Possible a Chinese product, there have been some documented counterfeit knock offs.
Great place to start. Exchange it with another plug and see if the problem moves with the plug or stays in #6
Jim Staib
www.finewoodboats.com


1947 Penn Yan 12' Cartopper WXH474611
1950 Chris-Craft 22' Sportsman U-22-1532
1957 Chris-Craft 26' Sea Skiff SK-26-515
1968 Century 17' Resorter FG-68-174

homeiste
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Re: 95hp "K" Blowby around Spark Plug

Post by homeiste » Tue May 07, 2019 7:16 am

Another possibility is a bad heli-coil repair job.
1960 18' Continental
1970 Boston Whaler Sakonnet w/ Bearcat 55 outboard

Ravenswood
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Re: 95hp "K" Blowby around Spark Plug

Post by Ravenswood » Tue May 07, 2019 2:04 pm

Thanks to all for their input.
Found the problem.
A close inspection of the #6 spark plug seat on the head revealed a fairly deep divot in the head surface where the metal gasket for the spark plug should seal against the head. Should have been caught by the machine shop when they checked the head, should have been caught by the boat repair when they installed the spark plugs or when they ran the engine.

jim g
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Re: 95hp "K" Blowby around Spark Plug

Post by jim g » Sat May 18, 2019 6:26 am

Thats a simple fix. Get a package of spark plug index washers. Put shipping tape on one side and cut the center out. Put some JB weld in the pit and put the washer on tape side down. Then screw the spark plug in. Wait a few minutes then unscrew the spark plug by hand while holding the washer down with a small screwdriver.

Remove move the washer after a few hours. Then install the spark plug with the thinest index washer.

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