[STEVE]

STEVE on March 26, 2022 at 6:52 pm #21289

Hi John;
I’m glad your engine is running well.
I asked for pictures because it’s very unusual for spark plugs to actually be broken. Glad my advice on the 5K ohm check was helpful.
Steve

[John]

John on March 25, 2022 at 11:56 am #21288

Hi Steve,
My A&P is the one that found them. He didn’t take a picture. He just said the lowers were broken. After I told him about the 5K ohm check you mentioned he went back and checked the rest and found the other three bad ones. Sounds like I was lucky that is all the problem I was having.

I took the plane around the pattern a couple of days ago on a warmer day and all CHT and EGT temps were much lower. Lowest I remember seeing them in the year I have had the plane. Definite improvement in performance.

Thanks again for the assist.

[STEVE]

STEVE on March 21, 2022 at 2:53 pm #21287

Hi John;
Wow! That’s surprising.
Please post a picture of the plugs that were broken?? I’m very interested in which part(s) were broken.
Thanks for the feedback.
Steve

[John]

John on March 17, 2022 at 6:29 pm #21286

Hi Steve,

Found a total of 5 bad plugs. 2 were physically broken including cylinder 2. 2 failed spark test and one had high resistance. Also found a broken intake gasket on cylinder 2 which was replaced. Going to take it out tomorrow for a long check ride, but I am fairly confident she will be purring again. Thanks again for the advice.

John

[STEVE]

STEVE on March 13, 2022 at 9:40 am #21279

John,
I suggest you check the electrical resistance between the spark plug spring contact inside the barrel of the plug and the center electrode at the firing end.

Any resistance over 5 K ohms will cause problems. Replace any plug with resistance over 5K ohms.
Best,
Steve

[John]

John on March 12, 2022 at 7:45 pm #21278

Hi Steve,
Thank you for the quick reply. The engine does not suffer from “morning sicknesss”. Just had an annual in October with new plugs. I know that doesn’t mean anything since new plugs can be bad, wrong gap, etc. also, didn’t have this problem before the annual. Will definitely try the swap.

I saw the rope trick in service instruction 1425A. Since he checked the cylinders iaw SB 388C I don’t think he saw the need. If the plug change doesn’t work, will try that for sure.

Thanks again. Should get the plane back Monday and will let you know.

John

[STEVE]

STEVE on March 12, 2022 at 7:16 pm #21277

Hi John;
It could be a spark plug. You can move the spark plugs from #2 to another cylinder to see if the “glitch” follows the plugs that were in #2; if one of the plugs is bad, just replace them both.
Do you get any roughness during the first start of the day? That smooths out in a few minutes? Mechanics call this first start roughness “morning sickness”. It’s an indicator that there is a build up of material, usually lead or carbon, between the valve stem and the exhaust valve guide. This build up prevents the guide from sliding smoothly in the guide. The build up is removed without pulling the cylinder by performing the “rope trick”
If the glitch stays at #2, it seems to me that since your monitor always indicates cyl #2 it would be worth it to perform what’s called the “rope trick” on #2 so your mechanic can run the proper size reamer through the exhaust guide.
In the rope trick, the keepers that “grasp” the valve stem are moved, then the valve spring cap and the valve springs are removed.
By moving the prop, your mechanic can lowered it away from the upper most position in the cylinder that’s being worked on. Then a soft rope is fed into the combustion chamber through the spark plug hole. Once the space is filled with soft rope, the valve is pushed down into the cylinder until the valve stem is out of the guide.
Then the guide is reamed back to size.
When it’s time to re installed the valve, it’s positioned at the valve guide with mechanical fingers through the spark plug hole, and pulled up into position using a magnet inserted down through the guide from the top of the cylinder.
Once the valve is all the way up into the guide and against the valve seat, the piston is moved up, which pushes the rope against the valve. Held in position by the rope, the valve springs, cap and keepers can be re assembled. It’s actually easy to do and doesn’t take much time.
I’m encouraged by the fact the engine seems to be running well.
Swap the plugs before your next flight–the results will indicate the next step you need to pursue.
Let me know how it comes out.
Steve

[John]

John on March 12, 2022 at 6:42 pm #21276

I have a 1969 32-260 with a recently Penn Yan rebuilt engine. The engine was installed in 2017 and has just over 400 hours since rebuilt. I have owned the plane for a year and until recently the engine ran flawlessly.

On two separate occasions after the engine had run for about an hour I felt a shudder run through the plane and got a CHT over temp alarm on cylinder 2. The mechanic checked the engine and found no issue after first time. Over temp and shudder went away after a second or two. Found SB 388C and was optimistic that this was all it needed. After the mechanic got the special tools all cylinders checked good. Next step is borescope. My concern is that nothing is found and this keeps happening.

Has anyone experienced this or have an idea of what else should be checked?