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KLC piston height

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jmears
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KLC piston height

Post by jmears » Fri Feb 10, 2023 11:42 am

Hello All,

I have a question for all you motor guys. My 1953 KLC has one piston that is lower than all the others when it is at top dead center. I have the motor out of the boat and partially disassembled, was getting it ready to take it in for a valve job. As I was rolling it over by hand I notice the piston at the rear, nearest the reverse gear (stamped #1) sits lower than the other 5 when it is at top dead center. I measured all 6 pistons when they are at top dead center and they all fall between .015” and .020” below the top of the engine block…..except the rear piston (stamped #1) measured .075” below the top of the engine block. So that one piston sits about .060” lower than the rest. That’s a 1/16” of an inch……seems very odd to me. My first thought was there is a different piston in that cylinder, but all 6 pistons have the same identification/part number stamped on them. Also, there is no slop or looseness when you roll that cylinder back and forth over top dead center, like you would see and feel if you had a severely worn wrist pin or worn piston pin bore or bad rod bearing and there was no engine knock/slap when it was running that would indicate worn wrist pin or rod bearing. So I don’t believe any of those parts are the culprit. Has anyone seen this before?

I attached a couple of pics. Cylinders 1 and 6 come to top dead center at the same time, so the 3 picks are with #1 and #6 at TDC. You can easily see the difference.

And thoughts would be appreciated.

Thanks,
John Mears
Attachments
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drrot
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Re: KLC piston height

Post by drrot » Sat Feb 11, 2023 10:05 am

Without removing the pistons and measuring them it is hard to say. But 1/16" is the compression height difference between a K series piston and a KL series piston.
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

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jmears
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Re: KLC piston height

Post by jmears » Sat Feb 11, 2023 1:49 pm

Thanks Jim,
Is it possible that this piston got stamped incorrectly at the factory? I'm sure mistakes happened back then too.
Thanks for the reply.

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drrot
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Re: KLC piston height

Post by drrot » Sat Feb 11, 2023 3:18 pm

Anythings possible. Until you pull them and check the numbers on the side and measure them you won't know.
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

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jmears
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Re: KLC piston height

Post by jmears » Sat Feb 11, 2023 5:17 pm

I will pull the pan off and remove the piston and measure this week and report back. Thanks for the help.

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jmears
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Re: KLC piston height

Post by jmears » Tue Feb 14, 2023 10:49 am

The piston and rod are removed. The piston has the correct measurement from the wrist pin bore to the top of the piston, of 1.6875". So the piston is not the problem.

Upon further discovery, the problem is obvious now....I have a bent / twisted rod. You can see the bend and twist in the attached pics. There is no damage to the piston, or any internal components of the engine. The crankshaft journal and rod bearing both look very good and the crank journal measures within spec all the way around. At some point in this boats history (before my ownership), it met with an underwater obstruction that bent the shaft strut and caused keel damage. Could such an abrupt impact have caused enough stress inside the motor (maybe as this cylinder was in the mists of its power stroke) to cause the connecting rod to bend and twist....but not break?

The motor seemed to run fine....even with this bent rod. But I had some low compression in a two cylinders and after removal of the cylinder head it was easy to see there were a few burnt exhaust valves/seats. Never did I expect to find a bent/twisted connecting rod.

Jim, do you have this connecting rod? The number on the side is 46390C?

Very much appreciate the help.

John
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Bilge Rat
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Re: KLC piston height

Post by Bilge Rat » Tue Feb 21, 2023 7:22 am

I suppose its possible that a violent stop at a higher RPM could bend a rod, but I would think the clutch pack in the transmission would slip sufficiently to prevent that. Another possibility is water in the cylinder causing a hydro lock condition. The hydro lock could have been fixed with a new head gasket or a replacement exhaust manifold but not diagnosed further.
1966 Lyman Cruisette 25 foot "Serenity Now!"
1953 Chris Craft Sportsman 22 foot "Summerwind"

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jmears
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Re: KLC piston height

Post by jmears » Thu Feb 23, 2023 11:01 am

Thanks Bilge Rat. I never gave water in the cylinder a thought, but it is very plausible and more than likely the culprit as there are no scars, dents, metal deformation on the piston top, etc. that you would expect to find to cause a rod to bend.
Thanks again,
John

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