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Zero compression on cylinder 5

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jim.eakin
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Zero compression on cylinder 5

Post by jim.eakin » Tue Jul 23, 2019 12:31 pm

I've been struggling with bringing up a rebuilt (so I was told) KBL engine. The engine would only start with gas poured into the carbs, then ran extremely rough. I rebuilt the carbs, finally figured out the choke cable (needed a stiff return spring that wasn't there when I got it), carefully realigned the throttle linkage all the way to the bottom of the steering column.

I finally decided to run a compression check (which I should have done before bringing the boat home!). Using my 40 year old Sears compression check tool, I got 160+/- on 5 cylinders, 0 on cylinder 5. I decided to take the head off to look around.

When I took off the nuts, one of them was not fully tight at cylinder 5. After I got the head off, I noticed this ding in the engine block around cylinder 5:
Ding in head around cylinder.JPG
The head gasket didn't really show any signs of leaking that I could tell.

1. Was the zero compression caused by the incompletely torqued bolt?
2. Was the zero compression caused by the ding next to the cylinder?

Will a new gasket fill in the ding? Can this be repaired with JB Weld? Or does this require that the engine block be resurfaced? Or even worse, a replacement block? Hoping to get the boat on the water this year.

I'm going to go ahead with a new gasket and carefully torque the nuts. I'll report the results this weekend. Comments welcome.
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1952 CC Riviera 18, KBL

jim g
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Re: Zero compression on cylinder 5

Post by jim g » Tue Jul 23, 2019 5:16 pm

To have zero compression on one cylinder you have to have a big hole or gap somewhere.

You ned to spin the engine over and make sure the valves are opening and closing and when they close they are fully seated.

The ding you have will not give you complete compression lose.

I had one come it one time that had no compression on one cylinder which turned out to be the rag the owner left in the intake when he had removed the carb then put it back on several days later. It had sucked itself up against the intake valve and was not letting air in.

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jim.eakin
Posts: 13
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Location: South Orange County, CA
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Re: Zero compression on cylinder 5

Post by jim.eakin » Tue Jul 23, 2019 5:49 pm

Threw a rod. When the head was off I was so tuned to watching the valves that I didn't notice that the piston wasn't moving.
IMG_5801.JPG
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1952 CC Riviera 18, KBL

jim g
Posts: 1002
Joined: Wed Dec 14, 2011 10:55 pm
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Re: Zero compression on cylinder 5

Post by jim g » Tue Jul 23, 2019 10:22 pm

That'll do it.

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