Update...After 6 Years She Left Me On The Road!

[TinCup]

I have owned my coupe for over 6 years now and in all of the outings we have been on she has always brought me home. Well today 9 cars set out on a 100 mile trip to the annual Pawnee, Ok. Steam Engine Show. This is an outstanding slice of Americana to see these turn of the century steam tractors and engines. Well just over 50 miles out while going up a hill I started to hear an knock. I let off the gas and the knock went away. It came back just as soon as I accelerated. I nursed it to a parking spot in downtown Perkins, Ok. One of our other club members drove out with a trailer and we brought it home. Next week I will drop the pan and see what kind of damage we have. No knocking at idle but definately there when I rev the motor.
2012 Pawnee Steam Engine Show

[spdway1]

Fuel knock?

[Jim Parker Toronto]

nice pictures, thanks for the link

[TinCup]

No it's definitely mechanical.

[H. L. Chauvin]

Up a steep hill sounds like the oil in the front connecting rod bearing dipper tray got low & a lack of bearing lubrication caused enough babbitt wear to cause a knock.

Always a good idea to stop when one hears any knock, no matter the cause of the knock.

[Tom Wesenberg]

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Originally Posted by H. L. Chauvin

Up a steep hill sounds like the oil in the front connecting rod bearing dipper tray got low & a lack of bearing lubrication caused enough babbitt wear to cause a knock.

Always a good idea to stop when one hears any knock, no matter the cause of the knock.

Isn't that the job of the oil return pipe, to keep the front filled when going up at a steep angle?

[TinCup]

In this case it was a low grade but over a quarter mile. Tom that is what I thought as well.

[Jordan]

I wouldn't think the hill had anything to do with it.

[RUNNERBUN]

Before you remove the pan try the following. Start your engine and increase the revs slowly until you can hear the knock, then short out 1 spark plug at a time. If you have a bad big end babbitt the knock will disappear when you short out the ignition on that cylinder. It will be very noticable. If the knock fails to disappear it may well be a bad main bearing. Also be sure to check that the timing gear nut has not come loose. I have had experience with a loose timing gear nut and it sure sounded like a big end bearing failing.

[juke joint johnny]

As Runnerbun says before taking any thing apart ;
loosen timing pin,
run engine at slow idle just so you can hear the knock,
turn the pin around and press the point against the timing gear,
if knock disappears you found the problem and are a lucky man!!!
I had the same problem with one of my cars and thought the whole thing
was coming apart , turned out it was just a loose nut!!!
Good Luck with it
John Cochran

[ericr]

Originally Posted by juke joint johnny

As Runnerbun says before taking any thing apart ;
loosen timing pin,
run engine at slow idle just so you can hear the knock,
turn the pin around and press the point against the timing gear,
if knock disappears you found the problem and are a lucky man!!!
I had the same problem with one of my cars and thought the whole thing
was coming apart , turned out it was just a loose nut!!!
Good Luck with it
John Cochran

I have heard of that recommendation before, but won't it obliterate the little depression we use for timing, which is barely detectable at best?

[James Rogers]

Before removing the pan, run a compression check. I find a blown head gasket can sound like a rod knock when it happens, especially when it blows between two cylinders and doesn't include a water port. Just remove the plugs and use your thumb to cover the holes, turn the motor with the starterand you will know it is a simple gasket change or something worse.

[juke joint johnny]

Ericr ; Those gears are preety tough ,it didn't harm mine but if it is loose you might find it,s a bit chewed up, and want to replace it anyway
John

[George Miller]

If you use the timing pin trick, just hope some one has not drilled the timing dimple real deep. Why not just short out the plugs until it changes the knock.
If it changes on 2,and 3 it will be the center main. That would be my pick.

[TinCup]

The Barn is Awesome!! I never even thought about the timing gear.

The knock is definately from the middle forward on the engine. I started it this morning and using my Dad's famous broom stick handle trick I listened for the knock while slightly reving the motor. Now that I have two fairly simple tricks to apply to check I will do those first before I drop the pan. I am using the Felpro B gasket on my Snyders 5.5 head and I have replaced several of these for other club members that have blown. Since I was driving around 50 when the knock started it certainly is suspect.

[TinCup]

Well I didn't have time to pull the pan but I did check the timing gear to see if it was loose and its fine. I checked compression across all cylinders all around 70. Shorted each plug while reving the motor and it had no impact on the knocking.

Tomorrow we are going to get messy and drop the pan.

[TinCup]

My first guess was center main bearing and unfortunately I was right. My buddy Scott helped me drop the pan this morning and it didn't take long to see all the shiny babbit in the pan. Everything else looked good and as this motor will eventually be coming out for an overhaul we went with a center cap out of another motor that had good looking babbit. Took quite a bit of working with the shims until we got what we wanted but the good news is that it's back up and running and sounds great.

Many thanks for all the barn suggestions and special thanks to Bob for coming through with a cap.