Knocking

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Model T Ford Forum: Forum 2012: Knocking
Top of pagePrevious messageNext messageBottom of page Link to this message  By Michael Deichmann, Blistrup, Denmark on Sunday, July 01, 2012 - 04:09 am:

Yeah - my T have had a knocking sound for some time (years actually) and now it have reach a level where I think I need to do something about it.

When I overhauled my gearbox and engine the first time (before my UK trip) I took out all the shims I could, and still turn the engine. It was done each bearing at a time with the other loose. When they where all done and tighten together - well - and with the new pistons and rings - I had to haul the car to get i rolling. :-) Once rolling it was tight but loose.
I've driven thousands of miles since.
Anyway - one of the rods and one of the main did have some shims left while the rest was now without any shims.
I THINK it is the rod with the shims that now are knocking as I think it is a rod that knocks.

Here is how it is - sometimes - and in particular when oil is cold - no or minimum knocking.
Under load - none or barely hearable knocking (could be so much else - come on - its a T :-)
Engine braking - the same or maybe a little louder.
Neutral throttle = throttle just mach up with speed on a level ground - muck knocking.
One thing that puzzles me is, that at the neutral throttle - if I retard the ignition, I can make the knocking disappear almost.
Also -if i go neutral - and kind of let the oil float - the hydrodynamic oil pressure in the bearing in question build up again and the knocking disappear - at least for a while.

At this point I have not done other analysis than what I can do during driving. I have not yet tried to short the plugs when it's idling to see if that will change the knocking (requires that I can get it to knock idling) and of course I have not yet had the inspection door off. That's what I'm planing for to do soon, but I want to eventual know what kind of spares I may need to have handy if it for example turns out to be one of the rods with no shims :-/

When occasionally in optimum conditions the knocking is not there - it simply hums like a bumblebee and goes 40 mph like it would never do anything else.

(Lets not turn this into a discussion of oil - I use to use SAE 30, have once used SAE 20 with excellent results and do really want to go back to that, but now I decided to try SAE 20W-50 and that is not right for a splash oiled engine like the Model T.)


Top of pagePrevious messageNext messageBottom of page Link to this message  By Bud Holzschuh - Panama City, FL on Sunday, July 01, 2012 - 08:27 am:

Michael

Wish I could contribute something useful to your problem but I can't as I haven't disassembled my engine as far as you have yet.

What I can tell you, is that my engine exhibits the same characteristics of little or no knocking under load of any king and a noticeable knock at idle (especially high idle). I always thought this unusual as my previous experience has always been greater knocking under load.

No one has been able to give me a satisfactory explanation for this behavior, I hope you get better results.

Cheers
schuh


Top of pagePrevious messageNext messageBottom of page Link to this message  By John Zibell on Sunday, July 01, 2012 - 09:06 am:

I have just had a fresh rebuild. My engine exhibited the same knock you describe. We did a tear down to re-do the magneto (that didn't work either) and to find the source of the knock. We discovered a problem at the second (middle) main. Either the bearing wasn't poured correctly, or the crank journal was ground incorrectly (out of line with one and three) The block is going back to the rebuilder to have the mains re-poured and a different crank installed that is ground correctly.

To check your second main. Purchase some one to three thousands plastigauge. Check the second main and see the reading (should be around 0.0015 inch) Then turn the crank 180 degrees and check again. You may discover the problem.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Val Soupios on Sunday, July 01, 2012 - 10:07 am:

If the knock is louder when the engine is cold, goes away when the spark is retarded and gets quieter as the engine warm up it might be a wrist pin. I had that problem with my '30 Plymouth and that's what it turned out to be. I know it isn't a Ford but I still went the full route of checking rods and mains before figuring out what it was!


Top of pagePrevious messageNext messageBottom of page Link to this message  By Harold Schwendeman - Sumner,WA on Sunday, July 01, 2012 - 10:19 am:

Not sure I fully understand this, and, not sure I could explain it if I did fully understand, however, as a novice, let me just say, be very careful with dealing with the "second" or center main bearing.

The center main can wear differently than the other main bearings. Instead of wear in the lower or bearing cap half of the center main, the wear commonly occurs in the top, or, engine block half of the center main bearing. This has to do with the fact that the heavy transmission hanging off of the rear of the engine, and supported only by the stamped sheet metal engine pan, can actually cause the pan to "flex" a very minute amount which tends to bend the crankshaft a very minute amount which tends to exert some pressure on the UPPER or engine block half of the center main bearing.

If this has occurred, and you remove a ship or two from ONLY the center main, you actually force the center crankshaft journal upward against the top or engine block half of the center main. This causes the crankshaft to actually flex a very slight amount with every revolution and could eventually cause you to become a member of the dreaded "two-piece crankshaft club"!

Again, not sure I explained that very well, but hopefully, someone much more experienced than me will either correct me if I'm wrong, or, explain more clearly if I'm right.

For what it's worth,......harold


Top of pagePrevious messageNext messageBottom of page Link to this message  By Harold Schwendeman - Sumner,WA on Sunday, July 01, 2012 - 10:23 am:

Sheeesh,......not "ship"; meant to say SHIM!


Top of pagePrevious messageNext messageBottom of page Link to this message  By Rick Goelz-Knoxville,TN on Sunday, July 01, 2012 - 10:41 am:

My 24 had a knock with only 150 miles on a new rebuild so i shorted the plugs and found #1 and#2 both knocking, so under i go and remove the inspection pan and take the cap off of # 1 and this is what i found, the cap was not flat causing one corner to be high, i put it on a flat surface and then filed the high places and removed the slag, i then plastigaged it and it is .002 on both sides and the top so i installed it and went on to #2, it showed even wear but it measured out to .003 so i pulled a shim rechecked it and closed it all up, no more knock, now i need to drive it some more and let it break in better.
Rick


Top of pagePrevious messageNext messageBottom of page Link to this message  By Roar Sand on Sunday, July 01, 2012 - 11:31 am:

Michael,
Your symptoms sound suspiciously similar to what I had in 1958.
We, girlfriend and I, were going to a senior party at Eidsvoll, about 60 km north of Oslo. I made a wrong turn and ended up in some very steep hills, that glazed the low gear band and rendered it useless, as well as starving the bearings of oil. That caused a loud rod knock.
The drive home was accomplished by minimizing the knocking as best I could by moving the throttle lever alternating between closed and wide open. Part throttle would cause very loud knocking.
To add to the story, we came to a hill we could not make in direct drive, so I backed up an uphill side road, rolled forward enough to get her in direct drive, gained momentum, prayed that no other cars were coming on the main road, which it didn't, and made the top of the hill.
I was in the middle of finals, so my dad did most of the work, but we did have the rods rebabbited, my dad bluing and scraping and fitting, and a few miles of road has passed under her wheels since then.
Roar


Top of pagePrevious messageNext messageBottom of page Link to this message  By Michael Deichmann, Blistrup, Denmark on Sunday, July 01, 2012 - 12:01 pm:

@Harold: I should have added that it's a '27 engine and gearbox, so it has the two ears on the hogshead so flexing the gearbox should not be the pitfall here.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Kohnke Rebabbitting on Sunday, July 01, 2012 - 12:43 pm:

My 24 had a knock with only 150 miles on a new rebuild so i shorted the plugs and found #1 and#2 both knocking, so under i go and remove the inspection pan and take the cap off of # 1 and this is what i found, the cap was not flat causing one corner to be high, i put it on a flat surface and then filed the high places and removed the slag, i then plastigaged it and it is .002 on both sides and the top so i installed it and went on to #2, it showed even wear but it measured out to .003 so i pulled a shim rechecked it and closed it all up, no more knock, now i need to drive it some more and let it break in better.
Rick



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If you give it .002 thousandths clearance, it is all ready broke in.


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