Engine knock

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Model T Ford Forum: Forum 2005: Engine knock
Top of pagePrevious messageNext messageBottom of page Link to this message  By cliff jones on Monday, February 04, 2008 - 07:44 am:

Hey guys could you please give your thoughts on a heavy knock in the engine of my 17 sedan? At idle there is no knock until I short #4 plug, slightly less when shorting #3 even less on #2 and nothing on #1.On the road the knock can be altered with timing like a rod bearing which seem ok.It still has straigt cut timing gears but I dont think that is the problem. I have adjusted the center main to .002" but made no difference.I suspect 3rd main bearing???


Top of pagePrevious messageNext messageBottom of page Link to this message  By Brendan Doughty on Monday, February 04, 2008 - 09:57 am:

It could also be cam shaft or crankshaft end play.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Royce on Monday, February 04, 2008 - 11:17 am:

Cliff,

I had a similar knock on #4 in my 1913 touring right after a rebuild. It would show up any time the timing was advanced and could be isolated by shorting #4.

I checked rod bearing clearance with plasti gage and all was good. I was about to pull the engine because I was convinced I had a loose rear main. In desperation I decided to pull the #4 piston and rod out which is a bit tricky with a 3 dip pan.

I took the rod up to Ron's machine shop to be checked and sure enough I had twisted the rod when I tightened up the wrist pin clamp. The guys at Ron's straightened the rod in their fixture while I waited. After reassembly there was no more noise and the engine has been performing great ever since.

Not sure if this is your problem but it is worth looking into before pulling the engine out.

Royce


Top of pagePrevious messageNext messageBottom of page Link to this message  By Wiillie in Houston on Monday, February 04, 2008 - 03:49 pm:

Royce, I am missing something in the connection with a slightly twisted rod and a knock from the same cylinder. Did the twist actually cause one side of the wrist pin to be lower than the other side? This could cause a excess drag on the cylinder wall?
Just curiosity, Willie
Cliff, pardon me doing a slight hijack, but we are still on knocks.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Jerry VanOoteghem on Monday, February 04, 2008 - 04:39 pm:

Knocks that show up when shorting plugs are most likely rod bearings or wristpins. You would also notice a heavier knock when letting off the gas as in engine braking.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Royce Peterson on Monday, February 04, 2008 - 06:50 pm:

Willie,

It causes the rod to rock forward and aft on the piston pin, making a knocking sound. At the same time it is scuffing up and down because the piston pin is not square with the bore. It was quite an obnoxious sound. It sounded just like a loose rod bearing knock.

Royce


Top of pagePrevious messageNext messageBottom of page Link to this message  By Norman T. Kling on Monday, February 04, 2008 - 09:19 pm:

If you have a loose main bearing it would be worse when you first start the engine when cold or when pulling hard like low speed up a hill or when first starting out in high. It would be almost non existant when going along at an even speed on a fairly level road. The rear main makes a low pitch rumbling noise and could cause the floorboard to vibrate. The spark retard makes quite a difference with main bearing knocks. I feel hesitant to make suggestions, because I have a knock in one of mine that I have had a hard time with. With the others I have been successful with tightening the bearings. Even the front pulley or the pin that goes through the front of the crankshaft which you turn with the starting crank, if loose can cause a knock, as well as loose cam bearings or loose timing gears.

Check out all of the above before you pull your engine.

By the way, did this knock come on suddenly, or did it gradually appear? How long has it been since you rebuilt of overhauled the engine. Did you do any work on the engine shortly before you noticed the knock? The answers to these questions would be helpflul in making a diagnosis.
Norm


Top of pagePrevious messageNext messageBottom of page Link to this message  By Alan Woolf on Monday, February 04, 2008 - 09:57 pm:

Look closely at the front cam bearing and check for excessive end play. Another thing to watch out for in the front cam bearing is an oblong mounting hole in the bearing shell. If the hole is oblong it can allow the bearing to walk back and forth on the mounting bolt and give a knock similar to what you have described. I had this problem with my 13 and I thought it was something else like a rod or main.

Alan


Top of pagePrevious messageNext messageBottom of page Link to this message  By cliff jones on Tuesday, February 05, 2008 - 06:07 am:

Thanks guys for taking the time to help.Norman the knock has been there ever since I purchased the car 2 years ago. It has not got worse in that time.Will check that front cam bearing before I go any further. Thanks again


Top of pagePrevious messageNext messageBottom of page Link to this message  By Bob Frink on Tuesday, February 05, 2008 - 08:28 pm:

I had a knock that I chased for years. I couldn't pinpoint it by shorting the plugs, and it didn't ever get much worse. I finally tore it all the way down, and found a wrist pin clamp bolt that would bottom out before it tightened onto the wrist pin. I was sure glad to find that one.
Bob


Top of pagePrevious messageNext messageBottom of page Link to this message  By Norman T. Kling on Tuesday, February 05, 2008 - 09:27 pm:

My suggestion would be to check all the rod bearings and then with the brake off put a large screwdriver behind the front pulley and try to pry the crankshaft forward. Careful not to try so hard that it will break anything. If you have end play in the crank, it will go to the back when you apply the hand brake, and then when you pry with the screwdriver it will go forward. One of my T's had a distributor on it when I bought it. It had some knocks so I was going to re pour the rod bearings. The men who pour the bearings suggested I check for endplay and it actually has almost 1/8 inch of endplay. No wonder it has a distributor. That much endplay would move the magnets too far from the ring to be able to use the magneto. Anyway if you find a lot of endplay, you most likely also have too much up and down clearance in the rear main and you would need to pull the engine to fix it. There are other posts or the book on the engine which will tell you how to take up clearance in the rear main bearing and how to remove endplay. The best way to remove endplay is to re-pour the main bearings or at least the cap.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Rich Colegrove on Wednesday, February 06, 2008 - 09:04 am:

After a couple hundred miles on a rebuilt engine, a knock developed in my car whenever spark was advanced. Spark plug test showed it to be in #1 cylinder. Found loose wrist pin bolt and corrected it, but knock was still there and we could not find any thing else mechanically wrong. Timing was set correctly. One day when slowly hand cranking, I noticed that each coil sparked longer (thru more degrees of rotation) than my other cars. This one had a newly purchased New Day timer when engine was rebuilt.(before I had read the bad things about the newer New Day timers here). Installed a new Anderson timer and haven't heard the knock since. Don't know if this helps, but thought I'd mention it.
Rich Colegrove


Top of pagePrevious messageNext messageBottom of page Link to this message  By Micheal Crowe on Wednesday, February 06, 2008 - 12:30 pm:

I rebuilt my engine with all new babbit, honed cylinders. Developed a knock, so we checked the bearings with plasti gauge. Still had a knock. Shorted out each spark plug and couldn't difine where it was. So we tore the engine down completely again, took the crank shalf out and put it in a lathe. There it was, the plate where the fly wheel bolts to the crankshaft was bent. Found a different crank shaft, had it ground to 20 under and put it back together. Engine runs great now!


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