Engine knock diagnosis

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Model T Ford Forum: Forum 2018: Engine knock diagnosis
Top of pagePrevious messageNext messageBottom of page Link to this message  By Dave Wilson, Saint John NB, Canada on Thursday, September 20, 2018 - 09:26 pm:

I "freshened" the motor in my 27 T a few years ago-new pistons, rings, rods, adjustable lifters, rebabbitted #3 main bearing cap. The bearing cap was fitted using Time Saver lapping compound. At the same time I re-bushed the transmission and installed a rebabbitted "4th main". In the past 6 months I have noticed a knock. I found that the crankshaft pulley was loose so I replaced it but the knock is still there. Today, I used a steel rod and listened to the various areas of the motor that I thought might be suspect. The noise seems most noticeable at the rear of the camshaft/valve chamber area and diminishes as I move down towards the crankshaft, or up towards the head. I had suspected a loose main but based on today, I'm not sure. Any suggestions before I remove the inspection pan and check the mains?


Top of pagePrevious messageNext messageBottom of page Link to this message  By John Zibell, Huntsville, AL on Thursday, September 20, 2018 - 09:37 pm:

Could be the cam bushing at the rear. If the front cam bearing has worn it may allow the cam to move a bit and strike the bushing.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Dave Hanlon N.E.Ohio on Thursday, September 20, 2018 - 09:53 pm:

I'm confused by "4th main". Ts only have 3 main bearings.
Do you mean #4 connecting rod bearing ?


Top of pagePrevious messageNext messageBottom of page Link to this message  By Frank van Ekeren (Australia) on Thursday, September 20, 2018 - 09:58 pm:

Dave,
sometimes the ball cap is referred to as the 4th main.


Top of pagePrevious messageNext messageBottom of page Link to this message  By John Noonan - Norton, MA. on Thursday, September 20, 2018 - 10:00 pm:

Dave, the ballcap that inserts into the rear of the trans at the u-joint is called the 4th main.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Dave Hanlon N.E.Ohio on Thursday, September 20, 2018 - 10:02 pm:

I see... thanks.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Joe Reid Central WI on Thursday, September 20, 2018 - 10:09 pm:

It is the fourth main, it supports the tail shaft of the transmission, without it you will snap your crankshaft. It needs to be in line with your engine.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Les Schubert on Thursday, September 20, 2018 - 10:13 pm:

Joe
I don’t disagree. But consider a “ floating transmission shaft” available from Dan Hatch


Top of pagePrevious messageNext messageBottom of page Link to this message  By Joe Reid Central WI on Thursday, September 20, 2018 - 10:17 pm:

How does it work, the issue is the engine pan. If you were to use the block in something else it does only have 3 mains.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Dave Wilson, Saint John NB, Canada on Friday, September 21, 2018 - 11:02 am:

Sorry for the confusion. The ballcap is often referred to as "4th main. I will try to be more technically correct in the future. Thanks for the input. I will check the cam bearings and bushing.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Norman T. Kling on Friday, September 21, 2018 - 12:28 pm:

You don't mention anything about the cam. I would suggest as others have noted, the rear bushing on the cam shaft to block. You also said you used adjustable lifters. Have you checked the clearance recently? A larger gap will usually sound like a click especially noticed at idle or slow speed. It does not change when pulling, loafing, or decelerating. Just a steady click dependent on the speed of the engine. If it is not a loose lifter, I would suggest you continue driving and see if it gets worse. A loose cam bushing will not cause the engine to seize, so it should not cause damage if you continue driving. If it continues to get worse, it might be loose piston, broken ring, wrist pin or rod bearing, or loose rear main bearing all of which will require partial or complete engine dissassembly to repair.
Norm


Top of pagePrevious messageNext messageBottom of page Link to this message  By Dave Wilson, Saint John NB, Canada on Friday, September 21, 2018 - 01:03 pm:

What is the quickest way to check the cam bearings and bushing?


Top of pagePrevious messageNext messageBottom of page Link to this message  By Dave Hanlon N.E.Ohio on Saturday, September 22, 2018 - 11:00 pm:

BTT.
Dave's question and....
What's the best way to check a ballcap or "4th main" ? What symptoms would you have ?


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