The Ford Barn

elba · 02-21-2014, 08:42 PM

My friend has a "B" 4 cyl in his A Model. It has a slight knock while accelerating. Low mileage engine since a professional O/H. We took the engine apart and the only thing we found was the babbit on the lower aft main had small pieces missing. Maybe 20%, at most, of the total babbit. Crankshaft is perfect. Like new. Would this cause a knock ? An old timer said it would. Any ideas ?

Bob C · 02-21-2014, 09:11 PM

Any babbitt missing on a low mileage professionally overhauled engine is a problem,
what else was done wrong

Bob

pat in Santa Cruz · 02-22-2014, 12:52 AM

A knock under load can be a main bearing problem. Given you found further evidence of main bearing trouble, I would imagine the others are problematic too. The center main takes the most abuse. Did you check it?

Kohnke Rebabbitting · 02-22-2014, 01:42 AM

Quote:

Originally Posted by elba

My friend has a "B" 4 cyl in his A Model. It has a slight knock while accelerating. Low mileage engine since a professional O/H. We took the engine apart and the only thing we found was the babbit on the lower aft main had small pieces missing. Maybe 20%, at most, of the total babbit. Crankshaft is perfect. Like new. Would this cause a knock ? An old timer said it would. Any ideas ?

Take pictures of the mains and other parts of the engine?

Mike V. Florida · 02-22-2014, 07:55 AM

What are the clearances?

James Rogers · 02-22-2014, 08:34 AM

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Check the pistons for scoring or other damage. Piston slap can sound like a slight knock.

George Miller · 02-22-2014, 09:50 AM

My advice is to always isolate the knock before you take anything apart. Short out each plug until you find the ones that change the knock.
My guise would be the center main is a little loose.

02-21-2014, 08:42 PM	#1
elba Junior Member Join Date: Sep 2013 Location: Alabama Posts: 4	Engine knock My friend has a "B" 4 cyl in his A Model. It has a slight knock while accelerating. Low mileage engine since a professional O/H. We took the engine apart and the only thing we found was the babbit on the lower aft main had small pieces missing. Maybe 20%, at most, of the total babbit. Crankshaft is perfect. Like new. Would this cause a knock ? An old timer said it would. Any ideas ?

02-21-2014, 09:11 PM	#2
Bob C Senior Member Join Date: May 2010 Location: So Cal Posts: 8,754	Re: Engine knock Any babbitt missing on a low mileage professionally overhauled engine is a problem, what else was done wrong Bob

02-22-2014, 12:52 AM	#3
pat in Santa Cruz Senior Member Join Date: May 2010 Location: santa cruz, calif Posts: 2,011	Re: Engine knock A knock under load can be a main bearing problem. Given you found further evidence of main bearing trouble, I would imagine the others are problematic too. The center main takes the most abuse. Did you check it?

02-22-2014, 07:55 AM	#5
Mike V. Florida Senior Member Join Date: May 2010 Location: South Florida Posts: 14,054	Re: Engine knock What are the clearances? __________________ What's right about America is that although we have a mess of problems, we have great capacity - intellect and resources - to do some thing about them. - Henry Ford II

02-22-2014, 08:34 AM	#6
James Rogers Senior Member Join Date: May 2010 Location: Asheville,NC Posts: 3,104	Re: Engine knock Sponsored Links (Register now to hide all advertisements) Check the pistons for scoring or other damage. Piston slap can sound like a slight knock. __________________ http://www.model-a-ford-4bangers.com/

02-22-2014, 09:50 AM	#7
George Miller Senior Member Join Date: May 2010 Location: NC Posts: 2,975	Re: Engine knock My advice is to always isolate the knock before you take anything apart. Short out each plug until you find the ones that change the knock. My guise would be the center main is a little loose.