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Old 03-23-2021, 07:53 PM   #1
Dewey29
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Default Engine knock at cruising speed?

I adjusted the main and rod bearing clearances last summer on my 29 roadster and she has run great for about 1300 miles. During the past 3 outings I've starting noticing a slight but consistent knock while cruising between 35 to 45 mph. It's only on level roads, not during deceleration or acceleration. Also noticed it goes away as I move the spark lever up? I plan to remove the pan again and investigate, but I'm asking if there is anything else to consider before diving back under the car?

Thanks in advance for any help guys!!!
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Old 03-23-2021, 09:02 PM   #2
Ernie Vitucci
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Default Re: Engine knock at cruising speed?

Good Evening...If retarding your timing makes it go away...your timing may be off. What is the position of your timing lever. Half way down, 3/4 down, all the way down? If the knock goes away with a minor adjustment, then make the adjustment and see what others will say about the problem...a number of parts can potentailly make the noise...Ernie in Arizona
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Old 03-23-2021, 09:12 PM   #3
nkaminar
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Default Re: Engine knock at cruising speed?

Ernie has a good point. It could be an ignition knock. Another source may be the rods as this is typical for a rod knock. Do you have a high compression head? It could also be piston slap or bend rods. If the big end of a rod moves back and forth when you turn the engine over by hand then the rod is bent. Another possibility is a worn or loose cam gear.
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Old 03-23-2021, 11:25 PM   #4
Dewey29
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Default Re: Engine knock at cruising speed?

I time the engine with a timing light and when lever is at the top it is TDC, 1/2 down is 20 degrees advanced. I'm running a stock model A head. It has a new crank gear and timing gear. Is the fact that by retarding timing it reduces the knock indicate an issue with a rod rather than a main bearing? I'm not hearing any knocking at idle or slow speeds.
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Old 03-23-2021, 11:39 PM   #5
Richard Knight
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Default Re: Engine knock at cruising speed?

Same question as Ernie, When you are at "cruising" speed where are you setting your spark lever ? It is very easy to over advance your timing and beat the heck out of your rod bearings.
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Old 03-23-2021, 11:46 PM   #6
Dewey29
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Default Re: Engine knock at cruising speed?

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About 1/2 down, 20 to 25 degrees advanced
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Old 03-24-2021, 07:45 AM   #7
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Default Re: Engine knock at cruising speed?

Deleted my post as it doesn't align with the original post, I hadn't noticed that he said the knock was under cruising, not acceleration. Other answers are better suited for discussion.
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Last edited by eagle; 03-25-2021 at 08:16 PM.
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Old 03-24-2021, 11:36 AM   #8
Jim Brierley
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Default Re: Engine knock at cruising speed?

Sounds to me like rods or wrist pins are on the loose side. Any other noises are not usually at the no-load position. 26* with a stock head is well within limits.
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Old 03-24-2021, 06:33 PM   #9
Gene F
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Default Re: Engine knock at cruising speed?

Are you a member of a local A chapter Dewey?
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Old 03-25-2021, 04:39 PM   #10
Dewey29
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Default Re: Engine knock at cruising speed?

Unfortunately we don't have any Model A clubs in Birmingham Al. I have a couple of friends here with lots of Model A experience and I've been discussing it with them as well.
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Old 03-25-2021, 04:42 PM   #11
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Default Re: Engine knock at cruising speed?

I really appreciate everyone's input!!!
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