Low end knock?

mike2u · Post by **mike2u** » Wed May 03, 2017 2:07 pm

I'm looking to see if there is a way to troubleshoot a problem I having with my scout car. She seems to burn a cloud of oil when warmed up, but a compression test came back fairly good, and all cylinders were about on par. I don't remember exactly what they were though. When driving I am really struggling to hit a meager 30MPH, and that is usually down a hill. I checked all brakes and nothing is hanging up. Engine seems to have a pretty good vacuum, and hold about 40 pounds of oil pressure.
Now, where things get interesting. The engine seems to have a peculiar sound to her, almost like a deep muffled bell ring. Only audible at idle. I have had the transmission off before, and with just the flywheel, the sound was still present. I realize this sounds like a classic engine knock, but i'm not sure on this one. The sound is so odd and muffled.

Any help is appreciated. Thanks.

Post by **artificer** » Wed May 03, 2017 2:45 pm

mike2u wrote:When driving I am really struggling to hit a meager 30MPH
This sounds like an ignition thing to check & reset carefully....point gap possibly closed up by the rubbing block not being lightly greased, advance operation & timing....
Engine seems to have a pretty good vacuum....
Have you checked with a vacuum gauge? What are the readings?
Get these things checked, right, then we'll see about this noise if it is still there.

Joe Gopan · Post by **Joe Gopan** » Wed May 03, 2017 3:04 pm

You can narrow down some knocks by pulling or shorting the Ignition wires one at a time and listening for a change in the knock.

mike2u · Post by **mike2u** » Wed May 03, 2017 3:23 pm

artificer wrote:
mike2u wrote:When driving I am really struggling to hit a meager 30MPH
This sounds like an ignition thing to check & reset carefully....point gap possibly closed up by the rubbing block not being lightly greased, advance operation & timing....
Engine seems to have a pretty good vacuum....
Have you checked with a vacuum gauge? What are the readings?
Get these things checked, right, then we'll see about this noise if it is still there.

I don't think I understand what your saying about the point gap. I assume your talking about that rubber like block that rides on the distributor shaft, and pushes the little finger that open and closes the gap. If its not greased, i could see advanced wear, but I guess i'm not sure how it would affect the gap. Please correct me if I am wrong here. Regardless, I will lightly grease it, and get an accurate vacuum reading. Where is the best spot to get this reading from? Windshield wiper motors?

Post by **artificer** » Wed May 03, 2017 4:46 pm

I don't think I understand what your saying about the point gap. I assume your talking about that plastic like block that rides on the distributor cam, and opens and closes the point gap. If its not greased, i could see advanced wear, but I guess i'm not sure how it would affect the gap.
wear causes point gap to close up & this causes a poor spark that breaks down under load thus loss of power
Regardless, I will lightly grease it
this should be a regular service operation & do not use much or get grease on the points. Check & set them @ 0.020" on one of the six highest lobe points on the distributor cam, if incorrect
and get an accurate vacuum reading. Where is the best spot to get this reading from?
anywhere there is full inlet manifold vacuum so any plug point between the carburettor & the engine block
Windshield wiper motors?
not usually full manifold vacuum

mike2u · Post by **mike2u** » Thu May 04, 2017 3:23 pm

So, I took another look at my scout today, and for the hell of it I decided to pull the plugs one at a time. I noticed that when I pulled the wires to cylinders 5 and 6, with the engine running, I did not notice a change. I swapped plugs around, and still observed the same thing. Good spark, gas on the plugs, but yet cylinders 5 and 6 seem dead. Is the next step another compression test?

Post by **artificer** » Thu May 04, 2017 4:07 pm

What were the vacuum gauge readings telling us?
That's why we are asking.

Another compression test [have you done one already? What were the results?] may be good to do but it is ahead of the game & doesn't tell us anywhere near as much as a vacuum gauge reading & the compression test MUST be done properly.

Was there good spark @ all 1,5,3,6,2,4 plugs?
There shouldn't be gas on the plugs, when they are/have been firing properly.

mike2u · Post by **mike2u** » Thu May 04, 2017 4:12 pm

All plugs had good, strong blue spark. The only plugs with gas on them were cylinders 5 and 6, and as previously mentioned, those cylinders also had a strong blue spark as well. I was unable to get a vacuum reading as I don't have a vacuum gauge. I will pick one up tomorrow and give it a test. When you say any plug point, could you elaborate a bit on that. Are there points build into the engine/carb where I can plug into?

Post by **artificer** » Thu May 04, 2017 4:30 pm

Vacuum plug/line will/must be below the carburettor throttle butterfly & on your engine will be in the centre of the inlet manifold leading off to the vacuum pump.
Disconnect this line & that is where your vacuum gauge will plug into. There is also an elbow that might be able to be used @ the rear as well as any gas type plugs that may be in the manifold.

mike2u · Post by **mike2u** » Thu May 04, 2017 4:36 pm

Many thanks. I will check this out and report back tomorrow.

Post by **artificer** » Thu May 04, 2017 5:26 pm

Just unhooking any vac line from the inlet manifold, even the one to the hydrovac & plugging that hole with your vac gauge will not affect engine operation & get a good reading.
Just remember to hook the line back up again.
Did you previously do a compression test?

mike2u · Post by **mike2u** » Thu May 04, 2017 5:45 pm

I did do a compression test a while back, but I don't recall what the readings where anymore. If I am correct, i thought they were all very close in differential, but its been a few years, and would be best to do it again.

mike2u · Post by **mike2u** » Fri May 05, 2017 1:01 pm

I hooked up a vacuum gauge to the engine today and with the engine running at idle, fluctuating heavily from 16-18 pounds. I should also mention that, the engine will only run with the carburetor leaned out as much as possible. As soon as I turn on the fuel mixture screw, she starts to fall on her face and die.

motto · Post by **motto** » Fri May 05, 2017 1:46 pm

There is no specific test for it but a broken valve spring could explain what's going on. It would be worth a look to eliminate that one. A bouncing valve throws everything out of whack.
Other than that do step by step what Artificer suggests.

David

Post by **artificer** » Fri May 05, 2017 5:19 pm

I should also mention that, the engine will only run with the carburetor leaned out as much as possible.

Only when you did the vacuum test or was this the same before you hooked in the gauge? Run engine @ about 800 RPM & tell us what reading, please.

G503 Military Vehicle Message Forums

Low end knock?

Low end knock?

Re: Low end knock?

Re: Low end knock?

Re: Low end knock?

Re: Low end knock?

Re: Low end knock?

Re: Low end knock?

Re: Low end knock?

Re: Low end knock?

Re: Low end knock?

Re: Low end knock?

Re: Low end knock?

Re: Low end knock?

Re: Low end knock?

Re: Low end knock?

Who is online