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Old 10-25-2020, 09:22 PM   #21
J Franklin
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Default Re: Help diagnosing engine knock

If you drop the pan, clean the pin, put a finger on the wrist pin and piston and have some helper with a wrench rock the crank back and forth carefully. you can feel too much clearance. Find a helper you can trust. A bent rod can give a knock also.
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Old 10-26-2020, 10:26 AM   #22
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Default Re: Help diagnosing engine knock

Quote:
We have just acquired a head puller so we can start working on this again.
Being that the head was off recently, you shouldn't need a head puller this time around.
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Old 07-21-2021, 01:57 AM   #23
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Default Re: Help diagnosing engine knock

Finally had a chance to work on the car again. I pulled the head and did not find any witness marks indicating that the pistons or valves were hitting the head. Cylinders 1,2, and 3 are quite oily and appear to be running very rich but 4 seems to be running lean (although all the spark plugs seem to read rich). A club member pointed out what appears to be a burn spot on #4. He thinks it might be from detonation which could be the source of the knock.

I put the head on the block without a gasket and measured the quench height and found the following.

Stock head
Cyl 1 .055
Cyl 2 .060
Cyl 3 .063
Cyl 4 .059

High compression head
Cyl 1 .035
Cyl 2 .043
Cyl 3 .048
Cyl 4 .043

Best 509 Gasket measured .060.

As far as my understanding goes, the gasket will compress to about .040, so with the gasket, the quench height would be anywhere from .075-.088 depending on the cylinder. From the limited information I have been able to find, this height would be sufficient for the Model A, correct? Should I be concerned that there is such a big difference in height on cylinder 1?

I am honestly not sure what I am looking for exactly so if there is something that stands out, please let me know.

Thanks!
Attached Images
File Type: jpg Head 1.jpg (63.8 KB, 41 views)
File Type: jpg Head 2.jpg (63.2 KB, 35 views)
File Type: jpg Head 3.jpg (60.3 KB, 34 views)
File Type: jpg Head 4.jpg (40.6 KB, 34 views)
File Type: jpg Block 1.jpg (43.0 KB, 44 views)
File Type: jpg Block 2.jpg (43.2 KB, 34 views)
File Type: jpg Block 3.jpg (39.6 KB, 35 views)
File Type: jpg Block 4.jpg (44.7 KB, 35 views)
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Old 07-21-2021, 06:47 AM   #24
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Default Re: Help diagnosing engine knock

The number 1 piston looks like it may have been hitting the head. There is a clean area around the rim.

I see you have measured the clearance without a gasket but still do this test: As others have stated, lay the head on the engine without a gasket and turn the engine over. If the head moves up when a piston hits it then the clearance is too small. Have the head machined to increase the clearance. If you can measure the amount the head moves up with a feeler gauge then that would be the minimum amount to machine. After machining, the gasket is insurance against the pistons hitting the head. If the head does not move without the gasket then your are OK.

I believe that thicker gaskets are available. That may be something to consider. The high compression head requires a Model B gasket, but you probably already know that.

I was going to suggest that the screw that holds the distributor in might be too tight but I see that you raised the distributor up a little as a test so maybe it is a non issue. But that could still be something to check. A tight screw will cause a slight knock.

I would not worry too much about the carbon. You probably have not run the engine enough to warm it up properly. It is not related to the knocking.

One other suggestion. Put the old head on and see if the knock goes away.
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Last edited by nkaminar; 07-21-2021 at 07:08 AM.
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Old 07-22-2021, 01:57 AM   #25
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Default Re: Help diagnosing engine knock

I put the head back on, but did not notice any movement. I also could not measure any movement, but I could not find a feeler gauge smaller than .010. I did hear what I thought sounded like multiple contacts so I pulled the head back off at one of the points. Turns out none of the pistons were at the top of their travel. I put the engine through multiple rotations and found that there was a knock most noticeable from piston 1. It knocks at about 3/4 of the way through its compression stroke, about 1” from the top, then knocks again at TDC. It knocks again 3/4 through the combustion stroke and again at BDC. Does this sound like it would be more associated with a bearing or a pin?
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Old 07-22-2021, 02:34 AM   #26
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Default Re: Help diagnosing engine knock

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Maybe take some chalk or something similar and mark the tops of the pistons and see for any marks on the head. This may not work as it could be hitting anywhere on the piston.

It has been my experience that hand cranking or even using the starter to turn the engine doesn't usually produce the knock. This is probably because most knocks are at a somewhat higher rpm. If it does, then either something is really wrong, loose, or it is something else.

If it is knocking before tdc on number one that rules out that the knock is caused by it hitting the head. That means it is somewhere else on that cylinder. Could be a wrist pin, rod bearing, or something valve related maybe. Have you tried to figure out what speed it is knocking at with the engine running? Camshaft speed is half of the crankshaft speed.
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Old 07-22-2021, 08:27 AM   #27
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Default Re: Help diagnosing engine knock

7-Zero,

Sounds exactly like a bent rod. Take the pan off and observe the rod on the crank as the engine is turned over by hand. If it moves back and forth on the crank then it is bent. You can have the rod straightened at a reputable machine shop. While the rod and piston are out check for a loose pin or loose rod bearing.
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Old 08-04-2021, 02:48 PM   #28
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Default Re: Help diagnosing engine knock

I found part of the problem, the babbitt in rod #3 is cracked and missing. Rods #1 & #4 have a small piece gone as well, and one of the rod caps has a crack in the babbitt. The clearances in all of the rods were at .015 so I am wondering if it was run loose at some point causing it to break up? A very small piece of babbitt fell out when I removed the #3 rod but there were no large pieces in the pan. The oil in the dipper tray had a white/silvery look to it.

I am trying to decide the next step, do a full rebuild or just replace the rods? What exactly would be involved in this and would it be worth while for a novice to attempt or would I just be getting myself into a bigger mess? In my head it seems doable, measure the crank for appropriate sized rods, get new rods, hone wrist pin bushings to fit. Easier said than done of course. The engine had good compression, 59-63psi. The ridge on the cylinder wall feels like it is mostly just carbon buildup as a lot of it can be scraped away. What are the chances of reusing the current pistons and just change out the rods? What what other things should I be aware of and or take into consideration? I have not checked the main bearings yet, so that could be a big deciding factor too. The crank has some marks, but I cannot feel anything with my fingernail, would it be okay, or would it need to be polished?

New babbitted rods are $99 so it would be about $500 to get new rods and have them honed. Not too bad price wise compared to a rebuild, but if I run into bigger problems it could get expensive fast.

Thank you for any help and advice!
Attached Images
File Type: jpg Rod 1.jpg (46.8 KB, 44 views)
File Type: jpg Rod 3.jpg (63.4 KB, 42 views)
File Type: jpg Rod 3b.jpg (52.7 KB, 43 views)
File Type: jpg Rod 4.jpg (55.1 KB, 41 views)
File Type: jpg Cap 1.jpg (74.5 KB, 38 views)
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Old 08-04-2021, 02:51 PM   #29
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Default Re: Help diagnosing engine knock

In addition to the above, I am still trying to figure out this other knocking sound. I think it is coming from the valve train. I pulled each rod away from the crank, one at a time, and rotated the crank as far as I could. The sound still remained so I am thinking it is coming from the valves. I checked the clearances and found that they are quite tight. Could this sound be caused by tight valves? Unfortunately it has the original style valves and lifters so I will have to figure out how to do valves too.

1 .013
2 .008
3 .007
4 .010
5 .010
6 .013
7 .006
8 .012

Here is a video, my placement was not the best, so it is more just for the audio. The knock is more a tick….tock sound, the deeper thunk is the hand crank.


Thank you!
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Old 08-04-2021, 02:55 PM   #30
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Default Re: Help diagnosing engine knock

If what you discovered is not the knock, then I would say it is time to pull the engine and disassemble it to find out what is going on. Sounds like it is in need of a rebuild at least partially.

If the cylinders and crank aren't scored up and can be lightly polished to a good finish, you are lucky and it will cost far less! As for your valves, the tight clearances usually don't cause a very loud knock. I haven't seen it. Those are all over the place though so you do want to adjust them and get them all to what they should be. The original style valves have to be pulled out and the end has to be ground for clearance. So you have to do it very carefully and probably have to take them in and out.
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Old 08-04-2021, 04:59 PM   #31
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Default Re: Help diagnosing engine knock

Have you looked at the main bearings?
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Old 08-04-2021, 05:01 PM   #32
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Default Re: Help diagnosing engine knock

You might want to read this thread and work out a deal if things can fit.

https://www.fordbarn.com/forum/showthread.php?t=301730
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Old 08-04-2021, 07:05 PM   #33
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Default Re: Help diagnosing engine knock

Wow, I think you starting taking the engine apart just in time. You could have thrown a rod through the block. I am with Chris, time for a overhaul.

You may be able to save the crank. Use a 1 to 2 inch micrometer to measure the journals. They should be round and not tapered within 0.0005 inch. You can use crocus cloth to polish the journals.

Install modern valves and adjustable lifters. If the cylinders are good you can leave them as they are if you are putting the old rings back in. Check the rings to make sure that there is not too much slop. Consult Les Andrew's book, MODEL A MECHANICS HANDBOOK VOLUME 1. He has a comprehensive section on engine overhaul. You will find your knock when you take the engine apart.

Start by taking the pistons out one at a time and turning the engine over to see if the knock goes away. By the time you have all 4 pistons out then the only remaining thing is the crank, the oil pump, the cam shaft, the valves, and the gears for the distributor and oil pump. If you still have the knock, start pulling out the valves. By process of elimination you will get to the cause.

Maybe start by pulling the starter and watching the ring gear on the flywheel as you turn the engine over. Perhaps it is hitting the bell housing. Just a guess.
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Last edited by nkaminar; 08-04-2021 at 07:26 PM.
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Old 08-05-2021, 06:23 AM   #34
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Default Re: Help diagnosing engine knock

I thought of one more thing. It is a little far fetched but possible. The valves will torque the camshaft in two different directions. When opening it is in one direction and when closing in the opposite direction. If there is something loose in the camshaft gear or if the camshaft gear is very worn the looseness will flip back and forth which may be making a clicking sound. Like I said, this is far fetched but a possible source for your knock. The test is to take all the valve springs out and see if the noise goes away.
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Step on the gas, for tomorrow I die.
Forget the brakes, they really don't work.
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My car grows red hair, and flies through the air.
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Old 08-05-2021, 10:13 AM   #35
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Default Re: Help diagnosing engine knock

Quote:
Originally Posted by nkaminar View Post
The high compression head requires a Model B gasket, but you probably already know that.
Why is that? Is that true with all head gasket brands? In my examination all you gain by using a "B" gasket is two steam holes in the gasket that are not in the block or the head.
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Old 08-05-2021, 07:13 PM   #36
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Default Re: Help diagnosing engine knock

The vendors may say that high compression heads require a model B gasket, but many people including me don't use them and don't have any issues. Copper all day long!
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Old 08-06-2021, 06:51 AM   #37
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Default Re: Help diagnosing engine knock

MC, Good question. It may be due to the way the area around the valves is formed. I guess the reason is the same as why sailors like rum.

Nobody knows.
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Step on the gas, for tomorrow I die.
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My car grows red hair, and flies through the air.
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