Help diagnosing engine knock

[7_Zero]

I realize it is difficult to diagnose through text, but I am hoping to get some ideas of things to check before digging deeper into it.

I recently purchased the car and the engine was supposedly rebuilt maybe 10 or 15 years ago. Based on some pitting in the valves I am wondering if it was more of a refresher than a complete rebuild. The previous two owners did not drive the car much and there are only 550 miles on the odometer, so I am assuming it only has that many miles since the ‘rebuild’ but we know what assuming does.

We drove the car around town for a couple weeks before taking it on a long trip and had no problems. On the trip however it started blowing radiator hoses (it has a pressurized radiator). After installing the third hose we watched for bubbles in the radiator and determined it to be a head gasket allowing combustion gasses to pressurize the cooling system. When we had the head off we decided to go with a 5.5:1 head, but unfortunately after the install the engine now has a knock.

The knock is audible at idle and when the engine is revved. You can hear it with the spark advanced or retarded. With or without the fan belt, clutch engaged or disengaged, and has no difference when disconnecting each of the spark plugs. Reversing the timing pin and putting pressure on the timing gear also yields no change.

Using a stethoscope, the sound is loudest at the front of the engine especially around the timing cover, timing pin and cam plunger area. Not sure if the knock has to do with the timing gear and cam, or if it is in the front main and only echoing through the timing cover? The engine had a two piece pulley that we originally thought was the cause so we replaced the pulley and also replaced the cam plunger and spring, but unfortunately it made no change.

Any suggestions on additional things to check, or is it just time to dig in to the bottom end?

Thank you for your help!

[Kurt in NJ]

Perhaps it has a larger bore and pistons hitting edges of head gasket, how did old head gasket compare to old one

[Wick]

Witch head gasket did you use?

[Jack Shaft]

Pull pan and check bearings,verify they are ok.

[Nosetime]

Did you verify piston pop up and gasket clearance? Pull head and check.

[1931 flamingo]

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Disconnect the fan belt and try again, use a long screwdriver or broom stick as a stethascope.
Paul in CT

[30 Closed Cab PU]

Perhaps possible the higher compression head and a new head gasket has increased compression to the point where it is time to check/adjust bearing clearances?

[katy]

When we had the head off we decided to go with a 5.5:1 head, but unfortunately after the install the engine now has a knock.

It could be a piston hitting the head. The test is to put the head on the block w/out a gasket and turn the engine over by hand to see if any of the pistons hit the head.

[PC/SR]

Agree with Nosetime and katy, could be hitting the head. Use Prussian Blue to check popup, gasket and side interferance. Similiar thing happened to a friends car. He ran it and broke the crankshaft. Might also try just laying the head in place without bolting down and see if it moves on rotation.

[Ernie Vitucci]

Good Morning...Katy is most likely right. If the original head is nice and flat, put it back on the car with a fresh gasket and see if the knock goes away. Were you able to see that a head gasket failure was the cause of the exhaust in the radiator? If so, then your number one piston is most likely tapping the head. When you remove the 5.5 head you should be able to see the evidence on the piston and on the head. Or maybe on the edge of the gasket, but it is most likely the piston to head contact. Ernie in Arizona

[Dave N.]

I can only offer my life lesson for my engine knock, but raise the distributor up from the new head about an 1/16 to 1/8 of an inch and than tighten it up again.

[Synchro909]

When I took delivery of my 1928 Tudor from the US, I didn't know the engine had had a "freshen up". The job they did on it was pretty lousy and when I put a 5,5 head on it, I too got a knock from it (sound familiar?). I stripped the engine and found 0.005" over sized gudgeon pins had been installed. This was done by either reaming or honing the bushes to suit, only they went too far and they were loose, causing the knock. A new set of bushes properly installed all is good now. It may be worth your while checking them.
BTW, the bronze they use in those small end bushes is nearly impossible to ream - terrible stuff.

[noyo55]

Back about 50 years back I had a similar knock--constant. Turned out a chunk came off the timing gear. It sounded just like a rod knock but was consant.

[darrowco]

I vote for checking the piston/head clearance. I had a similar knock and traced it down using an accelerometer and an oscilloscope - the knock lined up perfectly with the exhaust stroke of #3. At that point, I realized that the recently skimmed head had gotten one skim too many. The engine turned over freely by hand - the knock only occurred when the piston was flung up while running and took up the slack. Once apart (for the 3rd time) the mark on the head was beeeaaarly visible. A little relief cutting in the head solved the problem.

[TerryH]

I also had a faint knocking sound that none of my Model A friends or I could identify. It ended up being a fiber timing gear going bad, which eventually failed. New gear installed and the noise went away.

[fundytides]

The engine in my car was "rebuiltl" back in the 60's but never run. When I started running it recently, it seemed quite noisy to me. At first I suspected an oil pump problem but I removed the plug on the side of the block and there is lots of oil flow. The engine has .125 oversize pistons. Would the gaskets available then have accommodated this oversize? Can I tell if the pistons are hitting the gasket or head without removing the head. The head was probably planed at the time as well. I am going to remove pan to check rods and also check valves for proper clearance. To me it is more of a "clatter" than a knock. All suggestions are appreciated.

[7_Zero]

Thank you all for your responses, I apologize it has taken so long to reply, things have been quite busy and I have not had a chance to work on the car.

Originally Posted by Kurt in NJ

Perhaps it has a larger bore and pistons hitting edges of head gasket, how did old head gasket compare to old one

Originally Posted by Wick

Witch head gasket did you use?

I believe the pistons are .060 as they are stamped 060-C. We used a Best 509 head gasket. The new gasket and old gasket appeared similar in size around the piston side of the engine, but the area by the valves and between cylinders was quite narrow on the new gasket.

Originally Posted by Nosetime

Did you verify piston pop up and gasket clearance? Pull head and check.

I did not verify piston pop up and gasket clearance, unfortunately this never crossed my mind as this is our first head gasket change.

Originally Posted by 1931 flamingo

Disconnect the fan belt and try again, use a long screwdriver or broom stick as a stethascope.
Paul in CT

Unfortunately this made no difference.

Originally Posted by Ernie Vitucci

... Were you able to see that a head gasket failure was the cause of the exhaust in the radiator?...

There was no major blowout in the head gasket, just a couple dark areas. We are thinking that since the previous owners did not drive it much after the rebuild that the head just did not get retorqued.

Originally Posted by Dave N.

I can only offer my life lesson for my engine knock, but raise the distributor up from the new head about an 1/16 to 1/8 of an inch and than tighten it up again.

Raised the distributor and no change, re-seated it, still no change. But it did make a difference on our other car.

Originally Posted by Synchro909

... I stripped the engine and found 0.005" over sized gudgeon pins had been installed. This was done by either reaming or honing the bushes to suit, only they went too far and they were loose, causing the knock. A new set of bushes properly installed all is good now. It may be worth your while checking them....

Any way to check the gudgeon pins without doing a full teardown?

Originally Posted by noyo55

Back about 50 years back I had a similar knock--constant. Turned out a chunk came off the timing gear. It sounded just like a rod knock but was consant.

This is one possibility that we were hoping it would be, but the timing gear looked good. Not saying we did not miss something though.

Here is a link to a couple videos. When running at higher rpms it is harder to hear, there are distinct knocks at the 8-9 second mark and again at 14-15.

We have just acquired a head puller so we can start working on this again.

Thanks!

[Patrick L.]

If you want to check the clearance between head, gasket and piston, just use some modeling clay.

[Synchro909]

Any way to check the gudgeon pins without doing a full teardown?

I did mine by taking off the head and sump, then pushing the pistons and rods up through the bores and out the top so yes, you don't have to do a full tear down. Rod bearings (and mains) would be checked at the same time. All that said, check the easiest things first.

[John]

Do check the piston to head clearance. A local club member recently installed a rebuilt engine with a new high compression head and had a similar knock. It turned out that the head was incorrectly machined and did not have the proper piston relief for his engine.

[J Franklin]

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.

[katy]

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.

[7_Zero]

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!

[nkaminar]

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.

[7_Zero]

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?

[chrs1961815]

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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.

[nkaminar]

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.

[7_Zero]

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!

[7_Zero]

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!

[chrs1961815]

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.

[Bob C]

Have you looked at the main bearings?

[J Franklin]

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

[nkaminar]

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.

[nkaminar]

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.

[The Master Cylinder]

Originally Posted by nkaminar

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.

[chrs1961815]

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!

[nkaminar]

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.