Mystery Engine Knock

[chrs1961815]

Been chasing an engine knock for a few weeks in my roadster. This is on a newly rebuilt engine with almost 1000 miles on it. Along with the knock a cylinder is misfiring (either 3 or 4, they both change a bit when shorting out). It is definitely coming from the back of the engine. The knock is not consistent in pattern and is quite loud. It is definitely at camshaft speed and in the top end.

Here is what I have checked:
Timing gear - no broken teeth, nice and tight;, plunger spring good
Compression test - all four cylinders are putting out over 60 pounds
Oil pan - taken off and crankcase inspected, nothing
Valves - valve cover taken off, clearances checked, no stuck valves (at least at time)
Just for kicks I put some marvel mystery oil in the gas to see if anything would happen, no change.


Me and many other guys have not been able to pinpoint where this noise is coming from' just on the top end in the back of the engine. The thing that seems to be making everybidy scratch their heads is that it is really loud at idle but once you increase the throttle it quiets and turns more into a rattle.

Anybody have any ideas as to what it is? We are all stumped!

[Bob Johnson]

How about a rod hitting the dip tray?

[chrs1961815]

Originally Posted by Bob Johnson

How about a rod hitting the dip tray?

No witness marks on the dip tray and the knock is not at crankshaft speed.

[alexiskai]

What about a visual inspection of the valves and piston heads on 3 and 4 via the spark plug holes?

[Werner]

CHRS...,


Is it conceivable that there is something loose in the clutch bell housing?

[Patrick L.]

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Does it seem like it could be coming from the starter ? Maybe a problem like Fred had.

[nkaminar]

The book Model A Ford Mechanics Handbook, Vol. I has a Troubleshooting Chart 4.6, Engine Noises on page 4-8.

Number 2 is Valve Noise which can be caused by loose valve stem or guide or stuck valve. The book recommends trying to squirt oil into the carburetor while the engine is running to try and loosen a stuck valve. I know you have looked at that but it could be that a valve is sluggish and not completely stuck so that it only happens when the engine is running.

[chrs1961815]

I have yet to look at the top of the valves, probably should pull out my small little inspection camera and look at that.

Is it possible that it could be from the bell housing? Seems weird that that would cause a misfire?

It is coming from the passenger side of the engine for sure.

[Marshall V. Daut]

Check your "Private Messages" in the top right corner of this web page.
Marshall

[Greg Jones]

Loose valve seat? I had that once, drove me crazy finding it.

[alexiskai]

Originally Posted by Greg Jones

Loose valve seat? I had that once, drove me crazy finding it.

I just had that this winter. Didn't manifest as a knock, but did lead to odd symptoms.

[chrs1961815]

I don't have valve seat inserts.

[nkaminar]

Another possible source of a knock is a tight distributor shaft or the screw that secures the distributor being too tight. But I don't think that is your knock. If there is a miss associated with the knock than I would suspect a sluggish valve. This may not work but I would try squirting some PB Blaster for other solvent type oil into the carburetor while the engine is running at a good clip. Lead used to lubricate valves. You might try some lead substitute, available at the auto parts stores.

[Chuck Sea/Tac]

Possibly a broken piston

[chrs1961815]

UPDATE:
Ran the engine with a modified valve cover that has the top half cut off to see what the valves are doing. One of the valves on cylinder #3 is sticky and was closing hard. Time to pull the head and take it apart.

[katy]

Originally Posted by chrs1961815

UPDATE:
Ran the engine with a modified valve cover that has the top half cut off to see what the valves are doing. One of the valves on cylinder #3 is sticky and was closing hard. Time to pull the head and take it apart.

I would suggest that you run some MMO or other top end lube for a while before pulling the head.

[alexiskai]

Since you know exactly which valve it is, I wonder whether you could remove the manifold (a lot easier than removing the head) and then apply a penetrating oil spray to the opened valve from underneath. Might dissolve whatever's making it stick.

[chrs1961815]

Before I took everything apart, I tried taking the cover off and spraying the stem with WD40 and also through the spark plug hole. I also sucked some MMO through the vacuum and in the gas. Didn't do anything.


So I took it apart yesterday and didn't find anything wrong with the valve itself, not bent. Nothing really on the stem of the valve. It fit perfectly in the valve guide with a little clearance on each side. I used some lapping compound on the stem and put it back together with lubricant.



Still have the sticky valve for whatever reason. I ordered some ball hones and I am going to take it back apart and hone a few thousandths off of the valve guide. At least that's the plan.

[katy]

Originally Posted by chrs1961815

I ordered some ball hones and I am going to take it back apart and hone a few thousandths off of the valve guide. At least that's the plan.

I didn't know that they made ball hones that small.

BTW, is it an intake or an exhaust valve that's sticking?

[ddweave]

Could it be a weak valve spring?

[nkaminar]

Also look at the lifter.

[chrs1961815]

It was an intake valve on cylinder number 3. I fidn't know they made hones that small either, they come even smaller than 11/32 too.

Valve springs were checked, they are all brand new and very strong.

[Patrick L.]

It was an intake valve, so the problem has been fixed ?

I don't think you'll find a hone that small, but, you can find a reamer.

I've loosened them up using grinding compound.

Most of the time the valve is fitted OK, maybe a tad tight, and will start hanging up because of 'crud' [ technical term] usually from sitting around not being used.

[chrs1961815]

They do sell ball hones that small, specifically a company in California called Brush Research. I bought some from them and I am waiting on them to come.

I verified it was an intake valve by watching the engine run with a valve cover that has the top half cut off.

[chrs1961815]

Update: still have the sticking valve. Mechanically it does not make any sense as the guide has plenty of clearance for the valve, a different valve and spring were put in with thr same results, and the lifter works fine. I am unsure of where to go from here as I have run out of ideas and gotten sick of tearing the engine apart after 4 or so times!!

[Marshall V. Daut]

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Check your private messages again.
Marshall

[GRutter]

Originally Posted by Marshall V. Daut

Check your private messages again.
Marshall

Why keep sending private messages?
We all benefit from each others experiences and shared knowledge.
If you have something to say, please just post it so we can all benefit from it.

[bbrocksr]

Originally Posted by GRutter

Why keep sending private messages?
We all benefit from each others experiences and shared knowledge.
If you have something to say, please just post it so we can all benefit from it.

After you've been on here a few years and you get tired of the "professionals " picking your posts apart you'll be sending private messages too.

Marshall has more Model A experience than most of the members on this forum and is very helpful.

Bill

[old31]

Originally Posted by chrs1961815

They do sell ball hones that small, specifically a company in California called Brush Research. I bought some from them and I am waiting on them to come.

I verified it was an intake valve by watching the engine run with a valve cover that has the top half cut off.

Interesting, i have not heard of the cut valve cover before.

1: Did it stop the oil splatter?

2: How high up did you cut the cover?

I ask because I need to do the same thing, but instead of cutting a cover I will make one from sheet metal.

[shew01]

Originally Posted by old31

Interesting, i have not heard of the cut valve cover before.

1: Did it stop the oil splatter?

2: How high up did you cut the cover?

I ask because I need to do the same thing, but instead of cutting a cover I will make one from sheet metal.

A picture would be great too. [emoji106]


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[nkaminar]

Chris, I am sorry you are having so many problems. In my mind, the only thing that makes sense is a sticking lifter. Unfortunately fixing a sticking lifter will require some work. You will have to take the pan off and remove the cam. You can keep the lifters up with cloth pins. You will have to remove the valve keepers and springs.

How have you determined that the lifter "works fine"?

The only other thing that I can think of is to use a heaver valve spring on that valve. I assume you have checked the spring. You could take the heaver spring out after a few thousand miles. I have stretched springs to increase the spring force.

[chrs1961815]

Originally Posted by old31

Interesting, i have not heard of the cut valve cover before.

1: Did it stop the oil splatter?

2: How high up did you cut the cover?

I ask because I need to do the same thing, but instead of cutting a cover I will make one from sheet metal.

The valve cover is cut in half horizontally more or less, maybe little taller than half. When running, there is not any oil splatter but the galley does fill up almost to the top of the valve cover which is why you have to be careful when you cut it.

Btw, Marshall was suggesting the valve could be bent but the original one and the new one was checked for straightness. Plus they are stainless so they are pretty hard.

[chrs1961815]

Originally Posted by nkaminar

Chris, I am sorry you are having so much problems. In my mind, the only thing that makes sense is a sticking lifter. Unfortunately fixing a sticking lifter will require some work. You will have to take the pan off and remove the cam. You can keep the lifters up with cloth pins. You will have to remove the valve keepers and springs.

How have you determined that the lifter "works fine"?

The only other thing that I can think of is to use a heaver valve spring on that valve. I assume you have checked the spring. You could take the heaver spring out after a few thousand miles. I have stretched springs to increase the spring force.

I spoke to an engine rebuilder who told me to the check if the lifter comes up and down fine and turns in the bore. Sometimes what happens is when people remove the old lifters they can nick the hole.

Btw, I should mention that the valve guides and valves are modern and the lifters are the adjustable type.

[katy]

Originally Posted by chrs1961815

Update: still have the sticking valve. Mechanically it does not make any sense as the guide has plenty of clearance for the valve, a different valve and spring were put in with thr same results, and the lifter works fine. I am unsure of where to go from here as I have run out of ideas and gotten sick of tearing the engine apart after 4 or so times!!

Possible problem w/the camshaft?

[GeneBob]

It just seems like it has to be the lifter or something in the lifter bore. I don't wish that frustration on anyone.

[nkaminar]

I am trying to think of how you might loosen up the lifter without taking it out. It may be possible. Try removing the valve cover, removing the valve spring keeper and spring, and tying up the valve. Then lift the lifter with the camshaft by moving the engine into that position. Then put a heavy-duty rubber band around the lifter and turn it by hand or with a drill motor until it loosens up. May take a long time. You can make a heavy-duty rubber band by cutting a slice out of an old inner tube.

[chrs1961815]

The lifter works great, and is not stuck what so ever at all. I just don't see it being that.

[nkaminar]

This is a real mystery, isn't it. I have run out of ideas. If it was my engine I would try a stronger valve spring.

[Patrick L.]

Hmmm, this is a real wonderment.
Valve and lifter are good.
I can't wait to hear about the fix.

[GeneBob]

Are you running a new cam, reground cam or original cam? A bad lobe might overheat the lifter?
Can you lift the lifter up and spin it or does it get tight at the top of its travel?
Does the adjuster on the lifter show wear like a hollow in it? Maybe it is not hardened?
Could the valve spring or keeper catch on anything (doesn't seem likely).

I am just trying to trigger a thought that will point to the cause of the problem. It seems like you have ruled out the valve end of the problem.

[Brendan]

did you talk to your engine rebuilder? what did he say?

[chrs1961815]

It is a reground stock cam. The lifter pulls up fine and I can twist it around.

[Patrick L.]

Stretching or shimming a spring may be a good idea.

[chrs1961815]

So some updates here: we took another look at changed our minds about the valves and decided to pull the engine where we found that the insert on cylinder number 3 was badly scored and damaged. Replaced the insert and sanded the crankshaft and put it back together with the same knock. It has still got us stumped. Back to the drawing board.

What I don't get is that the problen does not go away when shorting out cylinders and it is hard to start and keep running (has to have the throttle pulled all the way down along with the spark advanced more than it should).

[Ernie Vitucci]

Good morning...have you considered changing the distributor and taking a good look at the gear at the bottom of the distributor shaft? Ernie in Arizona

[Bob Johnson]

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A real stumpper. Since you have taken the engine apart have you tried listening for the knock with the cylinder head removed and using the starter to rotate the engine? You said that the knock is more noticeable at idle so it might show up using the starter to rotate the engine. With the head off the starter should be able to turn the engine faster than with the head on. Plus you can see some of the moving parts.


Just a thought
Bob

[chrs1961815]

I have not changed out the distributor but I was considering doing that. I rebuild distributors and I rebuilt this one so it is pretty much as new as the engine.

As for Bob's suggestion, we have previously tried to see if we could hear it hand crabking and using the starting to turn the engine and had no luck. But last night I sat there cranking it with the starter for a while and was hearing a knock and the speed slowing down. That has got me stumped! Might be worth giving your suggestion a try. We have previously ran it with a half valve cover to watch the valves.

[jimTN]

1. center or front main loose.
2. Flywheel loose.
3. Crank end play.
4. Camshaft end play or loose cam bearing.
5. Why did you have a scored rod bearing?????

[kimlinh]

is the piston hitting the head? The engine may have been fine when it was first rebuilt but a cracked piston could be giving you trouble now. Buy the way, I hope I'm wrong.

[chrs1961815]

The head has been off many times along with the pan. Had it on a stand to pull the rod and piston and inspected everything else. Cylinder walls and pistons looked fine. Pistons have been checked to make sure they are hitting the head and they are not. I am running a pretty thick head gasket anyways.



As for the scored bearing, the rebuilder said that it could have been a lack of oil because of a tight clearance or a possible particle of debris or something got inside there. We will never know. He made sure there was plenty of clearance and I made sure that the journal and bearing were clean and had no dust or anything.

[McMimmcs]

Originally Posted by Marshall V. Daut

Check your "Private Messages" in the top right corner of this web page.
Marshall

Unfortunately private messages defeat the purpose of a forum! We all want to learn!

[McMimmcs]

Did you have a professional rebuild the engine ?

[chrs1961815]

Originally Posted by McMimmcs

Did you have a professional rebuild the engine ?

Antique Engine Rebuilding supplied the rods, bearings, pistons, valves, valve guides, camshaft and crank. They fitted the crank and the mains. I put the rest together.

[Rob Doe]

Chris, I just got here and didn't read from the start, just page 3. It seems to me that just one missing cylinder would not create the start problem that you describe. It wouldn't run well, but it would start and run.

Could you have a model B timing cover? Check #1 piston to see if it is TDC when your pin drops in. I can look in the plug hole and see the top of my #1.

Shooting from the hip here.

[Rob Doe]

I read recently where a few guys get their timing gear improperly aligned on installation. But you said the engine had 1000 miles on it. It surely ran and drove okay for that many miles? Or were they put on before this rebuild?

[tinkirk]

What are using for a cam gear?


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[nkaminar]

Chris, If you still have the pan off, turn the engine over by hand and see if one or more big end rod bearing is moving back and forth on the crank. This would be an indication of a bent rod which would cause an engine knock and is hard to diagnosis.

[chrs1961815]

Okay:
I am using a new fiber gear from AER. Last October my timing gear went bad (must have been a bad one from a few years ago). Since then I put a lot of miles on the new one and an inspection of it tells that it is not the problem.


The timing cover is an A cover for sure. I just changed it out after the problem started because the motor mount holes had stripped out. Same problem.


I am starting to lean toward a bent rod as it seems I have covered everything else. Rob is right about the hard starting and running - that is what is the weird part.



The crank ends of the rod can move side to side a bit on the crank but I was told this is normal.

[nkaminar]

The hard starting and knock are probably not related.

The rod moving side to side on the crank is not normal. Have a good machine shop check the rod, or rods, that is/are moving.

[chrs1961815]

To be clear, it looks like the crank ends of the rods are not wide enough to fit the whole journal of the crank. They are a good 1/8 inch short. I don't see how it could not knock for a long time if this was the problem - I also don't see how twisting could do this.



I will compare some original rods to a crank tomorrow just to see.

[chrs1961815]

Okay so here is another update:
Engine completely disassembled and we discovered that all the bearings and the crank had been scored along with some of the cylinders and pistons. Mains are OK. Cause is oil not getting to those plays but the passages are all free and the pump appears to work well but needs to be taken apart for sure. One thought that I hope somebody can answer is about my oil pan. I have the first design oil pan with the screw in dipper tray - is this dipper tray lower than a regular pan? That would cause no oil to come to the bearings.

[nkaminar]

Chris,

It seems like you may have found your problem. You may be able to use a borescope to see if the dippers are reaching far enough into the tray. You can knock the breather tube out of the engine. It is a tight fit.

It is normal to have 1/8 inch front to back clearance between the big end rod bearings and the rod journals. A bent rod will push the big end of the rod back and forth and bang into the journal shoulders. The geometry is not obvious. A straight rod will just stay in one place even with the clearance. The only reference I could find that mentioned the back and forth movement of the rod if bent is https://www.mtfca.com/discus/message...tml?1500638368.

[jm29henry]

Is it possible that you’re intake and exhaust manifold and intake are not machine correct as no makings a good seal hence hard starting noise and poor running

[katy]

Are the rod cap dippers facing the proper way? That is, towards the camshaft?

[chrs1961815]

Yes the dippers were facing the right way.

I think I am on to the cause of why this happened, need some more research!