Banger rod knock

[Special Coupe Frank]

Hope I don't say something stupid here...

When you say # 4 Rod has "approx 2 mm play", do you mean from side-to-side on the crank journal, or "up-and-down", in the direction of rod travel ( perpendicular to the crankshaft) ?

Suggest you remove the rod-caps, one at a time (keep track of how many shims are on each bolt, and which side), and inspect the babbit: there should be an " X -shaped " groove in the bottom of each cap, and the babbit surface should be smooth and shiny. A bearing that is "wiped-out" will often have no groove left, or the babbit may look like it has "smeared-into" the groove: this is from the bearing getting warm enough to soften the babbit, which then "runs" or get mashed into the groove.

If the babbit looks decent, the next step would be to replace the cap and see if you can adjust the bearing clearance, using either Plastigage or the foil-square method. If you wind-up with all the shims removed and STILL have too loose a bearing, then you would have to change the rod. I may be wrong, but I do not think it is possible to remove / change a rod without removing the piston and rod from the block, which requires removing the cylinder head.

After checking all the rod bearings and journals, do the same check on the main-bearings.

If a main-bearing is wiped-out, there's little you can do to fix it without pulling the engine, and sending the block out for new babbit or conversion to insert bearings; at this point, you might as well do a full rebuild.

I would NOT seriously consider mixing an inserted rod with babbit rods - it will probably not balance with the other rods/pistons, and would cause destructive vibrations.

If you were "feeling" the knock through the pedals, that sounds to me like a loose main bearing or a loose flywheel. Unless the engine is knocking so bad / loudly that it literally sounds like a jack-hammer, rod-bearing knocks are not usually "felt".

Another very common source of "knocking" in the Model A engine is the camshaft: frequently, the thrust-spring and plunger in the timing cover fails, allowing the cam to "walk" fore and aft in the block; each time it hits against something (block, or timing cover) it will make a heavy knock. An easy check to to remove the side cover from the cam gear, and use a screw-driver to try to move the cam gear back and forth: if it moves more than 1 or 2 mm, the thrust plunger is either stuck in its bore,or the spring behind it is broken. Usually this knock is most pronounced at idle speeds / low RPMS.

Hope this helps some... if the problem turns-out to be a failed rod-bearing, you might get by with swapping-in a decent rod, as a short-term repair. More importantly, try to determine WHY the bearing failed: mos common cause is lack of lubrication. Make sure all the dipper-wells in the dipper/baffle tray hold oil and that there are not any holes rusted in the wells. If there is a hole in the well, oil will run-out, and there is nothing for the dipper to catch, and the rod bearing will starve for oil.

It would probably be a good idea to remove the valve cove, clean out any sludge, and make sure all the drains are clear. The oil circulates by being pumped up to the valve chamber, and from there it flows by gravity to all the engine bearings (cam, mains, rods).

Good luck !

[Gerard]

pm send

[Rokkern]

Yes I meant play up and down, not sideways.
All the rods have sideways play like normally rods have.
1,2,3 is tight up and down. 4 is 2mm up and down.
Unscrewed the rod cap, no shims that I could see. So removing any is impossible. at 2mm of play that would be a lot of shims to remove and I think the rod bearing would probably be pretty oval too. It´s in for a more solid repair than the shims removing unfortunately.

Everything else looked good, so I`m really not sure what caused it to give up. Maybe plugged oil channel, to deep or a hole in the oil pickup baffle, metal fatigue maybe (it has been sitting since 1964 until 7-8months and after welding a rust hole in the oil pan (YES REALLY!!!!- the oil pan which has to be the best lubricated part on the whole car) the previous owner only drove back and forth to the gas station etc.
The sound came within a short timeline 3-10 seconds. And then was the same until I parked it. Strange. I would have thought a rod knock to appear more gradually and then getting worse and worse, nut stabilise. But yes, this rod bearing is definetly gone.
Thank´s for the advise about the cam gear, I´ll check into that before I put the pan on. The knock is definetly from rod number 4, at 2mm play there´s no question in my mind about that.

[Tom Wesenberg]

You might even just change the #4 rod cap and shim as needed, if you want to do a quick easy repair. Measure the rod journal diameter of course and get the cap to match. As I recall someone in the northwest sells main caps by themselves, so why not a rod cap also.

[Special Coupe Frank]

Oil pans can "rust" from the inside-out.

Acids form in the crankcase of older engines, ESPECIALLY those without thermostats, and those that see short-trip usage...

I have a '29 engine currently torn-down for inspection, and there are holes eaten in the dipper-wells on # 2 and # 3, one of the baffles has the bottom edge eaten away, and the oil-pump spring broke right at the clamp, all due to acid corrosion from the blow-by contaminants and condensation.

The bottom of the oil pan is a rough and jagged as a fresh piece of 80-grit sandpaper. No "red / brown rust", but acid etching.

I discovered all this after scraping the sludge out of the oil pan, then soaking-down with an aggressive caustic cleaner such as Castrol "Super-Clean" or "Purple Power"... remove all the grease and oil and left clean metal behind. It doesn't remove or "convert" rust, so if there was "rust", it would have still been there.

[Tom Wesenberg]

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I had the same thing happen as Frank.
I bought an oily looking pan at a swap meet, that for some dumb reason still had 2 to 3 quarts of oil in it. When I got it home and dumped the oil and rinsed out the sluge, I could see daylight through about 8 pin holes, all from acid etching.

[Rokkern]

That actually make my feel a whole lot better than to think the engine has sat without oil for 50 years.
The cam has a lot of spot`s but not so much wear.

Still wondering if it is possible to remove the rod from the underside of engine?

[Special Coupe Frank]

Originally Posted by Rokkern

Still wondering if it is possible to remove the rod from the underside of engine?

Not sure if the piston will clear the main-bearing webs/saddles...


It's not difficult to pull the cylinder head...

[31 A4door]

If there is no Babbit left you can only get new babbit installed or buy another rod from the vendors. Not sure you can put inserts in without changing to full pressure oil system.

Measure your crank to make sure it is round.

[James Rogers]

Inserts can be run in a splash system with no problem. They would all need to be changed and the crank would have to be re-ground to be good.

[Kurt in NJ]

Yes, a rod can be removed from the bottom with only the pan removed, I have done it, ---but if you have the original center lock wristpins I don't think it will be easay to move the wristpin ---and if end clip and the wristpin has been pushing on the on the clip and raised a burr ----or if the crank has counterweights ---
I positioned the crank where the piston could be pulled down the most, rotated it 45 degrees or so, removed the clip and using right angle snap ring pliers to grabbbb the inside of the pin, then by using thew pliers and the rod together I walked the pin over--probably 10 min of playing ---it all just fit and there wasn't any danger of the oil rings popping out ---my replacement rod was 15 grams heavy---I lost 5 mph top speed, and have more vibration, although ALL the babbit came out(and I drove it 5 miles) there was no crank damage from the failure

In your case with the end play you also should take off the rear cap --this also can be done in the car if the crank is not counterbalanced.

[Rokkern]

Thanks !
It looked as it was doable removing the rod from the underside. My head gasket is leaking quite a bit so I might still go that route, haven´t made up my mind yet. Good to know it´s an option.
Could you explain what you mean by taking off the end cap ? how would that help with the end play ? Trying to learn..

And yes the crank will be measured with a micrometer to make sure it´s within specs. It looks, very good though, I´d be very surprised if it is worn looking that good. On the other hand, I`m quite surprised to see how messed up the bearing is when the crank is that good.

I`m also kind of stuck as for what actually caused the bearing to fail. Maybe a clogged oil passage, already worn rod bearing (there where no shims). Open for suggestions.
An A expert I visited today here in Norway told me it was because I cruised at 50mph sustained speed. Seeing how many here on the forum actually cruise at 50 for sustained speed I doubt that was the problem, but please correct me if I´m wrong. I used 10/40w synthetic oil. Could that be the problem?

[Allanw]

If there's no shims, it was probably already worn out.

[jcheshire31]

You should be able to cruise at 50 all day with stock running gear, as long as the car is sound. Especially the motor. Older babbit + constant 50mph = a bad day. Every motor has their own smooth spot at the top end so I can't completely justify saying it was because you were going 50mph. As for the oil you were using, I know a lot of people, including myself that run that weight of oil. Of course that is a whole other can of worms that I know none of the barners want to see opened again. As for your next rebuild, if you want to retain the stock running gear, but want a little more top end and insurance I would suggest inserting and balancing everything. JMHO

[Rokkern]

Haha, I dislike those oil threads myself. As long as I`m not doing something everybody is having trouble with I`m gonna call it good. Thanks and nno more comments on the oil please

Yes I agree, the babbitt was probably already in bad shape with no shims It´s likely the clearance already was on the large side. And good to hear that 50 mph is a likely cause for my old and already worn babbitt to say goodbye. I like to run my stuff hard and fix fast when it breaks.

@ Gerard, sent you an email.

[Special Coupe Frank]

Well, if that A is old and tired, ( or sticky and clogged-up with sludge), you will be fixing it often from running it hard and fast.

As I've gotten older, I have learned ( the hard way) that when trying to use old machinery, it is almost always best to disassemble, clean things-up, remove all old grease / oil / gunk, make sure all lubrication passages are clear, then re-lube and re-assemble and enjoy.

I'm in the process now of completely disassembling / cleaning / re-lubing a 1930's Black & Decker electric valve-seat grinder. It was working when I got it, but upon disassembly, I found that all the grease / oil was hardened & gritty. To actually put the tool into service as-is, it would have destroyed itself in short order.

Once I'm finished cleaning and re-lubricating it, it will definitely out-live me.


Just a thought...

SC Frank

[Rokkern]

As you are my professional go to guys I just wanted to add some pics, let me know if you see something very wrong. Piston to the right is the piston that came out an are going in again. Any idea when it`s from? Would give me an idea of when the engine was done last time. It´s std bore.



the car:

[1931 flamingo]

Your babbit is shot and peeling.
Paul in CT

[Special Coupe Frank]

Rokkern,

Glad to see you pulled the head !

The Bearing in the rod, second from the bottom has lost nearly all its babbit ( you can still see trace of the diagonal oil-grooves to the left side of the photo). What does the babbit in its matching cap look like ?

The fact that the engine is still standard bore, and seems to have Ford pistons and original style rings suggests that it has NOT been "done before", or at most, valve-grind and re-ring, and bearing adjustment.

The cylinder bore your pictured looks okay at a glance, for an old engine... any ideas how many miles / km are one the car / engine ?

Are there any shims / babbit left in the other rods ? Pics ?

If that is the only rod / bearing that looks like that, I would go looking for a cause of oil-starvation: blocked dipper, hole in dipper-well, blocked oil feed from valve chamber, etc.

If your bearing journals are good, you could replace that worn-out rod/cap, de-glaze the cylinder walls with a hone, clean all the carbon out of the combustion chambers / valves, surface the head, lap the valves and adjust, then put it back together, run-gently to re-seat the rings, then drive it for the rest of the summer...

[Kurt in NJ]

It's hard to see in the pictures but I think you have some original pistons, later replacement pistons have clips on the end of the wristpin to keep them in the piston, the original pistons had a clip in the rod that fit in a groove in the center of the wristpin ---if this is what you have and you are looking for a replacement rod without changing the piston you will probably need to find a rod that was done a long time ago, --or NOS, most rods done now will not have the groove cut in the wristpin bushing for the centerlock clip, it was not uncommon for 1 piston or rod to be replaced in the old days, from looking at your pictures it looks like the engine was burning oil, the coloring of the valves leads me to think they were seating ok, by taking one of the piston rings and measuring the end gap at the top of the cylinder --then pushing it down measuring again you can get an idea of the taper in the cyl, the taper would be about 1/3 of the change in the ring gap, taper of .010--.020 isn't uncommon in "original" engines ---rings were cheap, and another set was put in again and again when labor was cheap and the proper job cost too much ----at .010 rings can cope with most times, .020 they don't work very well or for long

I have never had any problems putting in cast iron rings without honing (glaze breaking), but have taken apart many engines that were honed in the chassis that had bearing / crankshaft troubles soon after due to honing debris ( honing debris embedded in babbitt becomes a crankshaft "lap")