Sudden Rod Knock

[JohnK]

I just took my Roadster Pickup on a 109 mile journey around Lake Tahoe, all was going great until Mile 100 just passed what was previously known as Squaw Valley when my engine developed a very pronounced deep knock. I pulled off to the side of the road and at idle the noise went away but if I reved the engine it would come back. I'm pretty sure it's the No.1 rod as when I grounded that plug it seemed to quiet down. I didn't want to send a rod through the block so I took the coil out of No1 and limpped home on 3 cylinders. That said, it would still have a light knock when the engine was under heavy load. So my question is, does that sound like a rod or a main bearing and if it's a main, is there any chance of adjusting it without taking the engine out?

[Erik Barrett]

Your connecting rod likely failed because it was not properly babbitted. Babbitt is more art than science and is no job for amateurs. This means the others are not far behind it. If it did not scratch the crankshaft too badly you may be able to put in a set of replacement rods from reputable vendors. Where are you located? I am in Auburn Ca.

[Allan]

John, I had the same thing happen with my barn fresh tourer buckboard. I limped her home and took off the pan inspection plate and found the no 1 rod had lost most of the babbit. The good news was i fixed it in the car. I loosened the pinch bolt on the wrist pin first. Then the rod was disconnected and the piston drawn down the bore far enough for the wrist pin to slide out and the rod removed. I dug out a good original rod and hand scraped the babbit to get a reasonable fit. This was then fitted up with the rod hanging down and I lapped the babbit in using timesaver.

The trickiest part was compressing the bottom piston ring to start the piston back up the bore. If you have alloy pistons that will not come into play for you.

That was 6 years ago. I was prepared to make subsequent adjustments to the rod bearing, but it has not been required.

Best of luck. Allan from down under.

[JTT3]

Allan, brilliant!

[Jerry VanOoteghem]

I have found that a knock under load is a main bearing. Usually, if you're going downhill and you let up on the throttle, and hear the knock then, it's a rod. When the front main went out in my speedster, I could run downhill as fast as I like with no noise, but when climbing a hill, it clattered like crazy.

Anyway, it's all conjecture and guessework until you remove the inspection cover and have a look. Let us know what you find. (And good luck to you on finding something easily fixed.)

[Norman Kling]

If you do a lot of hill climbing, the front of the engine sometimes starves for oil. A good help for this is an outside line. The ones I use are attached to the magneto plug. They can also be attached to the side of the crankcase near the flywheel and up to front of crankcase. In fact the one I use works so well that I ran the car for about 10 years without the funnel on the inside oil line. The magneto had stopped working and I ran it on battery for 10 years. I rewound several magneto coil rings and so decided to fix my magneto. I found the funnel at the bottom of the crankcase and it had been hit by the magnets and cut the coil ring. That is why the magneto had stopped working. Anyway, I would recommend an outside oil line if it does not already have one.
Norm

[JohnK]

Ok so I took the inspection cover off, there were a few small chunks of Babbit in the dips (4 dip pan). I took the front rod cap off and it looked OK but the babbit in the rod itself was crumbling on the edges (see photographs), luckily the journal looks to be in good shape although I haven't measured for taper or out of round. I must also add that I fitted a mag post oiler and I try and run with a little more oil because of the hilly country. This car is also a daily driver and I put probably 300 miles on it this summer so I'm amazed that it held for so long. (maybe 45mph down the Truckee River was a little excessive but I'm 19 what can you expect lol)

Unfortunately, I'll have to wait until I trailer it out to Colorado where I have a proper garage to take the rods out and re-babbit them.

[Jerry VanOoteghem]

Well, that does not look so good. You've at least got rod troubles. Hopefully, not mains too.

[Joe Reid]

How do the wrist pins feel? How loose was the rod on the crankshaft?

[JohnK]

Joe,

The rod wasn't as loose as I expected it to be but it did have a tiny (could barely feel it) amount of vertical play and a nonzero amount of end play. also, the wrist pins seemed tight but the engine has .060 positions so I wouldn't be surprised if the little end is generally tighter. I think I'll just put it back together so I can get it onto the trailer and really tear into it in CO.

[NoelChico]

I lost a rod last year due to my stupidity and had Gene French re-babbit it for me at the correct size. I had first ordered an already re-babbited rod but it weighed way different than mine so I returned it and he graciously rebabbited mine. I replaced the rod without removing the head due to the head gasket shortage. I unbolted the big end and brought the piston down enough to access the wrist pin and put a steel rod through the wrist pin jammed against the block. This prevented twisting the rod as I loosened the wrist pin bolt. I was able to slide the wrist pin out and remove the connecting rod. On getting the connecting rod back, I used timesaver to get proper big end clearance, then removed it from the crank and replaced the wrist pin in the piston, which had not exposed the bottom ring. Again, a steel rod through the wrist pin wedged against the block allowed me to tighten the wrist pin bolt without putting a twist on the rod. I bolted up the big end after adding correct shims and assembly lube, checked that it cranked easily, and replaced the inspection pan. I'm back on the road.

[JohnK]

Well I found a new rod with good babbitt and after scrapping and fitting, it seems to have solved the problem (thank gosh for alloy pistons idk how you would get the bottom ring in otherwise!). Just for kicks I tried to tighten the other rods, but they locked the engine so I'm taking that as a win.

Thanks for all your helpful advice!

[Allan]

Good job John. Good idea to check the others while you had the bottom cover off. When I did the rod on my barn fresh buckboard, I took out the horseshoes around the pan and cleaned out a swag of crud and carbon at the same time.

We were having difficulty getting the bottom ring up the bore until a local diesel mechanic came by. He used the ring compressor we thought would never fit!

I love the way some of these none to exact fixes work. I did not want to disturb the patina on my old car, not even to take the head off. So we did what worked. I did measure the crank out of curiosity. It was smooth, a little oval and a little tapered. Given the rest of the motor is likely to be just as worn elsewhere, there was no point fritzing about something being a little less than perfect. When i first started the car after her 62 year slumber, she started and ran like a beaut. My son switched to mag on the dash and she didn't miss a beat. How good is that? Two days later while idling as I opened the workshop door, The generator came to life too, and still works, untouched, some 7 years later.


Sometimes we just have to take a back seat and go along for the ride.

Allan from down under.

Allan from down under.