The Stovebolt Site Forums The Shop Area Driveline Engine noise

Hi Folks,
Took my 55 series II for a ride last weekend and heard a funny noise from the engine.
At 1800 RPM it rattles!
Doesn't use any oil and doesn't smoke, runs and idles great, even the fuel consumption is OK. It also doesn't overheat and when it rattles, the oil pressure doesn't changeand is always very good.
The truck has 76,000 miles on it and is all original.
I'm in Germany so it is tough to find help.
Friends in my car club say it sounds like a rod bearing.
How can I check the bearings without taking the motor apart?
If it is a rod bearing, I'd be interested to buy a reconditioned 235 motor. Does anyone have a suggestion as to where I mght be able to buy one? If it is a rod bearing, the crank is probably shot so a rebuilt motor is probably the best way to go.
Many Thanks!!

If it is a rod bearing you can kill one spark plug at a time and the noise should change on the bad cylinder for that rod.

Hey sepp,

Here is my amateur stovebolt engine input opinion. I just rebuilt my first 235 a few months ago and its the first engine I have ever done. If you have the time and space permitting since you are in Germany, after you do the test that Pre 68' Dave explained and you confirm that it is a bad rod bearing why not replace it yourself? If everything else is ok such as compression, the head, oil pressure etc. then I would keep what you have and do it yourself.

If you crank is scored you can have it checked and turned down then replace the bearings. Most of the motors I see for sale usually needs to be rebuilt and if they are rebuild they are wanting between 2k - 3k. A while back Tom from Stovebolt Engine Company had a 261 rebuilt for sale, when I was searching but I decided to do my own 235 rebuild with the upgrades I wanted (intakes, carbs and cam) and it cost me about 3500 USD just for parts and machine work. Seeing how easy everything was in those motors just pricy for parts, I would do the repair on what you have since you know everything is original and you know what you have. Plus if you decided to upgrade anything such as cam or what ever you can do it then. It might be a good time to give it new rings also.

I guess the first thing is to verify the where and what the noise is. I guess is what I am trying to say is if you are going to replace the motor you have to pull it out anyway. If you are going to pull it out why not drop the pan and check it out it might be a whole lot cheaper to repair than getting a reconditioned one. Plus now you have to worry about what the other guy did or did not do.

Just check out the simple things first before you do a major job.

good luck

Many Thanks Pre`68 Dave and Tiny Jaime!
GREAT input.
A couple of thoughts:
1. There is no noise at idle. It comes on at 1800 RPM. Don't know if I can drive the truck on 5 cylinders without hurting something. Guess I'd have to keep pulling plug wires until I find the noisy rod bearing. Is this practicle?
2. Have also given thought to rebuilding it myself. Before I pull the engine I may be able to drop the pan with the egine in the vehicle. This way I could check the rod bearings and measure the rod journals. Is this a good idea? Replaced the rear main seal by dropping the pan with the engine in. Should be able to check the rod journals the same way.
Appreciate Any and all suggestions.
Thanks

It is unusual for a 235 with 76000 miles on it to have rod bearing problems. I suppose the speedo could have been changed at one time or had a broken speedo cable.

You can drive the truck with one plug wire off at a time to test. I would just make sure the wire is grounded so the spark does not jump somewhere you do not want it to.

I also wonder if maybe you are hearing the engine ping. Does the "rattle" change depending on the load you put on an engine. A rod knock usually is heard just as you let up on the gas. Pinging is heard while stepping down on the gas.

If you do pull the pan than yes that is the time to check everything and change the rear seal.

If you rev it up a little under from under the hood, you can see if the rattle happens just as it comes off load and the rpm starts to drop. This would be my test for a rod knock. With a rod knock there will be crankshaft damage.

yes, I was wondering if you'd tried hearing the noise standing still and reving above 1800

Bill

WARNING!!!! Please be absolutely positive this is not an exhaust leak. I have had exhaust leaks/manifold leaks that sound like horrible internal engine noises. Also something rattling at it's natural frequency. Some sheet metal piece or component. While it's making "funny noise" use a broom stick to "listen". Touch one end to every part of engine and other areas and put other end near ear. When you find location, sometimes you can quiet it by pushing on it. Or maybe change the tone. That gives you a good start to figuring it out. Please describe what "funny noise" means exactly. I hope it is just something vibrating or exhaust leak. If it's a "tinny" rattle, that's loose metal (good). If it's "knocky" that could be exhaust leak (good) Depends if broom stick says valve cover or pan or block or bell housing or.. It can also be spark knock which is a timing issue or possibly carb. Bottom line: No need to panic and start tearing everything apart, remember you say all parameters are good. Be gentle with driving/running it until diagnosed.

Many thanks for your help.
I'll try the plug wire suggestion and get back to you.
I installed an electronic ignition (Pertronix) complete with IGNITOR coil and set the timing. Could be just a bit advanced - maybe 5 degrees or so. Starts and idles great. Acceleration is also very good.
Knock or rattle occurs when I step on the gas at an engine speed of 1800rpm or more. Goes away when I let off.
Do you think it really could be just a timing issue? Guess I could retard to the factory setting to find out.

I only get the funny noise, which is definately a knock,. when I exceed 1800 RPM and give gas. There is no knock when I let off the gas and the exhaust system is new so I doubt it could be an exhaust leak.
There are lots of things like tailgate chains and whatever that could be making noise but it is definately coming from the engine compartment.
I have a stethoscope so I'll try listening at idle but when I last tried this there was nothing but normal engine clatter.
I have a funny feeling that if it isn't a bearing it could be pre ignition. Maybe the advance isn't working correctly.

One more thought for Pre'68 Dave and Bartomos....
Can I disable the vacuum advance by disconnecting the vacuum line at the Carburetor base and in doing so prevent ignition advance / preignition?
Seems to me that a knock that only comes in above 1800 RPM could definately be ignition related if it isn't a rod bearing.
Thanks!

Disable? If it can't advance the spark to catch up with speed, It will be "late" and that would cause knocking. Make sure vacuum diaphragm is OK and vac source is reliable. Apply suction to hose, see if it moves lever and holds. A new exhaust means it could be leaking. You have to always recheck manifold bolts after several heats and cools, especially when new, and new gaskets. Problem with broom or stethoscope is 1800 is way too fast for that engine to do at rest without load, I believe? Did you say that it does the sound at fast idle or under load (driving)? How do you know it is 1800 RPM? tach? It is possible that it is spark knock or exhaust leak somewhere at some connection. I am sticking with those until you do a "rod bearing test" as described, which I know nothing about. I do not recommend too much driving in case it is internal components. Maybe someone will advise when to tear down. I guess you don't have a little dieseling do you? Run on after key is off? That would be caused by timing issue or exhaust leak, believe it or not.

It is so easy to retard the timing a few degrees, I would try that first.

Bartomas,
Thanks for the input. Especially your explanation of the vacuum advance function.
Noise is only heard when driving and under load. Never at idle. Yes, I installed a tach so I could see when the noise occurs.
I'll try the plug disconnect suggested by Pre'68 Dave and will re set the timing to factory spec.
Exhaust and vacuum advance checked out OK today when I got back from a brief test drive. I'll check tightness of all bolts before my next test drive.
In addition to the knocking noise, I am test driving because I am trying to adjust the hand brake so both rear wheels brake equally. Have replaced drums, wheel cylinders, linings, etc. but can't sem to get the hand brake to brake evenly.
Thanks, I'll get back to you later this week.

Hand brake not equal is small problem. If one wheel locks it's not going anywhere unless you live on Pike's Peak. Noise is important to figure out ASAP. Please answer dieseling question.

Here's some more info for Bartomas and Pre'68 Dave.
Today I reset the timing and adjusted the idle. The latter is not very important. Also changed the oil to 10W-30.
Knock is still there but does not seem as obvious as before. It's all very subjective so the noise level may not be important. Also, it is non existent when cold. Only when things are really hot does it occur under load at 1800RPM and above. If I go faster it seems to go away.
Do you think it could be the heat riser valve?
Tell you why I'm beginning to think it is not necessarily internal engine related. I live in an area where there is a lab that tests oil and lubricant samples of long term durability test engines. They do this for all the major German auto manufacturers.
As I was going to change the oil anyway, I asked if they would test my oil. They agreed and I just got the results. NO ABNORMAL CONTAMINANTS. Just ash and carbon which are normal combustion by products. The oil had 2500 miles on it but there were no metal (bearing) particles in it.
Now what??
HMMMM

To trouble shoot anything, you must isolate various things you can without damaging. If you think it is the riser, take it off or wire it good after warm up or somehow eliminate it temporarily. Do this with any other item you may think of. Your oil test does not prove anything to me. I guess it's good to know you are not chewing up anything. There are many guys on here who could tell you if they could hear it. Most of the mechanics you will find are OBD trained or replace and hope, like me.

I was just thinking about your earlier post where you said you changed the coil.
There have been a number of posts recently where to long of coil mounting bolts were used and the bolts were hitting a pushrod.
Shouldn't affect noise on load but not coast but...
Just a thought.

Knock could very well be a ping,as described by SIR Bartamos. There is also an octane regulator,on your distributor. If your octane is too low,you will also get a ping,usually occuring,as you describe,at a higher R.P.M.,or under load. Rod knock USUALLY quiets down,under load,(accelleration). Get out a broom handle,or length of garden hose,and use as a stethoscope,just like Bartamos suggested.Hopefully,this is just a timing issue,or up grade your fuel. Hope this helps.

How reliable is the fuel on your side of the pond? What octane are you using and what is the elevation where you live? These can all lead to spark knock (which by the way, always occurs exactly when you say your noise occurs). You will know that your timing is set correctly if you hear a slight spark knock when accelerating under load that goes away once you reach a steady speed. You should try to retard your timing until the spark knock goes away, then advance it one degree at a time on your octane selector until a slight spark knock occurs under load. Timing that is set with too much advance will cause a backfire.

Here's an update on my noise problem.
This is my third try to send this. Don't know why but when click submit it erases everything.
We only have unleaded 95 octane gasoline, here. No regular.
Changed my oil, adjusted the valves and set the timing to workshop manual specs. Then I went for a drive. The noise I have still only comes in at 1800rpm and above. At 2500 rpm you can't hear it anymore. The noise is only there when the engine is thoroughly warmed up. There is no noise at idle - hot or cold.
Sometimes I think I can hear it under acceleration when the engine is warm. It is always there at 1800 rpm and above. Seems to go away at speeds over 2500 rpm. Haven't gone over 3200 rpm so I don't know what happens there.
Oil pressure and water temp do not vary once warmed up.
With the factory timing spec there is somewhat less acceleration. Prviously the timing was set at about 5° andanced. Please note that I do have a Petronix electronic ignition installed. I didn't touch the octane selector as I don't really understand what it does. Also, I did not disconnect the vacuum advance when I adjusted the timing. Not sure if I should have disconnected it.
Appreciate any new comments or suggestions. Am afraid I have a bearing problem and would be interested in a rebuilt engine. As things stand, I don't dare drive more that a few miles from home.
Am really getting tired of chasing this noise and maybe a rebuild would put an end to it.

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Did you make sure to disconnect the vacuum advance from the carb when setting the timing? You have to dis connect the line, then Plug the line to the carb with a golf tee, then set the timing, then reconnect .

It really depends on the carb whether you need to disconnect the vacuum line.
Rochester Mod. B has the vacuum taken above the butterfly so there is no vacuum to the advance at an idle so unhooking it is unnecessary.

That is extremely low miles for that engine, a good engine. If you are monitoring heat, oil pressure, rpm, compression test shows good and no smoking, just drive it. Don't be in a hurry to rebuild unless you have a good builder, all the parts available, machine shop available (in Germany? Hell yeah) and $$. BTW: EU95 is U.S.91 Octane. Who knows? maybe try octane booster and adjust Dizzy a few more times. Those engines run like a Pfaff on steroids. You got a whole lot of good info here from 68Dave on down the posts. Re Read and absorb and breathe and drive the Autobahn in your dreams.

The octane selector is just another way to adjust the timing. Once you set the timing by loosening the hard-to-reach screw behind the distributor, you can make minor adjustments to the timing with the octane selector. It was designed for making adjustments if you were to fill the fuel tank with gas of differing octane than what you originally set the timing for. The octane booster bracket has reference marks to allow you to return to the original timing setting without needing a timing light. For your purpose, it is a great feature to quickly troubleshoot your possible timing problem without using a timing light.

Thanks for the explanation 52CARL!
Unfortunately, I can't read the markings on my octane selector.
It's been painted over and all I can see is that it is set in the middle which should be zero.
For my information, looking down at the distributor cap - if I turn the distributor clockwise that should retard the timing. Turning the distributor counter clockwise should advance the timing.
Am I correct??

Here's another update on my noise problem.
At the suggestion of a good friend, I added two cans of WYNNS
to my freshly changed oil. That stuff is really thick and guess what? The noise went away.
I recently changed my oil to 15W-30 oil because I read this in the Service Manual. My friend said it is too thin and I should think about 15-40 or something thicker.
After my WYNNS experience, I think he's right!

Many thanks to all of you who offered help with my noise problem. Guess I'm OK now. I think the noise is a rod bearing but I am going to wait until it comes back before tearing things apart. Maybe I'll pull the motor in the winter.....

That is correct.

While we are on the topic of spark knock caused by too much spark advance for the octane rating of the fuel, what mechanical parts are involved to make the noise?

From Wikipedia,

Knocking (also called knock, detonation, spark knock, pinging or pinking) in spark-ignition internal combustion engines occurs when combustion of the air/fuel mixture in the cylinder starts off correctly in response to ignition by the spark plug, but one or more pockets of air/fuel mixture explode outside the envelope of the normal combustion front.

The fuel-air charge is meant to be ignited by the spark plug only, and at a precise time in the piston's stroke cycle. Knock occurs when the peak of the combustion process no longer occurs at the optimum moment for the four-stroke cycle. The shock wave creates the characteristic metallic "pinging" sound, and cylinder pressure increases dramatically. Effects of engine knocking range from inconsequential to completely destructive.

I said Pre-Ignition in my other post, that's what I call it, but it is not the correct term for a timing issue.(I corrected my post) Spark Knock is correct. Pre-ignition is from excess heat causing combustion in the chamber, different issue.