The Stovebolt Site Forums The Shop Area Engine Shop 235 lower end knock?

bear with me please! I"m no mechanic so my question may sound ridiculous to some, but I'm gonna post it anyhow! My motor which is not suppose to have many miles on it, has a lower-end or bottom side knock upon bringing up the rpm's, I like some other person on the pages, recently had some work done(had the timing gear replaced as it spun thru the keyway) I was gonna drop another motor(used) in as a replacement, because I didn't no any better, and came to find out it had little compression. sorry for the rambling, any how to make this story short, the head was removed from the poor compression motor and put on the motor with the spun gear. the pan was removed and the ol' boy said that it looked real good, other than the rear bearing being adjusted improperly. when I went to get it it ran and sounded real nice to the untrained ear like mine. I' ve driven the 47' chev, 1&1/2 ton flat-bed all of 10 miles real gently. but now while I let it run at idle, admiring the quiteness of the engine, I on only a few occassions I pick the idle up gently and hear a knock! darn! I keep thinkin its just me and that it'll go away..Is there any hope of that? the old boy did say he saw some limited damage on the bearing but thought it would be okay and to take it easy to break it in. phhhhhhhuh, that is even confusing to me.........

Bax, I had the same thing happen to my '54, 235. It was only noticeable while idling. It turned out to be a loose crankshaft pulley (harmonic balancer). Pull the v-belt back and fourth and if the pully moves, there's your problem. If so, you'll have to remove it and replace the woodruff key that keys it to the crankshaft and maybe the pulley itself. I hope that's all it is. Best regards, Jacques

What a bummer , all that effort , and now a failure . It sounds like the engine just has to come out again . Silly question here , did the engine installer remember to put oil in the sump ? . Did you prime the oil system before start up ?
If it is a bearing knock , and it sounds like it is , , then there is no option but to pull the motor and have another look . Check all the bolt torques and bearing clearences as you are disassembling it . Write it all down , then refer to the manual , to see what it was supposed to be .
A knock just won't go away by it's self.
Did you use a stethescope to check the location of the noise ?
If not , try using a short broom handle , place one end on the block and grip the other with your fist . place your ear against your clenched thumb and first finger , now gently open your thumb and first finger . Listen to the engine sounds . Shift the stick to other locations on the motor , any noises will be easily trasnmitted up the stick . making it easier to pinpoint the location of the sound .
Tell us what you hear .

Like Dusty say check everything dowel is a fine way and oil is a good idea
Be careful with the stick.....I'm not kidding. I have seen people so intent in finding the noise they got hurt

Check the oil first!!

Let us know everyone here will jump in and try to help

I hope your good at reading

Yeah , I forgot to say , " keep the stick out of the fan " .

thanks 4 the investigative ideas and ?'s, I will look into them in the morning.

Also check for crankshaft end-play. How much will the crank move forward and backward in the engine? Also check for loose flywheel or clutch. What is your oil pressure when idling?

Chip

Dusty the results are in regarding the broomstick sounding pole and the info isn't to good. The souds are definately eminating from the # 6 cylinder area near the pan. I went to see the ol' boy who did the wo0rk and he says he'll look at it and seems to think that its a rod bearing and not the main. Any thought as to how serious of a fix this is, that being the case. And can this be done while its still in truck? I spoke to a fellow here in Phoenix and he says there is some noise down that way when the engine is not under load. And to answer the question posted about oil pressure at idle, it seems to be about 30#'s., but this seems to be irregular, as some times when I look its has no reading at all, could this imply some blockage in the flowthru filter ?

Rod bearing sounds like a plausable diagnosis. If the crankshaft is not damaged, the fix is easy. Drop the crankcase pan, locate the bearing and replace it. Takes longer to drop the pan than to replace the bearing. If the crank is scored, it will need to be removed to be properly repaired. Radiator comes off, clutch comes off, then crank is removed. That's a lot more work, and I doubt if the mechanic will do it anyhow.

As far as the oil pressure, 30 is darn good in a 235 at idle. The lack of pressure at times is a major concern. The problem is usually worn bearings, allowing too much oil through. Be sure the mechanic hears about your oil pressure problem, too. It doesn't sound like he did much of a rebuild on the engine, in all honesty. That's why we encourage people to do the work themselves on these old sixes, and many of us will even provide on-site instruction when needed.

Fred T, your knowledge is appreciated. Oil pressure issue, could be do to worn bearings? Do you mean rod and or crank bearings? And how about an poorly functioning oil pump? Is it possible for it to be eratic? :confused:

Oil pump, I've never seen one go up and down, just low pressure constantly. All it is is two gears that mesh and turn to move oil. They do wear out, and should be replaced when the engine is rebuilt.

Low pressure due to bearings is usually due to worn cam or main bearings. I'm trying to remember for certain the oil flow on a 235, I think the oil passage for the #6 rod comes through the rear main bearing. If that bearing is to loose, the #6 rod would not be getting enough oil. If I'm wrong on this, hopefully someone will correct me. My books are at home, I'm not.

On your mechanic. Have you done business with him before? What is his shop like, neat and clean or are there parts piled high and a floor so dirty you can't see it? These are things to look for when picking a shop.

I'm curious about your cam gear. Did it come off the end of the camshaft as one piece, or did it fracture and break apart? You had to remove the cam and have a new gear pressed on, right? Did anybody check the condition of the cam bearings?

The truck is a '47, right? But if you have a 235 that has 30 PSI oil pressure at idle, you prolly have a later model engine, from '54-'62. No 235 motor ever had full-flow filters. They have either a bypass system that uses a drop-in cartridge, or no filter at all.

I think Fred T is right, the oil flow in a '54-62 235 is from the pump to the mains. At the rear main it splits the oil to the rear cam bearing and the #6 rod bearing. I'd also have to double-check this.

Does the engine knock all the time, or only under certian conditions?

Bad rod bearings usually knock most of the time the engine is running.

Bad mains can cause low oil pressure. They will knock at idle or low speeds, or when the clutch is pressed in.

Bad cam bearings cause low oil pressure and some valvetrain noise. I have seen bad cam bearings drop an engine's oil pressure, which then makes a marginal crank bearing go to knocking. Improperly installed new cam bearings will also cause similar problems.

Bad oil pump relief spring can cause erratic or low oil pressure, but it isn't very common.

Plugged oil pump pickup can also cause erratic oil pressure.

Let us know what you find.
Good luck,
Chip