The Stovebolt Site Forums The Shop Area Engine Shop Knock on #1 cylinder

I've got a knock coming from #1. It goes away if I pull #1 wire off. I'm not on the road yet so this is just running it in the driveway. Pressing my fingers to the underside of the pan quiets it down but I can still hear it and feel it too. I'm thinking my next step is to pull the pan to get a better view. Not sure if I can see up to the underside of the piston to see any cracks. If I don't see anything obvious then I'm going to pop #1 journal and see if that shows anything. Any suggestions?

Dennis

Sounds like the rod may be hitting the dipper trough. All you can do is drop the pan & see what you have. I take it this is a 216 in your 1940. If it is the rod brg., some of the rods on those can be removed without pulling the head. #1 is one of them.

Ooops sorry Wrenchbender, I forgot to say this is a 1960 235.

It sounds like you've got a cracked piston skirt or a loose wrist pin. Since 235 rods are clamped to the wrist pin with a bolt, a worn wrist pin bushing isn't a possibility, but a loose clamp bolt is.

Another problem can happen if the wrist pin clamp bolt was torqued without supporting the pin- - - -that can twist the rod and cause an obbball-sounding knock as the piston twists back and forth as it travels from top to bottom of the cylinder. I always clamp a big tapered punch in a vise and slip the wrist pin over it before tightening the clamp bolt. Some people hold the big end of the rod in a vise, and put a lot of twisting force on a very flimsy rod. No Bueno!
Jerry

I know everyone will say that the combustion is causing the additional stress, BUT anyway: If it does not do it when plug pulled and it's still going up and down, it should be still making noise with some of those reasons given above. Just the change in direction should make it slap. So why don't you tighten up the exhaust manifold and check it for leaks and cracks (near no. 1) just to have something to do in your spare time...and use a broom handle or a real stethoscope to listen.
ALSO, Jerry can give you a test done thru the plug hole to test to see if anything moves just for fun. (rod knock test)

I've been making knocks go away or at least have a major reduction in noise for over 50 years by shorting out spark plugs. Cracked pistons and loose wrist pin bushings are the most common knocks that change when a plug quits firing, but even a rod knock will reduce a bunch with no combustion load applied.
Jerry

OK, I dropped the pan for inspection. First checked that the bearing cap and wrist pin nuts were tight. Check. Couldn't see any evidence of damaged skirt. Took off the rod cap and checked the bearings. Worn some, of course but didn't look bad to me. No copper showing. Same upper and lower. Anything else I can check from underneath?

Dennis

Well if you can't get any movement or noise just study other cylinders and see if you see any small difference in looks, position of parts, color, wear pattern, chips, rubs, heat burnish, with super powerful light, bla bla bla...take some pics for yourself.
Would it make sense to rotate motor and crawl back under a few times to get different stroke positions?

Yeah, I'm going to crawl under again with a more powerful light and inspection mirror. The piston was at the bottom of the stroke. I pushed it all the way up after taking the cap off to get a slightly different view. This is a good use for the yoga mat. This is the only kind of yoga I do.

Dennis

Turn the crankshaft journal to the side as far as possible, and pull the piston down as low in the cylinder as it will go. It's not likely to be able to move far enough to expose the piston rings, but you might be able to see enough of the piston skirt to check for cracks where the Invar anti-expansion strut surrounds the wrist pin. Use one of the high-intensity LED flashlights that are available at most parts stores. That's the most likely place to find a crack. Just be careful not to nick the surface of the crank journal with the side of the connecting rod.
Jerry

Invar anti-expansion strut? Say what? You mean the Flux Capacitor Generator? Jerry, those are only on DeLoreans. Get with the program.

The ones that really ate pistons were the 1955 and 56 265 V8's- - - - -same problem, not enough aluminum surrounding the strut that made the egg-shaped cam ground piston get round when it got hot. the average was 2 or sometimes three cracked pistons per engine. 235's weren't as bad, but the same companies contracted with GM to make 235 pistons as the V8's.
Jerry

I did as you suggested HR. What I could see looked fine. I'm going to look again in the morning. Maybe most of the drips of oil will be gone by then. Let me ask you this. If multiple cracked pistons were fairly common then sounds like I could drive this for a while. No?

Dennis

It's just fine, until it's not. If a piston skirt comes all the way off, the piston turns sideways and pokes the end of the connecting rod and the wrist pin through a cylinder wall.

Do you play poker? I'd like to get you into a high-stakes game and wait for you to draw to an inside straight if you're willing to bet you won't have a catastrophic failure with an audible knock.
Jerry

Until it's not. Ha! Just thought I'd put it out there. If I were to do a rebuild I might rather do a 261 block and put my stuff on it. Suppose I could pull the head and replace just the one piston and get it back on the road and plan for a more thorough build over the winter. Can't wait 'till tomorrow to get another eye full of oil.

Dennis

I took a couple of photos this morning. Looks like a crack on the piston surrounding the forward part of the wrist pin. I don't know how to get more than one click of magnification with PhotoBucket but hopefully it is good enough. I don't see anything on any of the other pistons.

Pic1
Pic2
Pic3

Dennis

Getting past all the popup ads on Photo-BS is frustrating. It doesn't look like you're able to get enough detail in the pictures to be of much help, but there's a work-around on the zoom. Hold the "control" button down on your keyboard and repeatedly push the (+) button on the top row of keys. Shrink it by hitting(-).
Jerry

I know, PhotoBucket has really gone down the toilet. Did you notice their advertisement to go ad free for $14.99/yr? That's rich.

I'm going to pull the head in the morning. I've got it ready. Should be fun.

Dennis

$14.99/year for a subscriber?
I am not a subscriber.

I would still see the ads/videos that block my screen and screw up my computer when I view your photos. I'll just continue to close the screen/page with your photos before it locks up my computer.

GO AD FREE for $1.49 ($14.99/year)
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I do not know the answer to this problem. I have Google Drive for photo hosting and it has no advertising.

I use Hunt101.com as a photo host. Unlimited bandwidth, and it's free!
Jerry

How about the idea of relaxing the "no pics directly posted in a thread" policy? How many out there are still using coal-fired computers which load too slow?

Got my vote.

Dennis

Carl & Dennis,

Some members, especially in Canada, supposedly pay for "bandwidth" usage (data flow), and some users are on slow connections. These users pay extra in $ and/or have very slow load-time when photos display in a thread.

There is also the matter of the cost of storage (on Stovebolt.com server). This can be substantial. Who will pay for that?

Finally, if the discussion board software cannot automatically resize photos, none of us want to see our screens screwed up displaying gigantic photos (trust me).

Nonethesless, I agree with you completely.

With a good pic host, it's simply a matter of a couple of mouse clicks to post a link. Saving a bunch of members a bunch of money and time by doing something that easy doesn't seem to be much of a chore. For instance:

http://www.hunt101.com/data/500/passin_thru.jpg

Jerry

I guess people could post/host on that Hunting Picture gallery, maybe in the Hunting Women section?

Works for me- - - - -some of them can share my hunting camp anytime!
Jerry

I have the piston out and I think I see a hairline crack inside bottom where the piston pin goes through. I'd feel better if it was more obvious to me. Is there a cheap way to verify it is a crack I'm seeing?

Dennis

Remove the wrist pin (remember the precaution about not twisting the rod) and clamp the piston in vise with a snug, but not overly tight grip. Use a thick piece of cardboard or some soft vise jaws to avoid scarring the piston. If it's an actual crack, it should open up as the piston skirt flexes a little.

Good luck!
Jerry

I didn't take the wrist pin out but instead took the assembly to an engine rebuild shop. They've been in business for years, 2nd generation, and seemed knowledgeable. He showed me where they usually crack and what I saw was somewhere else and was apparently a parting line from casting. He did say that sometimes the crank end-play or dampener can give the same sounding symptom and removing a plug wire can change the harmonics and sometimes make it go away. I just checked end-play and have .007 so no issues there. My next check is to take the radiator/condenser out and make sure the dampener is on tight. The dampener has been refurbished since I've started this project.

Dennis

The dampener is on tight and no movement when I grab with both hands and try to move it in/out. Any other suggestions as to what the issue might be?

Dennis

Have you checked the connecting rod for bend or twist? The machine shop that's advising you sounds like they might understand how flimsy stovebolt rods are. It's very easy to bend one while installing pistons, and a bent rod can cause all sorts or oddball wear patterns and noises.
Jerry

Did not specifically talk about the rod but he was all over it with back-lit magnifying glass. There are no unusual wear marks on the cylinder or piston though. Is a bent rod something I could check for myself? Everything looks really good except signs of debris through the bearings. I have not pulled any crank caps to check there but I don't think the crank gives this symptom.

Dennis

It requires a special fixture that clamps the rod into it and compares the alignment from end to end, both for bend and twist. It used to be a standard check when rods were reconditioned as part of any good engine overhaul, but newer engines have gone to short, very rigid rods and most "machinists" have never heard of the procedure. Even the guy who does my crankshaft grinding had never heard of straightening rods when I brought up the subject recently.
Jerry

OK. Since there are no oddball wear patterns, can I assume there is no appreciable twist to the rod?

Maybe I should plastigage the rod bearings. How much clearance is enough to give a rod knock sound? I don't think they are all that bad though.

Dennis

Anything close to .003" will start to knock. Since you've got the pan off already, it's good insurance to install a new set of rod bearings. Polish the crank journals with fine-grit emery cloth using a shoeshine motion, clean it up thoroughly with spray solvent like brake or carb cleaner, and plastigauge the new bearings as you install them. A set of rod bearings the correct size is cheap insurance, compared to ruining a crankshaft or putting a hole through the side of the block.

I'm sure you know the old saying about "assume"- - - - - -check it and be sure! Why cut corners now when you've already done the grunt work of taking everything apart?
Jerry

Yes, I've heard that saying and resemble that remark. Wish I had a 261 short block ready to go though.

Dennis

There are several sets of 235 rod bearings on Ebay, some for under $50.00. That sounds like a cheap insurance policy to me.
Jerry

I'll take a look HR. By the way, it Plasti-gaged between .0015 and .002.

Dennis

That clearance sounds good. If the bearing isn't scored too badly it can probably be re-used. How is the clearance between the wrist pin and the piston? That's hard to measure, but if there's any noticeable slop or wobble, that's too much. Normal wrist pin to piston clearance is down around .0005" or less. Before the days of throwaway engines, we would hone the pin bores out and install slightly oversized wrist pins to get the clearances right.
Jerry

Still haven't found anything to explain the problem. After reviewing this thread I see bartamos mentioned exhaust leak. I do see signs of it leaking around #1 and some around #5. Would this cause a rod knock sound?

Dennis