The Stovebolt Site Forums The Shop Area Engine Shop Bottom end knock - rod bearings - removed 1 & 6.

Hi guys, Ive done a few searches "bottom end bearings" "engine ID".

But it may be that my English English is getting in the way of the search engines American English ;-).

My 1952 3100 has a mid rev range, part load, worse when warm, knock.

I have used the FAQ procedure to redo the tappets twice now and at idle the engine is almost silent. So I think that perhaps I need new Big End bearings/shells (that is those white metal bearings that go between the bottom of the conrod and the crankshaft.

I was told when I bought the truck from San Fran that the engine was a "later 235"

SO I have a couple of questions, having never replaced the bottom end shells on an engine before.

How do I make sure I get the right shells? I assume this means ID-ing the engine. Can anyone here help with that?
I can get the serial numbers from the engine or post pictures if that helps?

Where to source shells from? I have used LMC truck in the US and a company over here (UK) before for parts, but nothing engine related.

Looking through the LMC catalogue I can see the appropriate items ie rod bearing.
However they appear hellishly expensive and therefore I wouldnt want to get the wrong ones!

Thanks for any help

I have now looked through the FAQ again, and my engine does seem to fit the criteria for being a later 235. ie 4 screws holding the cam cover on, shorter side cover which doesnt go up to the spark plugs.

numbers I have off the engine.

B48 348 850
0225 I4I F54M <- stamped in just next to dizzy
G836 848 GM26
A154

many thanks in advance.

If you have connecting rods with replaceable bearings, (1953-62 235 and 261 engines) the first thing you will need to do is measure the crankshaft to see if it's been reground to an undersize to correct wear at some time in the past. The standard size rod journal is 2.3115-2.3125 inches. Undersize bearings are readily available in -.010", -.020", and -.030" sizes, with the occasional .001", and .002" undersizes available to compensate for minor wear without regrinding a slightly worn standard-size crankshaft. The crankshaft journal MUST be smooth and round, regardless of the undersize, before fitting new bearings. If the crankshaft rod or main journals are egg-shaped or scored, the crank must be reground to a smaller undersize, or the bearings will wear out rapidly. That involves a complete engine teardown and overhaul. There are usually plenty of bearings available on Ebay at reasonable prices, so once you determine what size replacement bearings you need, don't get robbed by one of the "antique" parts vendors. 235 rod bearing sizes didn't change from 1953 to 1962, with millions of replacements made, so they definitely are not scarce items!
Jerry

Jerry, Thanks for that post its exactly what I needed.

I'll let you all know how I get on

Neil..please accept our apologies for the search engine feature we have here. It is very difficult to manuever and everyone remarks about it so don't feel bad for not finding the info there but am very happy to see that you've gotten what you need from our contributors. Good luck with your engine rebuild, it is not as bad as it is intimidating for those who haven't done it before.

Come back often and please keep us posted on your progress and oh yes, pictures please.

Here's an example of an ebay listing:

http://cgi.ebay.com/ebaymotors/54-5...arts_Accessories&hash=item3f0009e38c

If the undersize is incorrect, the vendor can usually supply the correct part- - - -just email or contact them through the ebay system. They use these auctions aqs a method of advertising their businesses.
Jerry

come back, are you kidding? this site is invaluable!

its on my top 10 thats for sure, you guys are like the old chinese guy in all the kung fu films, except not living in the mountains, and not old or Chinese....err anyhoo.

I'll post some pictures as I go.

So the story so far.

My engine appears to be a 2nd gen 235 (4 bolts on cam cover, smaller pushrod cover plate.

The "knock" disappears when removing the lead from Piston 6 near the cab

The next step then is to drain the oil, remove the pan and remove the rod cap to view the bearing shells, this will tell me if the bearings are worn and whether they are STD or undersize.

I have ordered some plastiguage from the ebay, will order the shells from the ebay US (nowt on UK ebay) and get some more SAE30 oil and oil pan gasket

A couple more questions if I can, before emabarking on this journey. What torque should the rod bolts/nuts be tightened to? I read mention of 40lb/ft but that seems to be mainly 1st gen 235s are the second gen the same?

google isnt helping with this one.

TIA

I think I posted a link to some pics, if not here they are:

http://i397.photobucket.com/albums/pp51/unity_n/trokita/004.jpg
http://i397.photobucket.com/albums/pp51/unity_n/trokita/003.jpg
http://i397.photobucket.com/albums/pp51/unity_n/trokita/002.jpg

I'll post pics of the process as we go.

Thanks for the help so far

piston 1 bearings:
http://i397.photobucket.com/albums/pp51/unity_n/trokita/bearings012.jpg
piston 6 bearings:
http://i397.photobucket.com/albums/pp51/unity_n/trokita/bearings008.jpg

Any thoughts?

the bearings have the following numbers on:
P6 - gmma 8587 350 t3
p1 - gmma 8587 9 N 4

I was hoping that these would tell me if the bearings were STD or undersize, anyone have any more info?

Many Thanks

Neil

Ouch! That second pic looks pretty nasty! What does the surface of the crankshaft look like? If there are score marks deep enough to catch with a fingernail, putting new bearings in will be a very temporary fix at best. I have had some success with polishing crankshaft journals with a long piece of fine-grit emery cloth, using a "shoeshine" motion, but be aware you're also going to be removing a small layer of metal and increasing the oil clearance a bit with the polishing operation. Those part numbers look like original-equipment bearing nunbers, which would suggest you're dealing with a standard-diameter crankshaft, but the only way to know for sure is to measure the crankshaft with a micrometer. Measure the diameter in several places, looking for out-of-round conditions, or taper from side to side. Out of round or taper should be less than one thousandth of an inch (.04 MM). Plastigauge is great for cheching oil clearance on a smooth crankshaft with good bearings, but it's not a substitute for accurate measurements. The area most likely to experience wear on the crankshaft rod journal is the upper side of the journal, facing the top of the block with the crank turned to the lowest point of piston travel.

Connecting rod torque specifications are 35-45 ft/lb, and main bearing torque is 100-110 ft/lb. I would reccomend checking all the bearings for clearance and bearing condition, rods and mains, as long as you've got the oil pan removed. Unless I'm badly mistaken, you're probably going to need to remove the crankshaft and get it reground undersize to restore the proper surface finish and oil clearance.
Jerry

Use this site to determine what year your 235 is.

http://clubs.hemmings.com/clubsites/chevytalk/GMhistory/1916-57cast.html

Good luck and keep us posted!

Hey Jerry,
Thanks for all the info. Yeah the crankshaft journal, its not pretty:
http://i397.photobucket.com/albums/pp51/unity_n/trokita/bearings011.jpg
God only knows what the hell happened to the engine, there was a lot of gritty sludge in the Oil Pan when I removed it.

from the other post above it looks like a 1956 235, probably from a car. So I now need to think about the way forward.

1.chuck some beaings in for 50 bucks and see how we go as I dont do mamany miles per year, maybe 2000?
2.Rip out the motor and have the crank reground/new crank if needed
3. rip out the motor and fit a small block/th350 combo
4. rip out the motor and fit something else Lexus V8/Volvo 5 cyl turbo/BMW Turbo Diesel

The plan was to Mustang II the front and 4 link the rear on Bags anyway so it was never going to be all original.

I would take choices 2 or 3.

Very slick truck Neil! My vote is for option #2 (most likely a regrind will do the trick). I've never had to opportunity to drive on "the wrong side of the road". How does it feel to drive on the "wrong side of the cab"?

Great looking truck. I would def go with option #2.

That big score mark in line with the oil passage tells the tale. A pretty large piece of debris from somewhere else in the engine found its way to the rod bearing, and created a divot that spun around between the crank and the bearing. This created more debris that continued to damage the bearing and the crankshaft. That's too nice a truck to butcher up with a hotrod job- - - - - -either find a serviceable 6-cylinder to drop in temporarily while you do a buildup on the current engine, or see if you can find a 261 engine somewhere for a modest upgrade while staying with a fairly original appearance. I hate to see good-condition original-appearing trucks hacked up with a V-8 IFS "improvement"!
Jerry

OK, in my ever-lasting quest to gleen every last bit of everyone else's experience, I pose the following question:

So what was the knock?! I get that the journal is scored badly, along with the bearing. But the actual knocking sound - is that the con rod slapping back and forth (up and down, I guess) on the crankshaft? Or is it the bearing sliding around? AND, if it's either one of those, I'm guessing you could actually recreate the knock by just shaking the rod by hand on the shaft while it's still torqued down?

Finally, for it to be this loose, would this engine reflect poor oil pressure? Or does that require more than one bad bearing situation?

Ahhh, the quest for stovebolt wisdom . . .

-Michael

The knock is caused by the piston/rod assembly getting a running start due to excessive clearance, and hammering into the crankshaft journal. The rod bearing is supposed to "float" on a thin film of oil, with no metal-to-metal contact, but when the clearance gets over about .003" or so it's impossible to maintain that cushion of oil. Once the hammering starts, the damage is progressive, causing more clearance, a harder knock, more metal particles dislodged, more scoring, more clearance, harder knock - - - - - -you get the picture. The increased clearance causes most of the oil pump output to go to the wide gap, dropping the pressure to the other bearings. The whole situation can be caused by a single grain of sand, or one flake of metal that begins the bearing-scoring process.

Engine assembly should be done in a surgically-clean environment, to prevent building in enough dirt to cause immediate, catastrophic bearing failures. Some NASCAR shops actually use "clean rooms" for engine assembly, with builders in special lint-free suits and booties, and a positive pressure environment with air lock entry, to assure clean assembly of their engines!
While it might not be necessary to build a street engine that way, I get pretty anal about starting with very clean parts, and keeping my engine assembly area in a very clean part of the shop.
Jerry

I have another 235 engine in the garden, out of my old 62 BelAir the bearings look the same, Would this crank fit the truck? ie be interchangeable with the 56 235 in there as there doesnt seem to be anywhere near as much scoring in that one.

Yes, as long as the correct size bearings are used, any of the 54-62 crankshafts should interchange with no problems.
Jerry

thanks Jerry thats good news

Also in reply to your question about the oil pressure. It may or may not drop as this happened. If the debris in the crank was thick enough it would cause a false higher pressure reading than it should. The bearing would go dry, while the oil is going somewhere else.

I have seen cranks get ruined because the owner never saw the oil pressure drop until the engine either locked up or tossed the rod.

My oil pressure was pegged at 30PSI (guage max) throughout. no drop in oil pressure for me, that said the oil pickup is on the inlet to the oil filter, dont know if that makes a difference?

Could someone let me know how heavy the stovebolt is? I guess I need to remove the engine to remove the crank (it being attached to the flywheel at one end!) and so will need to buy a stand to work on it

kg or lbs is fine, Thanks

I don't remember the exact weight, but they are HEAVY! The big concern, besides weight, is the length of the engine and the leverage it puts on the stand. I modified the 4-wheel stand I use on the stovebolt engines with an extension about a foot long, with an extra caster wheel. That prevents any kind of tip-over if things get a little off-balance. Definitely get a stand that extends past the end of the crankshaft snout to prevent any possibility of overbalancing the assembly, and the heavier the weight rating, the better!
Jerry

IIRC, they're somewhere around 650 pounds.

When I built up my most recent 261 a couple of years ago, I weighed all of the parts as it went together. The total weight, with bellhousing, flywheel, clutch, and transmission was 687 pounds. Here is a summary table. The flywheel and pressure plate are aluminum; the transmission is an iron 1958 passenger 3-speed.

As Jerry says, you need a good engine stand, with enough wheelbase and track to keep the center of gravity well within the wheel footprint. I started with a three-wheel stand that was fine for a small-block V-8 and nearly had a tip-over when I tried to rotate just the short block of the 261. I bought the best four-wheel stand that Cummins Tool sells, which I believe is similar to Harbor Freight's version.

Hoyt

Wow, that is quite the detailed table. Thanks for sharing that data!