The Stovebolt Site Forums The Shop Area Engine Shop a knock or not? bearings or something else?

hi guys

so my 235 developed a slight knock. a good check over with the stethoscope indicated it was coming from mid bottom of the engine.

knock is always there even on idle getting louder with rpm.

i dropped the pan and had a poke arond.


1st impression was all the rodend caps were tight no excess wear radially was evident when jiggled. i took the oil pump cap off and there is some play in the driven oil pump gear shaft. i can rotate it maybe 5 degrees - could this be a source of knock?

im going to pull off the caps and take a looksee at the bearings. im hoping that the lack of jiggle means if they are worn then i could get away with just inserting new bearings and not pullout the engine/crank regrind
(engine stays in truck) is this a pipe dream? has anyone ever fixed a small knock by just fittibg new bearings in situ?


fingers crossed.

what year engine

56 car engine.

update: i took a look at the bearings and only a tiny amount of copper s showing and crank bearing surfaces dont look too bad.....was begining to think i could save it, then i took a look another main and discovered weird marks on the bearing surface. the surface is smooth but has like a dark brown craze like marking on it. it also has what to me looks like a crack........ either way i think it needs pulling so i wipped out the engine. only took a couole of hours, a job made easier by the fact the PO (who was cleary a twat based on the miriad of other cock ups ive dscovered) hadnt bothered to bolt down them front engine mounts!

As long as all the crankshaft journals measure out round within .001" with a micrometer, and not tapered, you can do a cleanup with a long strip of fine grit (#400 or finer) cloth-backed sandpaper and a shoeshine motion on the journals. Pulling the crankshaft all the way out of the block is almost a complete teardown situation because of the way the front timing plate and crankshaft interact. It requires removing the camshaft and lifters, fuel pump, etc., and then the backing plate for the timing gears. If you choose to polish the crank and fit new bearings with the crank in the block, be sure to clean it thoroughly with spray degreaser to avoid putting any sandpaper residue into the new bearings! Good luck, and remember to use the same size bearing as the engine had during the teardown. An oldtimer can have a reground crankshaft and undersize bearings from a previous overhaul. The bearing undersize, if any, will be stamped on the backside of the bearings, and rod and main journals are sometimes ground to different undersizes. Good luck!
Jerry

Could this be from a loose wrist pin? They are clamped to the rod, but might be loose in the piston? Crazing on the bearing surface could be from heat? It is not something I have seen often so I don't know for sure. Hotrod Lincoln has a good tip for cleaning any small scratches. We used to call the sand paper he is talking about "Crocus"Cloth. It came on a roll and had different grits and widths as I recall.

I've seen a "spider web" pattern on crank journals before. It is a kind of acid etching caused when the oil has gotten very acid and usually with some water in it and sat for a long time. Usually find a deep layer of sludge in the pan.

That is good to know. Thanks!

hi guys got the engine out and crank bearing surfaces look good but therevis this weird what looks like an L shaped crack in the middle of one of the crank bearing surfaces on one main. its in middle of the journal weird place for a stress crack and the L shape is weird for a crack


am i right to assume a small knock could be from mild bearing wear and putting in new bearings (assuming crank isnt too badly scored) will cure?
has anyone got experience of this?
cheers

.

heres some pics of the crack?

http://drmike.smugmug.com/Other/Truck/45775233_BgPQZt


what do youbguys think? just a scratch? it catches my nail so it has depth...

Take the crank out of the block and see if it comes out in two pieces. If not, it still maybe cracked enough to knock. Pictures are hard to see, but looks like the crank does have a crack in it.