small block HELP...keep spinning the same bearing

[JohnM]

Fresh update.....The crank has about a 30 thousandth deep mark/gouge on one side of the journal. When we took the cap off to look at that bearing, while engine was still in the car the crank was smooth on that side we could see. Once the engine was tore down and the crank out, the opposite side had the gouge. I am not sure why just on one side, as the crank spins the loose bearing should have been rubbing all the way around?

I was told the the new crank prior to install miked up great etc...oil holes were nicely opened up etc. The crank will now be closely isnpected which might turn up something

again the engine ran for only 45 minutes or so till the knock started

The piston did not hit the head...like on the first problem that started this whloe off. That probelm was running for a while

The accident was a front end collision...but almost all fiberglass and fiberglass shock damage...the only metal that got hit was one of the bumper out riggers got bent. I hopefully attached a photo

During this most recent rebuild....no new connecting rods were installed...all were supposedly checked reconditioned etc etc.

I am installing new rods now as I think that is the problem, probably one bad rod...

no new cam bearings were installed...prior rebuild...but are now being installed, on the engine builder

I gotta believe since the builder is eating all of this new rebuild...and new crank, etc etc. he either cut a corner, forgot to do something...or was a little lax ?? on the old connecting rods....what can I say

This will proabably be the most detailed rebuild ever!

I will try to photograph the crank this weekend

John

[Jac Mac]

Another unlikely one, but anythings possible in todays world, Had that rod been resized to 351c(2.436")tunnel size & fitted with 351w (2.427" tunnel)bearing insert?

[Keithc8]

I have seen this happen on new engines on start up a few times. Did you prime the engine real well before starting? I like to prime the engine and turn it in about 4 different spots to get the oil through all of the passages real well. A lot of times if the engine was hard to start it will wipe the oil of the bearing and cause the bearing to grap the crankshaft and hurt it on start up. The bearing then gets oil and it runs for a little while and you notice it more when the oil gets hot and thins out.
The number 3 and 7 rods are the last one to get oil because they share the number 4 mains journal and they are the last pair that share a journal and split the oil to that journal. The number 5 main just feeds one rod and can get 3/4 the oil that number 4 mains gets and the rods gets more oil because it is not sharing it.
I feel that this happened on start up and maybe this rod journal was bigger or out of round but that should have been caught when put in. These are some of the resons we like to dyno test the engines before they leave because this way we can make sure they are broke in right and that we did our job right. Even with all of this we still have a problem every now and then.
Make sure that the oil galleys in the block are not blocked anywhere. You are reading the oil pressure right out of the pump before the oil really gets to any of the bearings or anything. There could be a restriction and you would not know it by the oil pressure gauge. Building engines can be a ***** for sure. Good luck, Keith Craft

[Jac Mac]

#1 Rod only feeds from #1Main, #2&5 Rods feed from #2Main @ 90°/270° , #3&6 Rods feed from #3Main @ 180° , #4&7 Rods Feed from #4Main @ 90°/270° , #8 Rod only feeds from #5Main.
Amount & duration of feed changes with options of: top main inserts only with groove, full grooved mains , cross drilling etc.

So assuming our man has cyl # correct his problem bearing is being fed from center main.

[Keithc8]

Jac Mac you are correct about the oiling and the rods. My mistake on that and I must have had a brain fart. The number 7 is the most common to have the problem and then the heat transfers to the number 3 but he had not heat.
Does sound like a dry oil start up problem or something possibly blocking one of the oil galleys. I have gotten a bad bearing and caused this before and could find no reason why it did it.
With the middle three mains feeding two rods each that is normally where you will see a rod bearing problem. Good luck, Keith

[JohnM]

Thanks Keith and Jac Mac,

I was told that the oil pump was spun up prior to me installing the motor. The engine builder came for the start up and break in. The engine builder was there the next day to pull the pan and poped the cap of the crank...was the first to see the bearing.

Probably just human error somewher along the line...or something we will never know.... bad baering etc..just one of thos things

Like I said in a earlier post it was probably be the most looked over rebuild...so lets see what happens

I should have it back one day next week and will keep you all informed

thanks for all your inputs

John

[sdfletch]

John,

I wonder if that block was magnafluxed. Pressure tested? Hot tanked? Never did see that in the posts. Oil galley problem?

f

[Jac Mac]

John, As Keith has mentioned sometimes things happen, for the most minor of reasons, that this has on the same bearing/rod on more than one occasion is a concern & I am sure neither you or the builder want a repeat performance.

Rather than rushing to get it back together, allow him some time to 'look' for what might be the cause.

A couple of ideas you might like to incorporate prior to & during assy.

1. Fit the crank/cam/lifters/oilpump/ and fit the pan without gasket. Now fill the pan with 20 or 30 weight oil, fit filter & prime oil pressure while turning crank slowly-observe thru the cyls that oil is flowing from All eight rod journal feeds and in similar amounts.
This serves three purposes-that you have no blockages & as a final flush of the oil galleries in the motor, & that you have not left any internal gallery plugs out.

2.Once the pistons/rods are fitted & torqued, ensure that each rod has side clearance on each journal and that both rods can be moved freely by hand to check this on any journal, while doing this check that the small end of the rod has side clearance between itself & pin boss of piston. By doing these checks you eliminate any bind or preload that could cause scuffing & failure of the bearings.

3.Like Keith I always start & test run on a test stand with radiator or cooling tower. It eliminates that 'quick run around the block' factor and makes retorque & valve spring replacement after cam break-in a lot easier.

cheers & good luck.

[Don]

Engine Crankshaft Bearings:

http://www.aa1car.com/library/ar797.htm

Club Hot Road posting:

http://www.clubhotrod.com/forums/showthread.php?t=38738

[JohnM]

Thanks everyone for the help and info and links.

During the first "build" 7 years ago everything was done. I had 3800 miles of easy driving...but never liked my oil pressure...then the accident, 5 months out of sight in a body shop....who knows

Then the spun connecting rod. During this second rebuild a few weeks back a new crank & bearings....conecting rods checked, sized, shaved etc etc. maybe a few corners cut? thinking it was basicly a fresh motor, throw in a new crank out of the box and new bearings and away we go

Now rebuild #3 after the same connecting rod spun...The builder is doing it all on his dime....I did buy new connecting rods...and I should of done that for the second rebuild.

I think this rebuild will be possibly the best ever!!

If all works out after this...and I think it will....I will still HIGHLY reccomend this engine builder.

If anyone is in the Cleveland area or wants to bring a motor this an this way...pm me direct and I will fill you in.

John

[c6ae]

I have seen rod bearings pounded out from a mix-up of spark plug wires. It is possible to have one cyl running advanced and another running retarded. It may not be noticed by an amateur as the engine could still run fairly well… meaning it won’t backfire etc.
The advanced cyl will hammer out the bearing; the retarded cyl may seize the piston…
On the 351 this seems unlikely but it could be a 1-3 mix-up.

[CHANMADD]

I would be almost certain that the problem is the rod. Once you run a bearing in a rod ,and more so if you spin the bearings, the rod big end is not going to be "round".
Even if you now machine that Big end again and make it round ,the first time you really spank that motor the rod is going to let go. Replace the rods.and spend the extra and get "H" beams from Eagle, they are reasonable in price and the quality is ,to my mind ,great! A clearance of 0.002" is exactly what I use when building motors, and it has always seemed to work for me.
New crank and rods and no more worries!!!!
Oh and you might as well put the longest rod in there that you can,so that you you get the most favorable Rod/Stroke ratio.....close to 1.6 or above.Might require new pistons ,but if you are building a ""Strong"" motor you might as well spend the little extra..100's not 1000' to get reliability!!!
John

[Jac Mac]

Chanmad--- John already has a rod ratio of 1.70/1 with his 351w's 5.956" rod /3.5" stroke.

[CHANMADD]

Wow ...That's awesome!! So high RPM should not be problem with the right rod.
John

[vector1]

Originally Posted by Jac Mac

Chanmad--- John already has a rod ratio of 1.70/1 with his 351w's 5.956" rod /3.5" stroke.

that is one heavy piston.

[CHANMADD]

Who mentioned the piston? Why is it so heavy?

[CHANMADD]

I know it's not a GoKart piston but they will still do 9000rpm!

[Jac Mac]

Dont know where the piston weight comment came from???

FWIW- Budget long rod 351w-- 351w crank (1.75"/1/2 stroke) + 400c/351m rod (6.58"c/c) + piston from 3.25" stroker 302w (1.165" comp height ) for total of 9.495".

Takes some work ( BE needs narrowed to 351w journal width & SE requires pin bush from 272 Y/Block )- + be real careful with valve to Piston clearance due to increased dwell @TDC. Rod ratio is then 1.88/1

[CHANMADD]

I like to Rev my motor...always have. My first car was in S.A. a 1960 Ford Anglia with little Kent 4 cyl pushrod engines and I used to rev that at 8500 all day long. My small block 400 now revs easily to 8000 all day long.
John

[JAM1775]

I had my 351W rebuilt after a bad problem from a BG carb. The shop swapped in a polished balanced crank from their shelf which saved time. Two bearings failed within 700 miles. Rebuilt again...by another shop . On a chassis dyno after break in the motor started knocking ...same two bearings burned. Only this time there was a warranty. The crank from the first shop was "rockwell tested" for strength . It was discovered the journals servicing the same two main bearings that kept wearing were soft. The shop rebuilt my motor....again.....and all I paid was splitting the cost of another shop supplied crank. The motor has been running excellent for 21K/ 6 years now.