small block HELP...keep spinning the same bearing

[vector1]

possibly your engine builder missed something. i would just pull the one rod and have it checked along with the rod throw diameter. be my guess since it is the same rod your clearance would be a little tight. make sure when you take it apart that the bearing chamfer is toward the outside, although i don't think it could be otherwise. rod bearing crush could be minimal also, too large on the big end to hold the bearing in place.

[blykins]

So the rod journal on the crank was unharmed, as was the other rod on the same journal?

[vector1]

.002 on mains and rods is pretty tight from what i've read.

[JohnM]

I will try to get some photos tonight

what does everyone think of those clearances??

John

[CobraEd]

If it had tight clearences but started knocking right away, I would say that journal had no oil. A tight journal will not knock. Musta been starved for oil. I would absolutely check the hole drilled between the main and the rod to ensure that it is clear all the way thru!!!!!


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[sdfletch]

vector1,

I believe he said the bearing spun out without damaging the journal. How could that happen @ 002? No blueing either.

f

[sdfletch]

CobraEd,

We will see. That builder is not happy.

f

[JohnM]

CobraEd

not sure until the head is pulled...but I think the knocking was maybe the piston just tapping the head after the bearing moved??

thats what happened last time

with the crank being brand new and all its "surface hardness" being fresh...and the engine ran for no more than 45 minutes. I think thats what saved the crank

the old crank was all chewed up...but it had been ground and I think most of the hardness ground out of it...if that makes sense


John

[sdfletch]

The only thing I can think of is that the rod id is elliptical. That would have been checked by the builder as well as twist, etc.

f

[Gaz64]

Did the engine builder wash the new crank and check for fluid flow through all of the oilways? As others have mentioned, either rubbish in the channel between your failed bigend and the adjacent main that feeds it, or insufficient crush on the bearing.

Did he measure bearing crush? I've dealt with an engine reconditioner that doesn't understand that term.

1 thou per inch of pin diameter is acceptable for bearing clearance.

[JohnM]

Hello All

Latest update.....I am not sure if this is blowing smoke or for real, but the current therory is a bad crank...its a new crank from SCAT, just a cast model

We originaly wanted a Eagle but couldn't get it in time so went with the SCAT

Anybody know anything about their quality etc on the cast models.

It didn't seem to be an oil supply problem...no discoloration from heat, no turning blue etc....

The builder is eating the crank...maybe it can be warrantied....45-60 minutes on the engine I picked up for the new connecting rods...he's doing all the labor, bearings, gaskets cleaning etc. etc.

I feel he is doing right by me

Any thoughts on the crank...I still think it was the connecting rods

John

[CobraEd]

OK, . . . . But what about the crank is wrong?

Journal too big?
Journal too small?
Journal not square side to side?
Journal out of round?
Journal stroke longer than the rest?
Oil passage too small?


It is fine to say it is the crank, but you should know WHY it is the crank, or you are shooting in the dark.


Ed

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[vector1]

so now it is a bad crank. what was it when he did the assembly?

[Jac Mac]

The only thing common to this problem is the block- you have changed crank-pistons-rods etc ,but all still in the same block and the same bearing ( # 3 if I read your posts correctly ) which feeds from the center main bearing. Now you mention that prior to the bearing problem occuring that the car was involved in a minor accident--- could this have hit the crank on the snout & damaged/cracked the center main web to create an internal oil leak and reduce supply to that bearing, remember this is the thrust bearing, any hits etc are felt here---- or is there a end float or spigot brg problem that is causing similar issues. The center ( or Any ) cam bearing can also cause a localised loss of pressure at each main journal if it has delaminated and lost some bearing metal.

[blykins]

From my experiences, Scat is better quality than Eagle. I'd rather have a Scat crank.

[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