Reply With Quotewhat were your clearances?
Just tore the blower motor down.
#1 wiped extreme with material hanging out the sides
#2 no copper showing slight pitting
#3 same as #2
#4 spun
#5 wiped
Could too tight of a belt cause this?
Do you need to set kevlar belts looser, tighter or the same as a standard belt?
It's a 500CI BBC Mark IV running 11 to 12 #'s boost.
what were your clearances?
sounds like too tight of clearances, low oil pressure or loss of oil pressure.
Brian
I have no experience with a blower motor.
Yea what they said. Did you "set" the rear main? end clearance?
Blower belts should all have about 3/4 inch of play in them regardless of material the belt is made out of. That is when the engine is hot. You don't want that belt pulling on the crank. If it's too loose then it can walk over a tooth (1/2" & 8mm) and bend the crank. Always have to keep an eye on the belt tightness between hot and cold.
Check the crank for straightness. Generally too tight a belt works on #2 main bearing.
As to what happened could be a world of things. This is how BBC die...by the mains. And usually spin #4.
Bent or cracked crank.
Line hone was never straight to begin with.
Not enough clearance. At least .003 and I like looser for flexy cranks.
Too much HP for the strength of the crank (crank flex)
Oil intersection holes not completly drilled through (I have seen that).
Any other oil pressure problem. When the oil wedge is lost for whatever reason then contact occurs. When that happens even for a millisecond the crank grabs that bearing and the bearing shrinks around the crank. Game over.
Just to sum it up..you can get away with a lot till the blower goes on.
Brad, what crank was in there?
Sounds like tight clearances. I run 35 clearances on the rods and mains, 40 wt oil and have 5 years on the bearings with over 150 passes. Looser clearances and heavy oil with a blower motor IMO is the way to go.
Check your oil pressure, you may be dropping it when you dont notice. In the BBC we had a loose pick-up cause the oil pressure to swing up and down a couple times. I thought it was the sending unit so we ran it again. Spun all but one bearing right off the trailer. :hammerhea
If it's blown and especially alcohol....I will fight like Hell for .0035 to .004. Been known to run .0045.
It was running fine for two years so I had to "fix" it.
Was running 5-6#'s boost so I put a chiller on it and ran the boost up to 11-12#'s. I knew I was on borrowed time at that point.
I can't remember the clearances when I assembled it last time but I followed the advice of George at Clay Smith. Still could have been some "assembler" error.
Oil pressure was always fine until it went away, rather quickly, one day.
I'm using the scat crank but will be stepping up if there is a problem with it.
If the clearances are too tight how long for the bearings to go away?
RE the 3/4" clearance when hot belt was definitely too tight, had 3/4" to 1" when cold.
Info, what do mean by "set" the rear main clearance? End play was checked.
Rod bearings are fine, a little pitting from some main bearing material.
I'll be taking it to Big Pete for a full analysis and machining.
Hell it's only money!
Oh yeah, It's getting a hat on this go 'round too.
It was running fine for two years so I had to "fix" it.
Was running 5-6#'s boost so I put a chiller on it and ran the boost up to 11-12#'s. I knew I was on borrowed time at that point.
I can't remember the clearances when I assembled it last time but I followed the advice of George at Clay Smith. Still could have been some "assembler" error.
Oil pressure was always fine until it went away, rather quickly, one day.
I'm using the scat crank but will be stepping up if there is a problem with it.
If the clearances are too tight how long for the bearings to go away?
RE the 3/4" clearance when hot belt was definitely too tight, had 3/4" to 1" when cold.
Info, what do mean by "set" the rear main clearance? End play was checked.
Rod bearings are fine, a little pitting from some main bearing material.
I'll be taking it to Big Pete for a full analysis and machining.
Hell it's only money!
Oh yeah, It's getting a hat on this go 'round too.
Brad, My engine builder says that the scat cranks are china forged and need more machining before you put them in an engine. He had me buy a new dragon slayer Callies crank for when I step up to a procharger or TT's. I had a simular experiance with my eagle crank. It was'nt bent. Just needed more machine work done to it. He says that a factory GM crank is stronger than all of the china forged cranks. Especially on blower, crank pulley applications. I'd step up to a better crank. Good Luck.
Posting Permissions