Another lesson in how NOT to build a BBB

check your cam lobes to see if they are ok. was the line bore checked? bearing clearances? possibly all of that metal that was floating around after the windage tray incident got to the bearings and they slowly wore out. could be many things. as far as a "pre broken-in" cam, nascar teams have a mock up block with an electric motor that spins the cam and lifters seperatly to break in, pretty slick.

 

Thrust bearing face appears the same on each side; not much happening there. I'd have the shop check the crank for true. Is it, in fact, straight?

 

Jim, It was never on a dyno so I can only guess at the power. This motor is a copy of Jerry S's stg2 pump gas motor from three years ago with some minor differences. Greg ported the heads 335/247. No girdle but went with a light balanced rotating assembly. Lightened pistons and aluminum rods with a recip weight of 877 grams and a bob weight of 1777 grams according to the balance sheet. The crank was offset ground .100" and with the over bore it's a 475 cu in. Also I remember the cam on Jerry's motor was a little off the 308s specs. Scott from Straightline did my cam and it's dead on spec. Outside of that, I tried to match what you did.

Paul, The block was align bored. Also, after the windage tray incident, I checked all the bearings and they were fine. I remember seeing a few flakes in the shells and I did remove them.

Thanks for the replies and Happy New Year :beer

 

Keep us posted, I for one am very interested to hear what you find as a cause for this failure.

 

make sure you spin it around with the new tray in place and make sure the rod bolts dont rub/hit ,if so tweak it,just a thought
ken

 

Andy,

Ya, lot of things are moving down in the bottom end at that power level (over 600 hp) and it doesn't take much to wipe a bearing, and once they touch and it lifts the first layer off, then it's just a matter of time till you see what you have there. All it has to do is partially restrict the oil passage in the bearing, and that will happen, even if the evidence of that is gone now.

I would try a girdle on the next rebuild, for better longevity.

 

Thanks for the insite Jim, I'm anxious to see how my main bearings look on my impending teardown. Is the block distortion due primarily to high RPM, high horsepower, or both?

 

Both..

RPM hurts them worst than pwr output, but big pwr and higher rpm go hand in hand..

JW

 

but big pwr and higher rpm go hand in hand..


HP = TQ * ( RPM / 5252 )


you make HP by increasing TQ or RPM or both. pull an extra 1000rpm ( while maintaining your torque number ) and that's nearly a 20% gain in HP. it's also nearly a 20% gain in the amount of force being applied to your main caps because you're getting ~20% more power strokes from the engine.

 

I had a 6500 RPM pill in the MSD and I did one 1/4 mile test on a back road after that last oil change. That's about the only time she hit 6500. I guess that's when it happened. Thank you for the diagnosis and advice.

Andy

 

Good Thread, I have been doing alot more reading than posting latley. Due to several bad experiences on my, How not to build a BBB. I thought that after all the engines I have built over my life. at home and at work. I could surley handle a BBB. Wrong. 2 detailed builds, 10 ballons of fuel ran through each build on a test stand, Cam bearing pailure build 1, Main bearing failure build 2. I plan on posting a tread on the the reason for the failures in detail later. Baisicly a binding oil pump, Bad line bore, and 2 local machinest. I might be a good idea for everyone with an engine failure to post their story for everyone to learn from. Just an idea ? Anyway I boxed up all my ENGINE parts and sent them to Mike at TA. I DID NOT SEND THE BLOCK AND CRANK. I bought them from TA. I wanted all my machine work done by the Pros ON EVERYTHING.

I WANTED TO BUILD THIS ENGINE FOR MANY YEARS. I POSTED A PIC WHICH PRETY MUCH SHOWS THE DETAIL TIME AND TESTING THAT WENT INTO EACH BUILD. I spoke with Jim at Tri Shield and Mike at TA and on my build and what caused the failures several times. for the Money, Machine work and time that went into this build. I could of just sent them all the cash the first time, spent less money, and already had my engine in the car. Just my .02 .

Richard...

 

Sure, but think of all the fun you have had! I have been through my engine several times and I'm about to do it again. Its discouraging sometimes but it is a challenge. Like golf, completely agravating at times, but when you solve a problem its a pretty sweet feeling. My major repairs/failures have been....

1st build, I burned a rod bearing because my adjustable oil pressure regulator was set to low. Fresh crank and bearings.
2nd build, I broke two pistons because of fuel supply issues with a weak fuel pump, replaced block, pistons and bent valves.
3rd build (in progress), 1 more broken piston, evidently caused by continued fuel supply issues.
No metal in the oil but I'm wondering what I will find on teardown.