"Crank pushed forward by converter" PROJECT

When the crank moves this much...(.075")...you've got problems.

 

First audible sign was ticking of the #4 lifter. Put a dial indicator on the pushrod and found lift was down by 0.030". While pulling cam, found crank endplay to be 0.075" while pulling the lower gear. Then I saw evidence on the inside of the timing cover...

 

I then decided the engine needed to be pulled. Here's more evidence on the starter...

 

I pulled the motor, heads and pan. The pan was clean but the inside of the filter had lots of fine metal particles in it. Thinking that the filter did a great jot I take the high road and ponder that this is a good excuse to upgrade to Stage 1 valves, and a better cam. Next thing I see is the windage tray mounting tabs, they are cracked/broken. Thanks to Bruno, a replacement is on the way. Next I remove the mains to check the bearings, hoping the crank is salvageable. Looks like the front caps took some abuse...

 

Main bearings have seen some abuse, the engine has ~3700 hard miles on her.

 

Here's the cam. I'm thinking the thrust bearing material may have caused the lifter to stop rotating, resulting in lifter/lobe failure. The domino's were falling o No:

 

Here's the rod bearings...

Tune in later for more updates.

Inputs welcome

 

Wow, that motor got worked!

 

Ouch

Looks like the block was twisting as witnessed at the parting. What was your bearing clearance?

 

Selling auto parts for a few years I came across a few people who told me this happened to their motor once they made a change to increase power. Either nitrous, a blower, or even a camshaft sometimes gives the engine enough power to inflate the convertor which pushes the crank forward and wastes the motor. Then when the load is off, the convertor resumes normal size and is never diagnosed as being the reason for engine failure. I ordered my torque convertor w/anti balloning plate. it was a bit more expensive but less than an entire new engine. Just look at the advertisements in some magazines they mention "this convertor will handle race engines with as much as 400 ft lbs of torque!!!" Yet our stock 455 has 510 ft lbs @ 2800rpm.

 

great pictures, thanks for taking the time to do that. I had an engine do the same thing to me, luckily I caught it in time.

 

I learned this the hard way too!
I put a cheap $100 "B&M" convertor I had new in my '72 Electra. the motor had some basic bolt-ons and great stg-1 iron heads. (all GS car hand-me downs). It was running low 14's at this point.
A few hard launches on the street and that convertor pushed the crank and ruined the entire thrust bearing. It was leaking oil by the balancer and I noticed the crank could be moved in & out by 1/4" or so!!! ou:

We learned our lesson and later turned 13:30's in that big electra with a switch-pitch set-up!! :eek2:
As for the B&M, I drained it, cleaned it up real nice and got my guy at the speed shop to give a store credit!!!! :TU:
He was a little mad though :spank:
No more cheap convertors for me on any vehicle!!

 

I think Jerry 455 hit the nail on the head. So much for saving a little money on that converter. Part of this hobby is knowing where you can get away with cutting corners and where you can't (or sometimes leaving it to luck).
Like most everyone else here, I've got a shelf and dumpster full of junk to prove it!

 

Sorry for your luck Craig. At least you caught it while it was still in one piece.

Cheryl

 

Greg had a cheap B&M in his old Polara. The snout was off by .030-.040". It took out the pump on the trans in about 20,000 miles. When we tried to get a refund B&M said that because it was a performance item their was no warrenty on it. B&M can kiss my behind :moonu:

 

I've seen this kind of a result on a stock 76 Fullsize Buick. No mods whatsoever. Could have been a weak factory convertor. Engine & trans had about 80K miles untouched.
You'd need some pretty good traction & faulty material/workmanship to baloon a convertor.

Tom

 

I would allign hone that block if it were me. The caps show the original surface at the parting line which means no allign hone was done. The difference in the main bearings would be a good indicator that you have a problem in the mains. This is a good time to upgrade to main studs, a switch from bolts to studs should be followed by a good allign hone job. The main bore needs to be straight and have no taper, taper in the mains will make the crankshaft walk.

 

Good advice Dennis.

Looks like I may need a new crank. The thrust surface of the crank is worn down about .050. Not sure it if its worth (or can be) welding

Lets assume I go with a new stock crank. Ive decided to upgrade to forged pistons. I had planned on using the stock rods, but would consider other possibilities, like offset grinding the crank, Chevy rods and custom pistons route.

My current deck height is calculated to be 10.535 (3.9/2+6.6+1.98+.005), I think stock is 10.57? The pin height I had with the Hypers is 1.98 and they were .005 in the hole (stock rod and stroke). Id like to stay with ~2.20 or more journals for strength. Reduced pin heights would allow longer rod I think. I would like to keep the first ring down at least .275" or so in case I eventually run nitrous.

Any inputs on part combinations that provide benefits at a reasonable cost?

 

That's really a shame that a company the size and reputation (?) of B&M thinks they make enough money or have enough customers that they can afford to lose a few.

 

Yum Yum

BUICK has an appetite for tranny's and crank shafts!!! :3gears: Oh how we pay to play :TU: It's only money, right!!!