Broken Crank

[mcress]

Has anyone ever had a crank break on their 6.2?
I just got thru pulling the engine from my '82 C20
and found the crank broken at the thro between the first and second rod journals. i've heard of improperly ground cranks breaking @5 or 6 journal but not on or near the throw....I just thought that this was a little odd...had normal oil pressure and H2O temps going to work when it happened...I've got a newer 6.2 (1988) to replace it with...bought it with 135,000 miles on it and have replaced rod/main bearings and rear main seal.
Is there anything else that I need to check before I get ready to install it while its out...The individual that I bought the engine from kept it serviced regularly and has had no problems with it...truck was wrecked....

[DmaxMaverick]

How many miles on it?

What kind of shape was the balancer in?
If the balancer insulator (rubber part) was hardened, not allowing "dampening", or softened (extruding), or was cracked or had missing pieces, I would point to it for the cause. That's usually it.

Same effect can be had at the other end with the flywheel, if it has one. Automatics don't have this problem because the torque converter does a good job of dampening any harmonics (only at that end).

[C.K. Piquup]

What shape is the`82 block in after crank breaking?Main webs crack-free?If undamaged hang on to it.You might want to use it for this next motor.`82s are up there with GI blocks as tuffies(stronger/higher nickle alloy).

[Dezman125]

Hi
You should consider the benifits of replaceing the timing chain,with either a new one or with a set of timing gears,a little more expensive.If you are going to keep the truck,the gears are worth the extra cost.

[gmctd]

To re-iterate the above -

New harmonic balancer

New accesory pulley\balancer (it's a balancer, too)

New timing chain and sprockets.

If you did the bearings by pulling the crank (I have done so), replace the head gaskets to prevent the dreaded '6.2 losing coolant - where?' syndrome.

And, the crank does break in the 6.2\6.5L series at the second main journal, caused by harmonic balancer and\or accessory pulley balancer failure.

If no damage to the block, check for fractures in the block webbing for #2,3,4 mains.

If they are clear, you've got a keeper

[84 C2B2]

I just purchased a parts truck and the owner stated the engine made a terrible noise ands vibration prior to shutdown. the "J" engine only has 140,000 miles on it but it shows signs of tampering. He didn't know the value of a small quantity of RTV works better than 3 tubes for a water pump replacement. Anyway, the bearings looked good, no problems with the head, balancer was not deterioated but the crank was brokenright behind the #2 connecting rod. You could see the cracks in the webbing on #2, 3, 4, and 5 main journals. #2 broke off easily and cracked all the way up to the camshaft journal. The only two things I noticed that might have contributed to it's demise was a destroyed pilot bearing and a worn out timing chain.

Jerry