Hi Im new to the forum and I sure could use some help I have a 86 K5 blazer with a 350 rebuilt engine that keeps eating starters. I have replaced fly wheel, starter bolts and heat plate, Starter work and sounds great for a few weeks then starts to make that aweful starter grinding sound, blew out the bottom end of one of the starters,

 

that could be a LOT of things... something as simple as a split engine block (at the starter hole) allowing for too much play when you bump the starter...
a chewed up flywheel from the busted starters will chew up the shiney new starters you drop in.
missalignment of the shim (if used) can cause problems
not using shims (when needed) can cause problems
bad or worn bendix spring in the starter...
not using the correct starter...

I am sorry there is a lot of variables in your question.
we have a 86 K5, with a 350 and it's eatting starters...

whave you done anything to it? has it been in an accident? did it just happen after the rebuild? when the old (last consistantly working starter) was on it's way out, did you keep using it even when it sounded like it was binding/grinding?
did it chug like *try to start* LURCH *try to start* lurch *start*?
does it sound like you are putting a screw driver in a fan that is going really fast when you try to start it... i guess like you'd imagine a robot pig squeeling would sound?

feed us info and we might be able to feed you better help :[... pics of the fly wheel, starter, and mounting location might not hurt either...

welcome to the forum BTW, and Canby sucks just for the record.



*EDIT* ok post edit I would suggest taking a peak at the block where the starter mounts. if the hole is wallowed out, or if the torque has split the block, then the starter will align sometimes and not align others causeing inconsistant starts. next time you are under there (and before thursday unless you have a large garage ) shine a good light on the block and do a sound inspection of the area. if that is the case you can use a SBC back brace to help align your starter along with a couple other things to salvage the rebuilt block. this is all speculation btw

im guessing that you are using a correct starter, and that you have a working knowledge of how to shim judging by what you said you have done in your edit BTW

 

It started after we swaped out the 305 with the 350, I have already replaced the fly wheel,starter bolts, and heat plate even though they looked good, I just don't know what else to check

 

i went through 3 flywheels and 5 starters, before someone "goofed" and gave me a flywheel that had i believe 1 or 2 too many teeth. problem solved. also went to a gear reduction starter and so far so good. the originals after the swap lasted about 3 months. after that a couple of weeks. now its been about 9 months and no problems.
oh and i badly want one of those robot pigs!!!