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New crankshaft?

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ruffcountry35

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i recently replaced the motor(350) and tranny(350TH) in my 81 k5 blazer. i drove it for about 200-250 miles before the bendix on the starter started to grind the teeth away at the flywheel and wouldn't start. i've replaced the starter and flywheel combo 3 times now and it will start only a few times before the problems continues. i've finally replaced the stock starter with a mini-starter along with a new flywheel and the problem still presists. do i need to drop the oil pan and replace the crankshaft?
 
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You have the right flywheel/starter combo? 168 tooth or 153 tooth flexplate? I would think the diameter difference to be too great for the 168 tooth starter to even hit the 153, but I dunno.

The starter positioning changed based on the tooth count of the flexplate/flywheel, which is why there are 3 holes in the block. IIRC, you need a starter with two bolts straight across from each other with the 168 tooth flexplate/flywheel.
 
I dont know if this applies to just old Chevys but you used to have to check the play between the starter and ring gear teeth by shimming the starter away from the block. If I recall the idea was to be able to slip a paper clip between the tip of a gear tooth and valley on the other. This prevented binding of the bendix and wear on either. I have some of the shims still and comparable ones can be had a good hardware store.
 
dyeager535 said:
You have the right flywheel/starter combo? 168 tooth or 153 tooth flexplate? I would think the diameter difference to be too great for the 168 tooth starter to even hit the 153, but I dunno.

The starter positioning changed based on the tooth count of the flexplate/flywheel, which is why there are 3 holes in the block. IIRC, you need a starter with two bolts straight across from each other with the 168 tooth flexplate/flywheel.
Click to expand...


He said he replaced the stock style with a mini-starter. Those usually work with both 168 and 153. They use the straigh across bolts and have two sets of holes in the starter body.


I doubt the crankshaft would be bad, unless the holes were drilled off center. Causing the flywheel/flexplate to not run true. When the motor was replaced, did it have a new or reground crank in it? If it was a reground stock one...then I'd look at shimming the starter differntly. If it was a new aftermarket (China) one, I'd pull the trans bolt a new flexplate on and check the runout of the ringear. Check it at differnt spot around the plate itself. And at the same spot in relation to the crank while turning it.
 
toomany said:
He said he replaced the stock style with a mini-starter. Those usually work with both 168 and 153. They use the straigh across bolts and have two sets of holes in the starter body.
Click to expand...

But it was doing it before. How do you set the mini-starters up for either flexplate? One set of holes moves it closer, other further away?
 
Got it. ruffcountry35 is your starter setup this way? What kind of clearance do you have between the bendix and the teeth on the flexplate when the bendix is out? Should be able to barely fit a straightened paperclip in there.
 
when the bendix shoots out from the starter properly, yeah the clearance is barely that of a paper clip. and i have tried shimming it and that doesn't help either, and after those days of it working it sometimes shoots out and gets stuck in between teeth and won't go back into the starter
 
This might sound stupid but check your initial timing. If you have too much initial timing you may be generating detonation in the combustion chamber. That added resistance to proper rotation would tear up both starter and flywheel. The cranking noise could mask the detonation.
Race cars start at " 0 " advance until they start. Try reducing your initial timing.
 
and you think that would allow the bendix to actually hit the flywheel without jamming up and grinding the teeth?
 
When the starter is enguaged, The solinoid actuates a lever to enguage the bendix into the starter. At the end of the lever travel the starting moror is electrified and the starter and bendix, in unison, turn the flywheel. The bendix is a one way clutch in that it will apply power in one direction only. Piston detonation ( pinging ) will add more resistance to the starter and bendix.
Check the initial timing. If you have an 81 HEI dist make shure the vacuum advance is on ported ( not manifold ) vacuum. If it is on manifold vacuum the timing would advance while you are starting the engine. While you are at it check the centrifical springs in the dist. They ( the dist springs ) could be offering no resistance ( to mechanical advance ) while cranking.
 
ok i kinda had a similiar problem on my blazer i switched a new motor in and it would start fine for a while and like three weeks later it would not start at all i changed out three flex plates and put three starters in it. the more i did it the more it seemed that it would take less time for it to not start. even two or three starts and it would be out of adjustment again. so i pulled the starter off my old long bed chevy and looked at all the starters i had got and they all seemed to be about a half inch taller than the one out of my truck so i put my old one in my blazer and it starts right up everytime no hesitation. so could be starter difference. size was top to bottom through the bolt holes
 
hey guys, back again

so i looked for flywheels with different teeth, pitch and such and still the same problem. i still checked the bearings in the crank just to make sure, and they were fine as well. i pulled off the flywheel from the old 350 i had in the garage and it had the same tooth count and everything.

i recently looked up the stamped number on the block in my blazer and it was from a 1970 caprice with 300 hp. i looked up the flywheel and starter for that and it still came up the same.

i'm at a complete loss with this and i've been looking thru these forums to see if any others have the same problem.

PLEASE HELP!
 
Bendix and flexplate binding means the starter needs to be shimmed. It took .060" of shims to get mine correct.
 
i've actually shimmed it one by one.i used the .040, and the .060 and i had the same problem. i also used both shims at the same time and it still wouldn't catch. when i took ANOTHER look at the flywheel today, i recognized that the flywheel had different wear on the teeth. sometimes the bendix would actually engage all the way and sometimes they would just barely hit, making it grind the teeth off.
 
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