storman

i noticed today as i removed the stockflexplate from my motor to replace it with a stronger sfi unit that the dowel is missing from the crank. cant remember if it was there before or not actualy i remember picking it up from the balance shop it didnt have one , new scat crank. is it necessary could this contributed to the breaking rotors in my tranny pumps we were blaming on the stock flex plate? this motor see 6500 rpm

Jay 727

I've had one 400 since 1988, it has never had a crank dowel. It has been built every way from stock to mid 12 second 1/4 mile times. It has had a saginaw three speed, four speed, t-10 four speed, th350, th400, 700R4 behind it and it's never given me any problems.

AlkyIROC

Since the 400 is externally balanced there needs to be some way to index the flexplate. If it isn't then the engine will be out of balance.

storman

steve if it was all balanced with out the dowel an i line up the holes were the dowel should be it should be ok though right.

Jay 727

Have you guys ever worked on an engine yourselves?
The flex plate won't go on unless all the holes are lined up, they are spaced un evenly. I don't care what you do the holes will only line up one way.
Try it, turn the flex plate 360 degrees on the crank. All six bolts will only line up once in one complete turn.

AlkyIROC

If you line up the hole where the dowel was, it should be fine.

The 400 flexplate should have a counter weight on it. It corresponds to missing weight on the crankshaft. Unless you spend the bucks to have a 400 crank internally balanced that's why you need the special balancer and flexplate/flywheel.

JoelOl75

I would replace the dowel. It positively locates the counterbalance as there is some rotational play in the bolt holes. Also the dowel has a small amount of weight to it as well.

storman

hey joel im afraid if i put a dowel in it will cause a imbalance as every thing was balanced with out the dowel. ive been running this motor like this for awhile now with no probs. im only changing the flexplate as i keep breaking pump rotors in the 700r4. my tranny man thinks the stock plate was flexing to much over 6000rpm that was when the rotors always break. this motor is external balanced with a ATI dampner. We are also instaling a deper pan an pickup to make sure the prob isnt from sucking air. what you think about the balance?

Jay 727

I think you're making a big deal of nothing. GM stopped using the dowel pin in cranks around the mid to early 70's. It didn't fall out of your crank and it's not contributing to the pump rotor breakage.

storman

sounds good to me

RB83L69

Right... none of the 400 cranks I have dealt with have had it... you just use the hole as a guide.

I'd suspect the real problem is that you need offset block dowel pins; it's quite common for the crank not to be centered in the bell housing flange. That puts a huge side load on everything in the front of the trans: pump bushing, rotor, etc.

storman

ok how would i check this an were would i get offset dowl pins. the mains were alighn bored.

RB83L69

Bingo....

The crank is now several thousandths up higher in the block than it used to be. It no longer lines up with the center of the trans moving parts.

The easiest way I know to check it is with a dial indicator mounted on the crank flange, and a manual bell housing.

You can get the pins from Summit, Jeg's, your local speed shop, etc. They only come in a few choices. Moroso or Milodon seems like the usual source. Most align boring is on the order of .010"-.015"; look for pins with offset in that neighborhood.

storman

dont want to say your wrong but the jegs tech said thats not gonna be a problem in a auto application. moroso offers a .14 jegs has a .07. refering to tranny builder now see waht he says.