Thread: How do I determine the number of flywheel teeth?

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I may have to replace the starter in my mid-70's GM 400ci small block. How do I determine the number of teeth on the flywheel (flexplate?) so I can buy the right starter? Can I simply count the number of teeth showing through the starter hole and map that to the total number of teeth?

Thanks for your help.
Dorsey

Based on the casting numbers, this was in a mid-70's GM truck, but I don't really know for certain. I have no idea of the diameter; I was hoping that someone might know of a simpler solution than pulling the engine. I saw a recent article (don't recall where) that showed how to count the exposed teeth through the starter hole to determine which of two possible tooth counts you had (on a hemi, I think).

I should have added that this is backed by a TH-350, not a clutch.

The only flex plates I see available for a mid-70's 400 are 168 tooth. My guess is that's what you have.

If you are going to count teeth.be sure to paint a white mark on 1st tooth so you know where you started...sounds simplistic, but sometimes the simple answer is the best answer.

I got up to 151 and lost track of the tooth I was on.

Dumb as it sounds---remove splash shield, pull spark plugs--lay under car with black marker and big screwdriver---count em, put a black mark on them as you count them---when you can't see any more teeth, use big screwdriver to engage teeth, pry against side of bell-housing and rotate engine till you see more unmarked teeth---repeat counting and marking untill you get to teeth that have black marks on them---stop counting.

As I look at the Speedway Motors catalog, for example, the main difference appears to be the bolt pattern, not the tooth count, which isn't even mentioned. Jegs offers chrome OEM starters in 168 tooth only, as does Summit.

Am I concerned with something that make no effective difference in replacing the starter? Considering the huge .030 clearance, the tooth count (153 vs. 168), does it matter that much?

Originally Posted by Dorsey

I may have to replace the starter in my mid-70's GM 400ci small block. How do I determine the number of teeth on the flywheel (flexplate?)
Thanks for your help.
Dorsey

I'm assuming that since you're replacing the starter, there's already one on the engine. Look at the mounting bolts on the starter. If they're directly across from each other, you have a flywheel with 153 teeth, If they're staggered / offset, you've got a flywheel with 168 teeth.

Bob

Thanks Bob, that's the kind of simple test I was looking for. As I said at first, I may have to replace a starter, so I will know what to look for.

Thanks to all for taking time to respond.
Dorsey

Jeez Denny---even you should know the answer to that one---Ya leave one bolt out---

We've needed some humor on these posts. Leave it to Denny to throw some stuff at us......LOL

It turns out that I didn't have to replace the starter after all. In order to test the cranking voltage, I had to disconnect the ignition wire at the solenoid, and while doing that, I found that the positive lead stud on the solenoid was loose. Once I tightened that, the problem was solved. Now, the starter hits full speed the instant I turn the key - no more intermittant slow speed problems. The cranking voltage is slightly low, but the starter seems fine and the engine starts immediately, so I'm going to ignore that for now.