I have a diagram, I have the 1 13/64" drill, I have access to the equipment to do the job...

But the diagram, while giving plenty of detail of how the holes are to be drilled and where they are to be located in relation to each other, doesn't appear to have a workable datum line.

Here's the diagram, if anyone can help me get started on this job I'd really appreciate it.

I'm not saying this is correct but years ago when I thought I was going to have to drill a flywheel for a 360 this is what I thought I saw:

1) establish the horizontal centerline through the pressure plate holes
2) establish the vertical centerline 90 degrees from the horizontal centerline through the center
3) establish the centerline of the middle hole by rotating 46 degrees 21 minutes clockwise from the vertical centerline through the center
4) establish the centers of the two outside holes by measuring 2.5 inches from the center hole at the 3.88 inch radius of the balance holes

Like I say, I never had to do this (found a flywheel) but this is the way I would have done it.

Thanks for responding, I really appreciate having someone who knows what they're about coming back to me.

Okay, just working from the beginning, that's where I have my problem...

The horizontal centreline on the diagram certainly looks like it's through the pressure plate holes, but I'm looking at a pressure plate which is many degrees out of sync with that. Which is actually why I'm asking the question.

If both flywheels I have had the pressure plate holes along that line I would go along with that, but even with just one of them not anywhere near it raises a question with me. This is exactly what I mean by having no datum point.

Actually, looking at the flywheel it appears to me that it's exactly 30° out from that diagram...

Is it possible that 143-tooth flywheels were drilled on that different axis? Mine is a 143-tooth.

Not an expert on the small block, but a search of the A body site states that pattern is 130T which cars used. A truck used the 143 tooth, so there may be a pattern out there for that. Unless trucks neutral balanced. Have to match FW to bell housing for starter engagement.

I believe that chart is for the 143T wheel which was used in trucks starting in 1972 while the 360 car 4-spd with the 130T wheel wasn't available until 1974.

I think you are looking with the flywheel pressure plate side up. Flip the flywheel over and look from the crank face side. That's where the diagram is drawn.
Doug

IIRC the 143 tooth is a truck flywheel and has a different drilling pattern. But don't take that as gospel, when I was contemplating this, it was with a 130 tooth flywheel.

Here is a 143T wheel.

Why are you dicking around with this? You can buy a brand new 143 tooth 360 balanced flywheel for under $90 at rock auto.

LUK LFW219

As for the drilling pattern, why would it be different for a 130 or 143 tooth flywheel? The imbalance needed is for the engine, the flywheel is irrelevant.

Top crank bolt hole looks offset. Maybe base your datum lines off that.

as a machinist, what bothers me, there is no mention of what angle the drill is sharpened to.
135* ? 118*? 90*? something else ?
just my life experience.
your mileage will vary.
and although not looking it up, if the flywheel is available from rock auto for less than $100.00, i wouldn't bother screwing around trying to balance one to the drawing either.

I agree that the datum line should be based off the crank holes as THAT is the item that your modifications are directly related. Datum off the pressure plate holes, as with the change in clocking, makes the entire process shot in the dark. Even if you are a little off, which drive me crazy as there should be base point, it's not likely to create an issue. JMO and the sentence below sums up some of this.

Balance tolerances on these factory setups was so poor, I doubt the drill cutting angle would make a material change in the acceptable range of error.

Just a guess here. There appears to be a locator hole in the pictured flywheel with the external balance reliefs. Does the flywheel in question have that locator. Bet it's on the datum line passing through the cranks centerline.

I'd prefer it to be spot on and for $100, wouldn't waste time on the process. Sell the current flywheel and buy a new one already balanced.

I've been asking that for years...common consensus is 118 degrees which is considered the standard.

Sniper, I can appreciate your curiosity here...

First, I live about 12,000 miles from Rock Auto and we have an exchange rate problem as well as a freight issue. I have three flywheels here and drilling them is possible if I can get the location right.

Second, the drilling pattern for the external balance is, of course, the same just as you say. I have read on different forums that its different but a lot of people who don't appreciate that fact get carried away there.

The drilling pattern, however, for the fitment of the clutch is clearly different. Could it be that it's exactly 30° different to the 130-tooth flywheel?

It is possible, but if it's possible (and it is) to drill to the same pattern as the 130-tooth flywheel it will (must) achieve the balance required.



The drawing says to be looking from the 'engine side' of the flywheel, so that's what I am doing.



Yes, a good point... I am pretty sure, however, that one of the diagrams I've seen was accompanied by a note saying 120°. I will be checking what my drill is, but it's a new and unused drill so I'd expect it to be right.

I have now taken pics of all four of my 143-tooth flywheels as well as a couple of 130-tooth flywheels...

I don't have time now to set these pics up, but I will do so in a few hours. I do thank everyone for their input, I really have to get somewhere with all of this and I think we will get that way.

Your location makes it more of a do it yourself situation without a doubt. Good luck with the job.

Can't you use the wider crank bolt spacing position at the 1 O'clock orientation the instruction picture to figure out the way to lay out the drilling pattern? Blow the pattern up to actual size and lay it in position to mark the drilling spots.

PM sent