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 Post subject: 7/16 versus 10 mm
PostPosted: January 2, 2018, 10:32 pm 
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Joined: January 31, 2012, 12:49 pm
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Location: Louisville KY
One more thing to worry about...

My GM 3.4 came out of an auto trans car. It uses the newer metric 10mm flex plate bolts.

The T5 flywheel is built for the old style 7/16" bolt, which is about 1mm larger (dia).

The good news is that it all bolts up, no new drilling required.

The bad news is that each hole has 1 mm of "slop" and since the holes are too big I can't just redrill them to make 'em larger.

Is that 1 mm gonna cause some real problems? Or only cause problems if I drive it competitively? Or a nothing-burger?

Best guesses and advice?

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 Post subject: Re: 7/16 versus 10 mm
PostPosted: January 2, 2018, 11:12 pm 
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geek49203 wrote:
Best guesses and advice?


I don't know, but since you are inviting guesses, I'll take one.

Once the bolts are torqued up, there should be no motion between the flywheel, the crank, and the bolts. If there was motion, the clamp surfaces would wear, and then the bolt torque would be relaxed, and the flywheel would fall off. I suspect that additional hole size won't compromise the clamping area, so it will still torque up properly, and there shouldn't be any "slop" if the bolts are torqued up properly.

Keep in mind that I have only once seen the business end of a 3400 crank, and that was while I was wrestling it into a trailer to scrap it.


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 Post subject: Re: 7/16 versus 10 mm
PostPosted: January 2, 2018, 11:14 pm 
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Joined: November 11, 2013, 4:47 am
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Three possibilities.

Get a flywheel with the correct size mounting holes. (you know you really want aluminum anyway!)
Shoulder bolts to correct the fit, maybe available from the speed shops, AP?
Last resort, corrective sleeves around the bolts.

Slop at the flywheel mounting bolts just seems like a really bad idea. :shock:

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 Post subject: Re: 7/16 versus 10 mm
PostPosted: January 2, 2018, 11:49 pm 
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RichardSIA wrote:
Three possibilities.


Yes, do want Aluminum it's on the list.
Shoulder bolts? Have a source? This has GOT to be a common thing with auto-manual swaps?
Finally, if I was to put a sleeve (and I've looked at it) we're talking about .5 mm or less on each side, which is pretty thin?

But I agree, something about slop in that flywheel doesn't seem to be prudent.

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 Post subject: Re: 7/16 versus 10 mm
PostPosted: January 3, 2018, 12:01 am 
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I meant to say ARP.
I had no luck at Summit Racing, but I don't know what a 3.4 is to do a search. https://www.summitracing.com/nv/search/product-line/arp-pro-series-flywheel-bolt-kits
You may need to contact ARP directly?

Sleeves could be made fairly easily on a lathe but shouldered bolts would be much better.

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 Post subject: Re: 7/16 versus 10 mm
PostPosted: January 3, 2018, 10:00 pm 
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just find a space between the bolts to put a dowl.

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 Post subject: Re: 7/16 versus 10 mm
PostPosted: January 5, 2018, 11:23 am 
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A dowel would be good, but awkward to do on an assembled engine.

I'd probably make some bushings to press into the flywheel to reduce the hole size. It'd be easy if you have access to a lathe. If not, you might try finding some tubing that's close, then spin it in the drill and file the OD down, then Dremel the inside out as needed.


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 Post subject: Re: 7/16 versus 10 mm
PostPosted: January 5, 2018, 12:15 pm 
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This is what I would do, easy peasy, and wouldn't cost much. Remember you are assembling this once, it's not going to be taken apart every oil change or spark plug change, it may never be taken apart for thousands of miles. And it offers peace of mind that it's done right.
Take your 10mm thread bolts and get 7/16" shoulder machined off the mating face of the hex head with still enough material to be able to comfortably put a socket on to torque to specs. See chicken scratch drawing below.

.5mm is equal to .020" shim stock, another alternative would be to cut a strip of Stainless Steel shim stock that would line the inside of the flywheel bolt hole and install the 10mm bolts. Remember you're only doing this once on assembly.


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 Post subject: Re: 7/16 versus 10 mm
PostPosted: January 6, 2018, 9:30 am 
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Adding to Perry's idea.
Look into "industrail fixture specialty bolts", that have an extended head. Typical two or three times higher than standard hardware. That would allow you to turn down the under side of the head so you would have full surface contact with the flywheel.
There is also specialty bolts that have over sized shank diameters. Check out Carr-lane or McMaster, APR may even have some thing that could be easily modified.
I would worry about using a thin spacer. You need hardened high strength hardware for this application. Dave W


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 Post subject: Re: 7/16 versus 10 mm
PostPosted: January 6, 2018, 7:57 pm 
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You could also drill and tap crank for 12mm flywheel bolts and drill flywheel to match.

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 Post subject: Re: 7/16 versus 10 mm
PostPosted: February 10, 2018, 5:59 pm 
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If you give me the length of spacer you need I could make a set for ya.


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 Post subject: Re: 7/16 versus 10 mm
PostPosted: February 11, 2018, 3:05 am 
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Adamm above is correct. The bolts clamp the flywheel on, they are not pins. A good 7/16" bolt provides about 10,000 lbs. of clamping force. The friction generated by that pressure keeps the parts from moving compared to each other. You could look up a table of clamping force for metric bolts. You need to use the right bolts and pay attention to wether they should have dry or lubed threads etc. and then torque them properly.

Do manual flywheels for that 4.3 engine also use the 10 mm bolts? I would check that, manual flywheels are heavier than auto flex plates so they may need larger bolts. It would seem they would only make one crankshaft flange though...

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 Post subject: Re: 7/16 versus 10 mm
PostPosted: February 11, 2018, 3:23 pm 
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Location: BC, Canada. eh?
If you can't find ARP bolts to fit, I'd go with horchoha's recommendation.

For anyone with a lathe, it's child's play. Making bushings, on the other hand, would be rather difficult, and they would be extremely fragile, as the difference in O/D between 10 mm and 7/16" is, as you've stated, only 1 mm. A bushing would have to have a wall thickness of only 0.5 mm, or a little under .020". While it could be done, I'd far rather go with the other option.

The machined shoulder wouldn't have to be thick - I would think that a bit more than 1/16" would be enough to comfortably locate the bolts in the holes. Owing to the weight of a flywheel, I'd prefer it to be precisely located so as to eliminate imbalance as much as possible. You don't want to induce shake on the end of your crankshaft... :shock:

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 Post subject: Re: 7/16 versus 10 mm
PostPosted: February 12, 2018, 12:58 am 
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Give ARP a call. They are very helpful. I ran into some questions about stud length when I was installing an older Raceline wet sump on my 2.3 Duratec and they were very approachable and helpful as I recall.


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 Post subject: Re: 7/16 versus 10 mm
PostPosted: March 13, 2018, 11:45 pm 
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Location: Austin, TX
Little late to the party but would these help?

http://performanceshock.com/index.php?m ... 7d4d9df71a

The height might be too much but the diameter is exactly what your looking for.


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