[oldman]

Long ago when I did my engine like 8 years or so, I ordered ARP flywheel bolts for a gen v and they did NOT fit I think the head and flange were too big for the counter bore holes in the flywheel. So it was to the dealer for stock flywheel bolts. My two engineers in house, (son and childhood friend) both MEs from top 10 schools, did some calculations and came up as a minimum of 11 ft lbs, 22 ft lbs and then 180 degrees, based on a 1.5mm thread pitch that is .75 mm I'm going from memory but that was about 45 foot lbs to get the angle. Oh ZL1 clutch disk and cover (pressure plate). GM spec calls for 45 degrees or about 35 ft - lbs of torque.

Well I'm thinking of doing a stronger maybe lighter setup after all these years of abuse. Like 1000 to 2000 full throttle run thru the gears.

I watch the ACT video and they say 45 ft lbs for OEM flywheel bolt torque. What we calculated years ago. Any input either way?



OH and the ARP head studs we calculated 10 ft - lbs less than ARP calls for, never had a problem and this is still way way way more clamp than stock of a LS engine.. just an aside.

[bishopts]

You might find a mechanic to backcheck the engineers if you want it to actually work .

[oldman]

see below... don't blow your flywheel up

[oldman]

Does anybody actually know the GM spec for this flywheel bolt which is similar the LS flywheel bolt?

I just ran a Grok 4 AI calculation of a M11x15m bolt with 12mm? (Grok) calculated working length toque to 22 ft -lbs and then 45 degrees using engine oil (no effect on the 45 degree), and it came to 117 ft -lbs which is a whole lot and I'm pretty sure even at my calculated stretch ( 8 years ago now and I'm old) I did not hit 117 ft -lbs. I just don't know but 45 degrees seems suspect as that is only .1625mm stretch on a working lenght of 11mm. For a grade 8 fastener the minimum spec is 12percent before failure. That is getting close to 1.9 mm which is more than 100x more. Of course we don't want it to fail but this is a torque to Yyiield bolt and ARP as well as LS (from memory) are not. Long story short these bolts should be over to much over 75 ft -lbs final torque, but from memory they were NOT. Anybody actually install a flywheel and know what final torque yielded 45 degree?

[bishopts]

Flywheel to crank? Or pressure plate to Flywheel?

flywheel to crank is 11 ft\lb first pass, 22ft\lb second pass, 45 degrees third pass

pressure plate to flywheel is 11, 26, 52 ft\lb

it shows L86, LT1, LT4 all use that same spec

[oldman]

yep and if you watch this video where he is NOT using torque yield bolts he is moving the wrench about 45 degrees in the second and third torque sequence. A torque to yield bolt MUST be twisted into its plastic range which is actually quite large. 22 ft lbs is basically seating the flyweel, 45degrees on a 1.5mm pitch bolt is a mere .1875mm or .0074 inches. Say the flywheel is 15mm thick, 1/100 thickness is .15mm so the bolt is being stretched just a hair over 1 percent along its non thread length.

Here from Grok4 AI "The plastic stretch, or permanent deformation, in a torque-to-yield bolt is defined by the standard 0.2% offset yield strength for most bolting materials. This means approximately 0.2% plastic elongation occurs when the bolt is torqued to its yield point"

Basically you got to get to .2% just to reach yield and then enter plastic deformity. Like I said, we did the calculations years ago and the pdf figure does not seem correct. Grade 8.8 should stretch 12 percent before failure per ISO spec, so not even close.

Where did you get this data? I see the same .pdf on Summit's site and every other site on the internet, but it cites no source. We are talking about a bolt similar to the LS bolt which like aftermarket stuff is NOT torque to yield meaning in general they take LESS turns. I'm glad I'm looking into this now and if I can't find a actual GM published source I'll probably go aftermarket and use ARP bolts.

I should note that I have happy with the stock ZL1 clutch, driveshaft and 1/2 shafts knock on wood I'be broken none that.