3800 using 5spd manual trans / flywheel and bolts

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3800 using 5spd manual trans / flywheel and bolts

Postby yellow3800 » Tue Aug 31, 2021 5:33 pm

Bump. ...potentially from 1984 when the first Fiero may have been mated to a 3800 ancestor. (3800 engines began in the 1960s officially separating “3.8” v6 with the popular name “3800” through major revision in 1988). On the other hand, I’m late to the party.

this post focuses on flywheel bolts. Why is there a snag here? See the video clip below to dive right in. I want to tell you that the “water is fine” but it isn’t. It’s gray.

I’m long winded. It’s necessary right? No apologies.

Let’s start this with a ten sec video. Thank you “85slivergt” for illustrating this so nicely.


This began for me through stopping a simple-easy trans fluid leak and has turned into blowing the doors off a commonly overlooked detail pertaining to flywheel bolts for a 3800 to manual conversion mostly from the fiero sector. Hat tip to you guys! This post is my attempt to summarize facts, misleading information, and present gray area opinions and options that you have in making your car into the next 3800 swap using our own 5spd getrag 282 manual transmission! Most info in this post is harvested from Fiero knowledge of the past ten plus years. I’ve built one 3800 car, my automatic car, and still prefer it that way for gearing alone. It’s first gear is useful unlike its manual counterpart. We can go 75mph at 30mpg using 1988 electronics. Now for those of you who prefer the manual transmission headache (my 2nd 3800 beretta), read on.

***Let’s start with a few premises:

Flexplate is the automatic transmission’s method of transferring power
Flywheel is the manual transmission’s method of transferring power

Beretta and Fiero (1988) flywheels are the same.
10.5” clutch circle, 6 holes, m8x1.25 to mount clutch
No dowels
Crank bolt hole dia .43” (and uses different bolts than discussed here)
142 teeth
11.929” OD
0.8” thick

3800 crankshafts use (8) 5/16”-18 bolts.
The ‘98-‘02 camaro flywheel differs in thickness and mounting to the crankshaft. Almost bolt a beretta clutch on and go!

Gm 3800 (5/16-18) crank-flywheel bolts (p/n 24505092) commonly used in this conversion are torque to yield at 15lbs plus 50 deg. Use them once and they are done. This means, buy new for every time they are put into service (torqued). These have a track record of not breaking and are preferred over ARP. Do not use washers. Using red or blue thread locker provides a dry torque reading. While this thread-locking step is optional, with more power, comes the greater propensity for bolts backing out and breaking and most commonly shearing.

Brian Kimmitt’s super duper quad 4 gtz was the main event for entertainment one evening in Biloxi Berettafest’s hotel parking lot after reused bolts backed out in town. These are beretta GM bolts and only serve as example here. I have reused bolts without thread locker on my anemic ‘89gt of stock power and they aren’t a problem for 20 years and counting. I feel fine there. But this thread is about over and well over 200hp/tq and the years of history that we have been plowing through because a book is not where the buck stops (there isn’t one). This is what hot rodding is. I’m glad to be here and thank you for hanging out in this corner of my garage with me.

ARP disallows use of their bolts in a flywheel application unless expressly designed for that application. (Source: phone conversation between our fiero cousins and ARP)

The bolt manufacturer determines torque spec. If GM says 15 deg plus fifty deg and you have ARP bolts, you better have ARP’s instructions and follow them instead.

All 3800sc engines are externally balanced due to their stronger connecting rods (than NA version) and the rotating assembly requires use of the flywheel to balance it all. Ignoring this by putting a neutrally-balanced (new) flywheel on and the vibration will be significant enough to notice in the car and will trash crankshaft bearings and that $13 rear main seal that you’ve so proudly replaced when the transmission was detached. So let’s not do this and save some frustration and hard learning.

Supercharged series 1 and 2 differ in flywheel imbalance; 2 and 3 I don’t know. This is largely unimportant because to start this endeavor, you MUST have the flexplate from its first life when it was mated to the auto transmission so that the new flywheel can be “match balanced” that is, to match the imbalance of the flexplate so that the rotating assembly spins as smooth as silk, or Amsoil if you prefer that.

If the sc engines flexplate or imbalanced flywheel (if you’re on your 2nd flywheel) is unavailable, the crankshaft must be removed and balanced as a rotating assembly. You probably can’t buy a series 1 flexplate from a local parts store to buy your way out of this problem. Engines were made at the factory en masse (not individually balanced). Therefore, all series one flex plates have the same balance. All series 2 flexplates will have their same balance.

Here we have a number of options to source a flywheel to get the engine to talk to a manual trans. (Source Link here: http://pontiacperformance.net/TechArtic ... 00-V6.html )

A summary (Quote) of the link above:

Why not use the Stock Fiero one? - the V6 flywheel has 6 crank bolt holes, 3800's need 8. You can't use the stock Fiero flywheel without extensive mod.

Option 1: modify a F-body Flywheel: The F-body flywheel (p.n.#24503285) is 1.110 inch thick. This needs to turned down to .840 inch to match the V6 Getrag flywheel thickness. Options? - rebalance the flywheel to match the flexplate removed from the engine...

Option 2: Modify a stock V6 flywheel. Due to lack of information on the 3800 imbalance this is the 1st method I chose. I would not do it again. You need to fill the 6 crank mount holes then have the solid plate drilled to match the 8 crank holes on the 3800. They are NOT evenly spaced - 1 is off by 3 degrees to act as a key.

Option 3: make a new flywheel (installation currently in progress) Cost wise, this is not that much more. $350-400. Prints can be found on the web page below. I will be using a bolted on imbalance weight to create the balance required. This setup will be installed in less than 1 month and I'll post results then. This print can be used as is for properly modifying the crank bolt pattern on a filled and drilled stock V6 flywheel. The print will be updated with backspacing details after I know more.

Option 4: Use part of the above options, leave the flywheel neutrally balanced and have the engine balanced so that it does not require external balancing. More $, better at high RPM. As with all high performance: How much $? answer: How fast do you want to go?

Option 5: By the ACE kit. They use Option 4, but their own design. Seems to work fine in the installations I have seen. I do not like their engine mount method but it seems to work for the few people I have talked to. I don't know how hard they drive their cars. I don't see how they properly support the front of the engine. I think they only use the forward tranny mount.

End quote

Additionally, we have these:

If you are rebuilding your engine and have easy access, give the crank to the shop from harmonic balancer to flywheel, match the crank threads to the larger diameter and stock v6 camaro bolts and have them balance it. You’ll have the truest results. This has been done without problems. Enlarging the wrong wheel drive 3800 crank mount holes may be too large, so I recommend the M10x1.0 conversion.

Our own Rettax3 spaced the trans and engine 1/4” instead of milling the stock near 1” camaro flywheel to .84”. .84” is simply a number that has worked in the Fiero community despite our flywheels coming new at 0.80”. This spacing solves porosity issues that arise in turning a flywheel down so far! A fiero guy had a flywheel milled to .84” and revealed porosity on his AMS brand flywheel. I too have an AMS brand because they are the most forthcoming in their spec sheet. Let’s hope that mine is good. Hat tip to Rettax3. I like this.

SPEC has dropped the ball. Their aluminum flywheel made for (us) the 3800 exclusively, has >3/8” bolt holes and will be sloppier than seen in this video. Their flywheel is 1/4” thicker. SPEC provides no guidance on crankshaft-flywheel attachment. They do not sell bolts. Washer use is unknown. (Think steel wheels vs alum wheels and the bolt seat angle of aluminum vs the more flat base of the steel’s lug nut and that this is absolutely imperative to have handled). Loose bolts have resulted from heat lessening the clamp load as the aluminum creeps it’s way inward on the mount holes. Steel spacers could fix this but my 6 local machine shops don’t like this idea enough to work on my stuff. Bear in mind that good aluminum loses almost half its strength at 400F deg. How hot does your clutch get?

West coast fiero sells a billet steel flywheel to avoid the porosity issue scare mentioned above. Bolt size is custom (tell them 5/16” bolts will be used for 5/16l bolts and get smaller than 3/8” holes) as they take your old one and provide the service of match balancing. My local machine shops don’t want to touch a cast one for fearing of compromising it. They will however work with a billet one. The series 1 could have 5-8 holes to mount it. When you see the pic of the billet series 1 from west coast fiero, it lacks a bolt circle so that it WILL work with any series 1 - 5 bolts or 8 bolt types. Late series 1 (my ‘94) and later have 8 mount holes.

Pertaining to option 1 above, using an oem (cast) ‘98-‘02 v6 camaro flywheel and milling it down to 0.84” thick measured from the crankshaft flange face to the clutch mount surface, we are left with more to be desired. The mounting holes are 3/8” diameter and the crankshaft of (all 3800s?) is 5/16” diameter. The crank uses 5/16”-18 bolts. We then see the result (slop) in the above video. ‘FieroRog’ makes flywheels for all series with balance. Hat tip to you and a public thank you! FieroRoger made my flywheel.

What about tapping the crankshaft to use 3/8” dia bolts?

Upping the bolt size to 3/8” dia DOES interfere with having the 5/16” threads. (Source ARP... sourced in thread link to follow) which means, that in recutting the threads does not give 100% material to use due to similar sizes. They overlap. However, a metric size does allow the conversion without overlap.

***Now that we have set some premises, let’s surface some gray areas.

The video above showing the wiggle, is acceptable. If the video link breaks, all we see here is a display of the flywheel being able to move after being bolted on (hand tight) . It shows the effects of putting a 5/16” bolt in a 3/8” hole. The reality is that, it has withstood the test of time when p/n 24505092 is used on slightly modded 3800 setups. Using grade >8 bolts from the store WILL result in failure. Guys, if this slop is okay, then hat tip to you. I do not know. More power and field experience tend to show that the margin is narrow. Keep in mind, this “serrated death wheel” spins 5000rpm under stress just slightly forward and IN LINE with the driver in a beretta. Drag racers consider “scatter shields” for when flywheels break loose. My car is a daily driver and yet I do not wish to risk anything in this capacity.

Clamp force negates shear load on the bolts. Meaning, bolts can have the thickness of toothpicks to tree trunks if the required clamp load is achieved, thus, negating the slop around the bolt. The reality is that most 3800s mated to manual transmissions are bolting their flywheels as seen in the above video.

Three local machine shops revoke the idea of making or adding spacers the simulate a shoulder bolt to remove the slop seen in the above video after condemning the slop. One shop suggested a threaded spacer (no air gap between threads at flywheel contact point and then back peddled the idea in favor of a redrill and tap of the crank to take a larger diameter bolt). One shop refused to help me (mill flywheel to .84” and match balance) because they didn’t want mounting bolt slop in the final result. This is when I found out that these camaro mount holes are bigger.

Finding a machine shop to weld the beretta flywheel holes and redrill the 8 pattern for this is harder to find today. You’ll need to avert this liability concern by using a home machine guy or otherwise not retail machine shop. I take this as a clue but also can attest that when done decently, this works. My first flywheel was made this way. My car is on its second flywheel. The first flywheel operated at .53” thick and Is heat damaged. My local machine shops do prefer drilling and retapping the crank over flywheel modification. If you have the tools and confidence go for it.

Shouldered bolts have a chance to have a stress point or fracture that is risky. Grade 10 bolts aren’t good enough.

above 400hp/tq range does shear the 5/16” dia bolts. It’s simply too much stress for them at this point. I’ve read numerous cases where some owners got to the point where we are in the rabbit hole and just converted back to the original trans to avoid this flywheel stuff.

Now with all that on the table, let’s keep going. Am I willing to risk using 5/16” bolts on the “serrated death wheel” spinning close to me housed by a CAST (brittle) aluminum case and then thin unibody sheeting? I may race. I may (absolutely will) tach it up just having fun. The car doesn’t know the difference, so I’m hoping for something better.

The next link shows a mod of converting the mount setup to M10-1.0. These have a larger diameter and as of this writing has withstood years and miles with more power than I’ve seen.

Let me reflect on this thread: http://www.fiero.nl/forum/Forum2/HTML/137293.html

This shows how to correct the slop using a larger diameter bolt. This is where I am gravitating toward being the right answer.

Coupling the idea of min sidewall thickness of the crankshaft flange concern with the existing large non-mounting holes in the flange, I have decided to drill and retap the crankshaft partially - meaning that I will use the 5/16-18 factory bolts where edge thickness is thin, and convert to M10 on the remaining holes. This also and perhaps most importantly minimizes risk of me messing up the drilling and tapping of the crankshaft by hand with it in the engine.

Yes I realize what I just said.

*************(Post the pix doing this here)*********

Here is my version of the above link performed April of 2021.

Thanks for the bandwidth.

Search words at end

What to use for Gm Buick 3800 flywheel bolts 5/16” 3/8” slop loose 3800v6 flywheel manual transmission trans getrag Muncie new venture gear 282 hm282 5MT40 ‘98-‘02 v6 camaro .84” 0.840” p/n 24505092 Chevy Beretta

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Re: 3800 using 5spd manual trans / flywheel and bolts

Postby Rettax3 » Wed Sep 01, 2021 11:32 pm

Excellent write-up, and technical information. If using the standard-size bolts on an un-modified flywheel, my recommendation would be to bias the flywheel against the bolts as they would be pushed under engine-load. Centering might be the 'correct' answer, but I'll stick with my 'bias'. A single drill-point with a steel locating pin press-fit into place might do as good a job with a lot less work, but you certainly handled the issue in a very permanent fashion -nicely done. I don't recall hearing of many pre-Series 2 engines pushing 400 HP/Torque outside of the TTA/GN 3.8 SFI Turbo engines, or a lot of Series 2/3 engines for that matter. That much torque would start scattering transmission parts if the tires were sticky enough to use the torque. My GTU pushes ~275 HP and maybe 300-330 torque, conservatively guesstimating, I can spin the tires at 60MPH 8) . I've got a few 3800s sitting around, an extra L67 Series II and a few Series III mills, N/A and SC, the Series III N/A has the same diminutive bolts you had in your crank, I suspect the SC engines are the same but mine isn't easily accessible.

I had to 'make' a flywheel for my Northstar Beretta Indy -"filled and drilled" a stock V-6 flywheel. You can buy them now (pricey), but at the time NOTHING was available. The center hole is smaller on the N*, so I had to make a spacer-sleeve for the 'hub'. As I recall, those were small-diameter bolts too, also eight of them, but at a slightly larger radius than the 3800.

I was never too concerned about the crank bolts, figuring that they would be engineered to withstand the same torque and sheering loads as the clutch pressure-plate bolts -if those could survive so could the crankshaft bolts. Thanks for the tip about ARP hardware. Spot-on about using the hardware manufacturer's torque specs if changing hardware. As to 'spinning wheel of death', that thing has to come loose from the crankshaft, break through the transmission's input shaft somehow, grind/smash through the aluminum bellhousing, then make it through the firewall and driver's controls like pedals and steering shaft, and the Berettas also have the steering-rack in the way on the firewall... I'm not too concerned. Scattershields are used because flywheels can overheat, crack, explode and send shrapnel through the transmission tunnel, not because they come loose and break through as one complete wheel. I'm not an expert on this, so take that opinion with a healthy dose of salt, but high-output racing engines producing 900 HP at 8,000RPMs in front of 50-year-old flywheels would give me more concern than a stock 3800 flywheel...

Drilling/tapping in-engine... Wow. Looks like you did a great job on it too. Probably a lot safer for it than handling the crank around a garage with power-tools and metal shavings. Thanks for sharing your experiences on this. :good:

1989 SuperCharged 3800 Srs-II (First)Six-Speed GTU
1990 Turbo 3.4 5-Speed T-Type
1990 4.0L 4-Cam 32-Valve V-8 5-Speed Indy GTi (Project)
1990 Stock(!) 3.1 MPFI Auto Indy
1995 LA1/L82 4T60E Z-26
1995 3.4 DOHC Turbo 5-Speed Z-26

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Re: 3800 using 5spd manual trans / flywheel and bolts

Postby woody90gtz » Mon Sep 27, 2021 10:17 pm

I always worried a bit about clutch/flywheel failure in my Beretta, due to the plane it rotates in. My neighbor exploded a clutch/flywheel several years back (RWD truck) and it did send shrapnel through the hood and blew through the bellhousing to pancake the exhaust against the frame. I have a steel bell in my Camaro now and doing a blanket in the new Beretta.

91 "SS" - WOT 3400/5spd - 13.29@101.6 - World's fastest N/A FWD Beretta
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