Flat washers under flywheel bolts?

Question for the group-

Why don't all flywheel bolts have washers? Every flywheel I have ever r&r'd looked ugly where the washerless bolts contacted.

Is there any reason I should not be running flat washers here? I always use red locktite on the bolts per SOP.

Thanks for any insight on this topic.

I try to use thin harden flat washers with thin head bolts, make sure the clutch anti chatter springs don't touch the bolt heads after torqueing before using it that way

The last ARP flywheel/flexplate bolts I bought specifically said not to use washers with them.

I have no idea why.

It’s been 30 years since I messed with a 727 or 904 but if I remember right they use thin headed bolts because of how close they come to the engine block. If you use a washer it would probably hit when you went to turn it.

I 'think' the small amount of distortion created by tightening the hardened bolts,with their specifically sized and machined area under the head, may help to create a locating effect that is normally accomplished with a dowel or tapered cone. Both of the last 2 would add additional machining steps and cost.I think a hard steel washer would elimate that 'freebie' effect mentioned in the beginning,as it 'may' act as a bushing between the 2 mating surfaces. Not sure if a dowel is included in the equation. That spinning flywheel creates some serious energy there,especially when try to move a 4000lb vehicle with sticky tires. Conical lug nuts on a street car comes to mind.Nothing textbook here, purely speculation and observation. Just my thoughts. Bill

I sheared grade 8 bolts a few months ago. I noticed on the ARP bolts they have a nice flat land under the head that looks pretty nice and was bigger then the land on the grade 8 bolts ATI sends with their flywheel and spacer kit. Plus the ARP bolts are 41something chrome moly.

ATI has issues with the flex plate they sell. I reused my old one because the converter bolt pattern is wrong on the new one.

If the OP is talking about an actual "flywheel" and not a flex plate you need to be careful the bolt heads don't contact the damper springs of the clutch disc like Cab said. I like the ARP bolts with a flange built in because they are easier on the flywheel. You might be able to get away with some thin hardened AN washers but double check it.

Gus

The main reasons are washers that thin will either be too soft and squeeze out or too hard(brittle) and break both conditions will cause flywheel/Flex plate to fail.

Millions have been built with no washers. All the flywheel bolt manufacturers DON'T supply washers. Good enough for me !!!

Keep in mind that the major auto makers look at saving parts of a penny per car, they are not worried about the motor or car after the warranty runs out
When it comes to high performance race parts I want to be as safe as possible, especially in the cars I build, drive and race and have to pay for the race parts
Jeremiah, 55 Ft Lbs. on the stock Mopar 7/16 flywheel bolts with red Locktite

Don't you think ARP would have tossed the idea around ?!?!?

I'm sure ARP did do a lot of thinking on the Mopar Flywheel and flex plate bolts they sale, hence the thin heads on both

Funny this post would pop up. I learned the hard way this year with the new motor. I cracked my convertor and messed up the hub. The cause ended up being that the bolts on the 8 bolt crank were riding against the convertor just slightly, but enough to cause runout. So... there are now .060 flat ground washers between the flex plate and convertor. Haven't made it back out yet.

Because flywheels flex and can break hardened washers. Then you have projectiles, and a loose crank bolt.

I don't know if this is correct, but I use thread locker on the threads, and carefully brush a very small amount of lube on the flywheel where the bolt head contacts it. Torquing is smoother, and does less damage to the wheel.

^^^I like that idea^^^.

Joe

Just be very very careful with lube and loc-tite. They do not get along well together at all.

Noted, thanks...

Joe

Edit, By the way, I ALWAYS clean the threads, both male and female with brake clean before applying thread lockers.

I thought I was the only one that done that When I build rear ends the shur-grip gets ARP lube under the head and red on the treads,the same for ring gear bolts

Gus

Your experience enforces the need to check converter free play, end play, and travel to the flex plates and fitment of the converter mounting lugs to the flex plate.
I've had the same problems but ended up using harden head bolt washers to fit between the flex plate and the converter mounting lugs to get it mounted up flush without having to bend the flex plate ears to make them fit flush against the flex plate

Don't worry there are not clutch hub springs. Those are for sissies! I have used a thin wave washers before but as mentioned a few of them came out intact however they were lightly lubricated for install. I always torque everything and a big 10-4 on the locktite. I have run solid mounts for years and a dab of red seems to be necessary in many places you would not normally have to address.

Yet they sell flywheel bolts with flat washers for the high end HEMI stuff. Hence my question. More of a curiosity than anything I guess.

The bushing example makes good sense. I guess I didn't really think too far into how much heat gets built up in the flywheel.

You know I'd never have a car with a flex plate!

I think I'll stick with the lube under the head, loctite on the threads and torque 'em down. Now instead of being nervous about the lack of washers I am paranoid they will cause problems.

Always ARP. You should see the bolts that I got from one of the vendors. They are grade 8 with the heads ground down. Very scary especially when I ordered them with all of the face plated 9310 gears. Nothing leaves my shop wearing hardware store bolts, especially on the rotating assembly. ACE is not the place for flywheel bolts.

Millions have not been built with 750hp moving 3600lbs through a solid disc clutch/aluminum flywheel to plant sticky 10.5" slick tires at 5000 rpm. That begs the question.



Some of the flywheel bolt manufactures that cover the entire motorsports spectrum *do* offer flywheel bolts with washers:

Example #1

Example #2

Example #3

I though maybe I was missing something.

Yes, I actually do think ARP has tossed this idea around lol.

Sorry to necro, but for anybody who might still come across this thread, which they will because I did while looking for something else, I feel like it's important to correct misinformation even though I realize none of it was given intentionally.

The bottom line is, none of the answers is actually correct in this thread for about 95%, maybe more, of applications. The reason being, about 95% of manufacturers use PLACE BOLTS, which you can read about at the following link and I guarantee none of you ever heard of them otherwise they'd have been mentioned in this thread, on critical fastener locations like flywheel bolts, oil pump bolts, camshaft retainer bolts, etc.

https://www.earnestmachine.com/sites/default/files/products/imported/BHP.pdf

You will be able to identify Place Bolts by the undercut in the bottom of the head and the six cut out lines in the top of the bolt head. This design allows the bolt to create far more clamping power than a standard bolt, even when using a lock washer.

If you remove a place bolt on any application that is the ONLY kind of bolt that should go back in that application location. Generally these are used on applications where the bolt is not particularly long, since longer bolt bodies are able to provide their own additional clamping spring tension, and where they are both difficult to get to if a bolt were to come loose AND would be likely to create a catastrophic end result if they did.

Did not intend to step on anybody's toes, but sometimes, like I did, you might go half your career AFTER professional schooling, and have never heard of them, until somebody slapped me upside the head with that information. Hopefully, some of you here or others who come along later, will be better informed for the info. Good luck.

Very cool and thank you for the explanation and link. "Now I know!"

I'm into bolts. Nice article. I've paid for flywheel bolts twice from "Mopar vendors" and received regular Grade 8 bolts at a big price. These guys make me very mad sometimes.

interesting article breeze. thank you sir !
i learned something, so you can say you taught an old dog.

In the pic are stock bolts and arp, was told 45 years ago at my first car repair job to never use any bolt that did not have the cutout head on a flywheel. Now I know exactly why. Notice the arp has even more contact area on the flywheel than stock bolt no cuts in head and they are undercut. I do all mockups to check and correct flywheel runout with 7/16 head bolt washers, even with a new flywheel the place bolts distort the [censored] of of the washers, worse on a used wheel. That is why I never use washers. Thanks for the info

I've wondered about the same thing. There are examples of both washers and non-washer flywheel bolts. I use washers if there is space for them. Typically you need a chamfered washer with a high strength bolt since the bolt will have a radius under the head. I don't think there is a problem if you use the correct washer for the bolt and if you have the clearance.

so using a flexplate, i use the ARP bolts with no washers, correct ?
or use grade 8 flat washers if i have the clearance ?

Just adding photos for reference since I am in the middle of trying to undo numerous mistakes on a car I bought last year.

Even without washers they bolt heads can hit... the previous owner tried to add clearance by using a hand grinder on the heads of the flywheel bolts, but it was not enough.

Looks like AMK has them for flywheel applications https://www.amkproducts.com/bulk-fasteners-products/?Product_ID=12702

Gus

That happens when people use a flywheel that has been cut a few too many times

Gus

I believe you are probably correct. the face of the flywheel is basically even with the ring gear.

Yep only good for an engine run stand now.

Gus

I was surprised as I read through this and was commenting to myself about "they are place bolts". Surprised it was a post from the past. Place bolts are used in several other locations including flex plate to tq, alternator bracket, cam, power steering valve.

Me too.
Glad to learn the automotive term “Place Bolts”.

In mining they are commonly called “Double A”
like the link to earnest machine has typed on the right.

I understand the undercut head because in Mech Engr education
class time is spent on “Stress Concentration Analysis”.

I now am wondering about whether
the six cut marks on the upper head surface are “cosmetic” just for human eyes to see
or are functional in that they affect either stress concentration
or act similar to “toothed lock washers.”

i'm almost betting the cut marks allow the bolt head to deform somewhat, affecting the clamping force.
just guessing this, as it seems this type of bolt head is only found in certain applications.
if it were just cosmetic, why take the time to add this feature ?
just my observation over the years.
i have no degree in anything, just [mostly] self taught skills from the school of hard knocks.

From the Earnest technical bulletin that "Darkbreeze" linked.

Here are the ARP instructions for their 7/16 flywheel bolts, they do have the undercut head. The other pic is stock flexplate and torque converter bolts...makes me wonder if the differing style is why you get a loose cracked thru the bolt holes plate every once in a while. Reading how the bolts work makes me think stock flexplates are one shot only to be safe.

thanks for kicking my butt when i needed it Jim !
after reading the bulletin, i immediately forgot what i read ! i need to get some of those supplements advertised on late night tv.
i think those products are meant to kill the spiders that make the cobwebs in my noggin.
i have now printed the bulletin, so i have no excuse to forget what it contains. [except forgetting where i put the print out. ]

re-reading the ARP instructions makes the use of
a special consistent specification lubricant
under the head of the ARP place bolt
“pop out” in importance

I thereby propose that:
all moparts members should
that from now till death
we will stick our finger into our ear deep enough
to get a bit of
“organic wonder grease”
that we will smear on the underside of every future bolt

i was told as a child, you do not stick anything larger than your elbow into your ear !