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Exhaust Manifold Fasteners

Started by smokuspollutus, March 31, 2021, 09:36:02 AM

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smokuspollutus

Hello everyone, getting in to the last stages of a build of a Cadillac 4.5 V8. Looking for opinions/experience when it comes to fasteners for the exhaust manifolds. From the factory, it used a mixture of studs and bolts. Would like to use all studs in the reinstall. Any guidance for what I want to buy and where I should source them? Assuming grade 8 hardware. Lock washers/lock nuts recommended in this application to prevent loosening? Any other tips, vendor suggestions?

Threads are M8x1.25

Thanks so much,

Anthony

TJ Hopland

Typically exhaust manifold bolts are not grade 8.  They do need some ability to stretch as they heat and cool.   Don't have any ideas where to get them for that engine.   Maybe a search with the tread size will turn up something?   Since its metric there has to be a lot of cars that use something similar.   Maybe you can find some Honda performance suds or something similar? 
StPaul/Mpls, MN USA

73 Eldo convert w/FiTech EFI
80 Eldo Diesel
90 CDV
And other assorted stuff I keep buying for some reason

35-709

Agree with TJ, use grade 5 for the exhaust.
1935 Cadillac Sedan resto-mod "Big Red"
1973 Cadillac Caribou - Sold - but still in the family
1950 Jaguar Mark V Saloon resto-mod - Sold
1942 Cadillac 6269 - Sold
1968 Pontiac Bonneville Convertible - Sold
1950 Packard 2dr. Club Sedan
1935 Glenn Pray - Auburn Boattail Speedster, Gen. 2

Bobby B

ARP and other manufacturers make High Quality Locking Exhaust Fasteners in Standard and Metric Thread Configurations. Most American Auto Manufacturers switched over to Metric years ago. Some GM/Ford uses mixed, making it even more Fun!  Easily sourced.....
                                                            Good Luck,
                                                                  Bobby



1947 Cadillac Series 62 Convertible Coupe
1968 Mustang Convertible
1973 Mustang Convertible
1969 Jaguar E-Type Roadster
1971 Datsun 240Z
1979 H-D FLH

savemy67

Hello smokus,

When using Metric fasteners, don't forget that the tensile strength is designated by Class, not Grade.  There are several Metric Classes.  A Metric Class 8.8 fastener is approximately the same tensile strength as an SAE Grade 5 fastener.  A Metric Class 10.9 is about an SAE Grade 8.

The shop manual covering your engine may call out the specification for the exhaust manifold fasteners.  Unless you have done some considerable modifications (headers, ported heads, etc.), the stock grade fasteners should suffice.

Respectfully submitted,

Christopher Winter
Christopher Winter
1967 Sedan DeVille hardtop

smokuspollutus

Thank you everyone for your input. Hadn't given thought to the need to be somewhat "stretchy", but it makes sense that you don't need incredible raw strength there, and the brittleness that comes along with that strength is not desirable given the life they'll live. I guess that was why I couldn't find grade 8/equivalent hardware for this purpose.

It seems like ARP is a one stop shop for this. After checking out their website, looks like they have a lot of offerings in that thread size, locknuts, etc. Almost everything seems like its made out of stainless steel though. Forgive me here if I'm wrong here, but isn't stainless "brittle" to some extent? As in, not the material you would want in this application?

I know, seems like a lot of effort for a minute thing. I just hate a ticking exhaust manifold (almost as much as I hate breaking a bolt on a 45 degree angle, inches from the frame). With the engine on a stand, now seems like the time to do it once (hence I am considering spending 100+ dollars on ARP hardware  ;D)

Thanks guys,

Anthony