Bore distortion vs head gasket type and thickness

General engine tech -- Drag Racing to Circle Track

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MikeB
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Re: Bore distortion vs head gasket type and thickness

Post by MikeB » Mon Mar 27, 2017 10:25 am

Geoff2 wrote:Agree with turbo that bore distortion comes from bolt holes, too close to the bore &/or tied to the bore. SBCs in particular have bolt holes close to the bore, & seem to suffer from distortion more than blocks where the bolt holes are farther from the bore, B/B Chrysler being a good example.
That probably wasn't an issue with the 265's 3.75" bore, and I doubt Ed Cole ever imagined going much bigger. I personally think the SBC was pushed WAY past its optimal bore & stoke given the 4.40" bore center and short deck. Seems to me like GM should have called it a day at after the 283 with its 3.875" bore. Same is true for reliable cam profiles being limited by the SBC's small diameter cam journals. But keeping the SBC alive probably had a lot to do with physical size and weight compared to a BBC.

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Re: Bore distortion vs head gasket type and thickness

Post by 4vpc » Mon Mar 27, 2017 4:54 pm

Do blocks with liners suffer much from bolt induced distortion?

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Re: Bore distortion vs head gasket type and thickness

Post by Newold1 » Mon Mar 27, 2017 6:47 pm

Yep, sometimes even more than solid blocks. For example the aluminum LS blocks with a thin liner that's really locked into the aluminum block they are actually easier to distort from improper machining, decking and clamping. These LS blocks must have good decking, torque plate boring and honing and good head tightening if you want to avoid distortion. If you have an iron block with iron sleeves properly installed and you have distortion from torquing on heads you can still distort the sleeve and actually loosen the sleeve in the block and that is bad news. Answer, check and deck that block if needed, use a torque plate to bore and hone the block and if you really want to pull cylinder heads down smooth and evenly use STUDS!

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Re: Bore distortion vs head gasket type and thickness

Post by redgoldstein » Mon Mar 27, 2017 9:14 pm

I put the head on big block 4.250 bore mopar stocker motor .027 cometic gasket it did not change more then .0003 so I did in again the same

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Re: Bore distortion vs head gasket type and thickness

Post by redgoldstein » Mon Mar 27, 2017 9:15 pm

why do I need a deck plate

bentvalves
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Re: Bore distortion vs head gasket type and thickness

Post by bentvalves » Wed Oct 11, 2017 6:32 pm

sorry to ressurect this one fellas, but rather than start a new thread.....

is a BOLT or a STUD going to distort the bore more?

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Re: Bore distortion vs head gasket type and thickness

Post by MadBill » Wed Oct 11, 2017 8:53 pm

Just gut feel, but I'd think a bolt might be worse, because its rotational friction within the thread would be adding to the mostly pure tension load of a stud.

(And to answer Red's March question, there's more to bore distortion than diameter change, e.g. hex-shaped bores. I've seen high mileage unmolested factory bores still showing crosshatching but with shiny 2" tall vertical wear stripes inboard of every head bolt thread.)
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