One Carb Or Two?
Posted 10 April 2022 - 12:42 PM
Is this mod worth doing on a fast road 1430cc car?
Are there copper gaskets available for the original 3/8" bolt holes?
I would like it but it mean i could only ever use the gearbox case on another 5/16" drilled and tapped block. Unless there are some sort of bolt sleeves about.
Moved Into The Garage
Posted 10 April 2022 - 05:58 PM
The conversion of going from 1/4 to 5/16" bolts here to me never made any sense. It's not a weakness with them and with normal careful preparation, isn't a point that it leaks from. Copper Shim gaskets in some applications can be ideal, but given here one side is cast iron and the other is an aluminum alloy it's not what I'd reach out for. If there's going to be any flexing here, it'll be on the gearbox side, the copper doesn't have any 'take up' in it to move with that, unlike paper. One up-side though is if you are chasing a particular thickness to shim the mesh of the Primary Gear to the Idler, this could be done with different thickness copper shim here, but I see they don't offer this.
Up Into Fourth
Posted 10 April 2022 - 06:13 PM
One Carb Or Two?
Posted 10 April 2022 - 06:21 PM
They will put this phrase on my grave,,,, "I believe back in the day"..... a very high reving race motor with a "thin flange" block, this could be a benefit, but... a normal road car.. no benefit whatsoever... and 95% of modern A and A+ blocks were / are thick flange blocks.... but I stand to be corrected again.
Mini Mad
Posted 11 April 2022 - 02:18 AM
I've always run 5/16" gearbox to block bolts on all my 1380's since the 1980's.
Only really did it as it was a modification recommended by David Vizard.
Never had any issues with it and not had any leaks from the MED copper gasket used on my last couple of builds.
I have also run my 1380 since the eighties (A) with 5/16. Never had a problem but question if it was really necessary.
Up Into Fourth
Posted 11 April 2022 - 09:03 AM
this mod can actually be a down grade, if you dont use decent grade bolts they can stretch more that the old ones you were replacing.
..is NOT a girl!
Posted 11 April 2022 - 10:37 AM
Stretch, if it's not permanent, isn't necessarily a bad thing - A+ waisted head studs.
A case of if it ain't broke don't fix it? If you stick with 1/4", don't break 'em before you even start by over tightening. It may be you need to swap the "clamps" too if you swap the gasket type, but that logic is also valid in reverse.
Speeding Along Now
Posted 11 April 2022 - 03:21 PM
"thin flange" block, this could be a benefit, but...
..is NOT a girl!
Posted 12 April 2022 - 10:23 AM
"thin flange" block, this could be a benefit, but...
Not sure going 5/16 on thin flange is an advantage.
The flange is approx 11/32 thick at the threaded boss (8.5/9mm)
Is it better having a 1/4 bolt going into something 1.5 times its diameter,(the usual recommendation), or a 5/16 bolt basically going into a thread equal to its diameter?
Someone cleverer than me can answer that.
No idea, but I imagine the rule of thumb is based on some rule of thumb depth of thread engagement too: possibly = to the fastener width. Stretch comes in again, along with pitch. Get it wrong & it'd be like tearing along the dotted line.
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