gearbox to engine bolts
Turbo Mini Forums

Does anyone do a decent bolt kit for mounting the gearbox to the block ( arp? ). I want to keep 1/4" size but want grade 8 or above. Ta Ryan

TurboDave16v on here used to do a nice caphead fixing kit. Not sure if he can still supply them?

If something is worth doing, it's worth doing half of.

I brought some from the US a while ago good quailty ebay jobby but its no longer in my history on ebay

why not do a bigger kit with most the bolts nuts washers studs to build a nice looking engine?
edit: like 12 point flanged stuff similar to the arp

Edited by Turbo This.. on 19th Aug, 2014.

I'd think there would be a lot of people who would jump on this V

I used 5/16" fasteners on the 1293 from this place:

http://www.aptfast.com/

They don't seem to list them anymore though.

On my latest 998, the whole engine uses 12 point ARP. I've used 1/4" block to gearbox bolts.

I'll see if I can find the part nos, otherwise it takes a few minutes with a rule and the ARP catalogue to find what you want.

Saul Bellow - "A great deal of intelligence can be invested in ignorance when the need for illusion is deep."
Stephen Hawking - "The greatest enemy of knowledge is not ignorance, it is the illusion of knowledge."

ARP part nos:

1/4" - 28 * 1.5 12 point bolt - pack of 5 - 740-1500

As above but 1" long - 740-1000

1/4"-28 12 pt nuts - pack of 2 - 300-8320

Saul Bellow - "A great deal of intelligence can be invested in ignorance when the need for illusion is deep."
Stephen Hawking - "The greatest enemy of knowledge is not ignorance, it is the illusion of knowledge."

I'll ask, why do folks feel like they need 5/16" bolts?

The tensile strength of a socket cap is 180K psi, which is more than the 120Kpsi of a typical grade 5 (three stripe) bolt. Hence a 1/4" 180K is actually stronger than a 5/16" 120K psi.

The weakest area of this joint is also the gearbox case, not the block. And by drilling to 5/16", this is arguably weakening the most compliant material component in the fastened joint.

The best thing anyone could do in my opinion, is to get your gearbox case on a mill, and spot-face the (cast) faces where the bolt head will be contacting. This will then apply equal pressure over the bolt head and create a more robust fastener joint.

The other thing to consider, is that all fasteners need torquing to the appropriate torque for the material used in the fastener to put the appropriate stretch into the fastener, but for this case, not so much that it yeilds the highest point on the (cast) alloy surface under the fastener the first time it is torqued and does a heat cycle.
Basically, a grade-8 5/16" insufficienty torqued, might not be any better than a grade-5, unless the fastened joint is so engineered and analysed, and a grade-8 5/16" sufficiently torqued for the fastener might be excessivly clamped for the interfaces (unless work is done to prep the surfaces).

Edited by TurboDave16V on 19th Aug, 2014.

I am starting to change over to studs and nuts. The past is the future!