[Healeys] six cylinder connecting rod bolt upgrade to ARP

[Harold Manifold]

Andy,

I wish you had sent this about 6 months ago. I tried the same approach but
couldn't find the ARP parts that would fit and settled on the replacements
of unknown origin.

Harold
 

-----Original Message-----
From: Healeys [mailto:healeys-bounces at autox.team.net] On Behalf Of A H List
Sent: Wednesday, January 03, 2018 2:42 PM
To: Healeys at autox.team.net
Subject: [Healeys] six cylinder connecting rod bolt upgrade to ARP

This might be of interest to some folk on the list.

A while ago I was looking at the six cylinder engine rod bolts and found
they are not available in high strength steel and the only options appear to
be used original or lucky-dip replacements of unknown origin. I looked at
several bolts from other engines and with the help of ARP tech support
settled on 454 Chev part number 135-6401 which are 1/16" too short and
0.0075" bigger diameter. This increases the torque from stock 50lbft to
80lbft or approx 60% higher clamping force as well as providing press-fit
location of the cap.

The caps needed spot facing to account for the reduced length which I
achieved with a 3/4" counterbore off Ebay
https://www.ebay.com/itm/253113534458 and a 7/16" pilot
https://www.ebay.com/itm/370673620820 Although the counterbore is for a
Morse Taper, it works just fine in a regular drill chuck.

I used a low cost adjustable HSS hand reamer
http://tradetools.co.nz/products/5620400 and increased the cutting diameter
gradually until the caps fit snugly onto the 'wave' section of the bolts.
There is so much variation in the stock bolt holes that some needed a lot of
reaming and some none. Bolts were installed using a brass hammer since I
don't have a press.

Some pics attached of the semi-finished rod, it has had the clamping faces
machined 0.005" each and now goes back to the engine shop for resizing the
tunnel. There are two ways of resizing, using a hone which is rather sloppy
or using a machine which is far more accurate as it doesn't increase the
sideways diameter. The bolt holes are extremely close to the bearing tunnel
so honing isn't a good option.

Cheers,
Andy.