[Healeys] Bottom end mods

Chris Dimmock austin.healey at gmail.com
Sat Jul 8 15:54:32 MDT 2017


Hi Andy,
My best advice is to start at 
https://www.bighealey.co.uk/engines/3000-bottom-end

The issue with stock rods is the bolts. Have a look at them. 7/16 x 2.5 inches long. I have recently worked out you can machine Pontiac ones to fit, but I haven't tried them yet. 

A standard crank and rod setup (with forged pistons, aftermarket harmonic balancer, crank & rods lightened and hardened) should be kept to around 6,000rpm. There is a major harmonic at around 6,200 - 6,300

A modern steel aftermarket crank & rods can be revved to 6,500 - 7,500 all day. Denis Welch pulled 8,500 rpm on Conrod Straight at Bathurst in 1998 in the heat of battle with Peter Hopwood, to retake the race lead. 
You know why it's called Conrod straight? Lots of broken ones.....

You should also seriously consider the gun drilled cam from DWR. This design is also popular and available for the A series. Cam wear and cam follower wear is the biggest single issue - even in stock road engines - due to the splash, drip and pray oiling system for lobes and gears. 

Here are my specs & Dyno sheets from 1998. http://www.myaustinhealey.com/dyno_sheet.html

Best
Chris


> On 8 Jul. 2017, at 12:45 pm, A H List <austinhealeyslist at gmail.com> wrote:
> 
> Question for those who have built race engines, what, if anything is
> necessary for survival at higher rpm in the bottom end of a six
> cylinder? This is an old race car from the 70s which hasn't run since
> then and we are getting it back together after it collapsed a piston
> due to detonation.
> 
> Previously the bottom end was bone stock apart from Jahns pistons-
> which don't appear to be of very good quality. I have gone with
> dome-top Ross forged pistons, will keep with stock rods and crank
> since it won't be a serious competition car, more of a weekend racer.
> 
> I know on the A series BMC engine it is common to strap the centre
> main bearing, is this something worth doing on the six? Any pics?
> 
> What about camshaft oiling? Most likely will go with a reprofiled
> original stick, however if there are known issues with this approach
> then I would look at a replacement.
> 
> Has anyone experienced a bottom end letting go due to inadequate
> strength of the stock crank/rods? What about rod bolts, are they
> available as uprated strength?
> 
> Flywheel- is the stock lightened manhole cover adequate?
> 
> What is a safe redline for the stock parts?
> 
> Appreciate any input/experience from the collective wisdom
> 
> Andy.
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