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Article: Building a Strong Short Block

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Posted on 11th May 2011

This article has been previously published by Seven Enterprises, most recently in our Spring 2011 mailer.


Performance Street MotorsThe crankshaft rotating assembly is the heart of the A-Series motor. The dated 3-main bearing design of the Mini’s crank and the big flywheel make it difficult to keep reliable. Here are some tips and parts suggestions that will help you build a reliable short block.

Performance Street Motors
We recommend a balance job of the rotating assembly, but many machine shops do not know how to do this in the correct sequence. Each component needs to be balanced individually by adding them one at a time to the assembly. Our machine shop is fully conversant with this procedure if you cannot find a reliable shop locally.

4-bolt center main cap FOR042Race Motors
When sustained high RPM are expected, the weaknesses of the A-series need to be overcome with modernized & improved components. The block usually needs line-boring, and that is the appropriate time to add at least a steel center main strap, such as FOR052. For a full race application, we suggest one step more, to a steel 4-bolt center main cap FOR042. National contenders will want a full set of steel mains, FOR042-SET for the ultimate strength and reliability.

A+ 1275 Crankshaft CAM6232Cranks
For street use, a freshly reground crank is adequate unless 020/020 or smaller. Even cranks with STD/STD or 010/010 journals may be inadequate for competition purposes, since they can be “mileaged out” and close to the failure point just from years of use. For a fresh start at a modest price, we suggest CAM6232 A+ crank and a set of A+ rods. For race use, a steel forged crank is standard fitment, such as Paul Ivey SEN0053 in Cooper S spec.

Vandervell bearing setEngine Bearings
We suggest only VP2 material Vandervell bearings for hot street and full race motors. A full selection is offered by Seven. Tested to 9000 RPM by Fortech Racing.

Cooper S Crank Pulley AEG0454Crankshaft Damper/Front Pulley
For street use, reconditioned front pulley CAM4929 should be adequate. For serious performance, we recommend the two-piece Cooper S setup. Choose C-AEG454 or FOR132 front pulley and 12A0367 or FOR133 damper. Contact our Tech Desk with your engine specs for guidance!

Cooper S 1275cc AE/Nural Piston 21253Pistons
For street-use 1275s, the AE 21253 is ideal, giving higher compression and greater reliability due to improved oil groove design. For race use, we offer UK made Mega piston range, or for the ultimate, JE custom lightweight pistons.

Hardware
Fasteners are the key to holding it all together, and the better the part, the less the chance of failure. A modest amount of extra cost in this area will be an insurance policy for saving your expensive crank, rods and gearbox. We strongly recommend ARP rod bolts and main cap hardware.